JP4945245B2 - Boron carbide composite and method for producing the same - Google Patents

Description

Cross-reference of related applications

  [0001] This patent application claims priority to co-owned US Provisional Application No. 60 / 524,916, filed Nov. 25, 2003. Further, this patent document is a co-owned partially continued US patent application Ser. No. 10 / 271,312 filed Oct. 15, 2002, which is a co-owned patent application filed Nov. 20, 2001. Co-owned US Provisional Application No. 60 / 329,358, filed Oct. 15, 2001, which is a partial continuation U.S. patent application Ser. No. 09 / 990,175, and Nov. 21, 2000. Claim priority of filed 60 / 252,489. The entire disclosure of these jointly owned patent applications is expressly incorporated by reference.

  [0002] The present invention relates to metal-ceramic composites, such as silicon infiltrated composites, produced by a metal infiltration process. More particularly, the present invention relates to reactively bonded and siliconized composites having boron carbide filler or reinforcement, and bulletproof armor structures made from those boron carbide composites. Also, the composite is extremely rigid and combined with its low specific gravity capability makes it an attractive candidate material for precision equipment applications such as machinery used in semiconductor manufacturing.

<1. Explanation of other related technologies>
[0003] In many applications, weight is not an important factor, and conventional materials such as steel can provide a level of protection against airborne threats such as ballistic projectiles and pieces. Steel armor offers the advantage of low cost and the ability to act as a structural member of the equipment in which they are incorporated. Over the last few decades, certain hard ceramics have been developed for certain armored applications. These ceramic armor, such as alumina, boron carbide, silicon carbide, offers the advantage of being lighter in weight than steel for the same ballistic impact stopping force. Therefore, low-weight armor materials are needed in armor applications where the lowest possible mass is important, such as (human) body armor and aircraft armor. The lower the density, the thicker the armor thickness that can be given with the same area density. In general, a thick armor material is preferable to a thin one, since a large armor volume can be adapted to overcome the incident projectile. Further, the impact of the projectile on the thicker armor plate causes the tensile stress on the opposite plate surface to be impacted less than would occur on the back side of the thinner armor plate. Therefore, for brittle materials such as ceramic, it is important to prevent brittle fracture due to excessive tensile stress on the backside of the armor, otherwise the armor is easily destroyed. Rather, by preventing their tensile stress, the kinetic energy of the projectiles can probably be absorbed completely inside the armor body, which energy absorption is in the form of numerous fractures, for example in the form of shattering, Obviously it forms a very large new surface of the material.

  [0004] U.S. Pat. No. 5,372,978 to Ezis discloses a projectile armor resistant armor made primarily of silicon carbide and made by hot pressing technology. Up to about 3% by weight aluminum nitride can be added to increase density. The finished product is characterized by a microstructure having an optimum particle size of less than about 7 microns. Destruction is between particles, indicating that it is crack deflection that absorbs energy. Furthermore, the ability to use cheaper and less pure silicon carbide without compromising the structural integrity of the material increases the economics of manufacturing.

  [0005] US Patent No. 4,604,249 to Lihleich et al. Discloses a composition particularly suited for armored vehicles. The composition is a composite of silicon carbide and steel or steel alloy. Silicon and carbon particles, optionally containing silicon carbide particles, are mixed with an organic binder and then placed in a mold to form a shaped body. The compact is then coked at a maximum temperature in the range of about 800 ° C to about 1000 ° C. The temperature is then rapidly raised to a range of about 1400 ° C. to about 1600 ° C. in an inert atmosphere at least at a pressure of 1 bar. In this temperature range, silicon and carbon react to form silicon carbide, thereby producing a porous body. Next, the holes are degassed in a vacuum chamber, and the porous body is immersed in molten steel or steel alloy. The metal fills the pores, producing a dense composite armor material.

  [0006] Weaver U.S. Pat. No. 3,725,015 discloses a composite heat resistant article useful as an armor material for protection against intrusion by ballistic projectiles, among other uses. These compositions cold press a powdered refractory material (which could be boron carbide) and about 10-35 parts by volume of an organic binder material or a carbonaceous material of elemental carbon. Forming a preform, heat treating the preform to convert the carbonaceous material to carbon, and then heating the preform into a temperature between 1700 ° C and 1900 ° C containing at least two metals. Prepared by contacting with a molten metal bath maintained at a constant temperature. Molten metal infiltrates into the preform, the refractory material matrix sinters, and at least one of the metal components reacts with carbon to form a metal carbide. Since the coefficient of thermal expansion of the metal mixture is close to or slightly greater than that of the refractory matrix, the shape of the composite cools to room temperature essentially without cracking and residual strain. Weaver states that there is no fixed factor in particle size other than the factor dictated by the properties desired for the final product, but a maximum size of about 350 microns is preferred for the particles of powdered material making up the pressed mixture. In addition, he recommends adding the same metal to the metal mixture as the metal component of the refractory material. For example, he states that if boron carbide is a refractory material, incorporating about 6% boron into the molten metal mixture prevents boron from eluting from the boron carbide.

  [0007] Weaver U.S. Pat. No. 4,104,062 discloses a high density aluminum modified boron carbide composition suitable as protective armor for ballistic projectiles. About 3 to 30% aluminum powder is mixed with about 70 to 97% by weight boron carbide. A temporary binder is added to the mixture and the compact is pressed. The preform is then hot pressed at a temperature of at least 500 psi (3.5 MPa), 1800 ° C. to about 2300 ° C. in an oxygen free atmosphere.

  [0008] U.S. Pat. No. 3,857,744 to Moss discloses a method for making a composite article comprising boron carbide. Specifically, a compact comprising a uniform mixture of boron carbide particles and a temporary binder is cold pressed. Moss states that the size of the boron carbide particles is not critical and that any size in the range of 600 grit to 120 grit can be used. The shaped body is heated to a temperature in the range of about 1450 ° C. to about 1550 ° C. and molten silicon is infiltrated. No mention is made that silicon contains molten boron or carbon. The binder is removed early in the heating operation. The silicon impregnated boron carbide body can then be bonded to an organic resin backing material to produce an armor plate.

  [0009] Bailey, US Pat. No. 3,859,399 discloses infiltrating molten silicon into a compact comprising titanium diboride and boron carbide at a temperature of about 1475 degrees. The shaped body further comprises a temporary binder which can optionally be carbonized. While titanium diboride remains substantially unaffected, molten silicon reacts with at least some of the silicon carbide to produce some silicon carbide in situ. The flexural strength of the resulting composite was relatively modest, about 140 MPa. Various applications are disclosed, including personal, vehicle and aircraft armor.

  [0010] Taylor et al., US Pat. No. 3,796,564, discloses a hard, high-density carbide composite ceramic material specifically intended for ceramic armor. The granular boron carbide is mixed with a binder, shaped into a preform and solidified. The preform is then heat treated with a controlled amount of molten silicon in an inert atmosphere at a temperature range of about 1500 ° C. to about 2200 ° C., and the molten silicon infiltrates the preform and reacts with some of the boron carbide. . The formed body includes boron carbide, silicon carbide, and silicon. Taylor et al. Stated that these composites are suitable as armor to protect against small-caliber, low-speed projectiles, even though they lack the optimal properties necessary to protect against large-caliber, high-speed projectiles. ing. They want a certain amount of boron carbide phase to react, but they often have excessive reactions that lead to cracking of the body, so excessive processing temperatures and excessively fine granular boron carbide are detrimental in this respect Recognize that. At the same time, they also find that excessively large sized particles are less strong and degrade ballistic impact performance.

  [0011] Any of the armored inventions described above have one or other disadvantages. Hot presses are expensive and have shape limitations. Hot pressed or sintered ceramics do not retain dimensional tolerances as well as reaction bonded silicon carbide (“RBSC”). Iron matrix composites are heavier than ceramic armor. Conventional RBSC armor with boron carbide reinforcement, often referred to in this document as “reaction-bonded boron carbide” or “RBBC”, simultaneously undergoes significant roughening of the microstructure due to reaction with the silicon infiltrant. Losing some of the boron carbide, especially the finer particle size boron carbide. This is shown in detail below. Even at relatively low temperatures of 1475 ° C., boron carbide can chemically react with molten silicon. For composites containing SiC fillers, the infiltration temperature of 2200 ° C. is too high and can lead to particle growth and deleterious roughening of the microstructure.

  [0012] As outlined in the prior patent literature, silicon carbide composites and boron carbide composites made by a silicon infiltration process were proposed and evaluated as armored material candidates decades ago.

  [0013] At the 3rd TACOM Armor Coordinating Conference in 1987, Vienicki et al. Reported ballistic impact testing of RBSC materials on sintered and hot pressed silicon carbide materials. Vienicki et al. Not only have RBSC substantially inferior to other silicon carbides, but also purer monolithic ceramics with minimal amounts of second phase and porosity have better ballistic impact performance than multiphase and composite ceramics. Got the overall conclusion to have. (D.J. Vienicki, W. Blumenthal, M. Slavin, C. Tracy, and H. Skele, "Armor Ceramics-1987", 3rd TACOM Armor Agreement, Monterey, CA (US Tanks- (Automotive Command (US Tank-Automotive Command), Warren, MI, 1987) 27-53.)

  [0014] Therefore, despite the price advantages of RBSC over sintered or hot pressed silicon carbide, the market preferred was a sintered or hot pressed monolithic ceramic product. In fact, according to several sources, in recent years there has been an increasing reputation that RBSC is not worth considering seriously as an armored material. Until the applicant's product was introduced, there was little RBSC armor on the market.

  [0015] The details of the ballistic impact event are complex. One theory that has been widely supported to overcome ballistic projectiles is that the armor must be able to destroy the projectile and cause it to decay before it penetrates the armor. The compressive strength and hardness of the candidate armor material should be important. The Taylor et al. Armor patent mentioned above, for example, suggests a correlation between strength and ballistic impact performance. They noted that when the size of the largest particle exceeds 300 microns, the shear modulus and ballistic impact performance of the failure are reduced. By keeping the size of the boron carbide below about 300 microns in diameter, their reactively bonded boron carbide bodies can obtain a shear modulus as high as 260 MPa for fracture, and for armor applications, the strength should be at least 200 MPa. They recommended that they should.

  [0016] It appears that there is an agreement in the armor development industry that hardness is really important to the candidate armor material, and in particular that the hardness of the armor should be at least as high as that of the projectile. However, the armor materials under test were difficult to correlate between mechanical strength (both tensile and compressive) and ballistic impact performance with respect to strength factors. Indeed, besides hardness, there does not appear to be a single static property that serves as a good predictor of good armor properties in ceramic materials. Instead, guidelines based on actual ballistic impact testing provided by armor developers to material developers suggest that candidate armor generally has a combination of high hardness and high modulus, low Poisson's ratio and low porosity It should have been (Vienicki et al., Pages 32-33).

  [0017] The inventors believed that the bulletproof performance could be developed at a lower cost compared to other armored ceramics such as hot pressed armor, so RBSC as a candidate armor material, and more specifically , Returned to RBBC again.

