GB2560509B

GB2560509B - Armour plating

Info

Publication number: GB2560509B
Application number: GB1703863.9A
Authority: GB
Inventors: Mccormack Desmond
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-03-10
Filing date: 2017-03-10
Publication date: 2019-07-24
Anticipated expiration: 2037-03-10
Also published as: GB2560509A; GB201703863D0

Description

Armour Plating [0001] This invention relates to armour plating and methods of manufacture thereof, in particular armour plating for vehicles.

BACKGROUND

[0002] Armour is used to protect important assets from projectiles or blasts from other sources. There are many different types of modern armour.

[0003] US 6357332 discloses a method of forming lightweight armour from a plurality of metal foils of a first metal interleaved with a plurality of metal films of a second metal. In the manufacturing process, the metal film of the second metal is heated above a melting point of the second metal and entirely reacted with some of the first metal to produce a plurality of compounded intermetallic layers between each of the layers of the first metal. In this method of the prior art, any air pockets present between the metal foils are formed into a solid composite material during the process. Although the prior art method uses a solid state diffusion bonding process, an impinging high-energy projectile onto the armour formed still produces a “metal flower”, with petals corresponding to each of the laminate layers. Thus, it can be seen that it is still possible to separate the layers along layer boundaries.

[0004] The present disclosure seeks to provide at least an alternative to armour of the prior art.

BRIEF SUMMARY OF THE DISCLOSURE

[0005] In accordance with the present disclosure, there is provided armour as claimed in claim 1.

[0006] Thus, there is provided armour which can be formed from a plurality of layers, but which, when assembled, provides a material strength equivalent to if the armour had been formed as a single block by casting, moulding and/or machining. Furthermore, forming the armour by diffusion bonding of a plurality of metal layers allows highly intricate designs to be developed by defining one or more void portions in facing surfaces of one or more of the plurality of layers, which could not be easily achieved using prior art casting and machining techniques for forming armour. It will be understood that it will be possible to determine if the armour has been formed by diffusion bonding by analysing the atomic microstructure of the armour and look for diffusion of atoms between two previously separated layers. It will be understood that examining the microstructure alone may not be sufficient where the layers used to form the armour are all of the same material. In cases where the layers used to form the armour are formed from the same material, each having substantially the same material microstructure, it will still be possible to determine that armour was formed by diffusion bonding where it would not otherwise have been possible to form the internal structure of the armour.

[0007] The provision of one or more voids within the armour allows an internal structure of the armour to be configured to best provide an effective armour. For example, the provision of the one or more voids may reduce a weight of the armour compared to armour of the same size, not having the described voids.

[0008] In other words, the interior microstructure of substantially all of the armour may be considered to be substantially the same as an interior microstructure of a block of the metal(s). Thus, the interior microstructure of the armour can be as if the armour was formed by a moulding and I or casting process. In particular, an interior microstructure of the armour will not be stratified into distinct layers. Atoms at a boundary between multiple plates used to form the armour will diffuse into the facing plate at the boundary. Thus, the armour will not have points of structural weakness at an interface between the original layers of metal used to form the armour.

[0009] It will be understood that the term armour as used herein means any material component for providing an armoured function to an asset to be protected, for example a vehicle in the form of a ground vehicle or an air vehicle, or a fixed structure such as a building. In one particular example, the armour is for protecting an armoured fighting vehicle (AFV). The armour may be a planar structure or alternatively may have an outer external surface having a 3D shape. The armour may be an armour plate.

[0010] It will be understood that the at least one void within the armour is to be understood to be a void within an internal structure of the armour. In particular, it is to be understood that the void is defined on substantially all sides by an internal surface of the armour. For the avoidance of doubt, it will be understood that a surface depression in an external surface of the armour and substantially open to an external environment of the armour cannot be considered to be a void.

[0011] An internal surface of the armour defining substantially the whole of at least one of the at least one void(s) may be formed from a single material. Thus, the at least one void may be defined by a surface originally defined by two neighbouring plates, each formed from the same material. Thus, the material properties of the internal surface of the void may be uniform.

[0012] The armour may be formed from a single material. The single material may be a single metal, or may be a metal alloy. Alternatively, the armour may be formed from a plurality of metals or metal alloys.

[0013] As used herein, the term empty does not preclude the void containing the materials of the external environment of the armour, for example air.

