WO2006083319A2

WO2006083319A2 - Method and system for reaction bonded ceramic armor formed in situ in a metal containment

Info

Publication number: WO2006083319A2
Application number: PCT/US2005/023703
Authority: WO
Inventors: Vector P. Kelsey
Original assignee: Simula, Inc.
Priority date: 2004-07-02
Filing date: 2005-06-30
Publication date: 2006-08-10
Also published as: WO2006083319A3

Abstract

A system and process for in-situ reaction bonded ceramics formed in a metal containment (200). In an exemplary embodiment a process for controlling the compressive stress in a ceramic insert includes selecting a metal according to predetermined criteria. Components for forming the reaction bonded ceramic are selected and introduced into a receptacle within the metal containment (202, 204). After in-situ reaction of the components (206), the system is cooled from the reaction temperature to a hold temperature (208). In an exemplary embodiment, the hold temperature is selected to impart a desired level of stress in the fully reacted ceramic insert after cooling to room temperature.

Description

METHOD AND SYSTEM FOR REACTION BONDED CERAMIC ARMOR FORMED IN SITU IN A METAL CONTAINMENT

BACKGROUND

Field of the Invention

The present invention relates generally to ceramic fabrication processes, and in particular to processes for forming ceramic bodies within a metal containment structure. Background of the Invention

High strength armor has traditionally been fabricated using metals such as steel, which is known for its strength and ductility. A disadvantage associated with the use of solely metal-based materials in armor is the high specific gravity of most metals, which imparts a large weight to vehicles, equipment or personnel equipped with the armor. Attempts to address this problem include the use of embedded ceramic inserts that are placed within a metal containment structure to form a composite ceramic/metal armor. Ceramic materials typically have much lower specific gravity than metals, so the overall weight of an armor occupying the same volume can be significantly reduced by use of a metal containment with ceramic inserts instead of a pure metal armor.

Examples of approaches to fabricating ceramic-containing armor in the known art include placement of ceramic tiles within titanium containment structures. For example, silicon carbide (SiC) tiles of approximate dimension 4" x 4" x l" are fabricated by precision machining and placed in a titanium containment structure containing pockets machined to similar dimensions as the ceramic tiles so that the tiles can be inserted therein. A disadvantage of the use of ceramic inserts in armor is the low fracture strength typical of most ceramics, rendering them more susceptible to fracture by a ballistic projectile. Although ceramics have high compressive strength, they have low tensile strength and are susceptible to tensile failure unless well contained by, for example, the titanium containment structure.

Precision machining of a ceramic insert can be used to ensure reasonable containment of the ceramic insert in a metal containment structure. In the example cited above, if the titanium pocket dimensions are precisely those of the ceramic insert, the ceramic tile is constrained on five sides (only the top is unconstrained) from expansion even when struck by a ballistic projectile. In this manner, the ceramic has little room to expand and the tendency to fracture may be reduced.

However, the process described above typically involves several complex and costly steps. In the first instance, fabrication of the ceramic tiles may involve hot pressing or hot isostatic pressing to form a reasonably dense ceramic before insertion in the metal housing. Additionally, expensive precision machining is required to obtain a close fit between ceramic and metal housing. In addition, after insertion, an additional hot isostatic pressing of the ceramics may be necessary to further improve the fit within the metal housing. These processes result in costs of current ceramic armor to be about $100 per pound.

Thus, a need exists for improvements in making high strength and lightweight armor. BRIEF SUMMARY