<2. Discussion on jointly owned patents>
[0018] US Pat. No. 6,503,572 to Wagoner et al. States that a reactively bonded or reaction-formed silicon carbide body is formed using an infiltrant containing silicon and at least one metal, such as aluminum. Teaching that you can. By modifying the silicon phase in this way, the physical properties of the resulting composite and the results of other important processing phenomena can be fine-tuned. These silicon carbide composite materials are of particular interest in precision equipment, robots, tools, armor, electronic packaging and thermal management, and the semiconductor manufacturing industry. Specific intended items of manufacture include semiconductor wafer handling equipment, vacuum chucks, electrostatic chucks, air bearing housings or support frames, electronic mounting and substrates, bridging and bases for machine tools, mirror substrates, mirror stands and flat panel displays Includes fixtures.

  [0019] McCorick et al., US Pat. No. 6,609,452, teaches that fine particle reactively bonded composites can provide superior ballistic impact properties, especially for small weapon foaming. “Fine particles” means that a size of about 100 microns or more should not exceed about 10% by volume of the morphological shape forming the microstructure of the composite material. The composite material is preferably loaded with one or more hard reinforcing substances, in particular silicon carbide.

  [0020] The teachings of these co-owned US patents are incorporated herein by reference.

  [0021] One object of the present invention is to produce a composite material that is lightweight, stiff, strong and substantially free of pores.

  [0022] One object of the present invention is to produce composite materials useful for precision equipment and nuclear energy applications.

  [0023] One object of the present invention is to produce a composite material by a silicon infiltration process characterized by a high proportion of boron carbide.

  [0024] One object of the present invention is to produce a reactively bonded boron carbide composite in which the chemical reaction between the boron carbide phase and the molten silicon infiltrant is attenuated or suppressed during processing.

  [0025] One object of the present invention is to provide silicon characterized by a boron carbide phase having a smaller or finer particle size than those without chemical reaction attenuation by attenuating the chemical reaction between boron carbide and silicon. It is to produce an infiltrated boron carbide composite material.

  [0026] One object of the present invention is to produce a bulletproof armor whose ballistic impact performance is at least close to commercially available ceramic armor such as alumina or hot pressed boron carbide.

  [0027] One object of the present invention is to produce bulletproof armor that is cheaper than hot pressed ceramic armor.

[0028] These objectives and other desirable properties can be achieved through the application and technology of boron carbide composites. According to a preferred but not the only embodiment of the invention, the molten infiltrant comprising silicon and one or more boron sources comprises at least some boron carbide and at least some reactive or “free” Contact with a porous mass that also contains carbon. The molten infiltrant infiltrates into the porous mass without the aid of pressure or vacuum, forming a composite close to the theoretical density. The silicon component of the infiltrant reacts with free carbon in the porous mass to form silicon carbide in situ as the matrix phase. Furthermore, the tendency of molten silicon to react with the silicon carbide component can be suppressed or at least greatly attenuated by alloying or doping silicon with one or both of a boron source and a carbon source. The composite thus obtained contains boron carbide dispersed or distributed throughout the silicon carbide matrix. There is also some residual unreacted infiltrant phase, typically containing silicon and small but detectable amounts of boron and carbon, which are also distributed or interdispersed throughout the matrix. Therefore, these composite materials can be abbreviated as Si / SiC / B ₄ C.

[0029] Reaction formed composites characterized by boron carbide reinforcement have comparable stiffness (eg, elasticity or Young's modulus) to their competitors characterized by conventional silicon carbide reinforcement, but with the same volume filling Lower specific gravity with material loading. Therefore, these B ₄ C reinforced SiC composites will find utility in applications requiring low mass and high stiffness, such as devices that often require precise motion control at high accelerations. Furthermore, because of the extremely high hardness and low specific gravity of boron carbide, these composites are attractive armor material candidates.

  [0030] In another embodiment included in the present invention, a composite featuring boron carbide reinforcement can be made by a siliconization process. Here, the preform is substantially free of carbon in a form that reacts with the molten silicon metal (eg, free of free carbon) or at least does not contain a sufficient amount of free carbon to react. Molten metal containing silicon infiltrates into a porous mass or preform without forming a silicon carbide phase in situ.

  [0031] In particular in the armor embodiments, the inventors have found that highly desirable armor materials can be produced when known hardness requirements are combined with a relatively fine-grained microstructure. In order to achieve this microstructure, it is important to minimize the degree of chemical reaction during infiltration and to minimize the formation of microstructures (recrystallization or other forms of sintering). For this purpose, the inventors recommend limiting the size of the objects (eg particles) that make up the hard filling material of the preform to be infiltrated. In general, the size of the filler particles should be kept below about 300-350 microns in diameter, and a very good performance to overcome the firing of small caliber weapons is at least 90 volumes of all morphological shapes or at least the ceramic phase. This is achieved when the% is kept at a size of about 100 microns. Therefore, the microstructure obtained by the boron carbide composite material designed for armored applications is characterized by limited size filler particles and the hard phase provided in the porous mass or preform. It is a microstructure in which the interconnectivity of the constituent objects is limited. In other words, the objects that make up the filler material should also have a small or negligible amount of interconnectivity with each other, such as by excessive sintering or recrystallization, or by excessive in situ formed SiC. Absent.

<Definition>
[0032] "Area density" as used herein refers to the mass of the armor system per unit area.

[0033] As used herein, "ballistic stopping power (ballistic stopping power)" means the rate of _{V 50} projectile per unit of total areal density.

  [0034] "Free carbon" as used herein refers to carbon that is intended to react with molten silicon to form silicon carbide. The term usually refers to the elemental form of carbon, but is not necessarily limited to the elemental form of carbon.

  [0035] As used herein, "inert atmosphere" means an atmosphere that is substantially non-reactive with the infiltrant or porous mass or preform to be infiltrated. Thus, this definition includes other gaseous components that can be considered as slightly reducing or slightly oxidizing. For example, a forming gas containing about 4% hydrogen with the balance being nitrogen will be used unless the hydrogen reduces the filler material and unless the nitrogen oxidizes appreciably the infiltrant or filler material. It can be considered as an inert atmosphere.

  [0036] As used herein, "mass efficiency" is the surface density (ratio of the homogeneous rolled steel armor required to provide the same ballistic impact performance as a given target surface density being tested. And expressed as a ratio.

  [0037] As used herein, "reactive bonded silicon carbide" or "RBSC" refers to a ceramic composite made by reactive bonding, reaction formation, reactive infiltration, or self bonding.

  [0038] As used herein, "reactive bonded boron carbide" or "RBBC" is a reactive bonded silicon carbide composite in which the composite filler or reinforcement (ie, the phases are bonded) comprises boron carbide. Means the material type or subset.

  [0039] As used herein, "reaction bonding", "reaction formation", "reactive infiltration", or "self-bonding" is a reaction with a silicon-containing infiltrant and at least some in situ. By infiltration of a porous mass containing carbon in a form capable of forming a ceramic composite containing silicon carbide produced.

  [0040] "Siliconization" as used herein means infiltrating a porous mass with a molten infiltrant containing silicon metal to produce a composite having a matrix containing silicon metal; At least the silicon component is substantially non-reactive with the porous mass component. Thus, “siliconized boron carbide” refers to a composite comprising boron carbide and silicon metal, but substantially free of silicon carbide formed in situ from the reaction of silicon metal.

  [0041] As used herein, "total surface density" is the surface density of a ceramic armor material plus the surface density of other materials that are appropriate to be considered as assembled parts of the components that make up the armor system Means. An example of another material could be a fiber reinforced polymer material often used for lining or housing ceramic armor plates.

Embodiment of the present invention

  [0051] According to the present invention, preferably a high volume ratio or one or more extremely hard silicon carbides to produce a very hard, very hard material as a reinforcing component of the composite. A mechanically strong composite material is produced that contains boron carbide combined with a hard material such as and is substantially free of pores. Furthermore, excellent materials, in particular excellent armored products, can be produced by careful control of processing conditions such as, for example, suppression of boron carbide phase reaction. Furthermore, the composites produced according to the present invention maintain better dimensional tolerances during heat treatment than hot presses and sintered bodies.

  [0052] As mentioned above, two candidate materials, silicon carbide and boron carbide, having very desirable hardness for certain applications contemplated by the present invention, are fully densified by conventional techniques such as sintering. It is difficult to do. While these materials are easy to hot press, hot presses have the drawback of being constrained by, for example, their cost and the geometry that can be produced without much machining.

  [0053] Thus, particularly for reasons of economy and manufacturing flexibility, the composite of the present invention comprises a porous infiltrant comprising silicon comprising at least one hard ceramic material comprising carbon and boron carbide. It can be produced by a reactive infiltration technique, usually referred to as “reaction formation” or “reaction bonding”, that contacts the mass. The molten silicon-based material infiltrates into interconnected pores in the porous mass or preform. The molten silicon includes an amount of one or more boron sources sufficient to attenuate the tendency of the boron carbide component to chemically react with the molten silicon. It is particularly preferred when the molten silicon also contains one or more carbon sources, and its presence also appears to help control this chemical reaction. Simultaneously with infiltration, silicon reacts with the carbon in the porous mass or preform to form silicon carbide, which typically has a “beta” SiC polymorph. The amount of infiltrant is generally provided in such an amount that the carbon in the porous mass or preform completely reacts with the silicon carbide, and any remaining material between the filler material and the silicon carbide formed in situ. Sufficient additional infiltrant is provided to fill the void space. The resulting composite material features a silicon carbide matrix formed in situ. The amount of filler and residual unreacted infiltrant is dispersed throughout the matrix. Because the residual infiltrant is often interconnected, it is often considered part of the composite matrix.

  [0054] For preferred processing conditions, atmospheres compatible with this type of infiltration include vacuum or an inert atmosphere such as argon, with vacuum being preferred. The vacuum need not be an “extreme” or high degree of vacuum, but is sufficient enough to be provided by a mechanical “roughing” pump. Infiltration tends to be more robust at higher temperatures, but it is even more intense, especially with undesirable side reactions of boron carbide components. Furthermore, it is more difficult to spatially constrain the infiltrant at high temperatures. Furthermore, higher processing temperatures tend to be more driven by excessive particle growth. For all of these reasons, the preferred processing temperature is generally one at which reliable infiltration is maintained, even if low. A temperature in the range of about 1450 ° C. to 1600 ° C. should be sufficient to infiltrate the silicon-based metal into the boron carbide-containing particulate mass in a roughing vacuum environment.