[0014] The void(s) may be sealed from an external environment of the armour. In some embodiments, the void(s) may be configured to be sealable from an external environment of the armour. Thus, the external environment of the armour may not penetrate into the void(s) of the armour providing the interior structure of the armour. Alternatively, at least one of the void(s) may be in fluid communication with an external environment of the armour. Thus, the at least one of the void(s) may be unsealed from the external environment of the armour.

[0015] At least one of the at least one void(s) may contain a first component. The first component may be a material, for example a fluid. Thus, it will be understood that the term component can be taken to mean a material in some instances. The material can be a solid, a liquid or a gas. The first component may be formed to be separate from the internal surface of the armour defining the respective void. Thus, the first component is not bonded to the armour by diffusion bonding.

[0016] The at least one void may be a plurality of voids. In some embodiments, at least some of the plurality of voids may be interconnected. In some embodiments, only some of the plurality of voids are interconnected. There may be a plurality of different groups of interconnected voids, each group of interconnected voids being unconnected to any of the other groups through the armour. At least some of the plurality of interconnected voids may be connected in a first direction, substantially parallel to a planar external surface of the armour. Alternatively or in addition, the at least some of the plurality of interconnected voids may be connected in a second direction, substantially transverse to a planar external surface of the armour.

[0017] The plurality of voids may be dispersed throughout the armour. The dispersion of voids through the armour may be substantially uniform.

[0018] The plurality of voids may occupy more than 10 percent of a volume of the armour. The plurality of voids may occupy more than 20 percent of the volume of the armour. The plurality of voids may occupy less than 70 percent of the volume of the armour. The plurality of voids may occupy less than 60 percent of the volume of the armour. The plurality of voids may occupy less than 50 percent of the volume of the armour. The plurality of voids may occupy less than 40 percent of the volume of the armour.

[0019] A subset of the plurality of voids different from the at least one of the plurality of voids containing the first component, may contain a second component different from the first component. Thus, some of the voids may contain a first component, whilst other voids may contain a second component. In some embodiments, there are a plurality of subsets of the plurality of voids, each subset containing a different component.

[0020] The subset of the plurality of voids may be dispersed throughout the plurality of voids. Thus, locations of voids containing the second component may be throughout the locations of voids. The subset of the plurality of voids may be dispersed substantially uniformly throughout the plurality of voids.

[0021] The first component and I or the second component may be a fluid. The first component and I or the second component may be a liquid. The first component and I or the second component may be a gas. Thus, the void(s) may be filled. The first component and I or the second component may be a solid.

[0022] The first component and I or the second component may be configured to enhance an ability of the armour to resist an impact of a projectile. Thus, the first component and/or the second component may fortify an impact resistance of the armour to an impact from a projectile. In some embodiments, the void is configured to fortify an impact resistance of the armour to an impact from a projectile. A shape of the void may be configured to fortify the impact resistance of the armour to the impact from the projectile. This effect can be termed a “passive” effect.

[0023] The first component and I or the second component may be a heat transfer fluid configured to flow through the void whereby to reduce a thermal detectability of armour by distributing heat across the armour. Thus, any “hot spots” of a vehicle or structure covered by the armour can be distributed across a region of the armour by a flow of the heat transfer fluid. This may increase survivability of the vehicle or structure covered by the armour by reducing the maximum temperature of the armour observable from an external environment of the vehicle or structure.

[0024] The first component and I or the second component may be configured to enhance an ability of the armour to interfere with an operation of a projectile. Thus, the first component and/or the second component may prevent a projectile operating as intended by attempting to disable or influence the operation of the projectile. This effect can be termed an “active” effect. In one example, the first component and I or the second component comprise a high capacity capacitor configured to store sufficient energy to vaporize a molten metal core of a projectile when the metal core penetrates through the armour into the void comprising the respective first component or the second component.

[0025] Thus, each of the effects provided by the first and I or the second component may be configured to increase a survivability of the vehicle or structure covered by the armour.

[0026] An aspect ratio of the void(s) may be greater than 3. Thus, the voids may be elongate voids.

[0027] It will be understood that the void(s) may take any of a number of shapes. The voids may have a plurality of different shapes. The void(s) may have a first portion having a first cross-section and a second portion having a second cross-section different from the first cross-section.

