COMPOSITE BODY MADE FROM A REACTION-BONDED MIXED CERAMIC INFILTRATED WITH MOLTEN SILICON

Abstract

A shaped composite body of a reaction-bonded, silicon-infiltrated mixed ceramic, the microstructure of which is determined by primary grains of crystalline B.sub.4C grains (1) of mean grain size d50>100 ?m and <500 ?m and a fraction of >10%, by weight, and <50%, by weight, and by primary grains of a finer silicon carbide with d50<70 ?m and a fraction of >10%, by weight, and <50%, by weight, and the primary grains are siliconized (3) bonded by secondarily formed silicon carbide with a fraction of >5%, by weight and <25%, by weight, in a silicon carbide matrix having a free metallic silicon (2) content of >1%, by weight, and <20%, by weight.

Claims

1. A shaped composite body of a reaction-bonded, silicon-infiltrated mixed ceramic, the microstructure of which is determined by primary grains of crystalline B.sub.4C grains (1) of mean grain size d50>100 ?m and <500 ?m and a fraction of >10%, by weight, and <50%, by weight, and by primary grains of a finer silicon carbide with d50<70 ?m and a fraction of >10%, by weight, and <50%, by weight, and the primary grains are siliconized (3) bonded by secondarily formed silicon carbide with a fraction of >5%, by weight, and <25%, by weight, in a silicon carbide matrix with a content of free metallic silicon (2) of >1%, by weight, and <20%, by weight.

2. The shaped composite body as claimed in claim 1, wherein the primary grains are siliconized bonded by secondarily formed silicon carbide with a fraction of >15%, by weight, and <25%, by weight.

3. The shaped composite body as claimed in claim 1, wherein the primary grains contained are of silicon carbide with d50<40 ?m, more particularly <10 ?m.

4. The shaped composite body as claimed in claim 1, wherein the density gradient is <2%, by weight.

5. The shaped composite body as claimed in claim 1, wherein the dissolved boron is contained within the free metallic silicon (2) in a proportion between >0.05 and <5%, by weight.

6. The shaped composite body as claimed in claim 1, wherein the shaping may be carried out by slip casting, pressure casting, uniaxial pressing, isostatic pressing, stamping or manual powder compaction.

7. The shaped composite body as claimed in claim 1, wherein the shaping may be carried out via a powder bed 3D printing process.

8. The shaped composite body as claimed in claim 7, wherein a mixture of SiC and B.sub.4C powder is built up by means of binder by powder bed printing to give a three-dimensional component and is subsequently siliconized.

9. The shaped composite body as claimed in claim 1, wherein the shaping takes place in plate form.

10. The shaped composite body as claimed in claim 1, wherein the shaping is performed with an envelope volume>200?200?200 mm.

11. The use of the shaped composite body as claimed in claim 1 as ballistic protection, wherein a backing material composed of one or more layers is provided, which is compressed with the mixed ceramic material to a basis weight<32 kg/m.sup.2 or <40 kg/m.sup.2 for selectable ballistic protection against one shot or multiple shots of an ammunition system.

12. The use of the shaped composite body as claimed in claim 11, wherein the backing material is designed for protection against ammunition containing tungsten or tungsten carbide.

13. The use of the shaped composite body as claimed in claim 11, wherein the backing material is made of at least one layer of one or more plastics, more particularly polyethylene or aramid, carbon fibers, glass fibers, metals and/or a combination of these materials and/or bonding material, more particularly adhesive foils.

14. The use of the shaped composite body as claimed in claim 11, wherein the shaping is provided for producing body protection panels, seat shells, backrests and combinations thereof and panels in aerospace protection.

Description

[0026] The invention is explained in more detail below with reference to exemplary embodiments.

[0027] FIG. 1 schematically shows a section of a microstructure.

