WO2007020634A2

WO2007020634A2 - Resistant ceramic material and method for making same

Info

Publication number: WO2007020634A2
Application number: PCT/IL2006/000943
Authority: WO
Inventors: Avigdor Zangvil; Michael Katz
Original assignee: CARBOSHIELD Ltd
Current assignee: CARBOSHIELD Ltd
Priority date: 2005-08-15
Filing date: 2006-08-15
Publication date: 2007-02-22
Anticipated expiration: 2008-02-15
Also published as: EP1922354A2; AU2006281014A1; WO2007020634A3

Abstract

The present invention relates to a method of preparing a resistant ceramic material by consolidation of SiC-AlN solution powder including synthesis of a SiC-AlN solid solution, followed by processing steps including crushing (if necessary), milling, sinter-aid addition, binder addition, granulation (if cold-pressed), cold forming and consolidation. This invention also provides a novel resistant ceramic material comprising primarily a homogeneous SiC-AlN solid solution or a homogeneous SiC-AlN solid solution that underwent phase separation, used for military and civil armor, and products that can withstand dynamic loading and are also wear resistant.

Description

RESISTANT CERAMIC MATERIAL AND METHOD FOR MAKING SAME

FIELD OF THE INVENTION

[001] The present invention relates to a method of preparing a resistant ceramic material by consolidation of SiC-AlN solution powder, and to novel resistant ceramic material comprising primarily a homogeneous SiC-AlN solid solution or a homogeneous SiC-AlN solid solution that underwent phase separation, used for military and civil armor, and products that can withstand dynamic loading and are also wear resistant.

BACKGROUND OF THE INVENTION

[002] The field of ceramic armor tiles and other ceramic armor articles is not new. Some important armor materials are silicon carbide (SiC), aluminum nitride (AlN), aluminum oxide (Al₂O₃) and boron carbide (B₄C). Different materials are used for different needs, and there are constraints to all candidate materials. For example, one is too expensive to produce, while another is not strong enough, etc.

[003] In addition to the difficulty in choosing the right system of materials, there are difficulties in regard to the production process. There are many ways to produce a ceramic armor article, e.g. hot-pressing, hot isostatic pressing and pressureless sintering. There are also various reactive processing methods. In all existing processing methods there are deficiencies. The process itself may be difficult to implement, too costly, or relying on raw materials that are too expensive. There is need for better materials and processes, to produce a ceramic component that is impact resistant, lightweight, inexpensive, reliable, controllable and reproducible. This is particularly important for armor for light vehicles and for protective personal waistcoats applications.

[004] Aluminum Nitride (AlN) is resistant to attack by most molten metals, most notably aluminum, lithium and copper. AlN is resistant to attack from most molten salts including chlorides and cryolite; it has high thermal conductivity for a ceramic material (second only to beryllia); AlN has high electrical resistivity; and has high dielectric strength; AlN may be attacked by acids and alkalis; and in the powder form is susceptible to hydrolysis by water or humidity.

[005] Silicon Carbide (SiC) is highly wear resistant and also has good mechanical properties, including high temperature strength and thermal shock resistance. Bulk SiC, as a technical ceramic, is produced in two main ways. Reaction bonded SiC is made by infiltrating compacts made of mixtures of SiC and Carbon with liquid Silicon. The Silicon reacts with the Carbon forming SiC. The reaction product bonds the SiC particles. Sintered SiC is produced from pure SiC powder with oxide or non-oxide sintering aids. Conventional ceramic forming processes are used and the material is sintered in an inert atmosphere at temperatures up to 2000⁰C or higher.

[006] Accordingly, the aim of the present invention is the development of an impact resistant ceramic material, which is applicable for manufacture of inexpensive, uniform, controllable and lightweight armor tiles and other articles.

SUMMARY OF THE INVENTION

[007] In one embodiment , this invention provides a method of preparing a resistant ceramic material by consolidation of a SiC-AlN solid solution powder comprising a. synthesis of a SiC-AlN solid solution, followed by b. processing steps comprising part or all of: crushing, milling, sinter-aid addition, binder addition, granulation (if cold-pressed or hot-pressed), cold forming, consolidation and heat treatment.

[008] In one embodiment, this invention provides a resistant ceramic material comprising primarily a homogeneous SiC-AlN solid solution. [009] hi one embodiment, this invention provides a resistant ceramic material comprising primarily a homogeneous SiC-AlN solid solution, which underwent phase separation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0011] Fig. 1 is an X-ray diffraction pattern of the synthesized and milled SiC-AlN solution powder, similar to that obtained in EXAMPLE 3 below, but with a 1 :1 ratio of SiC:AlN in the solid solution. It shows the typical peaks (at the correct locations and relative intensities) of a SiC-AlN solid solution with approximately 50% SiC and 50% AlN.

[0012] Fig. 2 is an X-ray diffraction pattern of the synthesized and milled SiC-AlN solution powder with Ti(QN) particles, similar to that obtained in EXAMPLE 2 below. It shows the typical peaks (at the correct locations and relative intensities) of a SiC-AlN solid solution with approximately 60% SiC and 40% AlN and also of Ti(QN). [0013] Fig. 3 is an optical micrograph of a polished and etched sample from a tile, similar to that obtained in EXAMPLE 3 below. It shows a dense, fined grained microstructure of the solid solution without visible porosity.