[0028] The present disclosure also extends to a method of forming the armour as claimed in claim 18.

[0029] Thus, a new method of forming armour is provided which results in armour having one or more internal voids, but having a material strength within the armour equivalent to a homogenous block of the armour. In particular, the method allows complicated configurations of internal voids to be manufactured, whilst ensuring the material properties are not degraded by a layer-based manufacturing method.

[0030] The armour may be an armour plate.

[0031] The method may further comprise inserting a component into the void(s) after the plurality of metal layers are joined by diffusion bonding. Thus, components for insertion into the voids need not be protected from the high temperatures used during the diffusion bonding process.

[0032] The plurality of metal layers may comprise at least three metal layers. The plurality of metal layers may comprise more than five metal layers.

[0033] At least two of the metal layers provided adjacent one another may be formed from the same material.

[0034] A thickness of one or more of the plurality of metal layers may be greater than 0.5 millimetres. A thickness of each of the plurality of metal layers may be greater than 0.5 millimetres. A thickness of one or more of the plurality of metal layers may be less than 10 millimetres. A thickness of each of the plurality of metal layers may be less than 10 millimetres.

[0035] The method may further comprise machining one or more of the plurality of metal layers to form the at least one void portion.

[0036] Where the first surface or the second surface of the metal layer is provided with a plurality of void portions, the plurality of void portions may be interconnected whereby to form a plurality of interconnected voids, the voids being interconnected in a direction parallel to the first surface. Alternatively or additionally, the void portions on a single metal layer may extend from the first surface to the second surface, whereby to form a plurality of interconnected voids defined by more than two metal layers, the voids being interconnected in a direction transverse to the first surface.

[0037] The plurality of metal layers may be heated to a maximum temperature less than a melting temperature of any of the plurality of metal layers. Thus, the structure of the voids in the armour may correspond substantially to the void portions defined in each of the metal layers because the manufacturing process for joining the plurality of metal layers together is carrier out whilst the metal layers are still in a solid phase.

[0038] The maximum temperature may be less than 95 percent of the melting temperature of any of the plurality of metal layers when measured in Celsius. The maximum temperature may be less than 90 percent of the melting temperature of any of the plurality of metal layers when measured in Celsius. The maximum temperature may be greater than 50 percent of the melting temperature of any of the plurality of metal layers when measured in Celsius.

[0039] The void portions may define one or more channels along the first surface or the second surface of the metal layer. The channels may extend substantially all the way along the metal layer. Thus, the void may be an open channel through the armour in a direction parallel to the first surface or the second surface of any of the metal layers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 is an illustration schematically showing a plurality of metal layers;

Figure 2 is an illustration of the plurality of metal layers of Figure 1 arranged in a stack;

Figure 3 is an illustration of armour formed from the plurality of metal layers shown in Figures 1 and 2 after a diffusion bonding process;

Figure 4 is a diagram showing a plurality of voids in the form of channels defined within the armour of Figure 3;

Figures 5 to 8 are schematic diagrams showing examples of layouts of void portions on a metal layer;

Figures 9 and 10 are schematic diagrams showing examples of layouts of voids defined within armour; and

Figure 11 is an example of a flowchart illustrating a method of forming armour.

DETAILED DESCRIPTION

[0041] Figure 1 is an illustration schematically showing a plurality of metal layers 100. The plurality of metal layers 101 in this example comprises a first metal layer 102, a second metal layer 104, a third metal layer 106 and a fourth metal layer 108. Each metal layer 102, 104, 106, 108 has a respective first surface 110, 112, 114, 116 and a respective second surface (not shown) opposite the first surface. The first surfaces 110, 112, 114, 116 and the second surfaces are arranged to be the surfaces of the metal layers 102, 104, 106, 108. Figure 1 also shows an enlarged schematic diagram of region A. Region A is of the fourth metal layer 108, having the first surface 116 and the second surface 118, opposite the first surface 116. In this example, a void portion in the form of a substantially hemispherical channel 120 is shown defined as a depression within the first surface 116 of the fourth metal layer 108. It can be seen that the channel 120 is one of a plurality of channels orientated parallel to each other and defined on the first surface 116 of the fourth metal layer 108. The channel 120 runs completely across the first surface 116. It can also be seen that channels are also shown on the first surfaces 110, 112, 114 of the respective first, second and third metal layers 102, 104, 106. The channels defined on the first metal layer 102 and the third metal layer 106 are arranged to be transverse to the channels on the second metal layer 104 and the fourth metal layer 108. The hemispherical channel 120 extends approximately halfway of the distance between a top portion of the first surface 116 and the second surface 118. It will be understood that different designs of void portion may extend different amounts into each layer. In some examples, it is important that the number, shape and layout of void portions of adjacent metal layers are configured such that deformation of the void portion is substantially avoided when the plurality of metal layers are joined together to form armour by a diffusion bonding process.