[0028] The invention relates to a shaped composite body composed of a reaction-bonded, silicon-infiltrated mixed ceramic, the microstructure of which is determined by primary grains of crystalline B.sub.4C grains of average grain size d50>100 ?m and <500 ?m and a content of >10%, by weight, and <50%, by weight. The microstructure is further determined by primary grains of silicon carbide with d50<70 ?m and a content of >10%, by weight, and <50%, by weight. The primary grains are silicized bonded by secondarily formed silicon carbide with a content of >5%, by weight, and <25%, by weight, in a silicon carbide matrix having a content of free metallic silicon of >1%, by weight, and <20%, by weight. FIG. 1 shows an example of a microstructure according to the invention. The wt % figures are percentages by weight. Content stands for proportion and/or fraction of a graining.

[0029] The invention thus relates to a reaction-bonded SiC/B.sub.4C having a B.sub.4C content <50%, by weight, and a mean particle size (d50) of the boron carbide>100 ?m, with a secondary SiC content<25%, by weight, and a metallic Si content<20%, by weight.

[0030] Preferably, the content of secondary SiC is between 15%, by weight, and 25%, by weight. A stable support matrix for the primary crystals B.sub.4C and SiC can thus be created, and thus the resistance to, for example, projectiles can be strengthened.

[0031] Particularly preferred is a shaped composite body having a B.sub.4C content between 30%, by weight, and 40%, by weight, and an Si content<15%, by weight, and a primary particle size of the B.sub.4C>200 ?m.

[0032] It is further particularly preferred that the primary grains included to be of silicon carbide with d50<40 ?m, more particularly <10 ?m. The density gradient may be <2%. The shaped composite body may further contain boron dissolved within the metallic silicon in an amount between >0.05 and <5%, by weight.

[0033] The microstructure of FIG. 1 shows the B.sub.4C content as primary grains 1, free metallic silicon 2 and a penetration composite of fine-grained primary and secondary silicon carbide 3.

[0034] The shaped composite body can be manufactured via pressure slip casting, which involves the preparation of a slip containing SiC/B.sub.4C particles as well as colloidal carbon and organic auxiliary substances. The resulting green body, is then contacted with liquid silicon and infiltrated at temperatures between 1500? C.-1700? C. During this process, the silicon reacts with the carbon to form secondary SiC.

[0035] In another embodiment of the invention, the shaping takes place by 3D printing, as this allows the realization of complex products, such as seat shells and backrests, for aerospace applications. The ceramics produced in this way, in combination with polymers (PE, aramid, etc.) as well as carbon fibers, glass fibers and/or metals, offer particularly efficient protection against WC/Co ammunition, especially against the M993 and M995 ammunition types.

[0036] It is a further object of the invention to use of the shaped composite body as ballistic protection. For this purpose, the shaped composite body is preferably coated with one or more layers of a backing material. For example, at least one layer of a backing material may be compressed with the mixed ceramic according to the invention. The backing material may further preferably be formed of several layers of one or more plastics, for example polyethylene, aramid, etc., carbon fibers, glass fibers, metal, for examples aluminum, steel, etc., combination of these materials and/or bonding material, for example adhesive foils.