  [0055] Boron carbide is a particularly attractive filler material candidate when the mass of the article is important due to its low theoretical density of about 2.45 to 2.55 grams per cubic centimeter. (The reported theoretical density range may be because boron carbide is not essentially a line compound, but instead exhibits a limited stoichiometric range.) The Young's modulus of boron carbide is silicon carbide. Boron carbide has a higher specific stiffness than silicon carbide because it is comparable to that of about 450 GPa. High specific stiffness is a valuable property in applications that require precise motion and control of motion, particularly in applications involving large loads or high accelerations. Furthermore, boron carbide is harder than silicon carbide. Thus, an RBSC composite (ie, “RBBC”), characterized by boron carbide as a reinforcing or filler material, has a higher hardness but a lower specific gravity than an RBSC composite having silicon carbide as a filler material. I will provide a.

  [0056] In an alternative embodiment, the present invention includes a boron carbide composite made by a "siliconization" process similar to the process of making "siliconized SiC". Here, typically a commercially available pure elemental silicon-containing molten infiltrant comes into contact with a porous mass of a ceramic material containing at least some boron carbide and is generally vacuum or inert gas (eg, argon ) Can be wetted by the molten infiltrant under processing conditions considered to be the environment. The ceramic material comprising boron carbide can be in the form of substantially disconnected particles, such as a loose mass of particles, or can be in the form of a lightly sintered or “unglazed” material, Or it can be heavily sintered and have a small amount of interconnected porosity. Unlike the RBSC process, here the carbon source in the porous mass is substantially depleted. Thus, siliconization is not as robust an infiltration process as the RBSC process. Accordingly, a somewhat higher infiltration temperature, such as about 1500 ° C. to about 2000 ° C., and / or a vacuum environment (eg, as opposed to an inert environment) will be required. However, to make siliconized boron carbide for armor applications, one should probably avoid higher infiltration temperatures and more severe sintering of preforms (for example, fillings) for reasons discussed further below. The present inventors recommend that it be more interconnected).

  [0057] However, under many conventional silicon infiltration conditions, boron carbide is at least somewhat reactive with molten silicon. One of the reaction products of these reactions is mostly silicon carbide formed in situ, but boron carbide is substantially unaffected by the infiltrant when attempting to maximize boron carbide loading. This is desirable if it can remain in place, i.e. if silicon has not reacted with boron carbide. In a reactive bonding embodiment, the present invention solves this problem by dissolving some boron in the molten silicon, thereby reducing the reaction activity between silicon and boron carbide. Pure silicon will eventually be saturated with boron and carbon when it reacts with the boron carbide phase in the porous mass or preform, but this approach is not possible with this porous mass or preform. Is not preferred unless it is "sacrificed" and the final commercial article is not manufactured. In many cases, the reaction between the porous mass or preformed boron carbide reinforcement and the silicon infiltrant resulted in cracking of the resulting silicon carbide composite. Instead, it is preferred to provide a boron source to the silicon-based infiltrant before the infiltrant contacts the porous mass or preform. Although any boron-containing material that can be dissolved in silicon can be useful in the context of the present invention, elemental boron and boron carbide are particularly preferred.

  [0060] Any number of techniques for adding a boron source material to a silicon infiltrant can be envisaged. A preferred approach according to the present invention is to support the preform to be infiltrated and to supply the infiltrant to the preform by a kiln device comprising a porous preform containing boron carbide. Specifically, the silicon-containing infiltrant can infiltrate a kiln apparatus (hereinafter referred to as “feeder rail” or “beam”) that includes at least some boron carbide. The kiln device can be provided in a porous state, such as a preform, or in an “infiltrated” state, such as a composite. A preform, often referred to as a “target” preform, intended to eventually become a commercial article after infiltration is supported on a kiln device. The silicon-containing infiltrant dissolves in at least some boron carbide in the kiln and is saturated with carbon and / or boron. Then, when this molten silicon continues to infiltrate the target preform that contacts the kiln apparatus, the infiltrated silicon will react very little with the boron carbide of the target preform. Kiln cracks resulting from the reaction of silicon with the kiln's boron carbide should not unduly affect the continued infiltration of silicon into the target preform. Of course, the support kiln device need not essentially contain boron carbide. Many boron-containing materials that can dissolve boron into the silicon component in the infiltrant should be satisfactory, but materials such as boron oxide may not be sufficiently fire resistant under heat treatment conditions. . In addition, the boron source need not be placed in the kiln apparatus, but before the molten silicon contacts the boron carbide of the subject preform, it is alloyed or, at best, any point in the silicon component of the infiltrant. Will be introduced in. For example, when making “lay-up” for infiltration, we distribute the loose silicon infiltrant at the bottom of the container containing the molten silicon infiltrant, for example, as a loose powder. Thus, it has been found useful to provide boron carbide particles. In addition, the inventors have noted that, at least in the RBBC embodiment, the presence of a boron nitride coating on the porous mass or preform to be infiltrated helps to suppress the boron carbide reaction.

  [0061] For silicon infiltrates that do not rely on reactive carbon in a porous mass or preform, such as a boron carbide siliconization process, in addition to the boron source, add a carbon source to the molten silicon; It would also be desirable to suppress the tendency of silicon to dissolve carbon from boron carbide. Of course, boron carbide provides a carbon source as well as a boron source, but it is desirable to provide an independent carbon source, such as many elemental carbon forms. These can be provided in the form of powder, for example, graphite powder, can be mixed with the material from which the feeder preform is made, or can be mixed with the silicon infiltrant, which are often in powder form Or provided in the form of a mass. In addition, the addition of carbon independent of the boron source can be a measure for suppressing the reaction.

  [0062] It should be noted that at processing temperatures of about 1550 ° C., a small amount of elemental boron, perhaps as little as 1% by weight of carbon, will dissolve in the molten silicon. In any event, these amounts should be sufficient to substantially inhibit the dissolution or reaction of boron carbide reinforcement in molten silicon.

  [0063] Preferred embodiments of the invention relate to a particular application of the boron carbide composite material as armor to stop ballistic projectiles. In order to overcome incident projectiles, their ceramic armor is usually characterized by being composed of at least two completely different materials. That is, the components of their ballistic impact armor system are characterized by a ceramic layer and a backing layer that are at least typically joined together. As the name suggests, the backing layer is placed behind the ceramic layer relative to the direction of travel of the projectile. Sometimes a layer or layers of protective material are also placed in front of the ceramic layer, usually to protect the ceramic from destruction by routine handling (or mishandling). The purpose of the ceramic layer is to “treat” impacting projectiles by flattening, crushing, eroding, etc. The role of the backing layer is to “capture” the treated projectile, as well as debris that scatters behind the ceramic layer. Typically, the backing layer can be greatly deformed without breakage. The backing layer can be made from a metal or alloy such as aluminum, iron or steel, titanium, etc., and in vehicle armor it can be the structure of the vehicle itself. If lightweight armor is required, the backing layer is typically a fiber reinforced polymer (FRP) material. Fibers used for these backings include polyethylene, aramid, and glass fibers. Known FRP backing materials are available from AlliedSignal Inc. Products currently registered by Honeywell International Inc., which refers to rolled products that are composed of two layers of unidirectionally stretched polyethylene fiber tapes that are cross-laminated at right angles and become nonwoven thermoplastic composites Although there is the name “SpectraShield”, several of those FRP backing materials are available on the market.

  [0064] Armor generally takes the form of a plate, but the plate need not be a flat regular polygon. Often, armor plates are shaped to match the underlying structure to be protected. For example, body armor is curved in one or more dimensions to better match the shape of the wearer, eg, the human torso.

  [0065] According to many persons skilled in the art of armor, what is required of armor material is to destroy and erode the impacting projectile before it enters the armor system. Vienicki et al. (Cited) is all that is required for the armor to have at least the same hardness as the projectile, but the level of performance is significant even if the hardness is further increased beyond the required "threshold" level Showed no increase.

  [0066] Thus, in addition to the motion control applications suggested above, boron carbide composites should be attractive candidates for armor materials, and as the prior art actually shows, other engineers have previously Attempts were made to use boron carbide composites as armor. Since armor is often defined by gross weight, armor systems with low volume specific gravity have been sought because armor can be made thicker from the same mass (which was previously desirable). One important aspect of the extremely high hardness of boron carbide is that non-rigid phases, such as metals, are tolerated in composites containing boron carbide and metals, while satisfying the overall hardness required of the composite, for example Other properties such as strength or toughness can be improved.

  [0067] The overall hardness of the boron carbide composite material of the present invention is proportional to the hardness of the components of the composite material and its volume fraction. With respect to the development of high performance armor materials, the armor embodiments of the present invention achieve a loading of a hard ceramic phase, such as high volume boron carbide, sufficient to satisfy the overall hardness considered important, And focus on limiting the size of the largest particles or crystals that make up the composite, especially the ceramic crystals. More precisely, substantially all the morphological shapes that make up the microstructure of the boron carbide composite must be less than about 350 microns in size. It is more preferred that substantially all these shapes are less than about 212 microns, and even more preferred that at least 90% by volume is less than about 100 microns. It is particularly preferred that the boron carbide composite has a size in which at least 90% by volume of the ceramic morphological shape does not exceed about 55 microns.

  [0068] Those upper limits on the particle size of the filler material used in porous masses or preforms can be achieved by sieving the filler, among other techniques. For example, 170 mesh and 200 mesh (US standard) screens produce particles with a maximum size of about 90 microns and 75 microns, respectively. Similarly, 45 mesh, 50 mesh, and 70 mesh (US standard) sieve screens pass particles of maximum sizes of about 350 microns, 300 microns, and 212 microns, respectively. It is particularly preferred that the boron carbide composite has a size such that at least 90% by volume of its morphological shape does not exceed about 55 microns.

[0069] One technique for maximizing the amount of hard phase in a composite is to produce a porous mass or preform that is loaded with a high volume into the hard phase, typically in the form of a hard filler material. It is to be. Highly loaded preforms can be made by dispersing and using filler material particles so that small particles can enter or fit into the spaces between larger particles. The adjustment of both parameters in the same material, because the two factors of essentially limiting or limiting the maximum particle size and maximizing the loading of the hard filler in the preform are mutually exclusive. Care must be taken. Fortunately, the present invention limits the size of the filler, e.g., restricting the size of the filler by such a method that at least 90% by volume of the filler is less than about 100 microns in diameter, while the It was relatively successful to obtain a preformed body filled with Even with a more conservative upper limit of maximum particles of about 100 microns, it is possible to produce preforms loaded with 65% or more by volume in a hard ceramic phase such as SiC and / or B ₄ C.

[0070] Some of the “larger” hard ceramic fillers used in the following examples have the following particle size distribution: Grade F240 CRYSTOLON® SiC (Saint-Gobain / Norton Industrial Ceramics, Worcester, Mass.) Has 90% by volume of its total constituent particles less than about 55 microns and 97% less than about 70 microns. Grade F320 CRYSTOLON® SiC has 90% by volume of its particles less than about 37 microns and 97% less than about 49 microns. These results were calculated based on the Eppendorf-Photodimentometer. According to sieve analysis, 220 grit TETRABOR® B ₄ C (ESK, Kempten, Germany) has 85% of its particles smaller than about 75 microns, and virtually all its constituent particles are smaller than about 106 microns. Is also small.

