A copper containing composition for additive manufacturing CROSS REFERENCE [0001] The present application claims priority to Australian provisional patent application No. 2023903965, filed 7 December 2023, which is incorporated herein by cross reference in its entirety. FIELD OF THE INVENTION [0002] The invention relates to a copper containing composition and method for additive manufacturing. The invention also relates to a method for producing the composition, and printed parts produced from the composition. However, it will be appreciated that the invention is not limited to this particular field of use. BACKGROUND [0003] The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field. [0004] The ability to create strong and conductive copper (Cu) components with desirable shapes is attractive for various applications where the complex component geometry and demanding properties are both required. Additive manufacturing (AM), popularly known as three-dimensional printing (3D printing), enables rapid fabrication of Cu components with high geometry complexity. There are many AM techniques, for example, some processes initially create green bodies that contain a lower density of Cu with a chemical binder and use post- processing such as infiltration to remove the binders. However, this increases the processing time and cost, and limits the design complexity of the printed component. Accordingly, AM techniques that use directed energy (e.g. laser or electron beams) to melt or sinter powders to directly create components may be preferable. However, these AM approaches that rely on directed energy still typically utilise pure Cu, which is intrinsically soft and has low laser processability, which may result in porosity in the produced microstructure that degrades the strength, ductility and conductivity of the final component. [0005] Although alloying Cu with other elements is commonly used to improve the strength as well as the laser processability, it often results in a dramatic decrease in conductivity and significant ductility loss. Alternatively, the addition of foreign particles to Cu can increase the strength while maintaining good conductivity, but the ductility is often sacrificed due to the agglomeration of particles, especially at the grain boundary.
[0006] Laser additive manufacturing of metals typically involves complex physical and metallurgical phenomena, for example, laser-powder interaction, liquid-to-solid (solidification) and solid-solid phase transformation. When the laser beam comes into contact with metal powders such as pure Cu powders with high laser reflectivity, substantial energy will be reflected and hence the powders may not be fully melted, thereby leading to cracks and pores in the parts. As a result, high energy density is required – for example, through increasing the laser power by e.g. using an expensive green laser – to produce high density Cu parts, but this is often beyond the capacity of the commonly-used fibre lasers. Although high-density pure Cu parts can be created by carefully controlling the processing parameters, the intrinsic low strength of the resultant Cu parts hinders it from wider applications. Alloying Cu with elements like Cr, Co and Zr through in-situ alloying, or re-alloy powder, enables improvement of laser absorbability, and can create strong phases or promote grain refinement that significantly strengthens the matrix. However, the electrical conductivity – which is the most important function of Cu – is often dramatically reduced. Alternatively, foreign particles can be used to reinforce Cu while maintaining high conductivity. It, however, remains challenging to achieve a uniform dispersion and distribution of particles in the Cu matrix. In particular, the foreign particles are commonly observed at the grain boundary, which is undesirable because it may degrade the ductility. The incompatible or even mutually exclusive properties of additively manufactured Cu parts make them less attractive for practical applications where a good balance of mechanical and functional properties is required. [0007] Accordingly, there is a need to produce alternative feedstocks for the AM process that are capable of producing copper-containing additive manufactured parts that have good mechanical properties, such as high strength and/or ductility and/or softening resistance, and that also may have an electrical conductivity that is comparable to pure copper printed parts. [0008] It is an object of the present invention to overcome or ameliorate one or more the disadvantages of the prior art, or at least to provide a useful alternative. SUMMARY OF THE INVENTION [0009] The inventors of the present application have surprisingly discovered that it is possible to additively manufacture high density Cu parts, by methods such as laser powder bed fusion (L- PBF), that have a unique combination of properties, e.g. high strength, conductivity, ductility and/or good softening resistance, through the addition of ceramic particles. [00010] As used herein, by additive manufacturing (AM) is meant selective laser or electron beam sintering or melting of powders to create dense parts. [00011] Without wishing to be bound by theory, it is believed that the ceramic particle additives increase the laser absorptivity of pure Cu, thereby potentially eliminating or reducing cracks and
pores in AM fabricated parts. Further, ex situ added ceramic particles in some cases may be transformed through additive manufacture (AM) into in situ formed, uniformly dispersed, and coherent nanoparticles in the Cu matrix, which may not only strengthen the material but also can maintain high conductivity in copper printed parts. In a first aspect of the invention there is provided a composition for additive manufacturing, the composition comprising: copper particles; and ceramic particles; wherein the ceramic particles comprise a conductive ceramic material comprising: a melting point of about 3000°C or less; a liquid copper wetting angle of about 90° or less; and reduced laser reflectivity compared to the copper particles. [00012] The presently disclosed compositions are advantageous for use in methods of additive manufacturing when compared to conventional materials in that the compositions can be used to create layers that can be adhered without the need for polymers, gelling agents and/or binders. This further negates the need for furnace treatments to prepare the final part. Indeed, the parts prepared using the disclosed compositions are effectively “bound” by energy. [00013] The following options may be used in conjunction with the first aspect, either individually or in any combination. [00014] The composition may be a powder. It may be a substantially dry powder. In certain embodiments the composition does not comprise any gelling agents, binding agents or polymers. [00015] The ceramic material may have a liquid copper wetting angle of about 90° or less, or about 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or 10° or less. It may have a liquid copper wetting angle of from about 0° to about 90°, or about 0° to about 80°, about 0° to about 75°, about 10° to about 90°, about 20° to about 90°, about 30° to about 90°, about 40° to about 90°, about 50° to about 90°, about 60° to about 90°, about 60° to about 80°, or about 65° to about 75°. It may be, for example, about 0, 1, 2, 5, 10, 20, 30, 40, 50, 55, 60, 65, 70, 75, 80, 85 or 90°. [00016] The ceramic material may be electrically conductive and/or thermally conductive. In certain embodiments, particularly where the part to be additively manufactured is intended to have a high electrical conductivity, the ceramic material may have an electrical resistivity of about 80, 70, 60, 50, 40, 30, or 20 µΩ·cm or less at 20 °C. It may have an electrical resistivity of from about 1 to about 80, or about 5 to about 80, about 1 to about 50, about 1 to about 30, about 5 to about 50, about 5 to about 30, about 10 to about 80, about 10 to about 30, or about 10 to about 20 µΩ·cm at 20 °C. It may be, for example, about 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, or 80 µΩ·cm at 20 °C. In certain embodiments, the ceramic material has an electrical resistivity of about 30 µΩ·cm or less at 20 °C.
[00017] In certain embodiments, the ceramic particles are dissociated prior to being added in the composition. [00018] In certain embodiments, the ceramic material may be thermally conductive. It may, for example, have a thermal conductivity of at least about 100, 150, 200, 250, 300, or 350 Wm
-1K
-1 at 20 °C. [00019] In certain embodiments, the ceramic material is selected from the group consisting of oxides, carbides, nitrides and borides. In certain embodiments, the ceramic material is selected from the group consisting of carbides, nitrides and borides. In certain embodiments, the ceramic material is selected from f-block or group 5 oxides, carbides, nitrides and borides. In certain embodiments, the ceramic material is selected from f-block or group 5 carbides and borides. In certain embodiments, the ceramic material is selected from the group consisting of carbides and borides, optionally conductive carbides and borides. In certain specific embodiments, the ceramic material is selected from the group consisting of VC, WC, WB, TaB
2, and LaB
6. In certain specific embodiments, the ceramic material is selected from the group consisting of VC, WC, TaB2 and LaB6. In certain specific embodiments, the ceramic material is selected from the group consisting of VC, TaB
2 and LaB
6. In certain specific embodiments, the ceramic material comprises LaB
6. As used herein, the term “group 5” with respect to oxides, carbides, nitrides and/or borides, means oxides, carbides, nitrides and/or borides including Vanadium (V) oxides, carbides, nitrides and borides; Niobium (Nb) oxides, carbides, nitrides and borides; Tantalum (Ta) oxides, carbides, nitrides and borides; and Dubnium (Db) oxides, carbides, nitrides and borides. As used herein, the term “f-block” with respect to oxides, carbides, nitrides and/or borides, means oxides, carbides, nitrides and/or borides including atoms from the f-block of the periodic table (i.e. atoms having from 57-70 protons, or from 89-102 protons), e.g. Lanthanum (La) oxides, carbides, nitrides and borides; Cerium (Ce) oxides, carbides, nitrides and borides; Actinium (Ac) oxides, carbides, nitrides and borides; Thorium (Th) oxides, carbides, nitrides and borides, etc. [00020] The ceramic particles may comprise about 90 wt.% or more of the ceramic material, or about 95 wt.% or more, about 97 wt.% or more, about 98% or more, about 99 wt.% or more, about 99.5 wt.% or more, or about 99.7 wt.% or more of the ceramic material. In certain embodiments, the ceramic particles comprise at least about 99% by weight of the ceramic material. In certain embodiments, the ceramic particles comprise 95% or more, 97% or more, 99% or more, or substantially pure ceramic material. [00021] The ceramic material may have a melting point of about 3000 °C or less, or about 2900, 2800, 2700, 2600, or 2500 °C or less. In certain embodiments, the ceramic material has a melting point below the heating temperature of the laser for the L-PBF process in which the composition