[0014] Fig. 4 shows square and hexagonal SiC-AlN sintered armor tiles, similar to those described in EXAMPLE 3, on an aluminum alloy block.

[0015] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0017] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0018] The present invention relates to a method of preparing a resistant ceramic material by consolidation of SiC-AlN solid solution powder, and to novel resistant ceramic material comprising primarify a homogeneous SiC-AlN solid solution or a homogenous SiC-AlN solid solution that underwent phase separation, that may be used for military and civil armor, and products that can withstand dynamic loading and are also wear resistant.

[0019] Both SiC and AlN are promising armor materials, although AlN has been of much less interest. SiC is a highly covalent compound (82%), while AlN is less covalent (57%). Solid solutions and composites of the two materials have several important advantages for ballistic applications. In one embodiment, the sintering temperature necessary for densification is lower for a SiC-AlN solid solution than for SiC alone. In another embodiment AlN can help reduce the amount of additives necessary for pressureless sintering (AlN itself can be used a sintering aid to SiC). In another embodiment, SiC and AlN allow good control of the microstructure (e.g., size and shape of crystallites, structure modulation), both during the initial formation of the microstructure and in subsequent treatments. [0020] In one embodiment, the SiC-AlN system is among only a few ceramic systems (another important one is the Si-Al-O-N system) where extensive solid solutions can form. In another embodiment, the SiC-AlN system possesses a miscibility gap, where precipitation or spinodal decomposition can occur by soaking the solid solution at certain temperatures, thus improving mechanical properties. IQ another embodiment, the addition of AlN can potentially improve antiballistic performance, because it is known to possess a structural transition at high shock wave velocity. Because of all these reasons, materials in the SiC-AlN system can have superior ballistic performance (a synergistic effect), if engineered properly, in spite of the fact that AlN itself has lower performance than that of SiC. At the same time, these materials can be processed more easily and more effectively than SiC itself.

[0021] The formation of the SiC-AlN solid solution from SiC and AlN requires temperatures of 2100° to 2300⁰C. if powders having particle sizes in the order of micrometers or larger are used. TWs can be achieved only by hot-pressing, because pressureless sintering is not practical at such temperatures due to material loss. Hot-pressing is a very expensive process, and renders the articles produced by it unaffordable for many armor or wear applications. In addition, hot-pressing does not allow the production of large or complicated parts. In addition, even at such high temperatures, the solid solution that is obtained is inhomogeneous: it contains regions with considerably variable SiC: AlN ratios, a fact that makes it extremely difficult to obtain reproducible microstructures and properties. On the other hand, at temperatures in which liquid phase assisted sintering can be performed without applying pressure (e.g. 1900⁰C) an extensive solid solution cannot be practically obtained, because of very sluggish diffusion. If nanometer-size powders are used, then more homogeneous solid solutions can be obtained at somewhat lower temperatures. However, nanometer-size powders are much more difficult to handle and are expensive. Therefore, there is need to use other methods for the formation of homogeneous SiC-AlN solid solutions. Several such methods are available, such as carbothermal reduction and self-propagating high temperature synthesis (SHS).

[0022] hi one embodiment of this invention, such homogeneous solid solution powders are produced by an in situ reactive process from certain precursors, rather than from mixtures of SiC and AlN. The resulting solid solution product undergoes processing steps such as milling, sinter- aid addition, binder addition, granulation, cold forming, and final consolidation. The parameters of each of these steps (milling conditions, amount and ratio of additives, temperatures, pressures, dwell times) are specifically determined so as to fit the solid solution composition, and are generally different from parameters used for processing of SiC, AlN, or SiC+ AlN mixtures. [0023] In one embodiment, the present invention provides a method of preparing a resistant ceramic material by consolidation of a SiC-AlN solid solution powder comprising a) synthesis of a SiC-AlN solid solution, followed by b) processing steps comprising part or all of: crushing, milling, sinter-aid addition, binder addition, granulation (if cold-pressed or hot-pressed), cold forming, consolidation and heat treatment.

[0024] In another embodiment, carbide, nitride, or carbo-nitride of a transition metal is embedded in step (a) or step (b). In another embodiment, the transition metal is Titanium or Zirconium.

[0025] In one embodiment, the SiC-AlN solid solution may be homogeneous. In another embodiment homogeneous solid solution of non-modulated structure includes SiC:AlN constant ratios within 10% error. In another embodiment, homogeneous solid solution of modulated structure includes SiC: AlN constant ratios within 10% error, when local composition is measured over areas larger than the modulation wavelength.

[0026] In one embodiment the microstructure of a SiC-AlN solid solution may consist of single- phase crystallites, homogeneous, without large deviation of composition from point to point within each crystallite; in another embodiment crystallites that exhibit a phase-separated structure, including modulation of compositions, with alternating regions that are richer and poorer in AlN content. In another embodiment, such modulated structures have been reported to contribute to the fracture toughness of the material. [0027] In another embodiment the average crystallite size (or grain size) of a SiC-AlN solid solution is between about 0.1 micrometers and 10 micrometers.

[0028] In another embodiment a SiC-AlN solid solution constitutes between 60 and 99% of the weight of the article.