An embodiment of the present invention includes a process for making high strength armor using in-situ formation of a ceramic insert within a metal receptacle. Preferably, the in-situ formation of the ceramic insert includes a reaction bonding process. In a first step, one or more receptacles designed to hold a^' ceramic insert are formed within the metal housing (also hereinafter referred to as containment or container). In a subsequent step, a precursor material containing ceramic particles or powder is introduced into the receptacles. The precursor material may, for example, be introduced as a loose powder, a pressed powder, a slurry, a tape, or as an injection molded material. In preferred embodiments, known ceramic materials such as silicon carbide or boron carbide are used as ceramic precursor material. The body of the precursor material may roughly assume the size and shape of the receptacle into which it is introduced, while retaining porosity within its body. In a subsequent step, a reacting agent is introduced into intimate contact with the ceramic powder material in the receptacle. The reacting agent is used to help form a binding material in the ceramic insert to be formed in the receptacle. In a further step, an infiltration agent is introduced into the mixture of ceramic precursor material and reacting agent, and the resulting mixture is heated to cause the infiltration agent to melt and inter-penetrate the porous microstructure of the ceramic precursor material containing the ceramic powder. The infiltration agent and reacting agent react with each other to form a product that serves to bind the ceramic precursor material into a dense, fully reacted insert containing ceramic or a ceramic composite. Additionally, the dense insert assumes the shape of the receptacle and extends to the walls of the receptacle used to confine the insert. In another step, the metal confinement and ceramic insert are cooled according to a predetermined cooling cycle. During cooling, the metal receptacle contracts more rapidly than the ceramic insert, and upon reaching ambient conditions (room temperature) the ceramic insert is tightly constrained by the receptacle and is placed under compressive stress. Accordingly, the resulting ceramic inserts have increased resistance to tensile failure when subject to ballistic impact.

In another embodiment of the present invention, a high strength armor system contains a metal housing with at least one receptacle containing a ceramic insert formed by an in-situ reaction bonding process. Preferably, the metal housing includes a titanium alloy material. The reacting agent is preferably carbon and the infiltration agent is preferably silicon. During in-situ formation of the ceramic insert, the carbon, ceramic precursor material, and silicon are heated to a temperature sufficient to melt the silicon and cause it to penetrate within porous regions of the ceramic precursor, and to react with the caτbon. In an exemplary embodiment, the ceramic precursor material is boron carbide (hereinafter also referred to as "B4C" ). After in-situ formation of the ceramic insert, the fully reacted ceramic insert microstructure may contain a B₄C phase dispersed in isolated or semi-isolated islands within a matrix of SiC formed from the reaction of the silicon infiltration agent with the carbon. Additionally, the fully reacted ceramic insert forms an intimate contact with the walls of the metal housing. After cooling to room temperature, the armor system comprises a metal housing including one or more lightweight ceramic inserts containing a SiCZB₄C microstructure. Extra resistance to ballistic penetration is imparted to the ceramic inserts by the compressive stress induced during cooldown of the armor after in- situ formation of the ceramic inserts.

In a further embodiment of the present invention, a process for imparting a controlled compressive stress to a ceramic body housed in a metal containment includes a step of selecting a metal containment according to a predetermined criterion. The criterion may be the plastic deformation behavior of the metal used for the containment. In a further step, a precursor ceramic material, a reacting agent, and an infiltration agent are selected in predetermined proportions for use in fabricating the ceramic body. The proportions may be determined based on the desired hardness or another related mechanical property of the ceramic body to be formed. Alternatively, the proportions may be determined by a desired linear thermal expansion coefficient ("α") of the resulting ceramic body. In a subsequent step, the precursor ceramic material, a reacting agent, and an infiltration agent are introduced into a receptacle in the metal containment. This is followed by an in-situ reaction step performed while the above ingredients are housed in the receptacle, resulting in formation of a ceramic body contained within the metal receptacle. In a subsequent step, the metal containment and ceramic body are cooled in accordance with a predetermined cooling cycle. In a preferred embodiment, the predetermined cooling cycle includes the step of reducing the temperature of the receptacle containing the ceramic insert to a second temperature at a controlled cooling rate, wherein the controlled cooling rate is sufficiently slow for the stress within the metal to be substantially relieved during cooling. Subsequently, the reacted housing containing the reacted ceramic body may be held at the second temperature for a predetermined duration, followed by a final step of cooling the reacted ceramic to ambient temperature. The ceramic insert thus formed exhibits a compressive stress level proportionate to the mismatch in α between the metal containment material and the ceramic insert, and the difference between the second temperature and room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram illustrating a system including a metal housing and ceramic inserts, according to an exemplary embodiment of the present invention.

Figure 2 illustrates a process for in-situ formation of a reaction bonded ceramic according to a preferred embodiment of the present invention.