[0037] Various application examples are described below: [0038] 1. Production of a body protection plate from the shape composite body according to the invention, for which purpose a pressure slip casting is used. First, an aqueous suspension is prepared consisting of colloidal carbon with a mean particle size of less than 1 ?m at a content of 10%, by weight, fine-grained silicon carbide with a mean particle size of 5-10 ?m at a content of 50%, by weight, and coarse-grained B.sub.4C with a mean particle size of 120 ?m at a content of 40%, by weight. For this purpose, 18%, by weight, water and 1%, by weight, organic auxiliary substances (wetting agents, fluidizing assistants, binders) are taken into account per 100%, per weight, solids. The slip is then cast on a die casting machine, using a porous plastic mold based on polymethyl methacrylate at a slip pressure of 40 bar, to form a multi-curved plate having dimensions of 350?275?9 mm. The thus formed shard is then dried in a circulating air drying chamber and converted via a reaction firing to a ceramic plate based on a reaction-bonded composite material consisting essentially of SiC and B.sub.4C as well as free Si. The resulting shaped composite body forms a body protection plate that can be used as a monolithic insert of a ballistic body protection vest. For this purpose, the shaped composite body consists, for example, of an obtained material comprising coarse-grain B.sub.4C with a content of 31%, by weight, fine-grained primary SiC with a content of 41%, by weight, fine-grained secondary SiC with a content of 17%, by weight, and free, metallic silicon with a content of 11%, by weight. [0039] 2. Production of a vehicle protection panel from the shaped composite body according to the invention, for which uniaxial press molding is used. First of all an aqueous suspension is prepared according to the composition described in Example 1, and further processed into a press granulate by means of a spray-drying process. Only the composition of the organic auxiliaries has to be adjusted and a pressing aid added. The granules are then filled into a square hard metal mold and pressed at a pressure of 1700 bar. The blank thus obtained is then subjected to reaction firing, to produce a ceramic plate based on a reaction-bonded composite material, consisting substantially of SiC and B.sub.4C as well as free Si, the latter having an edge length of 50 mm and a wall thickness of 9 mm. The shaped composite body thus obtained forms a polygonal protective plate that can be used for the efficient lining of large areas in vehicle protection. [0040] 3. Production of a helmet from the shaped composite body according to the invention, for which a 3D printing process is used. The shape is built up layer by layer from a shapeless graining consisting of SiC and B.sub.4C, in a mixing ratio of 70%, by weight, SiC and 30%, by weight, B.sub.4C, the B.sub.4C powder being based, for example, on a grain size distribution known from an industrial refractory ceramic under the designation 100/F and thus having characteristic values of d10=75 ?m, d50=115 ?m and d90=160 ?m. The finer-grained SiC powder is based, for example, on a grain size distribution known for an industrial appraisal grain under the designation F180 and thus has an average particle size d50=65 ?m. The selective consolidation of the grains takes place at the locations specified by a CAD model used as a basis, by the dropwise introduction of an organic binder, preferably furan resin, which is applied via inkjet print heads. The CAD model used here, which corresponds to the final component geometry, permits the generation of complexly shaped structures. Following these two sub-steps, the construction plane is lowered by a predefined layer thickness, which in this case is 300 ?m. This sequence of steps is repeated iteratively until the layer-by-layer construction of the CAD model is concluded. The complex-shaped pre-body obtained in this way has a porosity of 45% by volume and is then infiltrated with an aqueous dispersion consisting of 30%, by weight, colloidal carbon as well as a dispersing aid and a wetting agent. After a first impregnation process, a complex-shaped ceramic preform is obtained in this way, consisting 87%, by weight, of the original SiCB.sub.4C powder mixture and 13%, by weight, of colloidal carbon. After a drying process and a possible second impregnation step, this ratio changes to become 79/21%, by weight, and to become 76/24%, by weight, after a possible third impregnation step. After a final drying process, the complex-shaped preform obtained in this way, is converted via reaction firing into a ceramic body based on a reaction-bonded composite material consisting essentially of SiC and B.sub.4C plus free Si. The material thus obtained consists, for example, of coarse-grain B.sub.4C with a content of 15%, by weight, fine-grained primary SiC with a content of 45%, by weight, fine-grained secondary SiC with a content of 24%, by weight, and free, metallic Si with a content of 15%, by weight. The complexly shaped preform obtained in this way can be used as the