is intended to be used. For example, in the case where the heating temperature is about 3000 °C or above, the ceramic material may have a melting point of about 3000 °C or less. In certain embodiments, the ceramic material may have a melting point of from about 500 °C to about 3000 °C, or from about 800 °C to about 3000 °C, about 1000 °C to about 3000 °C, about 1500 °C to about 3000 °C, about 500 °C to about 2800 °C, about 1000 °C to about 2800 °C, about 1500 °C to about 2800 °C, about 2000 °C to about 3000 °C, or about 2000 °C to about 2800 °C. It may be, for example, about 500, 600, 700, 800, 900, 1000, 1100, 1200, 1500, 1800, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, or 3000 °C. In certain embodiments, the ceramic material has a melting point of about 2800 °C or less. [00022] The ceramic material has reduced laser reflectivity compared to the copper particles at a specific wavelength. It may have a laser reflectivity which is from about 0.1 % to about 99.5 %, or from about 2 % to about 99 %, about 4 % to about 99 %, about 6 % to about 99 %, about 8 % to about 99 %, about 10 % to about 99 %, about 15 % to about 99 %, about 30 % to about 99 %, about 50 % to about 99 %, about 75 % to about 99 %, about 0.1 % to about 97 %, about 0.1 % to about 94 %, about 0.1 % to about 90 %, about 0.1 % to about 80 %, about 0.1 % to about 70 %, about 10 % to about 75 %, about 25 % to about 75 %, about 40 % to about 75 %, about 50 % to about 75 %, about 60 % to about 75 %, about 10 % to about 60 %, about 10 % to about 50 %, about 10 % to about 40 %, or about 10 % to about 40 % of the laser reflectivity of the copper particles. It may be greater than or equal to about 0.1 %, 1 %, 2 %, 3 %, 4 %, 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 16 %, 23 %, 30 %, or 36 % of the laser reflectivity of the copper particles. It may be less than or equal to about 99 %, 97 %, 94 %, 92 %, 89 %, 87 %, 85 %, 82 %, 80 %, 77 %, 75 %, 68 %, 62 %, 56 %, or 49 % of the laser reflectivity of the copper particles. In certain embodiments, it may be, for example, about 0.1 %, 1 %, 2 %, 3 %, 4 %, 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 13 %, 16 %, 20 %, 23 %, 26 %, 30 %, 33 %, 36 %, 39 %, 42 %, 46 %, 49 %, 52 %, 56 %, 59 %, 62 %, 65 %, 68 %, 72 %, 75 %, 80 %, 82 %, 85 %, 87 %, 89 %, 92 %, 94 %, 97 %, or 99 % of the laser reflectivity of the copper particles. The specific wavelength may be a wavelength within the range of from about 350 nm to about 2000 nm, or from about 475 nm to about 750 nm, about 475 nm to about 670 nm, about 475 nm to about 600 nm, about 350 nm to about 600 nm, about 350 nm to about 1000 nm, or about 475 nm to about 2000 nm. The specific wavelength may be, for example, about 350, 375, 400, 450, 500, 600, 650, 680, 700, 750, 800, 900, 1000, 1200, 1400, 1500, 1700, 1800, 1900, or 2000 nm. In certain embodiments, the ceramic material has reduced laser reflectivity compared to the copper particles at all wavelengths within the wavelength range (for example, at all wavelengths from about 350 nm to about 2000 nm, or from about 475 nm to about 750 nm, about 475 nm to about 670 nm, about 475 nm to about 600 nm, about 350 nm to about 600 nm, about 350 nm to about 1000 nm, or
about 475 nm to about 2000 nm). In certain embodiments, the wavelength at which the laser reflectivity is reduced is in the range of from about 475 nm to about 750 nm, optionally from about 475 nm to about 670 nm, optionally from about 475 nm to about 600 nm. [00023] In certain embodiments, the ceramic material reduces the laser reflectivity of the copper particles. A 0.1, 0.2, 0.5, 1, 2, or 5 wt.% concentration of the ceramic material in a composition with copper particles may reduce the laser reflectivity (at a specific wavelength) of the composition (as compared with a substantially identical composition but without the ceramic material), by at least about 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, or 20%. The ceramic material may reduce the laser reflectivity by from about 0.1 % to about 30%, or from about 0.5 % to about 30%, about 0.5 % to about 20%, about 1 % to about 20%, about 1 % to about 10%, or about 0.1 % to about 5%. It may reduce the laser reflectivity by about 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, or 30%. The specific wavelength may be a wavelength within the range of from about 350 nm to about 2000 nm, or from about 475 nm to about 750 nm, about 475 nm to about 670 nm, about 475 nm to about 600 nm, about 350 nm to about 600 nm, about 350 nm to about 1000 nm, or about 475 nm to about 2000 nm. The specific wavelength may be, for example, about 350, 375, 400, 450, 500, 600, 650, 680, 700, 750, 800, 900, 1000, 1200, 1400, 1500, 1700, 1800, 1900, or 2000 nm. In certain embodiments, the ceramic material reduces the laser reflectivity of the copper particles at all wavelengths within the wavelength range (for example, at all wavelengths from about 350 nm to about 2000 nm, or from about 475 nm to about 750 nm, about 475 nm to about 670 nm, about 475 nm to about 600 nm, about 350 nm to about 600 nm, about 350 nm to about 1000 nm, or about 475 nm to about 2000 nm). In certain embodiments, the wavelength at which the laser reflectivity is reduced is in the range of from about 475 nm to about 750 nm, optionally from about 475 nm to about 670 nm, optionally from about 475 nm to about 600 nm. [00024] In certain embodiments, the composition comprises a substantially uniform dispersion of the Cu particles and ceramic particles, wherein the Cu particles have at least a partial coating of the ceramic particles. In certain embodiments, the ceramic particles at least partially coat a surface of the copper particles. In this context, “substantially uniform” means that the Cu particles, and ceramic particles are substantially homogenously distributed in the composition. It may mean, for example, that any 1 cm
3 sample of a 1000cm
3 composition will have the same concentration (within about ±5%, ±10%, or ±20%) of each of the two components as the bulk (1000cm
3) composition. In this context, “a partial coating of the ceramic particles”, means that the Cu particles have at least a portion of their outer surface, e.g. at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of their outer surface area coated with the ceramic particles.
In certain embodiments, at least about 20% of the outer surface of each Cu particle is coated with ceramic particles. [00025] The composition may comprise from about 0.01 wt.% to about 20 wt.% ceramic particles, or from about 0.02 wt.% to about 10 wt.%, about 0.05 wt.% to about 10 wt.%, about 0.05 wt.% to about 5 wt.%, about 0,6 wt.% to about 1.9 wt.%, about 0.1 wt.% to about 5 wt.%, about 0.1 wt.% to about 10 wt.%, about 0.1 wt.% to about 15 wt.%, or about 0.1 wt.% to about 20 wt.% ceramic particles. It may, for example, comprise about 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, or 20 wt.% ceramic particles. In certain embodiments, the ceramic particles are present in an amount of from about 0.1 wt.% to about 5 wt. % in the composition, optionally from about 0.6 wt.% to about 1.9 wt.%. In certain embodiments, the ceramic particles are present in an amount of about 1 wt.% in the composition. [00026] The weight ratio of ceramic particles to Cu particles in the composition may be from about 1:2000 to about 1:5, or from about 1:1000 to about 1:10, about 1:500 to about 1:10, about 1:500 to about 1:20, or about 1:100 to about 1:20. It may be, for example, about 1:2000, 1:1000, 1:500, 1:100, 1:80, 1:70, 1:60, 1:50, 1:40, 1:30, 1:20, 1:10, or 1:5. In certain embodiments, the weight ratio of ceramic particles to Cu particles in the composition is from about 1:500 to about 1:20. [00027] The ceramic particles may be any shape. They may be, for example a regular shape, such as a substantially spherical shape, or they may be an irregular shape. In certain embodiments, the ceramic particles are nanoparticles. The ceramic particles may have an average diameter of from about 0.5 nm to about 100 µm, or from 10 nm to about 100 µm, 50 nm to about 100 µm, 10 nm to about 50 µm, 50 nm to about 50 µm, 100 nm to about 50 µm, about 1 nm to about 1000 nm, about 1 nm to about 500 nm, about 2 nm to about 500 nm, about 2 nm to about 100 nm, about 2 nm to about 20 nm, or about 2 nm to about 10 nm. They may have, for example, an average diameter of about 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, 20, 50, 100, 200, 500, or 1000 nm, or about 1.5, 2, 5, 10, 20, 50, 70, or 100 µm. In certain embodiments, the ceramic particles have an average diameter of about 20 nm or less. In certain embodiments, the ceramic particles have an average diameter of about 10 nm or less. In certain embodiments, the ceramic particles have an average diameter of about 100 µm or less, or about 50 µm or less. [00028] The ceramic particles may have particle size distribution D
90 of from about 0.1 µm to about 500 µm, or it may be from about 0.1 µm to about 50 µm, about 0.1 µm to about 10 µm, about 1 µm to about 50 µm, about 5 µm to about 50 µm, about 1 µm to about 20 µm, about 5 µm to about 10 µm, or about 5 µm to about 25 µm. It may be, for example, about 0.1, 0.2, 0.5, 1, 1.1, 1.2, 1.5, 2, 5, 10, 11, 12, 15, 20, 50, 100, 200, or 500 µm. The ceramic particles may have a particle size distribution D50 of from about 0.05 µm to about 50 µm, or it may be from about 0.05
µm to about 30 µm, about 0.05 µm to about 10 µm, about 0.1 µm to about 30 µm, about 0.5 µm to about 20 µm, about 0.5 µm to about 10 µm, or about 0.5 µm to about 5 µm. It may be, for example, about 0.05, 0.1, 0.2, 0.5, 1, 1.1, 1.2, 1.5, 2, 5, 10, 11, 12, 15, 20, or 50 µm. The ceramic particles may have a particle size distribution D10 of from about 0.01 µm to about 20 µm, or it may be from about 0.01 µm to about 5 µm, about 0.01 µm to about 10 µm, about 0.1 µm to about 20 µm, about 1 µm to about 10 µm, about 3 µm to about 6 µm, about 3 µm to about 10 µm, or about 0.3 µm to about 2 µm. It may be, for example, about 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 1.1, 1.2, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, or 20 µm. [00029] The composition may comprise from about 70 wt.% to about 99.9 wt.% Cu particles, or from about 75 wt.% to about 99 wt.%, about 80 wt.% to about 90 wt.%, about 85 wt.% to about 97 wt.%, about 90 wt.% to about 99.9 wt.%, about 95 wt.% to about 99.6 wt.%, or about 85 wt.% to about 90 wt.% Cu particles. It may, for example, comprise about 70, 75, 80, 85, 90, 91, 92, 95, 96, 97, 98, 99, 99.1, 99.2, 99.5, or 99.9 wt.% Cu particles. The Cu particles may comprise about 90 wt.% or more Cu, or about 95 wt.% or more, about 97 wt.% or more, about 98% or more, about 99 wt.% or more, about 99.5 wt.% or more, or about 99.7 wt.% or more Cu. In certain embodiments, the Cu particles comprise at least about 99% by weight of Cu. In certain embodiments, the copper particles comprise 95% or more, 97% or more, 99% or more, or substantially pure copper. [00030] The Cu particles may be any shape or size. They may be, for example a regular shape, such as a substantially spherical shape, or they may be an irregular shape. The Cu particles may have an average diameter of from about 5 nm to about 5000 µm, or from about 50 nm to about 5000 µm, about 100 nm to about 5000 µm, about 500 nm to about 5000 µm, about 1 µm to about 5000 µm, about 5 µm to about 5000 µm, about 10 µm to about 5000 µm, about 10 µm to about 1000 µm, about 20 µm to about 200 µm, or about 10 µm to about 100 µm. They may have, for example, an average diameter of about 5, 10, 11, 12, 15, 20, 50, 100, 200, or 500 nm, or about 1, 2, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 500, 1000, 2000 or 5000 µm. In certain embodiments, the copper particles have an average diameter of from about 20 µm to about 200 µm. [00031] The Cu particles may have particle size distribution D90 of from about 1 µm to about 5000 µm, or it may be from about 1 µm to about 500 µm, about 1 µm to about 1000 µm, about 10 µm to about 50 µm, about 5 µm to about 50 µm, about 10 µm to about 20 µm, about 5 µm to about 10 µm, or about 5 µm to about 25 µm. It may be, for example, about 1, 1.1, 1.2, 1.5, 2, 5, 10, 11, 12, 15, 20, 50, 100, 200, 500, 1000, 2000, or 5000 µm. The Cu particles may have a particle size distribution D
50 of from about 0.5 µm to about 500 µm, or it may be from about 0.5 µm to about 300 µm, about 0.5 µm to about 100 µm, about 1 µm to about 300 µm, about 5 µm to
about 200 µm, about 5 µm to about 100 µm, or about 5 µm to about 50 µm. It may be, for example, about 0.5, 1, 1.1, 1.2, 1.5, 2, 5, 10, 11, 12, 15, 20, 50, 100, 200, or 500 µm. The Cu particles may have a particle size distribution D