  [0071] The fine particle size limitation defined in the present invention can actually be a substitute for high mechanical strength, or at least set a lower limit on the mechanical strength of the composite material. Limiting particle size is necessary but not a sufficient condition to give brittle materials high strength, so traditionally achieving high strength targets has been one of the quality metrics of manufactured ceramics or composites. it was thought. In general, in brittle composite materials, particularly those produced by infiltration, many of the defects have a significant impact on the mechanical strength of the resulting composite. These are non-uniform filler material distribution in the preform, for example, incomplete infiltration of the preform, filler material where porous and / or unreacted carbon or other reactants remain in the preform. Or including excessive grain growth during the heat treatment of any silicon carbide produced in situ. Those defects will probably also impair the ballistic performance of the material.

  [0072] The boron carbide composite microstructure of the present invention has a different mode (eg, intragranular) from a prior art composite made with silicon infiltration technology, which has a larger, interconnected microstructure. On the other hand, it may break at the grain boundary). Whatever the exact reason or mechanism of operation, the inventors have found that RBBC materials of limited particle size and limited connectivity ceramic phase are useful for stopping projectiles from ballistic projectiles, especially from small weapon launches. We found it to be very effective.

[0073] hard filler component of the boron carbide composite of the present invention is much harder than the silicon component (for example, about the Si versus about 2900~3580kg / mm ² Knoop hardness of each _{B 4} C 1100kg / mm ² (Vickers)), the overall hardness of the composite greatly depends on the relative amount of each phase. Thus, when the composite end-use article is armor to protect against ballistic projectiles, especially when the residual infiltrant phase component is softer than silicon, the composite has a large volume ratio of the hard phase. It is important to include, the contents of which are discussed in detail below. In reaction formed silicon carbide composites, some of the silicon carbide is produced in situ. Accordingly, it is possible to form a highly loaded composite with silicon carbide by infiltrating silicon into a porous mass containing a large amount of carbon. Also, this approach is not preferred for reasons discussed in more detail below. Instead, it is desirable to infiltrate while reacting a porous mass or preform that is highly loaded with a hard ceramic phase of filler material rather than carbon. In an alternative embodiment, a preform that is highly loaded with a hard filler material with little or no reactive carbon is infiltrated (eg, “siliconized”) with molten silicon or a silicon-containing metal.

  [0074] When the porous mass or preform includes boron carbide, no additional carbon source is required because the silicon of the molten infiltrant can react with the boron carbide. This is the approach adopted by Taylor et al. (And other researchers) in the '564 patent discussed above. This approach is undesirable if the goal is to maximize the hardness and / or boron carbide loading of the resulting composite. In particular, boron carbide has a higher hardness and lower specific gravity than silicon carbide. Therefore, the reaction of boron carbide and silicon to produce silicon carbide (plus silicon boride) gives up a high hardness material in exchange for a low hardness and high specific gravity material. Therefore, it would be desirable to minimize the reaction of the boron carbide component. Therefore, when an object of high hardness and low specific gravity is desired, such as an armor system, and boron carbide is used as the filler material in the reaction bonded composite, the carbon source other than boron carbide is a porous mass or preform. Should be present inside.

  [0075] In the siliconization process, there is little or no reactive carbon present in the porous mass. However, in the absence of at least a small amount of carbon, molten silicon will dissolve the carbon from the porous mass of silicon carbide. It is therefore desirable to supply a carbon source to the molten silicon, possibly to the saturation point, before the molten silicon contacts the porous mass to be infiltrated. Beyond this concentration, excess carbon will precipitate as SiC formed in situ. Again, silicon can incorporate some carbon into the solution by first contacting the molten silicon with a carbon source such as elemental carbon or silicon carbide. The carbon source can be provided by the same technique used to provide the boron source to the silicon infiltrant. The problem with this molten silicon, which dissolves carbon from porous masses or preformed boron carbide, is generally the reaction because there is more than enough reactive carbon to saturate the silicon and inhibit this reaction. This is not a problem for reactive infiltration systems, such as RBBC.

  [0076] Techniques for maximizing the volume loading of filler material in porous masses or preforms are well known and usually provide a size distribution such that smaller particles tend to fill gaps between larger particles. A plurality of filling material bodies, for example, a form of mixing particles is used. However, there is a size distribution limit in the degree of particle size distribution. For example, if there is a possibility of chemical reaction, smaller particles tend to be more reactive than larger particles because of their large total surface area because boron carbide is present in these silicon infiltration systems. At some other end of the scale, large size filler material particles will begin to reduce the strength of the composite and will be degraded by brittle fracture mechanisms due to the introduction of critical size defects into the material. Furthermore, there is uncertain evidence in the prior art that RBSC bodies containing large or relatively large particles, whether related to strength, were not good armor materials. Thus, the present invention overcomes this problem by providing a technique that allows relatively fine boron carbide particles to be infiltrated during the reaction bonding operation and not consumed for reaction with the incoming silicon infiltrant. . The possibility of making fine-grained RBBC is not only beneficial for armored applications, but also beneficial for many precision instrument applications. In particular, the fine particle size allows a finer shape to be ground or machined into the material, even though the high strength gained by the fine particle size composite material is not critical.

  [0077] Any known technique can be used to produce a porous preform that can be infiltrated with a molten infiltrant containing silicon, but highly loaded with one or more fillers Techniques that appear to be able to better produce such preforms, particularly relatively thin preforms, are, for example, sedimentation, slip molding, or thixotropic molding using a liquid phase. However, other well-known ceramic processing techniques, such as a dry press, can also be fully satisfied depending on the particularity of the composition and the article being formed.

  [0078] Recently, it has been known to alloy infiltrant metals used to make reaction-formed silicon carbide bodies, and the metal phase of the formed object contains components other than silicon. (See, for example, co-owned US Pat. No. 6,503,572.) For example, in the present boron carbide composite system, the infiltrant includes an alloy of silicon, boron, and copper, in the formed boron carbide composite. A phase containing metallic copper or a copper alloy or a copper-silicon intermetallic compound can be produced. Objects containing their alloy infiltrant phase are often softer but tougher than similar objects with essentially pure silicon as the infiltrant phase. Despite the reduced hardness, reaction bonded boron carbide composites with alloyed infiltrant phases should still function well as armor materials. For example, compressive strength or toughness characteristics are important factors contributing to good ballistic properties, especially when combined with high hardness. For example, enhanced toughness can contribute to the improved multi-blow capability of the resulting armored product and / or contribute to improved durability, which is also important for daily handling in the market. I can do it. In addition, it is easy to add other (not silicon) metal to the infiltrant in the siliconization process.

  [0079] Again, the porous mass of the present invention always contains some amount of boron carbide. Without advanced techniques such as doping silicon infiltrant with a boron source and, if necessary, with a carbon source, the boron carbide component of the porous mass reacts with the molten silicon and carbonizes. There is a tendency to produce silicon plus silicon boride. In the present invention, the system was designed so that boron carbide never reacts in large quantities with molten silicon. Thus, the boron carbide component can be considered a substantially inert filler material. In addition to boron carbide, the porous mass can incorporate one or more of those other filler materials. This means that the filler material is substantially non-reactive with the molten infiltrant under local processing conditions. One type of those filler materials that is particularly preferred is silicon carbide because molten silicon wets silicon carbide more easily than other inert materials such as oxides. However, at least some amount of other filler materials that do not wet as much as boron carbide or silicon carbide under local processing conditions, but achieve wettability and infiltration of the entire porous mass with molten silicon It should be possible to mix. Examples of these alternative filler materials include titanium diboride, silicon nitride, and aluminum nitride. Especially if the porous mass contains a reactive carbon source, and this carbon source is interconnected, such as in the form of a coating on the packing, it is a “non-wetting” packing material (eg aluminum oxide) It is also possible to achieve the wettability and infiltration of the porous mass with molten silicon.

  [0080] The filler material comprising the porous mass to be infiltrated can be provided in many different forms including particles, platelets, flakes, whiskers, continuous fibers, microspheres, agglomerates and the like. Particles are often preferred for reasons of economy and availability.

  [0081] Although not possible with visual inspection, X-ray diffraction techniques can be used to distinguish a reaction-formed silicon carbide matrix from any silicon carbide that can be present as a reinforcing or filling material. . Specifically, the reaction-formed silicon carbide is typically a beta polymorph, at least under the present processing conditions. In contrast, most commercially available particularly normal grade silicon carbide is the alpha form most used as a filler material. Thus, at least approximate quantitative data can be obtained for each relative amount present in the complex.

  [0082] A wide range of sized packing material bodies, for example objects in the size range of a few millimeters to microns, can be successfully infiltrated using a reaction forming process. Again, when the goal is the manufacture of objects that contribute to bulletproof armor, virtually all the morphological features that make up the ceramic components of the filler and composite are about 300-350 microns, preferably about 212 microns or less. Must be kept in size.

  [0083] Previously, the inventors recommended that the size of morphological features (eg, crystals, etc.) be kept below about 100 microns. However, if certain reaction conditions are maintained in the control described in the following section, particles somewhat larger than about 100 microns can be used and still achieve good ballistic impact performance.

  [0084] In addition to limiting the maximum size of the filler object that makes up the porous mass, the porous mass of the filler material should not be exposed to excessive temperatures, particularly during infiltration. In this regard, the present invention provides for infiltration of a porous mass of boron carbide particles (plus added carbon) without causing a reaction between boron carbide and boron doped silicon infiltrant at a temperature of about 1550 ° C. Successful. Here, “excess” also refers to the temperature at which the ceramic particles can grow to a discernable extent. For example, the transition from beta to alpha crystallographic form of silicon carbide occurs at about 2050 ° C. Crystallographic transition is often accompanied by broad grain growth, which can be observed as microstructure roughening. Depending on the exact conditions, it is possible to heat to a slightly higher temperature (probably about 2100 ° C.) and prevent this recrystallization, but it is unknown what happens to the boron carbide component at this temperature It is. Furthermore, it should be recommended that no infiltration or post-treatment of the infiltrated mass should be performed at temperatures above about 2000 ° C. Again, as far as the production of the boron carbide composite is concerned, the lowest temperature that achieves the objective is generally preferred.

  [0085] Furthermore, in a reaction bonded composite system, the high volume fraction of the hard phase is not from the production of a large amount of in situ formed silicon carbide phase, but instead a highly packed mass of hard ceramic filler material. Should be achieved by designing. For example, the porous mass to be infiltrated preferably contains free or elemental carbon as a carbon source to form silicon carbide in situ. This amount of free carbon should be (generally) limited to an amount not exceeding about 10% by volume of the porous mass, and preferably not exceeding about 5-6%. Thus, in general, the amount of silicon carbide produced in situ should be limited to no more than about 24% by volume of the final composite, and preferably no more than about 12-14%. Among the problems resulting from excessive reaction during the infiltration process is a rapid rise in temperature due to the exothermic nature of the chemical reaction between silicon and carbon. These rapid increases in temperature lead to cracks due to local thermal expansion. Also, the conversion of elemental carbon to silicon carbide is accompanied by a volume expansion of about 2.35 times. Therefore, a large amount of reaction is also harmful from the viewpoint that a large volume change can cause cracks.