basic element of a ballistic helmet for head protection, with production via of the 3D printing process described here allowing the creation of an ergonomic, potentially individualized helmet geometry. [0041] 4. Production of a seat shell from the shaped composite body according to the invention by means of 3D printing. As described in the previously described example, a powder bed-based 3D printing process is carried out, whereby the mixing ratio in this case is 60%, by weight, SiC and 40%, by weight, B.sub.4C. This leads to a reduction in the resultant density of the fired component, which is why the production of such material compositions is particularly suitable for the aerospace sector. The material obtained in this way consists, for example, of coarse-grained B.sub.4C with a content of 21%, by weight, fine-grained primary SiC with a content of 40%, by weight, fine-grained secondary SiC with a content of 24%, by weight, and free, metallic silicon with a content of 15%, by weight. In this embodiment, using appropriate CAD models, weight-optimized seat shells can be obtained in this way for use in various aircraft, such as helicopters. The seat shell thus produced has a size of around 300?300 mm, a wall thickness of 9 mm and a height of 200 mm, and is ergonomically shaped. The associated backrest has a length of 500 mm, a width of 300 mm and a height of 100 mm, and is likewise ergonomically shaped. Such large components can be manufactured without cracks. Machining via subtractive processes is no longer necessary. [0042] 5. Production of an aerospace protection panel from the shaped composite body according to the invention by means of 3D printing. As described above, a powder bed-based 3D printing process is used to produce the shaped composite body according to the invention, in which case the mixing ratio is 50%, by weight, SiC and 50%, by weight, B.sub.4C. The material obtained in this way consists, for example, of coarse-grained B.sub.4C with a content of 26%, by weight, fine-grained primary SiC with a content of 35%, by weight, fine-grained secondary SiC with a content of 24%, by weight, and free, metallic silicon with a content of 15%, by weight. This leads to a further reduction in the resulting density of the fired component, which is why the production of such material compositions is particularly suitable for the aerospace sector, and here more particularly for large-volume elements, such as aerospace protection panels. The side element produced in this way has dimensions of 1200 mm?800 mm?9 mm, for example. [0043] 6. Production of a ballistic protection, in particular against an ammunition system with a tungsten carbide core, from the shaped composite body according to the invention, with, for example, a weight per unit area of 2075 g/700 cm.sup.2=33.5 kg/m, comprising the mixed ceramic infiltrated with silicon in, for example, a format of 240 mm?305 mm?9.1 mm, 1790 g, with a backing, for example, which preferably has 27 layers of polyethylene and preferably 8 layers of carbon fibers, with, for example, a weight per unit area of 385 g. The mixed ceramic and the backing may be compressed together under temperature and pressure, and preferably in an autoclave. The result is a ballistic protection against 1 shot of 5.56?45 M995 with tungsten carbide core. Protection in this respect means no penetration by the bullet with a backface deformation of 39 mm in the test. In general, the backing can be made of aramid fiber layings, polyethylene (PE), carbon fiber layings, glass fiber layings and/or a mixture thereof. Furthermore, the backing can preferably be attached to the mixed ceramic on one or both sides. Generally speaking, therefore, 1 shot of M995 with tungsten carbide core can preferably be stopped at a basis weight of <32 kg/m.sup.2. [0044] 7. Production of a ballistic protection, in particular against an ammunition system with tungsten carbide core, from the shaped composite body according to the invention, with, for example, a weight per unit area of 2342 g/700 cm.sup.2=33.5 kg/m, comprising the mixed ceramic infiltrated with silicon in, for example, a format of 240 mm?305 mm?9.1 mm, 1792 g, with a backing, for example, which has preferably 39 layers of polyethylene and preferably 8 layers of carbon fibers, with a weight per unit area, for example, of 550 g. The mixed ceramic and the backing may be compressed together under temperature and pressure, and preferably in an autoclave. The result is a ballistic protection against 2-shots of 5.56?45 M995 with tungsten carbide core. Protection in this respect means no penetration by the bullet with a backface deformation of 29 mm on the 1.sup.st shot and 37 mm in the 2.sup.nd shot in the test. The backing can generally be made of aramid fiber layings, polyethylene (PE), carbon fiber layings, glass fiber layings and/or a mixture thereof. The backing, furthermore, can preferably be attached to one side or both sides of the mixed ceramic. In general, therefore, 2 shots of M995 with tungsten carbide core at a distance of 100 mm can be preferably stopped for a basis weight of preferably <40 kg/m.sup.2.