Figure 3 is a schematic diagram illustrating a cross-sectional view of a ceramic insert in a metal receptacle, according to an exemplary embodiment of the present invention. Figure 4 illustrates a process for imparting a controlled compressive stress in a ceramic insert according to exemplary embodiments of the present invention.

Figure 5 illustrates a cooling curve employed during processing of ceramic inserts according to embodiments of the present invention.

Figure 6 illustrates three different cooling schedules, designed to impart three different levels of compressive stress into ceramic inserts, in accordance with embodiments of the present invention.

Figure 7 illustrates schematics of ceramic inserts prepared according to the cooling schedules in Figure 6a.

Figure 8 is a schematic diagram illustrating a system including a metal housing and ceramic inserts, according to another exemplary embodiment of the present invention.

Figure 9 illustrates a cooling curve employed during processing of ceramic inserts according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Figure 1 is a schematic diagram illustrating system 100 including metal containment 102 and ceramic inserts 106. Preferably, ceramic inserts 106 are formed by an in-situ reaction bonding process as described in more detail below. Ceramic inserts 106 are formed within receptacles 104 fabricated in metal containment 102 that is used to house ceramic inserts 106. After in-situ formation of ceramic inserts 106 in metal receptacles 104, preferably performed at elevated temperatures necessary to carry out the reaction bonding process, system 100 is cooled to room temperature according to a predetermined schedule. In the embodiment shown in Figure 1, ceramic inserts 106 have a square shape. For example, ceramic inserts 106 may have dimensions of about 4" x 4" x 1". In the above example, the depth of receptacles 104 fabricated in metal containment 102 may be about one inch, although embodiments are envisioned in which the receptacle depth can be greater or less than the ceramic insert thickness of one inch.

Ceramic inserts 106, by virtue of their fabrication within metal receptacles 104 in accordance with embodiments of the present invention, have increased resistance to ballistic impact. It is well known to those skilled in the art that ceramic materials have low tensile strength compared with typical metals, and are more susceptible to tensile fracture. However, as is well known to skilled artisans, ceramics have significantly higher compressive strength than tensile strength. When an unstressed ceramic is subject to a ballistic impact, the impact forces may distribute within the ceramic causing tensile failure. It is known to those skilled in the art that ceramics placed in a containment subject to ballistic impact on a front surface generally fail due to reflected shock tensile waves from the back surface of the ceramic. Ceramic inserts 106, formed at high temperature by reaction bonding are under compressive stress after formation when cooled to room temperature. Thus, under typical use conditions, the compressively-stressed inserts present a stress barrier to a ballistic projectile which must be overcome before tensile stress forces can act upon them to cause tensile failure. Accordingly, the system illustrated in Figure 1 presents an increased resistance to ballistic impact compared to a system containing unstressed ceramic inserts.

Figure 8 is a schematic diagram illustrating system 800 containing hexagonal inserts 806 located within receptacles 804. An advantage of the arrangement illustrated in Figure 8 is that stress risers that may exist in square tiles with 90 degree corners are substantial, if not completely, avoided. Furthermore, embodiments of the present invention include ceramic inserts of virtually any shape, determined by the receptacle in which the ceramic insert is formed.

Figure 2 illustrates a process for forming an in-situ reaction bonded ceramic insert in a metal housing, according to an embodiment of the present invention. In step 200, receptacles are fabricated within a metal containment. The size and shape of the receptacles are designed in accordance with the desired ceramic insert to be fabricated therein. In an exemplary embodiment of the present invention, the metal containment is Ti6A14V (also hereinafter referred to as "titanium alloy"), a metal alloy known to those skilled in the art.

In step 202, a precursor ceramic material is introduced into the metal receptacles. The precursor ceramic material may be in loose powder form, a slurry, or a tape. Alternatively, it may be introduced by dry pressing a powder, injection molding, or other techniques known to those skilled in the art. As listed in Table I, in exemplary embodiments, the ceramic precursor material may contain predominantly B₄C, SiC, SiO₂, TiB₂, TiC, or TiN. Preferably, the ceramic precursor material is then thermally processed to remove materials such as water or binder material. In exemplary embodiments the thermal processing is performed at temperatures ranging from 500-1700 ⁰C. As is well known to those skilled in the art that the thermally processed ceramic precursor material to be used for forming a reaction bonded ceramic contains a high degree of porosity.