[0086] However, the inventors have noted that many prior art reaction binding documents, such as those warned above just before, have been recognized by the inventors as "overreaction" processing conditions. Is clearly disclosed. The result is excessive particle growth and individual particles or morphological shapes (eg, particles) coalesce or fuse into large particles. For example, see FIG. 8A. In contrast to this rough microstructure, we have produced a silicon infiltrated composite material with good ballistic impact performance and a microstructure similar to that shown in FIG. 8B. did. This microstructure is characterized by minimal chemical reaction, little or no SiC recrystallization, and minimal coalescence, often referred to as “aggregation”. It should be pointed out that these two figures are characterized by SiC as filler particles and not B ₄ C, but do not deny the points shown. Therefore, as long as we can continue to produce ceramic-rich composites with these microstructures (originally provided as individual objects) that exhibit minimal hard filler particle interconnectivity through silicon infiltration techniques, We argue that the particle size of the filler can be increased to about 100 microns or more, and still provide acceptable ballistic impact performance in armored applications. For example, it may be possible to increase the size of the filler particles to about 212 microns, or perhaps in the range of 300-350 microns.

  [0087] Accordingly, the microstructure of the resulting armor grade boron carbide composite material of the present invention provides interconnectivity of the body and other hard phases comprising boron carbide provided in a porous mass or preform. Is a kind of restricted object. In other words, the objects that make up the filler material should also have a small or negligible amount of interconnectivity with each other, such as by oversintering or recrystallization, or excessive in situ SiC formation. Absent.

  [0088] Although not necessary, the carbon source added to the porous mass or preform for the reaction bonded embodiment of the present invention is typically in the form of elemental carbon such as graphite. In many applications, particularly those requiring high hardness, it is desirable that the resulting composite silicon carbide be at least partially interconnected. This result is more easily achieved if the carbon in the porous mass or preform is interconnected. In addition, the interconnected carbon in the porous mass or preform helps infiltration in terms of speed and reliability. In a preferred embodiment, carbon is introduced into the porous mass as a resin. This mixture can then be formed into the desired shape. Curing of the resin provides a free-standing porous mass, such as a preform. During a subsequent heat treatment, typically in a non-oxidizing atmosphere, or an intermediate firing step, the resin is pyrolyzed into interconnected carbon to produce a preform containing at least about 1 volume percent carbon. . The resin infiltration and pyrolysis cycle can be repeated one or more times if an increase in carbon content is required.

  [0089] Reaction bonded boron carbide composites are generally less expensive to manufacture than hot pressed boron carbide bodies. Not only can multiple RBBC bodies be heat treated simultaneously, but the tool (typically graphite) will withstand longer than those used in hot pressing operations.

  [0090] As noted above, the present RBBC composites are expressed or measured with accurate net dimensional tolerance acquisition, eg, hot pressed boron carbide armor tiles as curved tiles for body armor applications. It can be manufactured to a net size and shape better. The inventors also expect that the siliconized boron carbide material exhibits better dimensional reproducibility than hot pressed boron carbide.

[0091] Tighter dimensional tolerances represent a performance advantage. Specifically, armor for armor manufacturing, particularly weight sensitive applications, typically measured at V ₅₀ projectile speeds at a specified maximum weight or surface density to meet a certain minimum ballistic impact protection level. Stipulated or confirmed. (For information, the ballistic impact test terminology in this document has the same meaning as the term described in MIL-STD-662F.) The purpose is high ballistic impact performance and low areal density, both factors being thickness The armor plate should be as uniform as possible because it varies with respect to the thickness. This is particularly true because the V ₅₀ value should be achieved at the lower limit of the allowed thickness range, ie the thinnest plate allowed, but the maximum weight is determined by the upper limit of the thickness range. I can say that.

  [0092] As long as the overall shape of the ceramic armor plate is within specifications, it is at least theoretically possible to recover the developed non-uniformity during heat treatment by polishing or machining. However, these post-processing operations are usually expensive and have little market feasibility in the body armor market. Therefore, the ceramic armor body must have a uniform thickness while still being heat treated.

  [0093] The conformity of the shape of the formed ceramic armor to the intended shape is also important. The ability to create ceramic armor plates with intricately shaped curves that faithfully reproduce the desired shape can be of great value to meet the shape and conformance requirements of armored products. RBBC materials that exhibit better thickness uniformity than sintered or hot pressed armor ceramics are expected to show better shape reproducibility than sintered or hot pressed products. Similar results are expected for siliconized boron carbide materials.

  [0094] The following non-limiting examples further illustrate the present invention.

( Reference Example 1)
[0095] This reference illustrates the production by reactive infiltration of a Si / SiC composite containing boron carbide reinforcement, ie Si / SiC / B ₄ C. More specifically, this reference example illustrates the infiltration of a silicon-containing melt into a preform containing an interconnected carbon phase derived from a resinous precursor and silicon carbide and boron carbide particles.

  [0096] A preform was prepared by a sedimentation process. Specifically, about 28 parts water was added to 100 parts ceramic particles and 8 parts KRYSTAR 300 crystalline fructose (AE Staley Manufacturing Co.) to make a slurry. The ceramic particle content is 220 grit TETRABOR® boron carbide (manufactured by ESK GmbH, Kempten, Germany, sold by MicroAbrasives Corp., Westfield, Mass.) Having a median particle size of about 66 microns and about 13 microns. 500 grit CRYSTOLON green silicon carbide (St. Gobain / Norton Industrial Ceramics) (grade 500 RG) with a median particle size of approximately equal weight ratio. Solids and liquids were roll mixed for about 40 hours in addition to plastic jars. The slurry was degassed for about 5 minutes in a vacuum of about 760 mm. About 15 minutes before molding, the slurry was roll mixed again to suspend any precipitated particles.

  [0097] A graphite support plate was placed on the shaking table. A rubber mold having a cavity of the desired shape to be molded was wetted with a surfactant (Sil-Clean, Plastic Tooling Co., Exton, PA). The wet rubber mold was then placed on a graphite plate and dried. The slurry was poured into the cavity. The vibration started.

  [0098] During settling, the liquid remaining on the top of the molded article was blotted with a sponge. After the particles had completely settled (about 3 hours), the vibration was stopped. The graphite plate, rubber mold, and internal molded product were transferred from the shaking table to a refrigerator maintained at a temperature of about −20 ° C. The molded article was completely frozen for about 6 hours, thereby forming a self-supporting preform.

  [0099] The frozen preform was released from the refrigerator and placed on a graphite curing tray. The graphite tray and preform were then immediately placed in a room temperature nitrogen atmosphere furnace. Ignition furnace, heat to a temperature of about 50 ° C. at a rate of about 10 ° C./hour, hold at about 50 ° C. for about 8 hours, then heat to a temperature of about 90 ° C. at a rate of about 10 ° C./hour Held at about 90 ° C. for about 8 hours, then heated to a temperature of about 120 ° C. at a rate of about 10 ° C./hour, held at about 120 ° C. for about 4 hours, and then at a rate of about 50 ° C./hour It was programmed to heat to a temperature of about 600 ° C., hold at about 600 ° C. for about 2 hours, and then cool to room temperature at a rate of about 100 ° C./hour. This calcination operation pyrolyzed the fructose and produced a well-bonded preform containing about 2.7% carbon by weight.

  [0100] Two “beam” or feeder rail preforms and a number of tile preforms were made using the process described above. Each tile preform had a mass of about 174 grams and an overall dimension of about 100 mm square x about 9 mm thickness. Each rail preform had the cross-section depicted in FIG. 1 and had dimensions of about 220 mm long x about 15 mm wide x about 25 mm thick. During infiltration of the tile preform, these rails will act as conduits that direct the molten infiltrant to the tile preform.

  [0101] Equipment was prepared to limit the infiltration process.

  [0102] As shown in FIGS. 2A and 2B, the inner surface of a grade ATJ graphite tray 31 (Union Carbide Corp., Carbon Products Div., Cleveland, OH) with dimensions of about 790 mm × about 230 mm × about 51 mm deep is shown as Model 95. Boron nitride slurry or paint 33 was spray applied using a Binks spray gun. Boron nitride paint was prepared by diluting about 1800 grams of LUBRICOAT boron nitride paste (ZYP Coatings, Oak Ridge, TN) to about 1 gallon (3.7 liters) with deionized water. Two relatively thin layers of boron nitride were applied with approximately room temperature air drying between the applications.

  [0103] The boron nitride coated tray was then placed in a large graphite chamber 35 having internal dimensions of about 825 mm long x about 270 mm wide x 320 mm high. The chamber was also characterized by means for supporting parallel rows of graphite dowel rods.

[0104] Referring now in detail to FIG. 2B, a 2-ply PANEX® 30 low carbon oxide fabric 44 (grade PW03, plain weave, 115 g / weight) weighing about 48 grams and measuring about 790 mm × about 230 mm. m ² , Zoltek Corp., St. Louis, MO) was placed on the floor of the coated graphite trays 31,33. Four boron carbide rail preforms 42 each having a mass of about 190 grams and a length of about 200 mm were placed on the fabric and placed parallel to the length of the tray. A mass of silicon 21 (Grade LP, Elke Metals Co., Pittsburgh, PA) containing about 0.5 wt% Fe (maximum) and remaining Si is then applied to the carbon cloth between the individual preform rails. Distributed more or less evenly on top. Calculations indicated that about 1510 grams of silicon infiltrant was required to fully react the elemental carbon and fill the gaps in the fabric, feeder rail preform, and tile preform. However, approximately 10% additional silicon was provided to the equipment.

  [0105] A graphite dowel rod 49 having a diameter of about 0.25 inch (6 mm) spray coated with boron nitride 33 was placed in a graphite holder or support 47. A total of 15 square tile preforms 41 (only 4 shown in the figure), also spray coated with boron nitride 33, were placed on each half of the tray across the ends of the two rails. . Since boron nitride tends to act as a barrier material to prevent excessive infiltration, the surface of the tile that is in contact with the boron carbide preform was not applied.

  [0106] The top of the chamber was covered with a loosely fixed (not hermetically sealed) graphite lid 34 characterized by a number of through-holes 36 of about 1 cm in diameter allowing exchange of atmosphere. The hole was covered with a piece of graphite felt 38 secured in place with a graphite block 40 which served as a stationary load, thereby completing the equipment.

  [0107] The completed equipment was then placed in a vacuum oven at about room temperature (eg, about 20 ° C.). A mechanical roughing pump was used to evacuate and then maintain the remaining rough vacuum at a pressure of less than about 100 millitorr. The lay-up was then heated from room temperature to a temperature of about 1350 ° C. at a rate of about 200 ° C./hour. After maintaining a temperature of about 1350 ° C. for 1 hour, the temperature was further increased to a temperature of about 1550 ° C. at a rate of about 200 ° C./hour. After maintaining a temperature of about 1550 ° C. for 1 hour, the temperature was reduced to a temperature of about 1450 ° C. at a rate of about 100 ° C./hour. Without maintaining this temperature, the lay-up temperature was further lowered to a temperature of about 1300 ° C. at a rate of about 25 ° C./hour, and then immediately cooled to about room temperature at a rate of about 200 ° C./hour.