10 of from about 0.1 µm to about 200 µm, or it may be from about 0.1 µm to about 50 µm, about 0.1 µm to about 100 µm, about 1 µm to about 20 µm, about 1 µm to about 10 µm, about 3 µm to about 6 µm, about 3 µm to about 10 µm, or about 3 µm to about 20 µm. It may be, for example, about 0.1, 0.5, 1, 1.1, 1.2, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, 20, 50, 100, or 200 µm. [00032] In certain embodiments, the composition may comprise one or more additional components. The one or more additional components may comprise a flowing agent, and anticaking agent, and/or a carrier. The carrier may be a solvent, e.g. an organic solvent. In certain embodiments, the solvent may be water. [00033] In certain embodiments, the composition is a feedstock for a 3D printer. The composition comprises copper particles and ceramic particles. [00034] In certain embodiments, the additive manufacturing is 3D printing. In certain embodiments, it is a powder bed fusion additive manufacturing process. [00035] The composition may be a solid or in the form of a liquid. In certain embodiments, the composition may be in the form of a suspension. In certain embodiments, the composition may be in the form of a sol. In certain embodiments, the composition is in the form of a powder, e.g., a solid powder. [00036] In a second aspect of the invention there is provided a method for preparing a composition for additive manufacturing, the method comprising the steps of: providing copper particles; and mixing the copper particles with ceramic particles to form said composition; wherein the ceramic particles are as defined according to the first aspect. [00037] The following options may be used in conjunction with the second aspect, either individually or in any combination. [00038] The copper particles, ceramic particles and/or composition may be as herein before described with respect to the first aspect. [00039] In certain embodiments, the method comprises a step of dissociating (i.e. substantially removing or dissociating any agglomerates) the ceramic particles prior to the mixing step. In certain embodiments, the dissociating is performed using a vibrator. In certain specific embodiments, the vibrator is an ultrasonic vibrator. [00040] Traditionally in AM, low frequency/low energy concentration powder handling techniques such as ball milling or mechanical shaking are used to mix and break apart agglomerates prior to printing. However, due to the smaller size of the ceramic particles, the
surface area to volume ratio is very high, and therefore a higher dissociation energy and frequency may be required to break up agglomerates than is typically possible using techniques such as ball milling. Thus, the inventors of the present application have found it is preferable to use high frequency/high energy concentration agitation techniques such as ultrasonic vibration to dissociate the ceramic particles. [00041] In certain embodiments, the dissociating and/or mixing are performed at a pressure below atmospheric pressure. The dissociating and/or mixing may be performed at a pressure of about 100, 50, 30, 20, 10, 5, 2, or 1 kPa, or less. In certain specific embodiments, the dissociating and/or mixing are performed at a pressure of about 10 kPa or less. Alternatively, the dissociating and/or mixing may be performed at a pressure at or above atmospheric pressure. [00042] In certain embodiments, the mixing is performed using a shaker, optionally an electromagnetic shaker. [00043] In certain embodiments, the mixing step is conducted in a liquid, which is subsequently substantially removed to produce the composition in a powder form. The liquid may comprise water and/or one or more organic solvents. The method may further comprise a drying step to substantially remove the liquid from the composition. The drying step may include a heating step. The heating may be performed at a temperature of greater than about 100, 150, 200, 250, 300, 350, or 400 °C for a period of greater than 1, 2, 3, 5, 8, 10, 12, or 24 hours. The moisture content of the composition may be less than about 5 wt. %, 2 wt. %, 1 wt. %, 0.5 wt. %, 0.2 wt. %, or 0.1 wt. %. It may be, for example, about 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, or 5 wt. % moisture. Alternatively, the mixing step may be performed in the absence of any liquid. [00044] The composition of the first aspect may be produced according to the method of the second aspect. The method of the second aspect may produce the composition of the first aspect. [00045] In a third aspect of the invention there is provided a method for additive manufacturing using the composition according to the first aspect. [00046] The following options may be used in conjunction with the third aspect, either individually or in any combination. [00047] The method may be a 3D printing method. It may be a powder bed fusion and/or a direct metal deposition or similar additive manufacturing process. It may use a laser, or an electron beam. The composition described herein according to the first aspect may be a feedstock for the additive manufacturing process. [00048] In certain embodiments, the method does not comprise a post-formation heating step. As used herein, the term “post-formation heating step”, means an additional heating step after an additive manufactured part has been formed. That is, any heating step which occurs after the step in which the final layer of the additive manufactured part is fused.
[00049] In a fourth aspect of the invention there is provided the use of a composition according to the first aspect for additive manufacturing. [00050] The additive manufacturing may be a 3D printing process, for example, a powder bed fusion and/or a direct metal deposition or similar additive manufacturing process. The composition as described herein according to the first aspect may be a feedstock for the additive manufacturing process. [00051] The use of the fourth aspect may incorporate the method according to the third aspect. The method according to the third aspect may be used in the use according to the fourth aspect. [00052] In a fifth aspect of the invention there is provided an additive manufactured part made from the composition according to the first aspect, or made from a composition prepared according to the method of the second aspect, or prepared according to the method of the third aspect. [00053] The following options may be used in conjunction with the fifth aspect, either individually or in any combination. [00054] In certain embodiments, the additive manufactured part has an electrical conductivity at 20 °C of about 50, 60, 70, 80, 90, or 100 MS/m or more, or about 95, 97, 98, 99, 99.5, or 99.7% or more IACS (International Annealed Copper Standard). [00055] In certain embodiments, the additive manufactured part has an elongation to failure of about 5, 10, 15, 20, 15, 30, or 40 % or more. [00056] In certain embodiments, the additive manufactured part has an ultimate tensile strength of about 80, 100, 120, 140, 160, 180, 200, 220, 250, or 300 MPa or more. [00057] In certain embodiments, the additive manufactured has a porosity which is at least about 0.5, 1, 2, 5, 10, 15, or 20% less than the porosity of a comparative part; wherein said comparative part has substantially the same shape and size as the additive manufactured part, and is produced using substantially the same conditions as the additive manufactured part from a composition consisting essentially of copper particles. [00058] In a sixth aspect of the invention there is provided a kit for additive manufacturing comprising: copper particles; and ceramic particles; wherein the ceramic particles comprise a conductive ceramic material comprising: a melting point of about 3000°C or less; a a liquid copper wetting angle of about 90° or less; and reduced laser reflectivity compared to the copper particles.
[00059] The following options may be used in conjunction with the sixth aspect, either individually or in any combination. [00060] In certain embodiments, the kit is used for an additive manufacturing process, wherein the additive manufacturing process comprises the following steps: mixing the copper particles and ceramic particles to form a composition; and irradiating the composition using a laser. [00061] In certain embodiments, the copper particles and ceramic particles are mixed before being subjected to an additive manufacturing process. [00062] In certain embodiments, the copper particles and ceramic particles are mixed within an additive manufacturing device. For example, the copper particles and ceramic particles may be loaded into separate containers within an additive manufacturing device which then mixes said particles to form a mixture to be irradiated with a laser during an additive manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS [00063] Figure 1 shows a multi-physics simulation and microstructure analysis of: a) 3D view of multi-physics simulation of pure Cu fabricated using the L-PBF process. Necking of the laser scanning track is visible as marked with a circle. The pores labelled with arrows between the scanning track and bulk material were left over after solidification. b) 3D view of multi-physics simulation of LaB6-Cu fabricated using the L-PBF process. In contrast to pure Cu, the uniform scanning track, deeper melt pool and higher melt pool temperature are evident. c) Top surface morphology, cross-sectional EDS elemental mapping and EBSD inverse pole figure (IPF) of L-PBF fabricated pure Cu. d) Top surface morphology, cross-sectional EDS elemental mapping and EBSD IPF of L-PBF fabricated LaB
6-Cu. High density and uniform dispersion of LaB6 nanoparticles are achievable in L-PBF fabricated LaB6-Cu. Scale bars: 100 μm (c
1, c
3, d
1, d
3); 20 μm (c
2); 200 nm (d
2). [00064] Figure 2 shows the characteristics of nanoparticles in a L-PBF fabricated part produced from an example inventive composition (comprising copper particles and LaB6 nanoparticles): a) SEM micrograph showing the homogeneous distribution and well dispersion of nanoparticles within one grain in the L-PBF fabricated LaB
6-Cu for maximizing the strengthening capability. b) SEM micrograph displaying the distribution of nanoparticles around grain boundary. Almost no nanoparticles are found to pine the grain boundaries. c) TEM observation of nanoparticles. d) High magnification bright-field TEM image showing the particle morphology. e) HRTEM observation of the interface between the nanoparticle and Cu matrix.
f) SEM image of a single-track sample (scale bar 20 µm). g) Higher magnification SEM images taken from the frame regions in f) (scale bar 2 µm). h) Higher magnification SEM images taken from the frame regions in g) (scale bar 200 nm). [00065] Figure 3 shows the tensile mechanical property and electrical conductivity of L-PBF fabricated parts: a) Tensile engineering stress-strain curves of L-PBF fabricated pure Cu, LaB
6-Cu, and LaB
6-Cu subjected to thermal exposure at elevated temperatures. b) Comparison of the yield strength, elongation to failure and electrical conductivity obtained in the present application with previous data of high-performance Cu, Cu alloys and Cu matrix composites fabricated by L-PBF, L-PBF plus heat treatment and traditional processing. c) SEM micrograph of fabricated L-PBF Cu material; scale bar: 200 µm. d) SEM micrograph of fabricated L-PBF LaB6-Cu material; scale bar: 5 µm. [00066] Figure 4 shows the compressive properties of geometrically complex L-PBF fabricated component: a) Compressive engineering stress-strain curves of L-PBF fabricated sheet-based gyroid lattice by using pure Cu and LaB
6-doped Cu feedstocks. b) Comparison of the compressive yield strength against relative density obtained in the present application with previous data. [00067] Figure 5 shows SEM micrographs and EDS analysis of powder feedstock and its corresponding laser reflectivity: a) 1.0 wt% LaB6 doped Cu feedstock. b) High magnification corresponding to the white frame in a). c), d), EDS mapping of pure Cu with 1 wt% LaB
6 addition. Overall uniform distribution of LaB
6 nanoparticles on the surface of Cu powder is visible after mixing. e) Laser reflectivity of pure Cu, LaB6 and 1.0 wt% LaB6 doped Cu at different laser wavelengths. After introducing 1.0 wt% LaB
6 nanoparticles, the powder mixture showed lower laser reflectivity than pure Cu powder, indicating improved laser absorptivity. [00068] Figure 6 shows Micro-CT characterization of the L-PBF fabricated pure Cu and LaB6- Cu: a) Micro-CT 3D images showing the pores and cracks in pure Cu. b) Micro-CT 3D images showing the pores in 1.0LaB6-Cu. c) Micro-CT 2D images showing the pores and cracks in pure Cu. d) Micro-CT 2D images showing the pores in 1.0LaB
6-Cu. e) Micro-CT 3D images showing the pores in 0.5LaB
6-Cu f) Micro-CT 2D images showing the pores in 0.5LaB6-Cu.