[0029] LQ another embodiment the method of preparation of homogeneous SiC-AlN solid solution including self propagating high temperature synthesis (SHS) via combustion nitridation of aluminum, silicon and carbon (Al-Si-C) or aluminum and silicon carbide (Al-SiC) under nitrogen gas pressure of up to 50 bar. In another embodiment, the raw dry-mixed powder of aluminum, silicon and carbon or aluminum and SiC is poured into a carbon felt-lined perforated stainless steel reactor or a similar gas-permeable reactor, then pressed or shaken to achieve a desirable bulk density and the reactor placed in a pressure chamber, where nitrogen gas pressure is applied. In another embodiment, ignition of the powder is achieved by tungsten wire heating, graphite strip heating, laser heating or similar means; the reaction propagates downwards and complete reaction is achieved. In another embodiment, the reactor and reaction propagation is in horizontal direction.

[0030] In another embodiment, the SHS method of solid solution can be described by the following two exothermic reaction paths: xAl +x/2.N₂(g) + (l-x)Si + (l-x)C → xAlN + (l-x)SiC (1) xAl +x/2.N₂(g) + (l-x)SiC → xAIN + (l-x)SiC (2)

[0031] In another embodiment, a transition metal powder is added and mixed with the Al-Si-C powders, to obtain, for example, Ti(C₅N) as separate particles along with or embedded in the SiC-AlN solid solution particles. This additional reaction path is:

Ti + yC + 0.5(l-y)N₂ → Ti(C_y,N_1-y) (3)

[0032] Addition of a transition metal powder provides (a) the formation of TiC from Ti and C is more exothermic than the formation of SiC from Si and C, although less exothermic than the formation of AlN from Al and N₂. The addition of Ti allows to obtain a stable reaction with higher Si: Al ratios, (b) The Ti carbonitride particles can act as a toughening phase. The ratio of C:N in the Ti(C₅N) compound, as measured from peak locations in the X-ray diffractions, is around a unity (y = 0.5), and decreases with increasing nitrogen gas pressure in the reaction chamber. In another embodiment the molecular ratio (which is also close to the weight ratio) of the SiC-AlN solid solution obtained is between about 92:8 to about 50:50. [0033] In another embodiment, the solid solution can be processed in water, in contrast to mixtures containing AlN powder (not in solid solution), which react with water.

[0034] In one embodiment, the reaction product of (a) (sponge-like product, SiC-AlN solid solution in the SHS process) is crushed in a jaw crusher or by other means, and sieved to < 250 μm size powder. In another embodiment, the powder particles themselves are composed of micrometer-sized crystallites, and this fine grained material is easy (relative to SiC) to further comminute.

[0035] In one embodiment, milling includes wet-vibration-milling in cylindrical rubber-lined steel containers with water or alcohol, and either tungsten carbide or SiC or SiC-AlN milling media such as WC, SiC or SiC-AlN. In another embodiment, the water is de-ionized water, in another embodiment the alcohol is isopropanol. In another embodiment, the containers are mounted on a vibrating plate, activated by a vibratory motor, for a time sufficient to reduce the average particle size to around 1 micrometer. In one embodiment milling is done in rubber-lined containers or in SiC containers on an attrition miller. In another embodiment, wet bead milling with 1-2 mm ceramic beads is used. In another embodiment, sub-micron powder is obtained by a high energy milling method, such as those mentioned above. [0036] In one embodiment, sintering aids for liquid phase sintering are a mixture of oxides of aluminum and yttrium and/or a rare earth (RE) element which are added to the powder. In another embodiment the mixture is homogenized in a ball mill using steel balls and de-ionized water. In another embodiment, total quantities of oxide additives for liquid phase sintering ranges between 4wt% and 25wt%, or smaller amounts (usually <2%) of oxides, carbon, boron and/or boron compounds are added for non-liquid phase sintering. In another embodiment, the final materials contain oxide or oxynitride intergranular phases, which are essentially products of the oxide sintering aid. In another embodiment, the weight ratio between alumina and the sum of [yttria + RE] is between 2 and 0.4.

[0037] In one embodiment, a binder is added if cold-pressing follows this step. In another embodiment, a binder mixture based on polyethylene glycol (PEG) or polyvinyl alcohol (PVA) is added. In another embodiment, a plasticizer such as glycerin is included in the binder mixture; in another embodiment, additional minor additives are included in the binder mixture to improve lubrication. In another embodiment, the weight percent of binder mixture, relative to powder weight, can be from about 2% to about 14%. [0038] hi one embodiment, granulation includes squeezing a moisture controlled mixture through mesh, in another embodiment it includes palletizing, in another embodiment it includes a spray drying process, in another embodiment achieving a granulated ready-to-press material with free pouring density of about 600-800 kg/m³ and a tap density of about 800-1200 kg/m³. hi another embodiment, granule sizes are generally between 40 and 400 micrometers. [0039] In one embodiment, uniaxial cold pressing in hardened steel dies (which may be equipped with harder inserts to reduce wear) is performed at pressures in the order of 1 ,000 bar. hi another embodiment, cold isostatic pressing at up to 4,000 bar may be added if higher final properties are desired. In another embodiment, instead of cold-pressing, another cold forming process, such as injection molding may be used following the sintering aid addition step, to allow for the formation of larger and/or more complex bodies, hi another embodiment, usable molding compositions include, in addition to the ceramic powder and major binder component, several minor organic components such as plasticizers for the main polymer which are intended as flow modifiers, and in another embodiment processing aids which are supposed to act as surfactants, to the ceramic and improve particle wetting.