[0108] Following this heating schedule, the chamber and its contents were recovered from the vacuum furnace, disassembled and inspected. The silicon infiltration melted and infiltrated into the carbon cloth, thereby changing the carbon cloth into a silicon carbide cloth. The molten silicon infiltrant also passes through the rail preform and also into the square tile preform and reacts with the elemental carbon therein to form a dense silicon carbide matrix composite with boron carbide reinforcement. Formed. Since each of the preforms was supported on the rail with linear contact, low to intermediate hand force was sufficient to separate the Si / SiC / B ₄ C composite tile from the feeder rail composite. .

( Reference Example 2)
[0109] Reference Example 1 except that silicon carbide particles were not used to make the preform and the particle size distribution of boron carbide was modified so that substantially all of the particles were smaller than about 45 microns. The technology was substantially repeated. Following the pyrolysis step, the preform contained about 75% by volume boron carbide particles and about 4% by volume carbon.

[0110] After infiltration, the ceramic material is nominally 75% by volume B ₄ C, 9% by volume reaction-formed SiC, and 16% by volume remaining Si (ie, Si / SiC / B ₄ C composite). Inclusive. The polished cross section was examined using a Nikon Microphoto-FX optical microscope. An optical micrograph of the material is shown in FIG. Clearly, careful selection of processing conditions including the addition of a boron source to the silicon infiltrant resulted in slight particle growth and interconnections, and thus the ability to maintain a relatively fine microstructure. It is confirmed. For example, the micrograph shows that the reaction between Si and B ₄ C is hardly visible as a result of the infiltration process.

( Reference Example 3)
[0111] Before supplying silicon infiltrant to layup, except that single layer TETRABOR® boron carbide particles (220 grit, ESK) were sprinkled on the carbon cloth between the feeder rails, for reference The technique of Example 2 was substantially repeated. The amount of silicon was concomitantly increased as in Reference Example 1 to offset the added boron carbide and maintain an excess silicon supply of about 10%.

(Comparative Example 1)
[0112] This example illustrates the fabrication of a silicon carbide composite armor plate that is highly loaded with fine particle silicon carbide filler. This example further illustrates the reuse of some of the components of the heat treatment equipment.

  [0113] Armored “breast pads” and four “feeder rail” preforms were prepared by a sedimentation molding process. Specifically, about 24 parts deionized water was added to 100 parts CRYSTALON unfired silicon carbide (Saint-Gobain / Norton Industrial Ceramics, Worcester, Mass.) And about 6 parts KRYSTAR 300 crystal fructose (A.E.Stay Manufacture. , Decatur, IL) to make a slurry. The silicon carbide particles consisted of about 65% by weight grade F320 (median particle size about 29 microns, bulk form) and the remaining grade 500RG (median particle size about 13 microns, round form). Solids and liquids were added to a plastic jar and roll mixed for about 40 hours. The slurry was degassed for about 5 minutes in a vacuum of about 760 mm. About 15 minutes before molding, the slurry was roll mixed again to suspend any precipitated particles.

  [0114] A graphite support plate was placed on the shaking table. A rubber mold having a cavity of the desired shape to be molded was wetted with a surfactant consisting of a 10% by weight aqueous solution of JOY dishwashing detergent (Proctor and Gamble, Cincinnati, OH). The wet rubber mold was then placed on a graphite plate and dried. The slurry was poured into the cavity. The vibration started.

  [0115] After the particles had completely settled (about 3 hours), the vibration was stopped. The liquid remaining on the top of the molded product was sucked up with a sponge. The molded product in the graphite plate and the rubber mold on the graphite plate was transferred from the shaking table to a refrigerator maintained at a temperature of about −15 ° C.

  [0116] Once the molded article was completely frozen, the rubber mold was removed from the refrigerator and the frozen molded article contained therein was released and placed on a graphite curing tray for drying and baking. The curing tray was processed into the shape of the outer side of the breastplate preform. The graphite tray and preform were then placed in a room temperature nitrogen atmosphere furnace. Ignit the furnace and heat to a temperature of about 90 ° C. at a rate of about 40 ° C./hour, then hold at about 90 ° C. for about 2 hours, then further to a temperature of about 600 ° C. at a rate of about 100 ° C./hour It was programmed to heat and hold at about 600 ° C. for about 2 hours and then to cool to room temperature at a rate of about 200 ° C./hour. This calcination operation pyrolyzed the fructose and produced a well bonded preform containing about 2 wt% carbon.

  [0117] The carbon content of the breastplate preform was increased by re-infiltrating a 70 wt% aqueous solution of KRYSTAR300 crystalline fructose. Specifically, the preform was immersed in the fructose solution for a total of about 20 hours. An excess air pressure of about 60 psi (410 kPa) was applied to the solution for the first about 2 hours to infiltrate the solution more quickly into the preform. After stopping air pressurization for 15 minutes, the pressure was returned to the same pressure. After maintaining the excess pressure for an additional 2 hours, the pressure was returned to atmospheric pressure and the remaining 20 hours of the preform was immersed in the solution. The breastplate preform was then removed from the fructose solution and wiped with a damp cloth to remove excess fructose solution. The preform was then re-pyrolyzed according to the same heat treatment plan as described above. In the second pyrolysis step, 3% was added to the total mass of the preform.

[0118] The breastplate preform had a mass of about 700 grams and had an overall dimension of about 318 mm long x about 241 mm wide x about 4.4 mm thick. The breastplate was slightly curved in length and width. The feeder rail preform was the same size as used in Reference Example 1 for infiltrating the square tile preform in terms of cross section.

  [0119] Next, an infiltration layup was prepared.

[0120] Referring to FIGS. 4A and 4B, a grade ATJ graphite tray 31 (Union Carbide Corp., Carbon Products Div., Cleveland, OH) having dimensions of about 790 mm × about 230 mm × about 51 mm deep.
A boron nitride slurry or paint 33 was sprayed onto the inner surface of the substrate in substantially the same manner as described in Reference Example 1.

  [0121] The boron nitride coated tray is then placed into a larger graphite chamber 35 having a slightly larger length and width dimension than the tray, but sufficient height to accommodate the longer dimensions of the armor plate. placed. The chamber also featured means 37 for supporting parallel rows of graphite dowel bars 39.

<Infiltration of carbon cloth and silicon carbide feeder rail>
[0122] Referring now in detail to FIG. 4B, a single PANEX® 30 low carbon oxide fabric 44 (grade PW03, plain weave, 115 g / m) weighing approximately 25 grams and measuring approximately 790 mm x approximately 230 mm. ² , Zoltek Corp., St. Louis, MO) was placed on the floor of the coated graphite trays 31,33. Four boron carbide rail preforms 32 each having a mass of about 190 grams were placed in pairs on half of each tray across the width of the fabric 44. Sprinkle sufficient silicon (grade LP, Elke Metals Co., Pittsburgh, PA, in the form of a lump) with about 0.5 wt% Fe (maximum) and the remaining Si onto the surface of the carbon cloth to The rails and any preforms placed on the rails were completely infiltrated. The top of the chamber was covered with a loosely fixed (not hermetically sealed) graphite lid 34 featuring a number of through-holes 36 of about 1 cm in diameter allowing the exchange of atmosphere. The hole was covered with a piece of graphite felt 38 secured in place with a graphite block 40 which served as a non-moving load, thereby completing the layup.

  [0123] The completed layup was then placed in a vacuum oven at about room temperature (eg, about 20 ° C.). A mechanical roughing pump was used to evacuate and then maintain the remaining rough vacuum at a pressure of less than about 100 millitorr. The layup was then heated from room temperature to a temperature of about 1350 ° C. at a rate of about 200 ° C./hour. After maintaining a temperature of about 1350 ° C. for 1 hour, the temperature was further increased to a temperature of about 1550 ° C. at a rate of about 200 ° C./hour. After maintaining a temperature of about 1550 ° C. for 1.5 hours, the temperature was reduced to a temperature of about 1450 ° C. at a rate of about 100 ° C./hour. Without maintaining this temperature, the lay-up temperature was further lowered to a temperature of about 1300 ° C. at a rate of about 25 ° C./hour, and then immediately cooled to about room temperature at a rate of about 200 ° C./hour.

  [0124] After this heating schedule, the chamber and its contents were removed from the vacuum furnace. The silicon infiltrant melted and infiltrated into the carbon cloth and rail preform, thereby converting the carbon cloth into a silicon carbide cloth to form a high density silicon carbide composite feeder rail. From the gravimetric method, it was found that there was about 770 grams of uninfiltrated silicon accumulated in the silicon carbide cloth. The contents of the graphite chamber were then reused to make a silicon carbide composite armor bib.

<Infiltration of preforms for breast pads>
[0125] About 1775 grams of other silicon 21 (grade LP, Elke Metals Co., Pittsburgh, PA) containing about 0.5 wt% Fe (maximum) and residual Si is infiltrated with a silicon carbide composite (eg, infiltrated). D) distributed on the silicon carbide fabric between the rails. A graphite dowel bar 39 spray coated with boron nitride 33, measuring about 0.25 inch (6 mm) in diameter, was placed in a graphite holder or support 37. Similarly, four breastplate preforms 11 spray coated with boron nitride 33 were placed on each half of the tray across the ends of the two rails (see FIG. 4A). The surface of each preform that contacts the rail was not applied. The top of the chamber was covered as described above to complete the layup.

  [0126] The graphite chamber and its contents were then heat treated in substantially the same manner as used for the infiltration of the carbon cloth and silicon carbide feeder rail preform.

  [0127] Following this heating regime, the chamber and its contents were recovered from the vacuum furnace and disassembled. The silicon infiltrate melted and infiltrated into the composite feeder rail and armor bib preform to form a dense silicon carbide matrix composite. Since each bib plate was supported by rails in line contact of its width dimension, light hand force was sufficient to separate the formed bib complex from the feeder rail. Only a light sandblast was required to remove some silicon infiltrate lumps that would leak through several points during the breastplate boron nitride application.

(Comparative Example 2)
[0128] The technique of Reference Example 2 was substantially repeated except that silicon carbide particles were used instead of boron carbide particles. However, as in Reference Example 2, the particle size distribution of the silicon carbide mixture was such that substantially all particles were smaller than about 45 microns. Following the pyrolysis step, the preform contained about 75% by volume silicon carbide particles and about 4% by volume carbon.

  [0129] After infiltration with molten Si, the resulting body consisted of 84% by volume SiC (original 75 and 9 formed in the reaction) and 16% by volume Si (ie Si / SiC composite). A typical microstructure of the material (optical micrograph) is shown in FIG.