The scanning resolution was 4 μm. The measured overall porosity of parts significantly reduces from 8.59% for the L-PBF fabricated pure Cu to 0.46% for the 1.0LaB6-Cu. Scale bars, 2 mm (c, d, f). [00069] Figure 7 shows SEM micrographs showing the surface morphology in LaB6-Cu fabricated using various L-PBF processing parameters: a) Laser power of 300 W and scanning speed of 400 mm/s. b) Laser power of 325 W and scanning speed of 400 mm/s. c) Laser power of 350 W and scanning speed of 400 mm/s. d) Laser power of 400 W and scanning speed of 400 mm/s. e) Laser power of 375 W, scanning speed of 400 mm/s, and hatching spacing of 0.1 mm. At a scanning speed of 400 mm/s, well-regulated laser scanning tracks were achievable on the surface of the nanocomposites at a laser power above 325 W. [00070] Figure 8 shows TiB
2 doped Cu feedstock and the microstructure of a L-PBF fabricated sample: a) 1.0 wt% TiB2 doped Cu feedstock. b) High magnification corresponding to the white frame in a). c) Laser reflectivity of pure Cu and 1.0 wt% TiB
2 doped Cu at different laser wavelengths. After introducing 1.0 wt% TiB2 nanoparticles, the powder mixture showed lower laser reflectivity than pure Cu powder, indicating the significantly reduced laser reflectivity. d) EBSD IPF image of the L-PBF fabricated sample showing its high density. e) SEM image showing the agglomeration of TiB2 nanoparticles around grain boundary. f) Tensile engineering stress-strain curves of the L-PBF fabricated pure Cu and 1.0TiB2-Cu. [00071] Figure 9 shows the morphology, microstructure and tensile mechanical properties of L- PBF fabricated pure Cu with 1 wt% LaB
6 microparticles: a) Pure Cu powder with 1 wt% LaB6 microparticles (˂10 μm). b) SEM observation showing the homogeneous dispersion of particles in a L-PBF fabricated sample with microparticles. The initial irregular microparticles were refined into nanoscale particles after L-PBF. c) Comparison of tensile properties of L-PBF fabricated pure Cu with 1 wt% LaB6 microparticles and nanoparticles. Comparable tensile strength and ductility were attained in L- PBF fabricated pure Cu with 1 wt% LaB6 microparticles and nanoparticles. d) Tensile engineering stress-strain curves of the L-PBF fabricated Cu with different additions of LaB
6 nanoparticles. The error bars represent the standard deviation of the mean. e) SEM image showing the nanoparticle agglomeration in the L-PBF fabricated 2.0LaB
6-Cu. Scale bar: 1 μm.
[00072] Figure 10 shows Gibbs free energy as a function of temperature for the reaction between La and B. The Gibbs free energy of the reaction between La and B was always below zero at a melt temperature below 2210 °C, suggesting that LaB
6 forms in the melt (i.e. during the L-PBF process). [00073] Figure 11 shows EBSD analysis and SEM micrographs of 1.0L-PBF fabricated LaB6- Cu after annealing at 550 °C and 1050 °C for 1 h: a) Inverse pole figure (IPF) of 1.0LaB6-Cu after annealing at 550 °C. b) Kernel average misorientation (KAM) image corresponding to a). c) Inverse pole figure (IPF) of 1.0LaB
6-Cu after annealing at 1050 °C. d) Kernel average misorientation (KAM) image corresponding to c). e) SEM image showing the nanoparticles after annealing at 1050 °C. f) The geometrically necessary dislocation (GND) density of the L-PBF fabricated 1.0LaB6-Cu calculated from Kernel average misorientation (KAM) data in (g). The GND density is estimated to be 8.03×10
13 m
-2. g) KAM image of the L-PBF fabricated 1.0LaB6-Cu corresponding to the EBSD inverse pole figure (IPF) map in (a). It is clear that annealing at 1050 °C did not result in obvious particle coarsening. Reduced dislocation density confirmed by the lower KAM value at 1050°C may have led to the decreased tensile strength and increased ductility. [00074] Figure 12 shows video camera frames during compression of porous fabricated components: a) Pure Cu. b) LaB
6-Cu. The occurrence of a localized shear band in the pure Cu component was resisted in the LaB
6-Cu component. [00075] Figure 13 is a schematic diagram which depicts the number of printing cycles (T1-T30) of the copper and 1 wt% LaB
6 powder, and the associated sampling points (C4, C8, C12, C16, C20, C24, and C29) where powder morphology was observed. [00076] Figure 14 shows SEM images (10 µm scale bars), with low magnification (x 500) and high magnification (x 2000) of virgin (prior to printing), the sampling points: C4, C8, C12, C16, C20, C24, and C29, and the waste powder after 30 cycles of printing. [00077] Figure 15 shows: SEM image (top) of the virgin powder mix, and associated EDS elemental analysis imaging of Cu, O, La and B (bottom) for: (A) Virgin powder mix; and (B) C20 (Cycle 20) sample.
[00078] Figure 16 shows SEM analysis of a copper and 1 wt% LaB6 powder sample, showing cube-shaped LaB6 particles having sizes ranging from 60 to 100 nm that are evenly distributed in the copper matrix: (A) 20,000 x magnification (1µm scale bar); and (B) 30,000 x magnification (100 nm scale bar). [00079] Figure 17 shows: (A) sampling of samples for tensile testing from printed blocks; (B) dimensions of samples; (C) printing of blocks; (D) and (E) printed blocks; (F) labelled samples for tensile testing. [00080] Figure 18 shows tensile test results for samples taken from blocks printed from (A)- (AE) samples from initial (A) to 30
th (AE) cycle. [00081] Figure 19 shows: (A) tensile strength; (B) hardness; and (C) elongation % mechanical properties for printed samples by number of printing cycles. [00082] Figure 20 shows the fracture surface of: cycle number 2 (high ductility sample) under: (A) low (70 x) and (B) high (300 x) magnification; and cycle number 4 (low ductility sample) under: (C) low (70 x) and (D) high (300 x) magnification. [00083] Figure 21 shows densification of the printed samples, by cycle number (from #0 to #30). [00084] Figure 22 shows densification compared to elongation for the printed samples by number of printing cycles. [00085] Figure 23 shows electrical conductivity for the printed samples by number of printing cycles. [00086] Figure 24 shows Atom probe tomography (APT) characterization of 1.0LaB6-Cu: a) 3D reconstruction of Cu, La and B distribution in the L-PBF fabricated 1.0LaB
6-Cu. b) Enlarged view of the precipitate-1 (P1). c) The 1-D concentration profile along the axis of the cylindrical volume-of-interest in (b). d) The enlarged view of P2. e) The 1-D concentration profile crossing P2. Both concentration profiles show depletion of La and B in Cu matrix. La enrichment is spatially correlated with B. Note that the La and B enriched zones do not correspond to the real shape and dimension of the LaB
6 nanoparticles due to the significant different voltages required for the evaporation of LaB6 and Cu during APT. The error bars denote the standard deviation of the mean. Scale bar, 20 nm (a). M: Matrix, P: Precipitate. [00087] Figure 25 shows softening resistance of the L-PBF fabricated 1.0LaB
6-Cu: a) The hardness of the L-PBF fabricated 1.0LaB
6-Cu subjected to thermal exposure at elevated temperatures.
b) Tensile engineering stress-strain curves of the L-PBF fabricated 1.0LaB6-Cu subjected to thermal exposure at 550 ºC and 1050 ºC. The error bars represent the standard deviation of the mean. [00088] Figure 26 shows XRD analysis of the L-PBF fabricated pure Cu and 1.0LaB6-Cu: a) XRD spectra of pure Cu and 1.0LaB6-Cu. a.u., arbitrary units. b) Enlarged image corresponding to the blue dotted area in (a). Only the diffraction peaks corresponding to Cu and LaB6 were detected. c) Enlarged image corresponding to the yellow dotted area in (a). XRD peak shift is not detected in 1.0LaB
6-Cu, indicating that the lattice parameter of Cu does not change with the addition of LaB
6. [00089] Figure 27 shows atom probe tomography (APT) characterization of the L-PBF fabricated 1.0LaB6-Cu: a) 3D reconstruction of Cu, La and B distribution in the L-PBF fabricated 1.0LaB
6-Cu. b) Vertical slice of the reconstructed APT volume. c) Enlarged image corresponding to the dotted frame in (b) and proximity histograms across P1, P2 and P3 showing depletion of La and B in Cu matrix. The error bars denote the standard deviation of the mean. d) Voltage history of dataset. This image shows significant voltage fluctuation caused by the different evaporation fields of LaB
6 and Cu. e) APT mass spectrum and indexing used for data analysis; data binned in width of 0.015 Da for display. Scale bars, 20 nm (a, b), 10 nm (c). M: Matrix, P: Precipitate. [00090] Figure 28 shows TEM characterization of the L-PBF fabricated 1.0LaB
6-Cu: a) Bright-field (BF) TEM image showing the LaB
6 nanoparticles. b), c) and d) Selected area electron diffraction (SAED) patterns corresponding to (a) obtained from different zone axes. It was evident that there was no specific orientation relationship between LaB
6 nanoparticles and Cu matrix. Scale bars: 500 nm (a), 5 nm (b-d). [00091] Figure 29 shows a comparison of tensile properties of AM fabricated pure Cu using green laser and electron beam with that of 1.0LaB
6-Cu. DEFINITIONS [00092] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting.