[0040] In one embodiment, binder removal (also called debinding or dewaxing) is done in flowing Nitrogen gas by slow heating at 10° to 100⁰C per hour to temperatures between 450° and 600⁰C, holding up to 4 hours at the maximum temperature, and cooling down at a controlled slow rate or cooling down naturally with the furnace.

[0041] In one embodiment, pressureless sintering is performed in Argon or Nitrogen atmosphere in a controlled atmosphere furnace at temperatures from 1850° to 2000⁰C and non-flowing gas pressure of less than 1 bar. In another embodiment the temperature is preferably between 1870° and 1950⁰C. In one embodiment the "green" tiles are enclosed in covered graphite containers; in another embodiment the "green" tiles are embedded in coarse SiC or SiC + Al₂O₃ powder in covered graphite containers. In one embodiment the heating rate is between 150° and 900⁰C per hour. In one embodiment the holding time at the maximum temperature is between 10 minutes and 6 hours, preferably 30 minutes to 4 hours. [0042] "Green" tiles refer to cold formed tiles before final consolidation.

[0043] In one embodiment, phase separation is optionally performed in the last step of the sintering of the solid solution powder, while reducing the sintering temperature to 1500-1900 ⁰C for 1 to 24 hours or more, resulting in a modulated structure. In another embodiment, the phase separation may be performed as a separate step after the sintering step, by heating the sintering product to 1500-1900 ⁰C for 1-24 hours or more, resulting in a modulated structure. In another embodiment, a key to the success of this process is the homogeneity of the solid solution obtained in the preparation of a SiC-AlN solid solution.

[0044] In another embodiment, hot isostatic pressing can be performed after the sintering step to provide higher density and better performance. In another embodiment, hot pressing of the homogeneous solid solution powder (or solid solution powder including transition metal carbon nitrides) may be performed.

[0045] Hot isostatic pressing is done at high temperature under high gas pressure. [0046] Hot pressing is a mechanical uniaxial pressure under heating conditions.

[0047] In one embodiment, the ceramic bodies may be used as-sintered (and heat-treated, if applicable), or may undergo diamond wheel grinding to achieve more accurate shape and dimensions. [0048] In one embodiment, the consolidation of the SiC-AlN solid solution and Ti(C,N) powder into resistant ceramic material includes cold pressing and/or cold isostatic pressing followed by liquid phase assisted pressureless sintering or non-liquid-phase sintering. In another embodiment, the consolidation of the SiC-AlN solid solution and Ti(C₅N) powder into resistant ceramic material comprises hot pressing. In another embodiment the consolidation comprises cold- pressing and/or cold-isostatic-pressing followed by non-liquid-phase-assisted pressureless sintering. In this the sintering additives may comprise small amounts of alumina, carbon, boron and boron compounds, and the sintering temperature may be higher than in liquid phase sintering. In another embodiment, the consolidation of the SiC-AlN solid solution powder into a resistant ceramic material is achieved by sintering followed by hot isostatic pressing.

[0049] In one embodiment, the cold forming process comprises cold pressing and/or cold isostatic pressing followed by non-liquid-phase assisted pressureless sintering.

[0050] In one embodiment, this invention provides a resistant ceramic material comprising primarily a homogeneous SiC-AlN solid solution. In another embodiment the SiC-AlN solid solution may comprise carbide, nitride or carbo-nitride of a transition metal, in anther embodiment the transition metal is titanium or zirconium. In another embodiment, another way to improve fracture toughness and ballistic performance is to include reinforcing titanium carbo- nitride particles.

[0051] In one embodiment of this invention, a resistant ceramic material of this invention may be used for the preparation of an armor material, in another embodiment for the preparation of a protective personal waistcoats, in another embodiment for the preparation of antiballistic resistance, in another embodiment for the preparation of a resisting to armor piercing bullets or in another embodiment for the preparation of an armor for light vehicles.

[0052] In one embodiment a resistant ceramic material, comprising 65 to 94 wt % of a highly homogeneous SiC-AlN solid solution (wherein AlN content is from about 8 wt % to about 50 wt %). In another embodiment, a resistant ceramic composite material comprise 0.5 to 18 wt% titanium carbonitride Ti(C,N). In another embodiment, a resistant composite ceramic material comprise up to 25 wt % of multiphase product of reaction and crystallization of melt of the following oxides mixture: aluminum oxide (AI2O3), yttrium oxide (Y₂O₃), a negligible amount of silica (SiO₂), and optionally ytterbium oxide (Yb2θ₃ ) or another rare earth (RE) oxide. In another embodiment, only a negligible amount of grain boundary phases that are products of non-liquid-phase sintering exist in the resistant ceramic material. [0053] In one embodiment, the shapes and dimensions of the components can be: tiles in sizes from about 2" x 2" (about 50mm x 50mm) to 300mm x 300mm or more, with or without curvatures; hexagonal tiles; rods; spheres; or more complex shapes.

[0054] The following examples are presented in order to more fully illustrate the preferred embodiments of the invention. They should in no way be construed, however, as limiting the broad scope of the invention.

EXAMPLES

Preparation of ceramic armor tiles including Ti (CN) EXAMPLE 1 [0055] In Example 1, the tiles had a square shape with nominal dimensions 50 x 50 mm and thickness of 6 to 6.5 mm. The armor tiles were manufactured from a material with the following nominal content of components:

(a) 81wt% of SiC-AlN solid solution, wherein AlN content was 30 mol%, which is close to

30wt%; (b) 9wt% of Ti(C₅N) particles; (c) 10wt % or less of multiphase product of crystallization of the melt of oxide mixture with the following composition: AI2O3 — 60wt %, and Y2O3 - 40wt%.