[0130] In the optical micrograph, the difference between the original SiC and the SiC formed by reaction could not be identified. Like the reaction-bonded B ₄ C of Reference Example 2, the reaction-bonded SiC ceramic shown in FIG. 5 does not show any SiC interconnection and clustering and can therefore maintain a relatively fine microstructure. there were.

(Comparative Example 3)
[0131] This comparative example shows the production of a composite by a reactive infiltration process, the composite being characterized by boron carbide reinforcement. The process was similar to Reference Example 1 with the following exceptions.

  [0132] Carbon cloth and feeder rails were first self-infiltrated and a total of 8 tiles from the rails infiltrated using another heat treatment were infiltrated simultaneously. In place of the boron carbide component, the feeder rail preforms featured silicon carbide as a wide range of reinforcement. More precisely, the feeder rail preform had substantially the same composition as that described in Comparative Example 1. A single layer carbon cloth was used instead of two layers. The amount of silicon infiltrant for the initial infiltration (cloth and rail) reacts completely with elemental carbon and fills the reinforcements that make up the rail and cloth, for example, the voids between the particles and the fibers There was some excess over the required amount calculated. The objects resulting from this initial silicon infiltration were silicon carbide composite fabric and feeder rail. From gravimetric analysis, it was found that there was about 800 grams of uninfiltrated silicon remaining in the silicon carbide cloth.

[0133] Approximately 602 grams of bulk silicon 21 (Grade LP, Eikem Metals Co., Pittsburgh, PA) was applied to a silicon carbide composite rail (eg, infiltrated) for subsequent heat treatment infiltrating the 8 preformed tiles. Distributed on the silicon carbide fabric during (soaked). Place eight preformed tile coated with boron nitride as in Example 1 on the infiltrated rails, supported by a graphite dowel rods coated with boron nitride as in Example 1.

[0134] The heating schedule for both infiltration operations was substantially the same as that described in Reference Example 1.

[0135] Following this second infiltration, the chamber and its contents were recovered from the vacuum furnace. The silicon infiltrant melted and infiltrated through the silicon carbide composite rail and into the tile preform to form a high density Si / SiC / B ₄ C composite. When the infiltrated tile was collected, it was observed that there was a zone with a diameter of about 1-2 cm extending into the tile from each contact point with each rail. These zones have shades that are slightly different than the remaining infiltrated tiles, each about a 2 cm long crack extending from the normal dark / non-dark boundary toward the interior of the composite tile. It was characterized.

[0136] In FIG. 6, which shows a typical microstructure, it is shown that the Si—B ₄ C reaction occurs. Structural roughening (eg, large ceramic populations within the Si matrix) is clearly identified. As some previous work, if allowed to Si-B 4 _C reaction occurs, the microstructure is significantly roughened. (See, for example, Bailey and Taylor et al., Referenced above.) A coarse microstructure results in a ceramic with larger size flaws, and therefore less strength.

<Characteristics of mechanical and physical properties>
[0137] After the fabrication process, various mechanical and physical properties of the reaction bonded ceramic composite were measured. The density was determined by a water immersion technique according to ASTM standard B311. Elastic properties were measured by ultrasonic plus echo technique according to ASTM standard D2845. Hardness was measured on a Vickers scale at 2 kg load according to ASTM standard E92. The bending strength of 4-point bending was determined according to MIL-STD-1942A, excluding the composite material of Comparative Example 1 using ASTM procedure No. D790. Fracture toughness was measured using a 4-point bend chevron notch technique and a screw-driven Sintech model CITS-2000 general purpose test machine under displacement control at a crosshead speed of 1 mm / min. Test specimens with dimensions 6 × 4.8 × 50 mm were tested with a load direction parallel to the 6 mm dimension and internal and external load spans of 20 mm and 40 mm, respectively. A chevron notch cut with a diamond blade having a width of 0.3 mm had an inclusion angle of 60 ° and was located at the intermediate length of each test piece. The dimensions of the specimens were chosen to minimize the analytical difference between the two calculation methods according to the analysis of Munz et al. (DG Munz, JL Shannon, and RT Bubsey, “ Fracture toughness calculation from maximum load in four points Bend Tests of Chevron Notch Spec.

  [0138] The density, Young's modulus, flexural strength, and fracture toughness of the present reaction bonded ceramic are provided in Table I. Where appropriate, results are provided as mean +/- 1 standard deviation.

[0139] The density of SiC-based materials is about 6% lower than monolithic SiC due to the presence of a Si phase having a relatively low density. Reduced density is important for applications where weight is specified, such as armor. The B ₄ C type material has a very low density and is similar to that of monolithic B ₄ C.

[0140] The Young's modulus of reaction bonded SiC and reaction bonded B ₄ C ceramic is essentially the same and can be advantageously compared to other high performance ceramic materials. Certain results, respectively 450, is as predicted based on the Young's modulus values for high density SiC of 450 and 120 _{GPa, B} 4 C, and Si. In particular, based on weight specifications, the reactive bond B ₄ C has a very high Young's modulus.

  [0141] Hardness is a very important factor for armor materials. Previous work has shown that when a projectile is destroyed, high mass efficiency is obtained only for hard armor penetrating projectiles, and armor must be hard to effectively destroy the projectile Indicated. (Eg, ML Wilkins, RL Landingham, and CA Hondel, “Fifth Progress Report of Light Armor Program”, report No. UCRL-50980, University of CA, Livermore, Jan. 1971, and C. Hsieh, “Ceramic-Faced Aluminum Armor Panel Development Studies”, Report No. 92 JPL-p-20, Report No. JPL-p-20. See Jet Propulsion Laboratory, Feb. 1985.

  [0142] However, it is difficult to compare hardness data in many published literature, as the results are highly dependent on test methods and techniques. Therefore, many different commercially available materials were secured in the present invention. The hardness measurements were then performed in the same manner for both the commercial material and the new reaction bonded ceramic of the present invention so that a true comparison could be made. Results are provided in Table II.

[0143] Reaction bonded SiC and B ₄ C ceramics have a very high hardness that exceeds both tool steel and WC / Co projectiles. In both cases, the Si / SiC and Si / SiC / B ₄ C composites have a hardness that more or less reflects the weight average hardness of the constituents. In particular, because of the very high hardness of monolithic B ₄ C, the reactive bond B ₄ C has a very high hardness value.

<Ballistic impact test>
[0144] The first ballistic impact test focused on the evaluation of the RBSC composite filled with the SiC of Comparative Example 1 against a commercially available hot pressed boron carbide. Candidate ceramic armor material was provided in the form of square tiles about 100 mm on one side. Some of the tiles tested had substantially the same composition as the silicon carbide bib of Comparative Example 1.

  [0145] The ceramic composite of Comparative Example 1 consisted of about 80% by volume silicon carbide with the remainder being silicon. The density of the mass was about 3.0 g / cc and the Young's modulus was about 360 GPa. Furthermore, this RBSC body, which is very similar in composition and treatment to this Comparative Example 1, had a 4-point bending strength of about 270 MPa.

  [0146] Ceramic tiles were attached to a SpectraShield (R) polymer composite backing layer (AlliedSignal Inc., Morristown, NJ) to produce an armor target for testing. This material is supplied as a 54 inch wide roll of two layers of unidirectional fibers embedded in a resin matrix, with one layer of fibers orthogonal to the other layers of fibers. A number of 12 inch (305 mm) sheets were cut from the roll. The appropriate number of these sheets were then laminated and consolidated in an autoclave for about 60 minutes at an applied pressure of about 150 psi (1.3 MPa) and a temperature of about 121 ° C., thereby forming a hard polymer composite plate. Following solidification, a backing plate measuring about 12 inches (305 mm) square was cut from a 54 × 12 inch (1370 × 305 mm) plate using a band saw or water jet. An approximately 5 inch (120 mm) square area in the center of the backing plate was lightly polished using 120 grit sandpaper. After cleaning the surfaces to be joined with isopropyl alcohol, candidate armor tiles were joined to the center of the backing plate using two layers of 76 micron thick urethane film adhesive. The bond was cured for about 30 minutes in a full vacuum oven maintained at a temperature of about 121 ° C., thereby forming a ballistic impact specimen.

  [0147] The weight of the backing plate varied with the number of laminates used, and the weight of the ceramic tiles varied with the thickness dimension of the polished ceramic tiles. However, in each case, the total areal density (the density of the ceramic tile plus the backing material) was maintained at approximately the same amount.

  [0148] A target for ballistic impact testing was assembled as follows. Ballistic impact specimens were placed in front of a 28-layer KM2 (600 denier) blanket with ripstop nylon and camouflage cordura coating to simulate a body armored outdoor tactical vest (OTV). The OTV mimetics and specimens were placed in front of a 100 mm thick Roma Plasticine model clay block that had been treated at a temperature of about 35 ° C. for about 6 hours. The test piece and the OTV mimetic were fixed to the clay block with conduit tape, and the clay block was supported by a steel support structure fixed to the test stand, thereby completing the target.

[0149] Two different types of 7.62 mm projectiles were used to shoot the target at a diagonal angle of zero degrees with varying speed. Table III shows the comparative ballistic impact test results for the first shot, and Table IV reports the results for the other shots. The basic unit of ballistic penetration resistance used in this test is the projectile velocity V ₅₀ where the target partial and full penetrations can occur equally. Normalizing V ₅₀ with respect to the total areal density gives a factor called “ballistic impact stopping force” in this disclosure.

  [0150] These results were extremely promising and suggested that it would be possible to produce reaction bonded SiC armor that could compete in performance with some of the major ceramic armor commercially available (eg, hot press). . Therefore, the present inventors continued the development of this technique, and led to the present boron carbide composite material.

<Ballistic impact test: 2nd>
[0151] In this second ballistic impact test, the RBBC material of Reference Example 2 was evaluated as a candidate armor and compared to the SiC-filled RBSC material of Comparative Example 2 and a commercially available hot press B ₄ C (control). In a series of tests, reaction-bonded SiC and commercial hot press B ₄ C were tested against a group of bullets as ballistic projectiles and reacted against an armor penetration (AP) group in the second set of tests. Bonded B ₄ C and hot press B ₄ C were tested.

  [0152] As in the first ballistic impact test, a 100 mm x 100 mm ceramic tile was bonded to a 300 mm x 300 mm fiber reinforced polymer plate.

<Ballistic impact characteristics>
[0153] Ballistic impact test results are provided in Tables V and VI. Test results for a group of 7.62 mm M80 bullets are provided in Table V for reaction bonded SiC and commercial hot press B ₄ C (control). The test results for the 7.62 mm APM2 group for reaction bonded B ₄ C and commercial hot press B ₄ C are provided in Table VI. In each case, the table provides the mass efficiency normalized with respect to the areal density of the system, the target mass efficiency, and the hot press B ₄ C control. The mass efficiencies in the table were determined based on the available data for uniform rolled steel armor (RHA) for the same impact. Specifically, mass efficiency was calculated by dividing the surface density of RHA required to give the same performance by the surface density of the test target.