[00093] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains. [00094] Unless the context clearly requires otherwise, throughout the description and the claims, the terms “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. For example, a composition, mixture, process or method that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process or method. [00095] The transitional phrase “consisting of” excludes any element, step, or ingredient not specified. If in the claim, such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase “consisting of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. [00096] The transitional phrase “consisting essentially of” is used to define a composition, process or method that includes materials, steps, features, components, or elements, in addition to those literally disclosed, provided that these additional materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention. The term “consisting essentially of” occupies a middle ground between “comprising” and “consisting of”. [00097] Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”. The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, “%” will mean “weight %”, “ratio” will mean “weight ratio” and “parts” will mean “weight parts”. [00098] The terms “predominantly”, “predominant”, and “substantially” as used herein shall mean comprising more than 50% by weight, unless otherwise indicated. [00099] As used herein, with reference to numbers in a range of numerals, the terms “about,” “approximately” and “substantially” are understood to refer to the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to + 1 % of the referenced number, most preferably -0.1 % to +0.1 % of the referenced number. Moreover, with reference to numerical ranges, these terms should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a
disclosure of from 1 to 10 should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, from 8 to 10, and so forth. [000100] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention. [000101] As used herein, the term “ceramic material” means a nonmetallic, inorganic material. In certain embodiments, it means a material selected from the group consisting of oxides, carbides, nitrides and borides. [000102] As used herein, the phrase “reduced laser reflectivity compared to the copper particles”, with respect to the ceramic material and/or ceramic particles, means that for at least one wavelength within a wavelength range, the reflectivity of the ceramic material powder and/or ceramic particle powder is less (at that specific wavelength) than the laser reflectivity of the copper particle powder of the composition. In other words, a powder sample of the ceramic material and/or ceramic particles should have lower laser reflectivity at least one wavelength as compared with a comparable powder sample (i.e. of comparable volume, density and/or dimensions) of pure copper particles (at that specific wavelength), optionally of pure copper particles having an average particle size of around 50 µm. In certain embodiments, the at least one wavelength is in the range of from about 475 to about 600 nm. For example, Al
2O
3 has negligible optical absorption at a wavelength of 1070 nm, so a powder sample of Al2O3 has a high or equal reflectivity at a wavelength of 1070 nm, compared to a powder sample of pure copper particles. In contrast, ceramics such as LaB
6, have appreciable absorption at a wavelength of 1070 nm, and hence a powder sample of LaB
6 has a lower reflectivity compared to a pure copper sample at a wavelength of 1070 nm. [000103] As used herein, the phrase “the ceramic material reduces the laser reflectivity of the copper particles”, means that for at least one wavelength within a wavelength range, the laser reflectivity of a composition comprising copper particles and the ceramic material (in a substantially uniformly distributed mixture) is less than the laser reflectivity (at that specific wavelength) of a comparable sample (i.e. having comparable volume, density, and/or dimensions) comprising only copper particles. In certain embodiments, the at least one wavelength is in the range of from about 475 to about 600 nm. For example, Al2O3 has negligible optical absorption at a wavelength of 1070 nm, so it is unlikely that the addition of Al
2O
3 particles to the copper particles would reduce the reflectivity of the powder composition compared to pure copper powder sample, at a wavelength of 1070 nm. In contrast, ceramics such
as LaB6, have appreciable absorption at a wavelength of 1070 nm, and therefore the reflectivity of a powder composition of LaB6 and copper would have a lower reflectivity compared to a pure copper powder sample at a wavelength of 1070 nm. ABBREVIATIONS [000104] AM: additive manufacturing; APT: atom probe tomography; BD: building direction; BSE: backscattered electron; CBS: concentric backscattered; CP-Ti: commercially pure (≥ 99wt.%) titanium; Cu: Copper; DED: directed energy deposition; DICTRA: Diffusion- Controlled Transformation; EP-PBF: electron beam-based powder bed fusion; EBSD: electron backscatter diffraction; EDS: energy dispersive X-ray spectroscopy; FIB: focused ion beam; FVM: finite volume method; HCP: hexagonal close-packed; ICP-AES: inductively coupled plasma atomic emission spectroscopy; IHT: intrinsic heat treatment; IPF: inverse pole figure; IVAS: integrated visualization and analysis software; LbL: layer-by-layer; L-PBF: laser powder bed fusion; Micro-CT: microfocus computed tomography; SEM: scanning emission microscopy; UTS: ultimate tensile strength; YS: yield strength. [000105] Preferred features, embodiments and variations of the invention may be discerned from the following Examples which provides sufficient information for those skilled in the art to perform the invention. The following Examples are not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. EXAMPLES Example 1: Cu powder [000106] Gas atomized oxygen-free Cu powder with a minimum purity of 99.95 wt%, globally spherical in shape and having a particle size ranging from 15 μm to 53 μm were used as a feedstock. Example 2: inventive LaB
6-Cu composition [000107] High purity (99.9%) LaB6 nanoparticles with the average size of 100 nm were used as an additive (Fig.5) to the Cu powder feedstock. [000108] LaB
6 nanoparticles were first ultrasonically vibrated for 0.5 h by using Retsch® UR 1 to dissociate agglomerates, followed by mechanical mixing with pure Cu powder in a Turbula for 0.5 h to ensure a homogeneous distribution. After the feedstock preparation, the powder mixtures were characterized by scanning emission microscopy (SEM, Hitachi SU3500) equipped with energy dispersive X-ray spectroscopy (EDS). Most of LaB6 nanoparticles electrostatically stuck to and coated the larger Cu powder. An overall uniform distribution of LaB6 nanoparticles on the surface of Cu powder was achieved after mixing (Fig.5). Micrometer-scale LaB
6 powder with particle size ranging from 1 μm to 10 μm were also employed in order to compare with the nanometer-scaled LaB6 doped Cu.
Example 3: comparative TiB2 composition [000109] High purity (99.9%) TiB2 nanoparticles with an average size of 100 nm were also mixed with Cu powder (Fig.8) using a similar process as for the LaB
6-Cu composition. Laser reflectivity measurements [000110] The laser reflectivity of the as-received powder and powder mixtures was measured using a double-beam UV-Visible-NIR Lambda 1050 PerkinElmer spectrophotometer equipped with a 150 mm integrating sphere in the 250-2000 nm wavelength range. Laser powder bed fusion fabrication [000111] The powder mixtures were subjected to laser powder bed fusion (L-PBF) manufacturing in a SLM125HL system (SLM Solutions Group AG) with a maximum laser power of 400 W and spot size of 80 μm. Based on preliminary parameter optimization carried out for pure Cu powders to obtain a built part with minimum defects, a laser power of 375 W, scanning speed of 400 mm/s, layer thickness of 30 μm, and hatch spacing of 120 μm were adopted as the optimal parameters to fabricate pure Cu and ceramic-doped Cu parts. In order to avoid the oxidation of the specimens during L-PBF, the fabrications were conducted under a high purity (≥99.9%) argon atmosphere with the oxygen concentration below 0.05 vol.%.316 stainless steel was used as the building substrate and was preheated to 200°C during L-PBF. [000112] Dog bone-shaped blocks were L-PBF fabricated samples for microstructure analysis and tensile tests. The blocks had a gauge length of 10 mm, gauge width of 2.5 mm, and thickness of 40 mm. [000113] Sheet-based gyroid lattice structures with a porosity of 70% and overall dimension of 30 mm × 30 mm × 30 mm were designed to contain 5 × 5 × 5 arrays of unit cells and fabricated by L-PBF using both pure Cu and nanometer-scaled LaB
6 doped Cu feedstocks for compression tests. Heat treatment [000114] In order to show the ability of resisting softening of inventive LaB
6-Cu structures, an annealing treatment for L-PBF fabricated specimens was performed at various temperatures ranging from 550 °C to 1050 °C for 1 h in a vacuum furnace, followed by furnace cooling to ambient temperature. Microstructure characterization [000115] All the metallographic samples were first grinded using SiC grinding papers followed by polishing using Al2O3 suspensions and etching in a corrosive reagent of 50 ml HCl, 20 mL Fe
3Cl, and 30 mL C
2H
5OH for 3 sec. The surface morphology observations of L-PBF fabricated specimens were conducted on Hitachi SU3500 SEM. The grains size, grain morphology and crystallographic orientation were characterized by electron backscatter diffraction (EBSD)
analysis on a FEI Scios field emission SEM. Prior to EBSD, the surface of the samples was electropolished as finishing step by using Stuers electrolyte D2. A scan step size of 1.2 μm was used for low magnification overview, and 0.2 μm for high magnification analysis and dislocation density calculation. In addition, the typical element distribution of the polished samples was analyzed by SEM and EDS at an accelerating voltage of 20 kV. [000116] To show the nanoparticle distribution, the electropolished samples were etched by gallium ions with focused ion beam (FIB) and SEM images were acquired at a 52° tilt to expose the nanoparticles on the sample surface using a FEI Scios FIB-SEM instrument. FIB was used to prepare TEM lamellas. A Hitachi HF5000 transmission electron microscope (TEM), equipped with a probe aberration corrector and symmetrically opposed dual EDS detectors and operated at an acceleration voltage of 200 kV, was used to comprehensively and thoroughly characterize the substructure characteristics of the samples in both TEM and scanning-TEM (STEM) modes. The diondo d2 micro-computed tomography (microCT) system was used to analyze the micropores in the L-PBF fabricated pure Cu and LaB6-Cu.2D slice image data were acquired through an X- ray source with the voltage set to 120 kV and the current set to 100 μA. The exposure time was 2000 ms with a scanning solution of 4 μm. Elemental analysis [000117] Compositional analysis of the 1.0LaB6-Cu (being parts printed using L-PBF from a Cu and 1 weight per cent (wt%) LaB
6 nanoparticles feed) was performed using atom probe tomography (APT). Although the atomic ratio of B to La appeared less than 6:1 (Fig.24), due to the formation of surface boron hydride and the trajectory aberration caused by the different evaporation fields of the nanoparticles and Cu matrix, the APT data approximately showed formation of nanoparticles rather than them dissolving in the Cu matrix (Fig.27). This indicates that the dissolution of La and B in the Cu matrix was very dilute, which minimized the reduction in conductivity. This is further supported by the XRD analysis, which showed that the lattice parameter of the Cu matrix is the same as pure Cu, suggesting that minimal La or B was dissolved in the solid Cu matrix (Fig.26c). In general, the APT elemental analysis supports the hypothesis that La and B tend to in situ form La–B nanoparticles, as negligible La and B were detected in the Cu matrix except for the La and B enrichment regions. The XRD (Fig.26) and TEM (Fig.2e) results confirmed that the nanoparticles are LaB