[0042] The metal layers 102, 104, 106, 108 in the present example are formed from similar metals. In particular, the metal layers 102, 104, 106, 108 are formed from alloy steel. It will be understood that the metal layers 102, 104, 106, 108 may alternatively be formed of one or more dissimilar metals.

[0043] In this example, the channel 120 (and the other channels) is formed by machining the metal layers 102, 104, 106, 108, for example by a routing tool (not shown). It will be understood that the channel 120 can be formed in any of a number of ways, for example casting.

[0044] The metal layers 102, 104, 106, 108 are arranged to be substantially the same length and width, but may each have a different thickness. In this example, the thickness of each of the metal layers 102, 104, 106, 108 is approximately 2 millimetres. The metal layers 102, 104, 106, 108 may have a length of approximately 1 metre and a width of approximately 50 centimetres.

[0045] Figure 2 is an illustration of the plurality of metal layers of Figure 1 arranged in a stack of metal layers 100a. Each of the metal layers 102, 104, 106, 108 is a separate layer, but provided adjacent one another with substantially no gap therebetween. As an example, the channel provided in the first surface 114 of the third metal layer 106 is now enclosed by the second surface of the second metal layer 104, providing a void in the form of an enclosed channel 122. As will be appreciated, the enclosed channel 122 shown in Figure 2 is open at both ends and runs all the way through the stack of metal layers 100a.

[0046] Figure 3 is an illustration of armour formed from the plurality of metal layers shown in Figures 1 and 2 after a diffusion bonding process. The stack of metal layers 100a is pressed together and heated whereby to promote diffusion bonding between the plurality of metal layers, resulting in armour in the form of armour plate 100b. The material microstructure within the armour plate 100b is substantially homogenous with grain growth across the former boundaries between the previously separate stack of metal layers 100a.

[0047] An example diffusion bonding process is described in more detail hereinafter with reference to Figure 11. However, it will be appreciated that the temperature must be below a melting temperature of any of the metal layers 102, 104, 106, 108 in order to prevent flow and collapse of the void portions defined in the facing surface between the metal layers. Similarly, the exact pressure will depend on the particular material(s) used for the plurality of metal layers 100 and the temperature to which the metal layers 102, 104, 106, 108 are heated. The pressure must not be so great that the pressure causes the deformation and collapse of the channels.

[0048] Figure 4 is a diagram showing a plurality of voids 124 in the form of channels defined within the armour of Figure 3. As can be seen, the voids in the form of channels 122 are distributed throughout the volume of the armour. In this example, each channel 122 is isolated from other channels, but is open to an external environment of the armour at each side of the armour.

[0049] Figures 5 to 8 are examples of layouts of void portions on a metal layer. Figure 5 shows a metal layer 126 having a plurality of void portions 128 defined on a first surface 130 of the metal layer 126. The plurality of void portions 128 comprise a plurality of first void portions in the form of first channels 128a and a plurality of second void portions in the form of second channels 128b. The first channels 128a are transverse to the second channels 128b and each intersect with each of the second channels 128b. Thus, the plurality of void portions 128 form a grid-like pattern on the first surface 130 of the metal layer 126, and would form an enclosed grid-like void within the armour when a further metal layer (not shown) is diffusion bonded to the first surface 130 of the metal layer 126.

[0050] Figure 6 shows a metal layer 132 having a plurality of void portions 134 defined partially on a first surface 136 of the metal layer 132. The plurality of void portions 134 each comprise a through-hole portion which extends from the first surface 136 through the metal layer 132 to a second surface 138 of the metal layer 132, opposite the first surface 136. Feature A’ shows an enlarged diagram of a cross-section through the metal layer 132, showing the void portion 134 defined in the first surface 136. Thus, the plurality of void portions 134 would form an enclosed void within the armour when two further metal layers are diffusion bonded to the first surface 130 and to the second surface 138 respectively. The enclosed void will extend through the region of the armour which corresponds to the metal layer 134 in a direction parallel to the first surface 136 as well as in a direction transverse to the first surface 136.