[0056] The tiles were produced using the following detailed steps, where the parameters of each step are critical for the achievement of the desirable properties of the product. a) Mixing raw material powders. 24.27g Al (D₅₀ = 28 micrometers) + 58.98 g Si (D₅₀ = 1 to 5 micrometers) + 27.93g C (-325 mesh), + 10.77g Ti (-325 mesh), total 121.95g, for

3 batches of SHS reaction. Dry mixing in ball mill, using a 1 liter high density polyethylene jar with about 500g of 6 mm steel balls, at 180 R.P.M. for 24 hours. b) SHS = Self Propagating High-temperature Synthesis. Poured 37.5g of the powder mixture layer by layer into a cylindrical perforated stainless steel reactor (lined with graphite felt; inner diameter about 25 mm, height 70mm) and lightly tapped layer by layer to obtain a uniform bulk density of about 900 kg/m³. Mounted the reactor in the pressure chamber and sealed the chamber. Pressurized with nitrogen gas at 35 bar. Ignited using a tungsten filament at a distance of about 1 mm above the surface of the powder. Reaction front downwards propagation was videotaped through the view port in the chamber wall, and temperatures were measured and recorded using 4 Type C thermocouples (one near the filament and 3 along the reaction path, inserted horizontally about 2mm deep into the powder). Ignition temperature was about 1350⁰C and the temperatures along the reaction path reached between 2000 and 2300⁰C. The reaction was complete within about 2 minutes. c) Crushing of the reaction product. The SHS reaction product was removed as one piece of a porous body from the carbon felt insulator. It was then crushed in a mortar and pestle, and sieved to obtain <250 micrometer particles. d) Steps (b) and (c) were repeated for 2 more batches of 37.5g each. The net weight of the product for each of the three runs was about 42 grams (the error being about 0.3 g due to some product adhering to the carbon felt insulation). The weight addition of about 4.3-4.5 g (from the original 37.5 g) represents the added nitrogen, theoretically about

4.4g for a full reaction, according to Reactions (1) and (3) shown above. The yield of SiC-AlN solid solution and Ti(C₅N) together could be determined by dividing the added weight by 4.4, showing values very close to 100%. This means that practically all the aluminum reacted with nitrogen (and all the Si with carbon) to form the solid solution, all the Ti reacted with C and N₂, and also that practically no materials were lost as gaseous phases. However, the % yield could not be accurately determined, because the exact C:N ratio in the Ti(C₅N) was not known. The bulk density of the sponge-like product was approximately 1 ,000 kg/m³. e) Vibratory milling to obtain micron-size particles. Vibratory milling was done in a rubber-lined steel container, having a volume of about 225cc. The 3 batches of powder were loaded into the container, together with isopropyl alcohol (about 70cc) and about 600 grams of 8mm WC-6wt.°/όCo balls as milling media. The mill was operated for 48 hours at a frequency of 50Hz (3,000 R.P.M.) and amplitude of about 5mm. The materials were then removed and dried in air at room temperature. The dried powder was then dispersed in de-ionized water with 0.4% addition of DARV AN-C® dispersant, using an ultrasonic bath for 30 minutes. f) X-ray diffraction (XRD) has shown that the milled reaction products were 2H (wurtzite)-SiC-AlN solid solution, sometimes with a minor amount of residual silicon, depending on initial composition. The peak intensities are in agreement with reported values for the solid solution. No peaks of SiC or AlN are seen, and there is no indication of any deviation from a homogeneous solid solution. In addition, peaks of cubic titanium carbo-nitride [Ti(C₅N)] are observed. g) Sintering aids addition. In this example, 7.2 grams (6wt%) of alumina and 4.8 grams

(4wt%) of yttria (both with particle size of 0.5-1.0 micrometers) were added to 108 grams of the SiC-AlN solid solution + Ti(C₅N) powder (in aqueous slurry), then mixed-homogenized in a ball mill using alumina cylinders as mixing media and de- ionized water for 16 hours. h) Binder addition and granulation. Polyvinyl alcohol aqueous solution was mixed with glycerin in a 84:16 weight ratio. This binder mixture was added to the inorganic slurry in an amount equal to 8% by weight relative to inorganic powder weight. Then mixed- homogenized in a ball mill using alumina cylinders as mixing media and de-ionized water for 16 hours. After drying to adequate level, the dough-like material was squeezed through a 212 micrometer sieve and dried, to obtain a granulated Ready To Press (RTP) material. Granules smaller than 63 micrometers were removed by sieving. i) Cold pressing. Hardened steel dies, with dimensions of 62x62 mm were used, with an 80 ton hydraulic press. In this example (making 2 tiles), the RTP material was weighed (62.06 grams per tile) and manually poured into the die and pressed at 500 bar (50

MPa) pressure, held for 90 seconds, and the green tile released from the die. It was then wrapped under vacuum in a polyethylene bag and cold-isostatically pressed in oil for 5 minutes at 2,000 bar (200 MPa). j) Debinding (pre-sintering). The tiles were loaded in uncovered graphite containers into a controlled atmosphere furnace. Debinding was done in flowing nitrogen by heating up the furnace to 535⁰C at a heating rate of 30 degrees centigrade per hour, holding at that temperature for 2 hours, and cooling down with the furnace. k) Pressureless sintering under argon atmosphere at a pressure up to about 600 torr in a graphite-hot-zone furnace. The "green" tiles were loaded into a covered graphite container, separated from each other with graphite felt sheets. The sintering cycle was as follows: Heating to 1,000 ⁰C at 400 °C/h heating rate, then to 1900 ⁰C at 900 ⁰CZh, then to 1920 ⁰C at 50 ⁰CZIi; holding 1 hour at 1920 ⁰C; cooling at 600⁰CZIi to room temperature.