6. Therefore, the externally added LaB6 particles that were irregular in shape and larger in size are postulated to have dissolved in the melt pools during AM and the observed LaB6 nanoparticles are the product of re- precipitation during solidification. Mechanical property testing
[000118] The dog bone-shaped tensile specimens with gauge dimension of 10 mm (length) × 2.5 mm (width) × 2 mm (thickness) were machined from the as-built parts along the vertical direction. Tensile loading in the direction perpendicular to the building direction was performed on an Instron 5584 universal testing machine equipped with an advanced Instron video extensometer at a constant strain rate of 0.001 s
-1. Four tensile tests were performed for each addition and heat treatment condition, and the average value was used as the testing result. After tensile testing, the fresh fracture morphology was inspected by using SEM. [000119] Uniaxial compression tests of sheet-based gyroid lattice structures were conducted along the build direction on an Instron 5584 universal testing machine. During compression, the samples were centrally located between two pressure plates and the top plate was moved with a strain rate of 0.001 s
-1 in accordance with standard ISO13314-2011. The compression process was recorded using a video camera at a rate of 50 frames per second. Frames extracted from these videos were then correlated with features in the associated stress-strain data, providing detailed information regarding the failure modes of Cu and LaB6-Cu. All gyroid lattice structures were compressed until the densification stage. Electrical conductivity testing [000120] The electrical conductivity was measured on three samples using a four-point probe method on a ZEM-3 electric resistance measurement system at room temperature. Results and Discussion [000121] Pure Cu and LaB
6-Cu parts were fabricated by L-PBF as discussed above. Despite the relatively high energy density used for laser melting, pure Cu parts produced by L-PBF showed discontinuous scanning tracks having a rough surface (Fig.1a), due to the balling effect. This leads to lack-of-fusion defects as the successive layers are fused. By contrast, the LaB
6-Cu fabricated part exhibited well-defined laser scanning tracks (Fig.1b). Additionally, the LaB
6-Cu had much higher density and relatively large grains as compared with pure Cu (Fig.6). In fact, with the increase in 3D printability, highly dense LaB
6-Cu samples could be 3D printed with a much wider L-PBF processing window (Fig.7). TEM-EDS analysis revealed that the La-and B- rich nanoparticles were homogeneously distributed in the as-fabricated part (Fig.1d). [000122] The LaB6 addition level was optimized based on part density and tensile testing results. After building samples with 0.5-2.0 wt% LaB
6 additions, it was found that 1.0 wt% addition was the lowest addition to ensure the density over 99.5% measured using micro-computed tomography (micro-CT) analysis (Figure 6). This was further confirmed through Archimedes’ method. In addition, this addition level also corresponded to the optimal strength and ductility compared to the lower addition of 0.5 wt% and higher addition of 2.0 wt% (Fig.9d). In contrast to 1.0LaB6-Cu, 0.5LaB6-Cu (0.5 wt. % LaB6 and Cu) printed parts had reduced density, and
nanoparticle agglomeration was observed in the 2.0LaB6-Cu (2.0 wt. % LaB6 and Cu) printed parts (Fig.9e), leading to a reduction in the strength and ductility. [000123] A comparative experiment using TiB
2 nanoparticles with the same particle size and addition level as the LaB6 was also performed using L-PBF. Compared to LaB6, TiB2 had a higher laser absorptivity (Figs.8a and 8b). As expected, the as-fabricated part exhibited very high density without any cracks (Fig.8c). However, a closer look at the microstructure using SEM showed that agglomeration of TiB2 occurred at the grain boundary (Fig.8d). This could be attributed to relatively high wetting angle between TiB2 nanoparticles and Cu melt. Furthermore, the relatively high melting point of TiB
2 may lead to incomplete melting of the particles. Accordingly, the solid solubility of Ti in Cu could inhibit the re-precipitation of TiB
2 from the melt and reduce the conductivity. The 1.0TiB2-Cu only achieved an ultimate tensile strength of 252 ± 4 MPa (Fig.8f) and an electrical conductivity of 91.2% IACS, which were both lower than for the 1.0LaB
6-Cu printed part. This confirms that both high laser absorptivity and the ability to achieve self-stabilization in the melt may be necessary to produce high-density and homogeneously dispersed Cu parts. [000124] LaB
6 nanoparticles were analysed using a focused ion beam (FIB) SEM at a 52° tilt, which allowed for exposure of nanoparticles on the Cu matrix surface. The LaB
6 nanoparticles were found to be uniformly distributed in the grain interior without apparent agglomeration at the grain boundary (Figs.2a and 2b). This is in contrast to other work using conventional manufacturing processes. [000125] The nanoparticles were characterized using transmission electron microscopy (TEM) which showed a uniform distribution of LaB6 across a grain boundary (Fig.2c). The LaB6 nanoparticle exhibited a cuboid morphology which was fully coherent with the Cu matrix (Figs. 2d and 2e). Given the initial irregular morphology of LaB
6 particles in the feedstock and the observed finer uniform particle size in the microstructure (Fig.5), the inventors postulate that the LaB
6 particles may have undergone a melting and subsequent solidification process during the AM process. To prove that the re-precipitation of LaB
6 nanoparticles directly occurs in solidification and to exclude the possibility of solid-state phase transformation induced by thermal cycling, an additional single-track experiment was performed using the 1.0LaB6-Cu (1 wt. % LaB
6 nanoparticles and Cu) feedstock and the same L-PBF processing parameters as the bulk sample. Despite the fact that the size and density of LaB6 nanoparticles in the single-track sample differ from those in the bulk sample due to layer-layer and track-track laser remelting that can potentially modify the size and density in the bulk sample, large number of rectangular- shaped nanoparticles were visible in the single-track sample (Fig.2f-h). This confirms the re- precipitation of LaB6 nanoparticles during solidification in the L-PBF process. In addition, a
crystallographic examination did not reveal any reproducible orientation relationship between the LaB6 nanoparticles and the Cu matrix (Fig.2e, Fig.28), which suggested an incoherent interface between the nanoparticles and the matrix. If the LaB
6 nanoparticles precipitated from the solidified Cu, they should display either coherent or semi-coherent interfaces with the matrix to lower the interfacial energy. As such, reproducible orientation relationships would be generally observed. Therefore, the LaB
6 nanoparticles appear to precipitate directly from the Cu melt during solidification rather than from solid-state phase transformations. A repeated test using micro-size (rather than nano-size) LaB6 particles as the additive confirmed that such a melting and solidification process appears to occur during L-PBF (Fig.5), which was further supported by a thermodynamic analysis based on HSC Chemistry software (Fig.10). Such uniformly dispersed, coherent nanoparticles are often desirable for high strengthened metallic materials. [000126] To evaluate the effect of LaB
6 nanoparticles on the mechanical and physical properties of fabricated parts, tensile testing and electrical conductivity measurement were performed for both pure Cu and LaB6-Cu fabricated parts. [000127] The pure Cu fabricated part showed an inferior ultimate tensile strength of 120.9 ± 1.4 MPa and an elongation to failure of 10.8 ± 1.1% (Fig.3a), with an electrical conductivity of 88.3% IACS (Fig.3b). This can be explained by the presence of relatively large cracks and pores in the microstructures (Fig.1c), owing to the low laser processability of pure Cu. In contrast, the 1.0LaB
6-Cu composition, when fabricated into a part, exhibited substantial enhancement of both strength and ductility, showing around 3.4 times the ultimate tensile strength and around 2.1 times the elongation to failure of pure Cu – yet with an improved electrical conductivity of 98.4% IACS (Fig.3b). [000128] In comparison to the as annealed pure Cu (yield strength of 80 MPa), the strength improvement in the newly developed LaB6-Cu is about 248 MPa (Fig.3). The major strengthening mechanisms are thought to include dispersion strengthening, dislocation strengthening and load-bearing transfer. In particular, dispersion strengthening could occur through dislocation bypass of the homogeneously dispersed LaB6 nanoparticles. In addition, a high density of dislocations is typically found in L-PBF fabricated parts, which is associated with the heating-cooling cycles stemmed from L-PBF. This is also true for the L-PBF fabricated 1.0LaB6-Cu (Fig.11f, g), leading to a dislocation strengthening contribution. [000129] Without being bound by theory, the inventors of the present invention postulate that the strength increase may be attributed to dispersion strengthening via LaB
6 nanoparticles, while ductility and electrical conductivity improvements may result from the higher density of the as- fabricated part. The outstanding strength and ductility combined with superior electrical
conductivity make the inventive LaB6-Cu manufactured part superior to conventionally and additively manufactured Cu and Cu alloys (Fig.3b). [000130] For example, the LaB
6-Cu fabricated part shows a good balance of strength and ductility compared with additively manufactured Cu alloys by L-PBF while with much higher electrical conductivity. Additionally, although LaB6-Cu fabricated parts show comparable electrical conductivity to Cu composites produced by conventional processes, its unique combination of mechanical properties, coupled with the shaping capability of AM, would be more attractive for applications where mechanically robust, electrically conductive as well as geometrically complex Cu components are required. Although graphene-reinforced Cu matrix composites produced in the art may have slightly higher electrical conductivity and ductility, the inventive L-PBF produced LaB6-Cu can achieve higher strength and unparalleled level of geometry complexity, yet at lower cost owing to the small additive level and much lower cost of LaB
6 when compared with graphene. [000131] In addition to the room-temperature tensile properties, the LaB6-Cu fabricated part also showed an excellent ability to resist softening. Cu and Cu alloys are often used in various applications in which they are subject to thermal exposures. After exposure to elevated temperatures, they may suffer from substantial strength loss, which can lead to service failures. Unlike Cu alloys and other oxide dispersion-strengthened Cu which show relative low softening temperature (typically below 600 °C) due to the coarsening of strengthening particles, the LaB
6- Cu fabricated part showed exceptional ability to resist softening at 550 °C, and even to 1050 ºC (Fig.3a, Figure 25), thought to be due to the thermal and chemical stability of LaB6 nanoparticles. [000132] Increasing the annealing temperature to 1050 °C still kept 80% of the yielding strength while maintaining higher elongation to failure of 28% (Fig.3b). SEM characterization demonstrated that such a high annealing temperature does not result in notable particle coarsening which is often detrimental to the strengthening effect (Fig.11e). The strength loss was mainly attributed to the reduction in dislocation density, as revealed and estimated by EBSD characterization (Figs.11c and 11d). [000133] The compressive properties of fabricated porous Cu components were next tested. As an illustrative example to show the ability of the LaB
6-doped Cu to bear compression loading, sheet-based gyroid lattice structures were fabricated by L-PBF using both pure Cu and LaB6- doped Cu feedstocks. The pure Cu gyroid structure showed inferior mechanical response to loading and underwent dramatic post-yielding softening at strain range of 15-20% (Fig.4a), due to the occurrence of localized shear band (Fig.12a). By contrast, the addition of LaB
6 to Cu not only remarkably enhanced the yield strength (4 times that of pure Cu), but also resisted the