Table I

In step 204, a reacting agent is introduced into intimate contact with (he ceramic precursor material. The term "reacting agent," as used herein, refers to a material designed to react with an infiltration agent that is introduced in an additional step. In an exemplary embodiment, the reacting agent is "introduced" into the ceramic precursor by decomposing a volatile carbon-containing binder material contained in the precursor during the thermal processing step, thereby leaving a residual carbon material that may coat or inhere in pores of the B₄C or SiC ceramic precursor. In another exemplary embodiment of the present invention, in step 204, the reacting agent is introduced as a dispersed powder, for example, SiO₂

In step 206, an infiltration agent is introduced into the ceramic precursor containing the reacting agent. System 100 is then heated to an elevated temperature sufficient to melt the infiltration agent, causing it to substantially penetrate the porous microstructure of the ceramic precursor and react with the reacting agent. Table I lists exemplary reacting agent/infiltration agent combinations. In a preferred embodiment, the reacting agent is a carbon material and the infiltration agent is silicon. During step 206, the silicon infiltration agent substantially reacts with the carbon material to form an SiC material that can form a matrix binding the formerly porous ceramic precursor microstructure. In an exemplary embodiment the resulting ceramic insert is a dense ceramic containing an SiC matrix interpenetrating and surrounding dispersed grains or partially connected grains OfB₄C.

In this embodiment, in step 206, the infiltration agent is aluminum (or an aluminum alloy). The aluminum is heated to 1100 ⁰C, for example, becomes molten, and reacts substantially with the SiO₂ to form a product OfAl₂Oa and silicon. The resulting ceramic insert is a composite of AI2O₃/ B_,C (or SiC)/Si. It will be apparent to those skilled in the art that the "ceramic" insert, as in this case, may be a ceramic composite including non-ceramic phases such as semiconductors or metals.

In still another embodiment of the present invention, step 202 and step 204 are combined as one. Thus, for example, SiO₂ powder is used as the precursor ceramic material in step 202, and is compacted into a metal receptacle. However, the SiO₂ powder also acts as the reacting agent "in intimate contact with" the ceramic precursor. In the latter embodiment, in step 206, aluminum is introduced into contact with the SiO₂ and forms an AI2O₃/S1 composite after in-situ reaction bonding is completed.

Therefore, many combinations of the above described ceramic precursor materials, reacting agents, and infiltration agents may be used to form an in-situ reaction bonded ceramic insert. Choice of the exact combination of materials used may depend on the balancing of mechanical and thermo-mechanical properties desired in the end product, as well as ease of processing, as discussed further below.

Figure 3 shows a cross-sectional view of an in-situ reaction bonded ceramic insert 106 formed in receptacle 104, illustrating that the insert is in contact with vertical surface 104a and horizontal surface 104b.

In step 208 (see Figure 2), the metal containment and ceramic inserts are cooled according to a predetermined schedule. In an exemplary embodiment, the schedule of cooling includes reducing the temperature of the reacted ceramic to a second temperature at a controlled cooling rate and holding the system at the second temperature for a predetermined time, before cooling further to room temperature. The above procedure is performed to avoid excessive mechanical loading, and to be able to impart a controlled stress into the ceramic inserts, as described further in the embodiments discussed below.

Figure 4 illustrates a process for imparting a controlled compressive stress in a ceramic insert contained in a metal receptacle, according to an embodiment of the present invention.

In step 400, a metal is selected for a containment that is to house the receptacle. The metal may be selected according to one or more criteria. Examples of selection criteria include the coefficient of thermal expansion of the metal and the mechanical strength of the metal. After in-situ formation of the ceramic insert at elevated temperature, the ceramic insert may occupy a receptacle as illustrated in Figure 3. Upon cooling to a lower temperature, the dimensions of the receptacle attempt to assume a smaller dimension whose value is determined by the value of the lower temperature and the linear thermal expansion coefficient (α) of the metal. Thus, the amount of shrinkage of the metal receptacle, and therefore the amount of stress imparted to the ceramic insert contained therein, can be tailored by varying α of the metal housing.