1) Removing from furnace and brush-cleaning. EXAMPLE 2

[0057] In Example 2, the tiles had a square shape with nominal dimensions 50 x 50 mm and thickness of between 6mm and 7mm. The armor tiles have been manufactured from material with following nominal content of components: (a) 85.4wt% of SiC-AlN solid solution, wherein AlN content was 30wt%; (b) 6.6wt% of Ti(C,N) particles; (c) 8wt % of multiphase product of crystallization of the melt of oxide mixture with the following composition: AI2O3 — 40wt %, and Y2O3 - 40wt%.

[0058] The tiles were produced using the following detailed steps, where the parameters of each step are critical for the achievement of the desirable properties of the product: a) Mixing raw material powders. 28.4Og Al (D₅o = 28 micrometers) + 44.35 g Si (D₅₀ = 1 to 5 micrometers) + 20.63g C (-325 mesh), + 6.63g Ti (-325 mesh), total 100.0 Ig, for 3 batches of SHS reaction. Diy mixing in ball mill, using a 1 liter high density polyethylene jar with about 50Og of 6 mm steel balls, at 180 R.P.M. for 24 hours. b) SHS = Self Propagating High-temperature Synthesis. Poured 33.Og of the powder mixture layer by layer into a cylindrical perforated stainless steel reactor (lined with graphite felt; inner diameter about 25 mm, height 70mm) and lightly tapped layer by layer to obtain a uniform bulk density of about 800 kg/m³. Mounted the reactor in the pressure chamber and sealed the chamber. Pressurized with nitrogen gas at 7 bar. Ignition and reaction proceeded as in EXAMPLE 1, Item 2. c) Crushing of the reaction product. The SHS reaction product was removed as one piece of a porous body from the carbon felt insulator. It was then crushed in a mortar and pestle, and sieved to obtain <250 micrometer particles. d) Steps (b) and (c) were repeated for 2 more batches of 33.0g each. e) Vibratory milling, powder dispersion and XRD were done as in EXAMPLE 1, Item 5, with similar results. f) Sintering aids addition. In this example, 4.52 grams (4wt%) of alumina and 4.52 grams (4wt%) of yttria (both with particle size of 0.5-1.0 micrometers) were added to 104 grams of the SiC-AlN solid solution + Ti(CN) powder (in aqueous slurry), then mixed-homogenized in a ball mill using alumina cylinders as mixing media and de- ionized water for 16 hours. g) Binder addition and granulation. Same as in EXAMPLE 1. h) Cold pressing. Hardened steel dies, with dimensions of 62x62 mm were used, with an 80 ton hydraulic press. In this example (making 2 tiles), the RTP material was weighed (60.0 grains) and manually poured into the die and pressed at 1,200 bar (120 MPa) pressure, held for 90 seconds, and the green tile released from the die. i) Debinding (pre-sintering). The tiles were loaded in uncovered graphite containers into a controlled atmosphere furnace. Debinding was done in flowing nitrogen by heating up the furnace to 535⁰C at a heating rate of 30 degrees centigrade per hour, holding at that temperature for 2 hours, and cooling down with the furnace. j) Pressureless sintering under argon atmosphere at a pressure of up to about 600 torr in a graphite-hot-zone furnace. The "green" tiles were loaded into a covered graphite container, embedded in coarse SiC + 5%Al₂θ₃ powder. The sintering cycle was as follows: Heating to LOOO ⁰C at 400 °C/h heating rate, then to 1900⁰C at 900 °C/h, then to 1930 ⁰C at 60 °C/h; holding 3 hours at 1930 ⁰C; cooling at 60O⁰CVh to room temperature. k) Removing from furnace and brush-cleaning.

Preparation of ceramic armor tiles EXAMPLE 3

[0059] The tiles had a square shape with nominal dimensions 50 x 50 mm and thickness of between 6mm. and 9mm. The armor tiles have been manufactured from material with the following nominal content of components:

(a) 90 wt % of SiC-AlN solid solution, wherein AlN content was about 40 wt %,

(b) lOwt % of multiphase product of crystallization of the melt of oxide mixture with the following composition: AI2O3 — 60wt %, and Y2O3 - 40wt%.

[0060] The tiles were produced using the following detailed steps, where the parameters of each step are critical for the achievement of the desirable properties of the product: a) Mixing raw material powders. 185.8g Al (D₅₀ = 28 micrometers) + 290. Ig Si (1 to 5 micrometers) + 124.Ig C (-325 mesh), total 60Og₅ for 3 batches of SHS reaction. Dry mixing in ball mill, using a 2 liter high density polyethylene jar with about l,500g of 6 mm steel balls, at 180 R.P.M. for 24 hours. b) SHS = Self Propagating High-temperature Synthesis. Poured 160. Ig of the powder mixture layer by layer into an oval perforated stainless steel reactor (lined with carcon felt, inner cross section about 18cm², height 100mm) and lightly pressed layer by layer to obtain a uniform bulk density of about 900kg/m³. Mounted the reactor in the pressure chamber and sealed the chamber. Pressurized with nitrogen gas at 35 bar.