appearance of shear band localization (Fig.12b), although slight softening behaviour did occur at a higher strain level (between 25% and 30%) (Fig.4a). [000134] Fig.4b summarizes the compressive yield strength of porous Cu parts versus their relative density. In general, lattice structures made from Cu or Cu alloys show increasing yielding strength with increasing relative density. The LaB6-doped Cu materials have a yield strength of 22.6 MPa at a relative density of 0.3, which is 4.5 times the strength of porous Cu with the same relative density. Besides, the yield strength of LaB6-Cu is comparable to that of porous pure Cu at a much higher relative density (that is, 0.439 and 0.485), making it attractive for applications where the total mass or volume of lattice structures is the critical design criterion. [000135] Overall, by combining the design freedom afforded by AM with the LaB6 and Cu feedstock, it was possible to achieve outstanding tensile and conductive properties, but also create geometrically complex components with superior ability to resist compressive loading. Comparison with AM fabricated pure Cu using green laser and electron beam [000136] In comparison to use of an infrared laser, AM using a green laser provides a pathway to produce highly dense Cu parts because the laser absorptivity of pure Cu can be substantially improved with a lower wavelength of about 515 nm. However, metal 3D printers equipped with a green laser are not currently commercially available. Furthermore, a green laser beam typically has a spot diameter over 200 μm, which is significantly larger than that of an infrared laser (~80 μm). A larger laser beam generally results in lower resolution of 3D printed parts. Hence, some pure Cu parts such as heat exchangers, which are geometrically complex and contain thin walls, cannot be readily printed with a green laser. More importantly, pure Cu is intrinsically soft and shows significantly softening at elevated temperatures. This has been a long-standing issue as most commonly used strengthening methods reduce the conductivity of pure Cu. Although a green laser 3D printer can be used to create pure Cu parts with a high density, the metal is still soft. Alternatively, AM with an electron beam (EB) enables the fabrication of high-density pure Cu parts, yet with a comparable fabrication feature size to those with an infrared laser. However, similarly to the use of a green laser, pure Cu components produced using EB-based AM technology typically show low strength and the inability to resist thermal softening at elevated temperatures. [000137] The tensile properties of 3D printed pure Cu using a green laser and electron beam were compared to those of parts printed from 1.0LaB6-Cu feed as shown in Fig.29. Although 3D printing with a green laser or an electron beam produced pure Cu parts with high ductility and conductivity, their strength (yield strength of 69-180 MPa) was as low as that of annealed pure
Cu. In contrast, the use of 1.0LaB6-Cu achieved much higher strength (yield strength of 347 MPa) without significantly reducing the conductivity (98.4% IACS). Reuse of mechanically mixed powders [000138] Reusing powder in laser powder bed fusion (L-PBF) process is important to render the L-PBF process economically feasible and sustainable. In view of this, the effects of powder use on the mechanical behaviour, densification and electrical conductivity on parts processed using L-PBF from 1 wt.% LaB6 and copper powder was tested. [000139] Parts were printed using a laser power of 375 W, scanning speed of 400mm/s (energy density of 260 J/mm
3). A virgin 1 wt.% LaB
6 and copper powder was cycled a total of 30 times, and powder morphology was observed of the virgin powder, and after printing cycles 4, 8, 12, 16, 20, 24, and 29 as shown schematically in Figure 13. The virgin powder was cycled up to 30 times.6kg powder was used for each printing, and after each printing cycle, the powder was sieved with a 63μm opening to remove any impurities and fused particles. Then approximately 500g new powder was refilled together with the previous stock so as to always ensure 6kg of powder was used for each printing. [000140] Powder morphologies of the powder samples at low and high magnifications are shown in Figure 14. [000141] The virgin powder (Figure 15A) exhibited spherical copper powder with a particle size ranging from 10-53 μm. Relatively larger copper particles always had many small satellite particles attached. Nano LaB
6 particles were almost uniformly attached to the copper powder particles, and had a particle size of 60 to 100 nm (Figure 16). [000142] Although there was no large difference between the virgin powder and reused powder, the reused copper powder showed defects with the powder exhibiting a non-spherical morphology. In addition, nano LaB
6 particles started to form agglomerates between copper particles in the reused powder with increasing printing cycles (Figure 15B). [000143] The waste powder (after sieving) was produced from spattering during the consecutive building cycles, and contained larger agglomerates which were typically larger than 100 μm particle size. [000144] Blocks were printed from the powder (Figure 17C) having the shape depicted in Figure 17A (and shown printed in Figures 17D and 17E), with samples 1-7, being 2mm thick horizontal slices with dimensions shown in Figure 17B and as printed in Figure 17F, used for mechanical testing. [000145] Tensile test results for the printed samples from each printing cycle are shown in Figures 18-19, and densification analysis of the printed samples from each printing cycle are shown in Figure 21.
[000146] Printing cycle number 4 had the lowest YS, UTS, as well as the lowest elongation (~20%). Investigation of its fracture surface (Figure 20C and 20D) showed that large voids and shallow dimples dominated the fracture morphology. [000147] Printing cycle number 2 had the highest YS, UTS and a high elongation (~28%). The fracture surface (Figures 20A and 20B) comprised many dimples and voids of various sizes. A higher fraction of area was covered with severe plastically deformed regions having ripple walls indicating that the sample from printing cycle number 2 had undergone a more intense ductile fracture than other samples. [000148] In summary, the chemical composition of the virgin, reused and waste powder was very similar. Cu-LaB
6 parts made from virgin and reused powder exhibited a comparable strength. However, the ductility was affected by the porosity of the printed samples. The electrical conductivity remained high with increasing number of printing cycles. These results show that the mechanically mixed power is suitable for reuse for at least 30 printing cycles. [000149] In summary, the inventors of the present invention have demonstrated a pathway that enables the fabrication of highly dense Cu parts with outstanding mechanical and physical properties through addition of ceramic (e.g. LaB
6) particles. The example inventive LaB
6-doped Cu exhibited 3.4 times the tensile yield strength and 2.1 times the elongation to failure of pure Cu, while possessing high electrical conductivity of an electrical conductivity of 98.4% IACS (International Annealed Copper Standard) and excellent ability of resisting softening at 1050 °C. The key to this approach is to introduce ceramic particles to pure Cu, which can enable enhancement of laser absorbability in the laser-powder interaction during L-PBF and self- stabilization and dispersion in the solidification process. The newly developed ceramic particle (e.g. LaB
6) containing Cu compositions for fabrication by L-PBF could be used in applications where more demanding mechanical and physical properties are required, and could advance the development of alloys with low laser processability. [000150] LaB
6 powder has a laser reflectivity of 30%, which is much lower than that of pure Cu (78%) (Fig.5). Without being bound by theory, the inventors postulate that the laser reflectivity of Cu feedstock can be reduced if a sufficient amount of additive LaB6 particles are capable of adhering on the surface of Cu powder. In addition, LaB6 exhibit a lower melting point of 2210 °C (Table 1, Table 2), as compared to other borides, such as TiB
2, which also exhibits a low laser reflectivity. The relatively low melting point of LaB6 and the capacity of achieving very high temperature by L-PBF offers the possibility of melting and solidification of LaB6 during AM, thus promoting in-situ formation of LaB
6 nanoparticles. Furthermore, LaB
6 exhibits a low wetting angle (71°) with molten Cu, and small attractive van der Waals potential (-127.2 ~ 0 zJ), L-PBF provides high thermal energy (27.6 zJ), which the inventors postulate may be important
for the nanoparticle dispersion and self-stabilization mechanism, allowing for a homogenous distribution of LaB6 nanoparticles in the Cu matrix. Table 1: The physical properties of conductive ceramics. Table 2: Physical properties of commonly used ceramics.
[000151] Without wishing to be bound by theory, the inventors of the present application postulate that oxides, carbides, nitride, and borides possessing low electrical resistivity may be beneficial to concurrently improve strength and retaining the high electrical conductivity of pure Cu. In general, three interactions between nanoparticles may be considered in molten metal: van der Waals potential, Brownian motion energy, and interfacial energy. The inventors postulate that highly dispersed ceramic nanoparticles may be achievable in molten metals (e.g. molten copper) by synergistically reducing attractive van der Waals forces, providing high thermal energy for dispersion, and creating a high energy barrier to prevent clustering. [000152] The inventors postulate, for example, that good wetting between molten Cu and ceramic nanoparticles may create an energy barrier to reduce the possibility of nanoparticles contacting with each other, thereby preventing clustering. The inventors postulate that the better the wetting between ceramics nanoparticles and molten Cu (smaller θ), the higher the energy barrier that prevents clustering of ceramic nanoparticles. [000153] Without wishing to be bound by theory, it is believed that the incorporation of ceramic nanoparticles having reduced laser reflectivity compared to pure copper particles, having a suitably low melting point such that they can be at least partially molten under the conditions of L-PBF AM (e.g. having a melting point below about 3000°C), and having a sufficiently low liquid copper wetting angle (e.g. less than about 90°), into copper feedstock may result in copper containing fabricated parts having desirable properties (e.g. improved strength, and/or ductility, and/or high conductivity). In other words, firstly, the additive particles possess much higher absorptivity (lower laser reflectivity) in comparison to Cu. Secondly, these particles are capable of achieving a uniform dispersion in Cu matrix which is thought to enable strength enhancement. [000154] Other embodiments of the invention as described herein are defined in the following paragraphs: 1. A composition for additive manufacturing, the composition comprising: copper particles; and ceramic particles; wherein the ceramic particles comprise a conductive ceramic material comprising: • a melting point of about 3000°C or less, or about 2900, 2800, 2700, 2600, or 2500 °C or less, or from about 500 °C to about 3000 °C, or from about 800 °C to about 3000 °C, about 1000 °C to about 3000 °C, about 1500 °C to about 3000 °C, about 500 °C to about 2800 °C, about 1000 °C to about 2800 °C, about 1500 °C to about 2800 °C, about 2000 °C to about 3000 °C, or about 2000 °C to about 2800 °C, or about 500, 600, 700, 800, 900, 1000, 1100, 1200, 1500, 1800, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, or 3000 °C;