In step 402, individual components of material that is to help form the ceramic insert are selected, including a ceramic precursor material, an infiltration agent, and a reacting agent. The proportion of the individual components are selected according to a desired composition and microstructure of the end product ceramic insert to be formed by in-situ reaction bonding. For example, if the desired ceramic insert is to comprise 50% B4C and 50% SiC, proportions OfB₄C precursor material, carbon containing material, and silicon, are selected accordingly. It will be apparent to those skilled in the art that the calculation of the relative proportions of components to be used for the ceramic inserts depends on the amount of "extra" material initially introduced with each component, such as excess material in a binder from which carbon is to be derived. The proportions of components may be chosen to impart a maximum hardness to the resulting ceramic insert. Alternatively, the proportions of components may be chosen in accordance with the resulting α of the ceramic insert.

In step 404, the components are introduced into the metal receptacle according to the sequence previously described in more detail in steps 202-206 of Figure 2.

In step 406, reaction bonding to form the ceramic insert in-situ in the metal receptacle is performed at a first temperature (also designated as Tl) chosen in accordance with the requirements of the materials used for the reaction bonding process. In an exemplary embodiment, carbon is used as a reacting agent and silicon is used as an infiltration agent. Accordingly, the first temperature, that temperature chosen to perform the reaction bonding process, is about 1500 ⁰C, which is sufficient to melt silicon, but well below the melting temperature of a containment material such as titanium alloy.

In another exemplary embodiment, SiO₂ is the reacting agent, and aluminum is the infiltration agent. Accordingly, in this exemplary embodiment, Tl is about 1100 ⁰C. The latter system affords the possibility of using ferrous materials as the containment material, for example, steels, whose melting point is too low to sustain the 1500 ⁰C reaction temperature employed in the former example.

In step 408, the system including the metal containment and ceramic inserts is cooled according to a predetermined cooling schedule to a second temperature, T2. In a preferred embodiment, the predetermined cooling schedule used is based on the ability of the metal containment to plastically deform (or "flow") during cooling to accommodate the differential thermal expansion between the metal containment and the ceramic inserts. For example, Ti6A14V exhibits an α of about 8.6x10^'6/K. Typical ceramics and composites used for inserts, on the other hand, have thermal expansion coefficients in the range of about 2 to 6xlO^'6/K. During cooling, the tendency of the metal to shrink faster than the ceramic induces the buildup of stresses which can be relieved by plastic flow of the metal containment surrounding the ceramic inserts. Excessive stress can therefore be averted by cooling at a sufficiently low rate to provide sufficient time for the containment to plastically flow. As illustrated in Figure 5, the predetermined cooling "rate" shown in step 408 may have different forms. Curve A, for example, is linear, curve C non-linear, and curve B, two separate regimes of differing linear cooling rates.

In optional step 410, the system is held at the second, "hold," temperature, T2, for a predetermined duration. The duration may be chosen to allow the metal containment to completely relax by plastic deformation before the temperature is lowered further. In other embodiments of the present invention, step 410 may be foregone, that is, the duration is zero.

In an exemplary embodiment, T2 is chosen based on a desired mechanical stress to be imparted into the ceramic inserts under actual use conditions. As discussed above, the fact that typical ceramic materials possess lower values of α than a typical metal housing material serves to impart a compressive stress into a ceramic insert as the metal receptacle contracts at a greater rate than the insert during cooling. Accordingly, for a given temperature change, the amount of stress imparted into the ceramic insert can be calculated based on the elastic moduli of the ceramic insert and the relative difference in thermal expansion coefficients (Δα _M-c) of the metal containment and the ceramic insert, assuming that plastic deformation of the metal containment does not take place. The biaxial strain in the plane of a ceramic plate-like insert in a metal containment cooled to room temperature can be estimated using the following equation:

Δε/ε =(T2-RT) (Δα _M-c)

where Δε/ε is the linear relative strain and RT is room temperature (K). For example, in the case of a plate-like insert, a value of 5XlO^-6ZK for Δα _M-_C (corresponding to an α of 3.6x 10^"6ZK for a ceramic insert in Ti6A14V) would produce a relative linear compressive strain in the plane of the ceramic plate of about 3xlO^'3 or 0.3% for a system cooled rapidly from 625 ⁰C to 25 ⁰C, assuming the mass of the metal containment were much larger than that of the ceramic inserts. In the case of a plate, because the top surface is free to expand, the actual stress σ within the plate can be calculated as σ =(E {Δα _M-cHT2-RT})Z(l-υ) where E and υ are the elastic modulus and Poisson's ratio, respectively, of the ceramic insert. Accordingly, the second hold temperature is designed such that, upon cooling in step 412, the ceramic inserts exhibit a desired compressive stress level at room temperature, or a desired operating temperature. In an exemplary embodiment, as shown in Figure 5, the cooling rate adopted in step 412 is sufficiently rapid that significant plastic deformation of the metal housing cannot take place, such that the metal receptacles containing ceramic inserts elastically shrink according to the known thermal expansion properties of the metal, thus imparting elastic stress into the ceramic inserts.

Figure 6 illustrates three different cooling schedules, D, E, and F designed to impart three different levels of compressive stress, relatively higher, relatively lower, and relatively lowest, respectively, in ceramic inserts formed thereby. In exemplary embodiments, after cooling from the hold temperature TZ in all three curves, the plastic deformation of the metal containment is minimal, thereby imparting the total elastic deformation into the ceramic insert that is anticipated based on Δα _M-_C and the difference between T2 and room temperature.

Figure 7 illustrates in schematic form more details of armor pieces 600 cooled in accordance with schedules D, E, and F. During cooling step 408 and hold step 410, it is assumed that all three schedules permit complete plastic relaxation of the metal containment housing the ceramic inserts. Accordingly, the amount of shrinkage upon cooling from Tl to T2 for ceramic inserts 604, 606, and 608 is determined by the small value of the thermal expansion coefficient of the ceramic. However, upon cooling to room temperature, the amount of shrinkage and therefore the compressive stress in the ceramic inserts, is determined in each case by the relative temperature difference between T2 and room temperature and the Δα M-_C- Thus, insert 604 has the highest value of compressive stress and insert 608 the least.

In an alternative embodiment, in step 410, the hold temperature is sufficiently low that plastic deformation rates in response to stress are negligible for the metal housing. Subsequently, upon cooling in step 412, the cooling rate employed can be arbitrarily slow, which imparts the advantage that thermal "shocking" to the ceramic insert that may occur with rapid differential temperature change, is completely avoided. In another embodiment of the present invention, illustrated in Figure 9, a cooling schedule of an in-situ reaction bonded ceramic is performed in multiple steps. In step 900, a ceramic insert is formed at temperature Tl by in-situ reaction bonding as described above. In a series of cooling steps, the ceramic is cooled to a second temperature T2, at which temperature the ceramic is held for a predetermined time before cooling to room temperature. During cooling from Tl to T2, the ceramic insert is held at a series of intermediate temperatures in stages 904 and 908. The exact schedule of cooling rate, intermediate temperature and hold time for intermediate steps 902-910 can be chosen so that stress buildup in the ceramic insert upon cooling can be more precisely managed and relieved. For example, the final hold step 912 can be chosen at a temperature T2 and for a duration, tj, so that the insert stress is minimal at time t_f, before cooling to room temperature. Accordingly, as described above, the final ceramic insert stress at room temperature can be well controlled by rapid cooling in step 914.

In accordance with the above procedure, a system containing ceramic inserts with controlled compressive stress can be fabricated by in-situ reaction bonding of ceramics in a metal receptacle. Costs associated with precision machining of ceramic inserts and process complexity required when ceramics are fabricated independent of the metal receptacle are avoided. Furthermore, the amount of compressive stress in a ceramic insert formed by in-situ reaction bonding in a metal housing can be easily tailored by choice of ceramic material(s), metal containment, hold temperature, and cooling rate, among other factors. In addition, because the in-situ reaction bonded ceramic process can be employed using a variety of materials, such as B4C, SiC, TiC, TiN, TiB₂, AI2O₃, and Si, the hardness of the mechanical insert can be independently varied for a given level of compressive strain desired in the fully formed insert. In other words, one might obtain the same thermal expansion coefficient by selecting the relative proportions of the above materials in numerous combinations, each of which produces a different mechanical hardness.