Ignited using a tungsten filament. Reaction front propagation was videotaped through the view port in the chamber wall, and temperatures were measured and recorded using 4 Type C thermocouples (one near the filament and 3 along the reaction path, inserted horizontally about 2mm deep into the powder). Ignition temperature was 135O⁰C and the temperatures along the reaction path reached between 2000 and 2300⁰C. The reaction was complete within about 2 minutes. c) Crushing of the reaction product. The SHS reaction product was removed as one piece of a porous body from the carbon felt insulator. It was then crushed in a 50mm round cylindrical die using a hydraulic press and sieved, to obtain <250 micrometer particles. d) Steps (b) and (c) were repeated for 2 more batches of 160. Ig each. The net weight of the product for each of the three runs was between 185 and 186 grams (the error being about 0.5 g due to some product adhering to the carbon felt insulation). The weight addition of 25-26g (from the original 160.Ig) represents the added nitrogen, theoretically 25.7g for a full reaction (1) shown above. The yield of SiC-AlN solid solution could be determined by dividing the added weight by 25.7, showing values from 99 to 100%. This means that practically all the aluminum reacted with nitrogen (and all the Si with carbon) to form the solid solution, and also that practically no materials were lost as gaseous phases. The bulk density of the sponge-like product was approximately 1,000 kg/m³. e) Vibratory milling to obtain micron-size particles. Vibratory milling was done in 2 rubber-lined steel containers, having a volume of about 450cc each, attached vertically on the vibrating plate. The 3 batches of powder were manually mixed in a bowl, divided into two equal parts (about 27Og each) and loaded into the two vibratory mill containers, together with isopropyl alcohol (about 200cc) and 8mm WC-6wt.%Co balls (about 1,300 grams). The mill was operated for 54 hours at a frequency of 50Hz and amplitude of about 5mm. The materials were then removed and dried in air at room temperature. f) X-ray diffraction (XRD) has shown that the milled reaction products were 2H (wurtzite)-SiC-AlN solid solution, sometimes with a minor amount of residual silicon, depending on initial composition. The peak intensities are in agreement with reported values for the solid solution. No peaks of SiC or AlN are seen, and there is no indication of any deviation from a homogeneous solid solution. g) Sedimentation was done by adding de-ionized water to the powder and adding 0.4% (relative to powder weight) of Darvan-C® as a dispersant, dispersing and mixing for 60 minutes in an ultrasonic bath, poured into a 400mm tall 2 liter measuring cylinders, then letting settle for 100 minutes and pumping out the top 95% of the volume of the slurry for use in the following steps. h) Sintering aids addition. In this example 6wt% of alumina and 4wt% of j'ttria (both with particle size of 0.5-1.0 micrometers) were added to the SiC-AlN solid solution powder (in aqueous slurry), then mixed-homogenized in a ball mill using alumina cylinders as mixing media and de-ionized water for 16 hours. i) Binder addition and granulation. Polyvinyl alcohol aqueous solution (84% by weight) was mixed with glycerin in a 84:16 weight ratio. This binder mixture was added to the inorganic slurry in an amount equal to 8% by weight relative to inorganic powder weight. Then mixed-homogenized in a ball mill using steel balls and de-ionized water for 16 hours. After drying to adequate level, the dough-like material was squeezed through a 212 micrometer sieve to for a granulated ready to press (RTP) material. j) Uniaxial cold pressing. Hardened steel dies, lubricated with stearin, with dimensions of

62x62 mm were used, with an 80 ton hydraulic press. In one example (of the 6 tiles), the RTP material was weighed (in an amount corresponding to the desired tile thickness) and manually poured into the die and pressed at 1 ,200 bar pressure, held for 90 seconds, and the green tile released from the die. k) Debinding (pre-sintering binder removal). The tiles were loaded in uncovered graphite containers into a controlled atmosphere furnace. Debinding was done in flowing nitrogen by heating up the furnace to 535⁰C at a heating rate of 30 degrees per hour, holding at 535⁰C for 2 hours, and cooling down with the furnace. 1) Pressureless sintering under argon atmosphere at a pressure of up to about 600 torr in a graphite-hot-zone furnace. The "green" tiles were loaded into a covered graphite container, embedded in coarse SiC + 5%Al₂θ₃ powder. The sintering cycle was as follows: Heating to 1,000⁰C at 400⁰CJh. heating rate, then to 1900⁰C at 900 °C/h, then to 1930 ⁰C at 60 °C/h; holding 3 hours at 1930 ⁰C; cooling at 600°C/h to room temperature. m) Removing from furnace and brush-cleaning.