[0051] Figure 7 shows a metal layer 140 having a plurality of void portions 142 defined on a first surface 144 thereof. The void portions are each contained within a boundary of the first surface 144. Thus, when a further metal layer (not shown) is diffusion bonded to the first surface 144 of the metal layer 140, each of the void portions 142 can defined a sealed void, unless a facing surface of the further metal layer has a void portion defined therein to correspond to the void portion 142 on the first surface 144 and configured to be in fluid communication with an external environment of the armour.

[0052] Figure 8 shows a metal layer 146 having a plurality of different shaped void portions 148, 150, 152 defined on the first surface 154 of the metal layer 146.

[0053] Thus, it will be appreciated that numerous and varied arrangements of voids may be formed from a plurality of metal layers, each having one or more void portions defined on either or both of the facing surfaces of the metal layers when the metal layers are arranged in a stack to be diffusion bonded together.

[0054] Figures 9 and 10 are schematic diagrams showing examples of layouts of voids defined within armour 156, 162. Figure 9 shows armour 156 having a first group of voids 158 and a second group of voids 160, each group of voids 158, 160 being interconnected and fluidly connected to an external environment of the armour 156.

[0055] Figure 10 shows armour 162 having a first group of voids 164 and a second group of voids 166, each group of voids 164, 166 being interconnected and sealed within the armour 162, such that neither the first group of voids 164 nor the second group of voids 166 is fluidly connected to an external environment of the armour 156. Thus, it will be seen that one or more groups of voids can be defined within an armour formed from multiple metal layers. Similarly, the groups of voids may or may not be sealed within the armour. It will be understood that where there are a plurality of groups of interconnected voids defined within the armour, some of the groups may be sealed from the external environment of the armour, whilst other of the groups may be in fluid communication with the external environment of the armour.

[0056] Figure 11 is an example of a flowchart illustrating a method of forming armour.

The method 200 comprises a first step 202 of providing a plurality of metal layers. Each metal layer comprises a first surface and a second surface. The second surface is opposite the first surface. Each metal layer is provided adjacent at least one other metal layer, such that at least the first surface or the second surface of each metal layer is facing the second surface and/or the first surface respectively of at least one adjacent metal layer. At least one of the first surface or the second surface of at least one of the metal layers has defined therein at least one void portion.

[0057] The surfaces of the metal layers may be formed to have the void portions already defined thereon. Alternatively, the method may also comprise, prior to the first step 202, forming the void portions by a method such as machining.

[0058] The method further comprises a second step 204 of pressing the plurality of metal layers together. At the same time, the plurality of metal layers are also heated. The combination of the applied pressure and heat is such that at which a deformation or collapse of the void portions does not occur. Generally, the applied heat is such that the temperature of the metal layers is below a melting temperature of any of the metal layers. For example, when the metal layers are formed from steel alloy, the method involves heating the stack of metal layers to a temperature of 400 - 600°C, which is below a melting temperature of the steel alloy. At the same time, the stack of metal layers are pressed together at a pressure of 4 bar.

[0059] The method further comprises a third step 206. In the third step 206, the plurality of metal layers are joined together by diffusion bonding after the exposure of the plurality of metal layers to the pressure and heat in the second step 204. The plurality of metal layers are kept under heat and pressure for a duration sufficient to ensure diffusion bonding occurs between the metal layers, for example for at least 8 hours. After the third step 206, it is no longer possible to observe a definitive boundary between each of the plurality of metal layers. When any two adjacent metal layers are formed from similar metals, after diffusion bonding has occurred, it will not be possible to determine the boundary between the metal layers by analysis of the internal material microstructure alone.

[0060] The method also comprises a fourth step 208 of forming armour having at least one void defined by the void portion(s) as a result of the diffusion bonding of the metal layers in the third step 206. In some examples, it is possible that the armour is already formed immediately following the third step 206 when diffusion bonding occurs between the plurality of metal layers.