• a liquid copper wetting angle of about 90° or less, or about 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, or 10° or less, or from about 0° to about 90°, or about 0° to about 80°, about 0° to about 75°, about 10° to about 90°, about 20° to about 90°, about 30° to about 90°, about 40° to about 90°, about 50° to about 90°, about 60° to about 90°, about 60° to about 80°, or about 65° to about 75°, or about 0, 1, 2, 5, 10, 20, 30, 40, 50, 55, 60, 65, 70, 75, 80, 85 or 90°; and • reduced laser reflectivity compared to the copper particles, optionally from about 0.1 % to about 99.5 %, or from about 2 % to about 99 %, about 4 % to about 99 %, about 6 % to about 99 %, about 8 % to about 99 %, about 10 % to about 99 %, about 15 % to about 99 %, about 30 % to about 99 %, about 50 % to about 99 %, about 75 % to about 99 %, about 0.1 % to about 97 %, about 0.1 % to about 94 %, about 0.1 % to about 90 %, about 0.1 % to about 80 %, about 0.1 % to about 70 %, about 10 % to about 75 %, about 25 % to about 75 %, about 40 % to about 75 %, about 50 % to about 75 %, about 60 % to about 75 %, about 10 % to about 60 %, about 10 % to about 50 %, about 10 % to about 40 %, or about 10 % to about 40 %, or greater than or equal to about 0.1 %, 1 %, 2 %, 3 %, 4 %, 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 16 %, 23 %, 30 %, or 36 %, or less than or equal to about 99 %, 97 %, 94 %, 92 %, 89 %, 87 %, 85 %, 82 %, 80 %, 77 %, 75 %, 68 %, 62 %, 56 %, or 49 %, or about 0.1 %, 1 %, 2 %, 3 %, 4 %, 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 13 %, 16 %, 20 %, 23 %, 26 %, 30 %, 33 %, 36 %, 39 %, 42 %, 46 %, 49 %, 52 %, 56 %, 59 %, 62 %, 65 %, 68 %, 72 %, 75 %, 80 %, 82 %, 85 %, 87 %, 89 %, 92 %, 94 %, 97 %, or 99 % of the laser reflectivity of the copper particles at a wavelength within the range of from about 350 nm to about 2000 nm, or from about 475 nm to about 750 nm, about 475 nm to about 670 nm, about 475 nm to about 600 nm, about 350 nm to about 600 nm, about 350 nm to about 1000 nm, or about 475 nm to about 2000 nm, or at about 350, 375, 400, 450, 500, 600, 650, 680, 700, 750, 800, 900, 1000, 1200, 1400, 1500, 1700, 1800, 1900, or 2000 nm, or at all wavelengths within the wavelength range of from about 350 nm to about 2000 nm, or from about 475 nm to about 750 nm, about 475 nm to about 670 nm, about 475 nm to about 600 nm, about 350 nm to about 600 nm, about 350 nm to about 1000 nm, or about 475 nm to about 2000 nm; optionally wherein the composition is a powder, optionally a substantially dry powder, optionally wherein the composition does not comprise a gelling agent. 2. The composition according to any one or more of the preceding paragraphs, wherein the ceramic material has an electrical resistivity of about 80, 70, 60, 50, 40, 30, or 20 µΩ·cm or less
at 20 °C, or from about 1 to about 80, or about 5 to about 80, about 1 to about 50, about 1 to about 30, about 5 to about 50, about 5 to about 30, about 10 to about 80, about 10 to about 30, or about 10 to about 20 µΩ·cm at 20 °C, or about 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, or 80 µΩ·cm at 20 °C. 3. The composition according to any one or more of the preceding paragraphs, wherein the ceramic particles are dissociated prior to being added in the composition. 4. The composition according to any one or more of the preceding paragraphs, wherein the ceramic material is selected from the group consisting of oxides, carbides, nitrides and borides, optionally wherein the ceramic material is selected from the group consisting of carbides, nitrides and borides, optionally wherein the ceramic material is selected from f-block or group 5 oxides, carbides, nitrides and borides, optionally wherein the ceramic material is selected from f- block or group 5 carbides and borides. 5. The composition according to any one or more of the preceding paragraphs, wherein the ceramic material is selected from the group consisting of VC, WC, WB, TaB2, and LaB6, optionally VC, TaB2 and LaB6. 6. The composition according to any one or more of the preceding paragraphs, wherein the ceramic material comprises LaB
6. 7. The composition according to any one or more of the preceding paragraphs, wherein the ceramic particles have an average diameter of from about 0.5 nm to about 100 µm, or from 10 nm to about 100 µm, 50 nm to about 100 µm, 10 nm to about 50 µm, 50 nm to about 50 µm, 100 nm to about 50 µm, about 1 nm to about 1000 nm, about 1 nm to about 500 nm, about 2 nm to about 500 nm, about 2 nm to about 100 nm, about 2 nm to about 20 nm, or about 2 nm to about 10 nm, or about 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, 20, 50, 100, 200, 500, or 1000 nm, or about 1.5, 2, 5, 10, 20, 50, 70, or 100 µm, or about 20 nm or less, or about 10 nm or less, or about 100 µm or less, or about 50 µm or less. 8. The composition according to any one or more of the preceding paragraphs, wherein the ceramic particles are nanoparticles. 9. The composition according to any one or more of the preceding paragraphs, wherein the ceramic material has a melting point of about 2800 °C or less. 10. The composition according to any one or more of the preceding paragraphs, wherein the copper particles comprise about 90 wt.% or more, or about 95 wt.% or more, about 97 wt.% or more, about 98% or more, about 99 wt.% or more, about 99.5 wt.% or more, or about 99.7 wt.% or more, 95% or more, 97% or more, 99% or more, or substantially pure copper. 11. The composition according to any one or more of the preceding paragraphs, wherein the ceramic particles at least partially coat a surface of the copper particles, optionally wherein at
least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of their outer surface area is coated with the ceramic particles. 12. The composition according to any one or more of the preceding paragraphs, wherein the ceramic particles are present in an amount of from about 0.01 wt.% to about 20 wt.%, or from about 0.02 wt.% to about 10 wt.%, about 0.05 wt.% to about 10 wt.%, about 0.05 wt.% to about 5 wt.%, about 0.1 wt.% to about 5 wt.%, about 0.1 wt.% to about 10 wt.%, about 0.1 wt.% to about 15 wt.%, or about 0.1 wt.% to about 20 wt.%, or about 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, or 20 wt.%, or from about 0.1 wt.% to about 5 wt. % in the composition, optionally from about 0.6 wt.% to about 1.9 wt.%. 13. The composition according to any one or more of the preceding paragraphs, wherein the ceramic particles are present in an amount of about 1 wt.% in the composition. 14. The composition according to any one or more of the preceding paragraphs, wherein the copper particles have an average diameter of from about 0.5 nm to about 100 µm, or from 10 nm to about 100 µm, 50 nm to about 100 µm, 10 nm to about 50 µm, 50 nm to about 50 µm, 100 nm to about 50 µm, about 1 nm to about 1000 nm, about 1 nm to about 500 nm, about 2 nm to about 500 nm, about 2 nm to about 100 nm, about 2 nm to about 20 nm, or about 2 nm to about 10 nm, or about 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, 20, 50, 100, 200, 500, or 1000 nm, or about 1.5, 2, 5, 10, 20, 50, 70, or 100 µm, or about 20 nm or less, about 10 nm or less, about 100 µm or less, about 50 µm or less, or from about 20 µm to about 200 µm. 15. The composition according to any one or more of the preceding paragraphs, which is a feedstock for a 3D printer. 16. The composition according to any one or more of the preceding paragraphs, wherein the ceramic material reduces the laser reflectivity of the copper particles, optionally wherein a 0.1, 0.2, 0.5, 1, 2, or 5 wt.% concentration of the ceramic material in a composition with copper particles reduces the laser reflectivity at a specific wavelength of the composition as compared with a substantially identical composition but without the ceramic material, by at least about 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, or 20%, or it may reduce the laser reflectivity by from about 0.1 % to about 30%, or from about 0.5 % to about 30%, about 0.5 % to about 20%, about 1 % to about 20%, about 1 % to about 10%, or about 0.1 % to about 5%, or it may reduce the laser reflectivity by about 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, or 30% at a specific wavelength within the range of from about 350 nm to about 2000 nm, or from about 475 nm to about 750 nm, about 475 nm to about 670 nm, about 475 nm to about 600 nm, about 350 nm to about 600 nm, about 350 nm to about 1000 nm, or about 475 nm to about 2000 nm, or at about 350, 375, 400, 450, 500, 600, 650, 680, 700, 750, 800, 900, 1000, 1200, 1400, 1500, 1700, 1800, 1900, or 2000 nm,
or at all wavelengths within the wavelength range of from about 475 nm to about 750 nm, optionally from about 475 nm to about 670 nm, optionally from about 475 nm to about 600 nm. 17. The composition according to any one or more of the preceding paragraphs, wherein the wavelength at which the laser reflectivity is reduced is in the range of from about 475 nm to about 750 nm, optionally from about 475 nm to about 670 nm, optionally from about 475 nm to about 600 nm. 18. A method for preparing a composition for additive manufacturing, the method comprising the steps of: providing copper particles; and mixing the copper particles with ceramic particles to form said composition; wherein the ceramic particles are as defined according to any one or more of the preceding paragraphs. 19. The method according to any one or more of the preceding paragraphs, comprising a step of dissociating the ceramic particles prior to the mixing step. 20. The method according to any one or more of the preceding paragraphs, wherein the dissociating is performed using a vibrator, optionally an ultrasonic vibrator. 21. The method according to any one or more of the preceding paragraphs, wherein the dissociating and/or mixing are performed at a pressure below atmospheric pressure, optionally about 100, 50, 30, 20, 10, 5, 2, or 1 kPa, or less, or about 10 kPa or less. 22. The method according to any one or more of the preceding paragraphs, wherein the mixing is performed using a shaker, optionally an electromagnetic shaker. 23. A method for additive manufacturing using the composition according to any one or more of the preceding paragraphs. 24. The method according to any one or more of the preceding paragraphs, which does not comprise a post-formation heating (e.g. annealing) step. 25. Use of a composition according to any one or more of the preceding paragraphs for additive manufacturing. 26. An additive manufactured part made from the composition according to any one or more of the preceding paragraphs, or made from a composition prepared according to the method of any one or more of the preceding paragraphs, or prepared according to the method according to any one or more of the preceding paragraphs. 27. The additive manufactured according any one or more of the preceding paragraphs, which has an electrical conductivity at 20 °C of about 50, 60, 70, 80, 90, or 100 MS/m or more, or about 95, 97, 98, 99, 99.5, or 99.7% or more, or about 50 MS/m or more, or about 95% or more IACS (International Annealed Copper Standard).
28. The additive manufactured part according to any one or more of the preceding paragraphs, which has an elongation to failure of about 5, 10, 15, 20, 15, 30, or 40 % or more, or about 10 % or more. 29. The additive manufactured part according to any one or more of the preceding paragraphs, which has an ultimate tensile strength of about 80, 100, 120, 140, 160, 180, 200, 220, 250, or 300 MPa or more, or about 180 MPa or more. 30. The additive manufactured part according to any one or more of the preceding paragraphs, which has a porosity which is at least about 0.5, 1, 2, 5, 10, 15, or 20% less than the porosity of a comparative part; wherein said comparative part has substantially the same shape and size as the additive manufactured part, and is produced using substantially the same conditions as the additive manufactured part from a composition consisting essentially of copper particles. 31. A kit for additive manufacturing comprising: copper particles; and ceramic particles; wherein the ceramic particles comprise a conductive ceramic material comprising: a melting point of about 3000°C or less; a liquid copper wetting angle of about 90° or less; and reduced laser reflectivity compared to the copper particles. 32. The kit according to any one or more of the preceding paragraphs, when used for an additive manufacturing process, wherein the additive manufacturing process comprises the following steps: mixing the copper particles and ceramic particles to form a composition; and irradiating the composition using a laser. [000155] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. In particular, features of any one of the various described examples may be provided in any combination in any of the other described examples. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.