EXAMPLE 4

[0061] Tiles were prepared similarly to the description in EXAMPLE 3. However, the sintering Step (1) was as follows:

[0062] Pressureless sintering under argon atmosphere at a pressure of up to about 600 torr, combined with heat treatment for microstructure modification. Pressureless sintering under argon atmosphere at a pressure of up to about 600 torr in a graphite-hot-zone furnace. The "green" tiles were loaded into a covered graphite container, embedded in coarse SiC + 5%A1₂C"₃ powder. The sintering cycle was as follows: Heating to 1,000⁰C at 400 °C/h heating rate, then to 1900⁰C at 900 ⁰CZh, then to 1930 ⁰C at 60 ⁰CZh; holding 3 hours at 1930 ⁰C; cooling at 400 ⁰CZh to 1800 ⁰C, holding 4 hours at 1800⁰C for phase separation; cooling at 60O⁰CZh to room temperature. Property Measurements

EXAMPLE 5

[0063] Density measurements by the Archimedes method showed values from about 3200 to 3260 kgZm³, depending on additives and other processing parameters. These values corresponded to 98- 100% of the theoretical density. [0064] Vickers micro-hardness tests (using 5N and ION loads) show mat the solid solution phase itself has hardness values of 2400 to over 2600 kgZm³. Vickers hardness using IOON load showed values of over 2000 kgZm³.

[0065] Ballistic tests were performed at a professional testing laboratory, by shooting 7.62 mm diameter 51mm long and 9.5 grams in weight Armor Piercing bullets (7.62x51 AP Type 61 IMI), at speeds of 830 to 860 mZsecond. The tiles were lightly glued on Al 2024-T3 backing block, 30 mm thick. All tiles of thickness 6 mm to 9 mm stopped the bullets completely, as evidenced by the fact that no penetration of the bullet core into the Al backing block (witness block) occurred.

[0066] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMSWhat is claimed is:

1. A method of preparing a resistant ceramic material by consolidation of a SiC-AlN solid solution

powder comprising a) synthesis of a SiC-AlN solid solution, followed by

b) processing steps comprising part or all of: crushing, milling, sinter-aid addition, binder

addition, granulation (if cold-pressed or hot-pressed), cold forming, consolidation, and heat treatment.

2. The method of claim 1, wherein the molecular ratio SiC-AlN of the SiC-AlN solid solution obtained is between about 92:8 to about 50:50.

3. The method of claim 1, wherein the resistant ceramic material may be homogeneous comprising modulated or non-modulated structure.

4. The method of claim 1, wherein milling is done in a vibratoiy mill or other high-energy milling device, with water or alcohol and milling media such as WC, SiC or SiC-AlN.

5. The method of claim 1, wherein the sinter-aid addition materials are oxides or oxy-nitrides of

Si, Al, yttrium (Y), as well as ytterbium (Yb), other rare earth (RE) elements, and boron or boron compounds.

6. The method of claim 5, wherein the total quantities of oxide additives for liquid phase sintering ranges between 4 wt% to 25wt%, or smaller amounts (usually <2%) of oxides,

' carbon, boron and/or boron compounds are added for non-liquid-phase sintering.

7. The method of claim 1, wherein carbide, nitride, or carbo-nitride of a transition metal is

embedded in step (a) or step (b).

8. The method of claim 7, wherein the transition metal is titanium or zirconium.

9. The method of claim 7, wherein the consolidation of the SiC-AlN solid solution and Ti(C ,N)

powder into resistant ceramic material comprising cold pressing and/or cold isostatic pressing

followed by liquid phase assisted pressureless sintering or non-liquid-phase sintering.

10. The method of claim 7, wherein the consolidation of the SiC-AlN solid solution and Ti(C₅N)

powder into resistant ceramic material comprising hot-pressing.

11. The method of claim 3, wherein the preparation of homogeneous SiC-AlN solid solution

comprising self propagating high temperature synthesis (SHS) via combustion nitridation of Al-Si-C or Al-SiC under nitrogen gas pressure.

12. The method of claim 1, wherein the cold forming process comprises cold pressing and/or cold isostatic pressing followed by liquid phase assisted pressureless sintering.

13. The method of claim 1, wherein the consolidation of the SiC-AlN solid solution powder into a resistant ceramic material is achieved by hot-pressing or by sintering followed by hot isostatic pressing.

14. A resistant ceramic material comprising primarily a homogeneous SiC-AlN solid solution.

15. A resistant ceramic material comprising primarily a homogeneous SiC-AlN solid solution,

which underwent phase separation.

16. The solid solution of claim 14, comprising carbide, nitride or carbo-nitride of a transition metal.

17. A resistant ceramic material of claim 16, wherein the transition metal is titanium or

zirconium.

18. The method of claim 1, wherein said resistant ceramic material is used for the preparation of

an armor material, protective personal waistcoats, antiballistic resistance, resisting to armor

piercing bullets or armor for light vehicles.

19. A resistant ceramic material of claim 14, wherein said resistant ceramic material is used for

the preparation of an armor material, protective personal waistcoats, antiballistic resistance,

resisting to armor piercing bullets or armor for light vehicles.

20. A resistant ceramic material of claim 15, wherein said resistant ceramic material is used for the preparation of an armor material, protective personal waistcoats, antiballistic resistance,

resisting to armor piercing bullets or armor for light vehicles.

21. A resistant ceramic material of claim 16, wherein said resistant ceramic material is used for

the preparation of an armor material, protective personal waistcoats, antiballistic resistance, resisting to armor piercing bullets or armor for light vehicles.

22. A resistant ceramic material of claim 17, wherein said resistant ceramic material is used for the preparation of an armor material, protective personal waistcoats, antiballistic resistance,

resisting to armor piercing bullets or armor for light vehicles.