[0061] When the void(s) are to be filled with one or more materials or other components, this can be done before or after assembling the plurality of layers into the armour by diffusion bonding in the third step 206. In particular, where the materials or other components are unsuitable to be subjected to the heat required for the diffusion bonding process, the one or more materials or other components can be inserted into the voids after the third step 206.

[0062] In summary, there is provided armour (100b) formed from metal. The armour (100b) is formed to define at least one void (122) within the armour (100b). The armour (100b) is formed by diffusion bonding.

[0063] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0064] Features, integers, characteristics, compounds or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention is as defined in the appended claims.

Claims

1. Armour formed from metal, wherein the armour is formed to define at least one void within the armour, wherein the armour is formed by diffusion bonding, and wherein at least one of the at least one void(s) is empty.

2. Armour as claimed in claim 1, wherein an internal surface of the armour defining substantially the whole of at least one of the at least one void(s) is formed from a single material.

3. Armour as claimed in any preceding claim, wherein the void(s) is/are sealed from an external environment of the armour.

4. Armour as claimed in any preceding claim, wherein the void(s) is/are configured to be sealable from an external environment of the armour.

5. Armour as claimed in any preceding claim, wherein the at least one void is a plurality of voids.

6. Armour as claimed in claim 6, wherein the plurality of voids are dispersed throughout the armour.

7. Armour as claimed in claim 5 or claim 6, wherein at least one of the voids contains a first component.

8. Armour as claimed in claim 7, wherein a subset of the plurality of voids different from the at least one of the plurality of voids containing the first component, contain a second component different from the first component.

9. Armour as claimed in claim 8, wherein the subset of the plurality of voids is dispersed throughout the plurality of voids.

10. Armour as claimed in any of claims 7 to 9, wherein the first component is a fluid.

11. Armour as claimed in claim 8 or claim 9, or claim 10 when dependent directly or indirectly on claim 8, wherein the second component is a fluid.

12. Armour as claimed in any of claims 7 to 11, wherein the first component is configured to enhance an ability of the armour to resist an impact of a projectile.

13. Armour as claimed in claim 8 or claim 9, or any of claims 10 to 12 when dependent directly or indirectly on claim 8, wherein the second component is configured to enhance an ability of the armour to resist an impact of a projectile.

14. Armour as claimed in any of claims 7 to 13, wherein the first component is configured to enhance an ability of the armour to interfere with an operation of a projectile.

15. Armour as claimed in claim 8 or claim 9, or any of claims 10 to 14 when dependent directly or indirectly on claim 8, wherein the second component is configured to enhance an ability of the armour to interfere with an operation of a projectile.

16. Armour as claimed in any of claims 7 to 15, wherein the first component is a heat transfer fluid configured to reduce a thermal detectability of an armour by distributing heat across the armour.

17. Armour as claimed in claim 8 or claim 9, or any of claims 10 to 16 when dependent directly or indirectly on claim 8, wherein the second component is a heat transfer fluid configured to reduce a thermal detectability of an armour by distributing heat across the armour.

18. A method of forming armour comprising: providing a plurality of metal layers, each metal layer having a first surface and a second surface opposite the first surface, and each metal layer provided adjacent at least one other metal layer, such that at least the first surface or the second surface of each metal layer is facing the second surface and/or the first surface respectively of at least one adjacent metal layer, wherein at least one of the first surface or the second surface of at least one of the metal layers has defined therein at least one void portion; pressing the plurality of metal layers together whereby to join the plurality of metal layers by diffusion bonding and to form at least one void from the void portion(s); and at the same time as pressing the plurality of metal layers together, heating the plurality of metal layers to promote diffusion bonding between the metal layers; wherein at least one of the at least one void(s) is empty.

19. A method of forming armour as claimed in claim 18, wherein the method further comprises inserting a component into at least one of the void(s) after the plurality of metal layers are joined by diffusion bonding.

20. A method of forming armour as claimed in claim 18 or claim 19, wherein the plurality of metal layers are heated to a maximum temperature less than a melting temperature of any of the plurality of metal layers.

21. A method of forming armour as claimed in any of claims 18 to 20, wherein the plurality of metal layers comprises at least three metal layers.

22. A method of forming armour as claimed in any of claims 18 to 21, wherein the method further comprises machining one or more of the plurality of metal layers to form the at least one void portion.