  [0154] Ballistic impact results show that the armor design using the lower cost reaction bonded ceramic had equivalent mass efficiency to the same design armor using the hot pressed ceramic. This enabled the production of cost-effective armor products for various applications. In FIGS. 7A and 7C, for example, aircraft armor and individual armor tiles were made from SiC filled RBSC. The vehicle armor plate of FIG. 7B was made from RBBC.

( Reference Example 4)
[0155] The procedure of Reference Example 1 was substantially repeated with the following exceptions.

  [0156] In the preforms, the ceramic particles consisted of nominal 45 micron and nominal 12 micron (median particle size) boron carbide particles (ESK GmbH, Kempten, Germany) mixed in a nominal 70:30 ratio.

  [0157] Following the freezing step, the gate from the sedimentation step was immediately removed with a band saw or the like.

  [0158] Prior to carbonization at about 600 ° C., residual water from the molding was removed in a drying step. Specifically, the frozen preform was placed on a graphite curing tray and placed in an air atmosphere convection oven maintained at a temperature of about 110 ° C. After maintaining the preform at a temperature of about 110 ° C for about 30-60 minutes, the furnace temperature was raised to about 180 ° C. After maintaining at a temperature of about 180 ° C. for at least 1 hour, the curing tray and preform were removed from the furnace and cooled to about 20 ° C., and the furnace was again cooled to a temperature of about 110 ° C.

  [0159] In a configuration in which reactive infiltration is carried out, instead of spraying the inner surface of the graphite tray 31 with boron nitride slurry or paint, these interiors are SAFFIL alumina fiber sheet material (Saffil) immersed in boron nitride slurry. Ltd., Cheshire, UK) and then dried.

  [0160] The lump-shaped silicon distributed on the carbon cloth contains therein boron carbide particles (same type as used in the preform) and THERMAX carbon black powder (grade N-991, Cancarb, Medicine Hat, Alberta, Canada). About 10.6 kg of silicon, about 0.42 kg of boron carbide particles, and about 0.11 kg of carbon black were required to infiltrate about 17.4 kg of the preform material.

(Example 5)
[0161] This example illustrates the preparation of a boron carbide / silicon composite by infiltrating a silicon-based metal into a preform that is substantially free of reactive carbon. In other words, this example shows the formation of a siliconized boron carbide composite.

[0162] The inner surface of an appropriately sized graphite tray was lined with an alumina fiber sheet material soaked in boron nitride as described in Reference Example 4 and dried. Then, about 70 grams of the boron carbide ceramic particle mixture described in Reference Example 4 was poured into a graphite tray simply backed with dry particles, instead of forming a preform, and the dry powder was in the form of a pyramid. The shape was processed loosely. A depression that was large enough to hold about 125 grams of bulk silicon metal (Elkem) was then formed in the middle of the pile of ceramic particles. The lined graphite tray and its contents were then placed in a larger graphite chamber with a loosely secured graphite lid that was placed in a vacuum furnace at room temperature and atmospheric pressure. The furnace was sealed, vacuum evacuated, and the temperature was increased from about 20 ° C. to about 1525 ° C. at a rate of about 200 ° C./hour. After maintaining at a temperature of about 1525 ° C. for about 4 hours, the temperature was reduced at a rate of about 200 ° C./hour. At a temperature of about 100 ° C. or lower, the pressure in the vacuum furnace was returned to the atmosphere, the furnace was opened, the graphite chamber was taken out and decomposed.

  [0163] It was observed that the silicon melted and infiltrated the porous mass of boron carbide particles to form a composite. The finely ground and polished section of the composite material was examined metallographically in an optical microscope. These micrographs are shown in FIGS. 9A and 9B, respectively, which show boron carbide particles dispersed in a metal matrix that appears to be primarily silicon metal.

(Example 6)
[0164] This example illustrates the preparation of a siliconized boron carbide composite.

  [0165] Boron carbide preforms were prepared by a dry press operation. Specifically, about 3% by weight of a 1% by weight aqueous solution of methylcellulose was added to 220 grit TETRABOR boron carbide particles (ESK GmbH, Kempten, Germany) and thoroughly mixed with an Erich mixer or the like. A quantity of this mixture is then loaded into a steel mold and pressed with a load of about 4000 pounds (1800 kg) to produce a tile about 4 inches (100 mm) square and about 3/8 inches (10 mm) thick. To do. The pressed tile is then dried at about 100 ° C. to remove water and then baked at about 2050 ° C. for about 10 minutes under about 0.5 atmospheres of argon to remove the temporary binder of methylcellulose. Sinter the boron carbide particles lightly.

[0166] Next, the unbaked boron carbide preform is infiltrated in substantially the same manner as in Reference Example 1. The resulting siliconized boron carbide body includes a matrix of silicon metal with some boron and carbon, and boron carbide embedded in the silicon metal matrix. Boron carbide is substantially chemically unaffected by the infiltration process and, for example, does not show any signs of melting or chemical attack by the molten infiltrant.

(Example 7)
[0167] This example illustrates another embodiment of siliconized boron carbide production.

[0168] Except for using methylcellulose instead of fructose, the preform composition is subjected to sedimentation in batches as in Reference Example 1 to prepare a tile preform. Subsequently, the sedimentation-molded tile is heated at a temperature of about 120 ° C. using the heating plan of Reference Example 1 under an argon atmosphere to remove water. After holding at a temperature of about 120 ° C. for about 4 hours, the preform is then heated at a rate of about 200 ° C./hour to a temperature of about 2050 ° C. to remove temporary binder, and B ₄ C and SiC particles Sinter lightly.

[0169] The unbaked boron carbide preform is then infiltrated in substantially the same manner as in Reference Example 1 except that the infiltration is performed at about 1750 ° C. The resulting siliconized boron carbide body includes a matrix of silicon metal with some boron and carbon, and boron carbide embedded in the silicon metal matrix.

  [0170] The boron carbide composite materials of the present invention have exceptional hardness and stiffness, small specific gravity and relatively high bending strength. The present disclosure primarily focused on the potential use of this material as bulletproof armor, where they are material properties where stiffness and small specific gravity are important materials such as robotics, tools, and other precision equipment industries. Many uses should be found. The composite material may also be attractive as a wear or wear resistant component. If the possibility of boron contamination is not an issue, the boron carbide composite material of the present invention has applications in the semiconductor manufacturing industry such as air bearing housings or support frames, mechanical tool bridges and bases, mirror stands and flat panel display fixtures. I can find it. The composite material could produce a desirable mirror substrate. In addition, these boron carbide composites may find use in the nuclear industry, particularly where neutron absorption is important.

  [0171] The ceramic armor of the present invention with the desirable properties of low specific gravity and high hardness should be particularly useful for small weapon shooting, for example, as body armor and aircraft armor. The boron carbide material will also find use as armor for ships and ground vehicles, eg, for more intense bombing.

  [0172] Those skilled in the art can make many variations and modifications to the invention as disclosed and exemplified above without departing from the scope of the invention as set forth in the appended claims. You will easily recognize that.

[0042] FIG. 1 is a cross-sectional view of a feeder rail described in Example 1. [0043] FIG. 2A is a front view of the equipment used to prepare the boron carbide reinforced silicon carbide composite tile of Example 1. FIG. 2B is a side view of equipment used to prepare the boron carbide reinforced silicon carbide composite tile of Example 1. FIG. [0044] FIG. 3 is an optical micrograph of a polished cross-section of the RBBC material produced according to Example 2. [0045] FIG. 4A is a plan view of the equipment used to prepare the silicon carbide composite bib according to Comparative Example 1. FIG. 4B is a front view of equipment used to prepare a silicon carbide composite bib according to Comparative Example 1. FIG. [0046] FIG. 5 is an optical micrograph of a polished cross-section of the SiC-filled RBSC material produced by Comparative Example 2. [0047] FIG. 6 is an optical micrograph of a polished cross-section of the RBBC material produced by Comparative Example 3. [0048] FIG. 7A illustrates several uses of an embodiment of the armor material of the present invention. FIG. 7B illustrates several uses of an embodiment of the armor material of the present invention. FIG. 7C illustrates several uses of the armor material embodiment of the present invention. [0049] FIG. 8A is an optical micrograph of an RBSC composite showing a coarse microstructure. FIG. 8B is an optical micrograph of an RBSC composite showing one of the limited interconnectivity of SiC ceramic components. [0050] FIG. 9A is an optical micrograph taken by polishing a cross section of the siliconized boron carbide composite material produced according to Example 5 and enlarging it about 50 times. FIG. 9B is an optical micrograph taken by polishing a cross section of the siliconized boron carbide composite material produced according to Example 5 to a magnification of about 200 times.

Claims (12)

A matrix component comprising an alloy comprising silicon metal, wherein a substance containing at least one boron and a substance containing at least one carbon are dissolved in the silicon metal;
And a reinforcing component comprising boron carbide A including composite material,
Dispersed before Symbol reinforcing Ingredient is throughout said matrix, said boron carbide is not affected by the alloy, and
The composite material is a composite material not containing β-SiC . The composite material of claim 1, wherein the reinforcing component comprises a plurality of filler material bodies, wherein at least 90% by volume of the filler material bodies are less than 55 microns in diameter.   The composite material of claim 1, wherein the reinforcing component comprises at least 65% by volume of the composite material. A component of bulletproof armor, the component comprising at least one ceramic layer and at least one backing layer disposed and bonded behind the ceramic layer;
The ceramic layer is
(A) a matrix comprising silicon-containing alloy and boron dissolved in the silicon; and (b) at least one reinforcing material comprising a plurality of boron carbide fillers dispersed throughout the matrix.
Comprises at least one boron carbide composites,
A bulletproof armor component in which the component does not contain β-SiC .   The bulletproof armor component according to claim 4, wherein the alloy further includes at least one substance containing carbon dissolved in the silicon. The bulletproof armor component of claim 4, wherein at least 90% by volume of the boron carbide filler is less than 100 microns.   The bulletproof armor component according to claim 4, wherein the composite material does not contain 30% by volume or more of the infiltrant phase. Providing a porous mass or preform comprising at least one filler material comprising boron carbide, wherein the porous mass or preform is substantially free of free carbon;
Providing a silicon-containing molten infiltrant in which at least one substance comprising carbon is dissolved;
Contacting the molten infiltrant with at least one porous mass or preform in a vacuum or inert atmosphere;
Infiltrating the molten infiltrant into the porous mass or preform, thereby forming a composite comprising the boron carbide dispersed in a matrix comprising the infiltrant;
And a step of solidifying the molten infiltrant.   The method of claim 8, wherein the infiltration is performed at a temperature not exceeding 2000C. It said reinforcing material accounts for 65% by volume of at least the composite, ballistic armor construction material according to claim 4.   The method of claim 8, wherein the boron carbide is provided as particles.   9. The method of claim 8, wherein the molten infiltrant further comprises at least one material comprising boron dissolved in the silicon.

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