The above process affords the ability to tailor formation of reaction bonded ceramic inserts according to materials cost, process simplicity, process temperature, system weight, and overall cost. The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents.

Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A process for making armor, comprising: fabricating, within a metal housing, at least one insert receptacle for containing a ceramic insert; introducing a precursor material containing ceramic particles into the at least one receptacle; reacting, at a first temperature, an infiltration agent with the precursor material and a reacting agent, whereby a reacted ceramic insert is formed; and cooling the metal housing containing the reacted ceramic insert in a predetermined cooling cycle.

2. The process of claim 1, further comprising introducing a reacting agent into intimate contact with the precursor material.

3. The process of claim 1, wherein the reacting agent comprises carbon.

4. The process of claim 3, wherein the infiltration agent comprises silicon.

5. The process of claim 1, wherein the precursor material comprises silicon carbide.

6. The process of claim 1, wherein the precursor material comprises boron carbide.

7. The process of claim 1, wherein the reacting agent comprises silicon oxide.

8. The process of claim 7, wherein the infiltration agent comprises aluminum.

9. The process of claim 8, wherein the precursor material comprises silicon carbide.

10. The process of claim 9, wherein the precursor material comprises boron carbide.

11. The process of claim 1 , wherein the predetermined cooling cycle comprises: cooling the reacted ceramic from the first temperature to the second temperature; holding the reacted ceramic at the second temperature for a predetermined duration; and cooling the reacted ceramic to ambient temperature.

12. A high strength ceramic armor system, comprising: a metallic housing configured to accept at least one insert in an insert receptacle; and at least one ceramic insert to be located within an insert receptacle, wherein the ceramic insert is formed by reacting a mixture comprising a first ceramic material, a reacting agent, and an infiltration agent all placed within the insert receptacle and heated to a first temperature.

13. The high strength ceramic armor system of claim 12, wherein the infiltration agent comprises silicon, and wherein, prior to reacting the first ceramic material, a reacting agent comprising carbon is in intimate contact with the first ceramic material.

14. The high strength ceramic armor system of claim 12, wherein the first ceramic material comprises boron carbide.

15. The high strength ceramic armor system of claim 12, wherein the first ceramic material comprises silicon carbide.

16. The high strength ceramic armor system of claim 12, wherein the infiltration agent comprises aluminum, and wherein, prior to reacting the first ceramic material, a reacting agent comprising silicon oxide is in intimate contact with the first ceramic material.

17. The high strength ceramic armor system of claim 12, wherein the first reaction temperature is sufficiently high to melt the infiltration agent.

18. A process for imparting a controlled compressive stress in a ceramic body housed in a metal containment, comprising: selecting a metal containment according to a predetermined criterion; selecting a filler material comprising a ceramic, an infiltration agent, and a reacting agent in predetermined proportions; introducing the filler material, the infiltration agent, and the reacting agent into a receptacle in the metal containment; reacting in situ in the receptacle at a first temperature, the filler material, the infiltration agent and the reacting agent, whereby a ceramic insert is formed; and cooling the receptacle containing the ceramic insert according to a predetermined cooling cycle.

19. The process of claim 18, wherein the predetermined criterion is the thermal expansion coefficient of the metal containment.

20. The process of claim 18, wherein the predetermined criterion is the plastic deformation behavior of the metal comprising the metal containment.

21. The process of claim 18, wherein the predetermined proportions are designed to produce a ceramic insert of a desired thermal expansion coefficient.

22. The process of claim 18, wherein the predetermine proportions are designed to produce a ceramic insert of a maximum hardness.

23. The process of claim 18, wherein the predetermined cooling cycle comprises: reducing the temperature of the receptacle containing the ceramic insert to a second temperature at a controlled cooling rate, wherein the controlled cooling rate is sufficiently slow for the stress within the metal to be substantially relieved during cooling; holding the reacted ceramic at the second temperature for a predetermined duration; and cooling the reacted ceramic to ambient temperature.

24. The process of claim 23, wherein the predetermined duration is sufficient for the metal containment to relieve internal stress by plastic deformation.

25. The process of claim 23, wherein the second temperature is selected in order to impart a predetermined level of compressive stress into the ceramic insert upon cooling to ambient temperature.