EP1380809B1 - Ceramic composite body - Google Patents

Abstract

A ceramic composite body comprises a layer A containing phases of a metal and a carbide of the metal, and a layer B containing silicon carbide particles partially bound via carbon binder phases directly via sintering bridges and having a pore volume of 10-35%. An Independent claim is also included for the production of a ceramic composite body.

Description

The invention relates to ceramic composite bodies comprising at least two layers, in particular for protective armor, which are suitable for civil and military applications. In particular, the invention relates to bodies of a multilayer material composite containing predominantly silicon carbide (SiC), comprising an outer material layer composed essentially of SiC bound in a matrix of free silicon (Si) and an inner material layer containing loosely bound SiC ceramic powder, and a method for their preparation and uses of these composites.

For protective armor against the ballistic impact of projectiles, depending on the area of application, different demands are placed on the bullet-breaking effect, multi-hit capability, component geometry or component weight.

In the civilian area, the mission focuses in particular on personal protection, armored limousines and protective vests. The requirements for the bullet-breaking effect are not so high, as in this area rarely with heavy weapons or medium and large caliber must be expected. High demands are placed, among other things, on component geometry and component weight. It requires complex parts, coupled with the requirement for the lowest possible component thickness or installation depth and low weight. The distance to the threat is usually very short and can be only a few meters. In the case of frequent multiple firing (referred to herein as "multi-hit") this results in hits close to each other. This results in the highest demands on the multi-hit capability of the protective armor.

In the military sector, a threat of high-speed and large-caliber missiles and explosive missiles is assumed. Although the demands on the component thickness and installation depth are lower than in the civil sector, a low specific weight of the armor material is of crucial importance here, too, because of the extremely high demands on the energy absorbing effect, the protective armor component must generally be made very thick.

The large distances to the target objects generally require large hit distances. Therefore, lower demands are placed on multihit capability here.

For armor in the military sector today flat plates are often used as additional armor for land and water vehicles and for helicopters, containers, containers, shelters and field fortifications.

An armor made of one or more armor steel plates is usually treated so that at least the threat facing side is extremely hard and thus bullet-breaking. The side facing away from the threat is ductile or toughened to absorb the energy of the projectile through material deformation. From this results also the structure typical for armor plates from other materials.

Compared to the metals, the ceramic materials have the advantage of higher hardness and lower specific weight. Since the monolithic ceramic shows a typical brittle fracture behavior during firing, ceramic plates (monolithic ceramics) burst to form many coarse to fine splinters. The use of ceramic plates without additional backing (support material and splinter trap) on the side facing away from the entrance of the projectile is not useful due to the splitter exit during firing. The bombardment generally completely destroys the respective ceramic plate. A multiple shot (multi-hit) can then no longer be held.

An armor with ceramic materials consists for these reasons preferably of two layers. The front panel of monolithic ceramics as possible has the task of deforming the rest of the bullet and possibly breaking the hard core. A deformable reinforcement, the backing, attached behind the ceramic plate, has the task of catching or absorbing the bullet, scraps and ceramic fragments and the remaining ceramic plate stabilize. It is also called absorber layer in the following. The backing generally consists of highly stretchable and tear-resistant fabrics (aramid fiber fabric, HDPE fabric, etc.), metal or plastics.

Modern material concepts lead to fiber-reinforced composite materials, the areas of monolithic ceramic (bullet breaker) and fiber reinforced ceramic have (absorber layer), as described for example in EP-A 0 376 794. The disadvantage of these concepts is generally the high price and the low availability of suitable fibers for fiber-reinforced ceramics. Thus, for the commonly used sintering process for the production of fiber-reinforced ceramic only relatively expensive carbon fibers of technical importance.

Another approach to achieve the projectile and splitter-absorbing effect of ceramic material is described in EP-A 0 287 918. In one of the listed variants, a multilayer armor plate is described, which consists of a conventional ceramic plate as a front plate and an underlying absorber plate of so-called chemically bound ceramic. The chemically bonded ceramic consists of hard fillers, such as fibers or ceramic powders, and a binder phase (or matrix) of cements modified with organic or inorganic polymers, which cure at low temperatures. The hard fillers lead to a blunting, deflection and fragmentation of the projectile.

However, the production of multilayer armor plates with complex geometry and a solid chemical bond between the two material layers is very complicated by this method.

A composite body having the features of the preamble of claim 1 is known from US-A 2002028294.

Compared to this prior art, it is an object of the invention to provide a ceramic composite body having a bullet-breaking front layer and an absorber layer fixedly connected thereto by means of a cost-effective production method that also permits complex component geometries.

This object is achieved by a composite body comprising at least two layers, characterized in that an outer bullet-breaking ceramic layer (front panel) consists essentially of a carbide and a carbide-forming metal, preferably SiC and Si (material layer A), and one with this firmly bonded inner layer (material layer B) containing weakly or loosely bound ceramic powder consisting essentially of SiC.

Furthermore, a method for producing such a composite body is provided in which the multilayer composite material is produced by the liquid infiltration of a porous green body of ceramic particles and carbon material by a carbide-forming metal, in particular silicon metal, wherein the liquid metal infiltration in a single common process step both the outside Ceramic layer of carbide and carbide-forming metal, preferably SiC and Si (material layer A), as well as the inner layer of weakly or loosely bound ceramic powder of predominantly SiC (material layer B) is formed, and both layers are firmly bonded together chemically.

The invention is based on the finding that powdered or particulate ceramic, similar to a sand bed, a very favorable absorption behavior against ballistic action shows, if the powdery material is mechanically stabilized, or held together. This cohesion is achieved according to the invention by the chemically firmly bonded ceramic layer (material layer A), as well as by the sintering process of the ceramic mixture of the green body in the region of the material layer B taking place during the metal melt infiltration.

The composite body according to the invention therefore comprises at least two layers, an outer material layer A containing phases of a carbide-forming metal and the carbide of this metal, preferably reaction bonded silicon carbide (SiC) and silicon, also referred to as SiSiC, and an underlying material layer B, through Sinter loosely bound SiC ceramic powder or optionally contains additional layers arranged behind it, in particular of the material A or of fiber-containing backing. Through these additional layers, the energy-absorbing effect of the armor is further improved.
Under loosely bonded ceramic powder, or particles in particular material is to be understood, the strength of which is at least 20% below that of the material of the material layer A.

In the preferred method of liquid metal infiltration - preferably with a silicon melt - a ceramic is formed in the material layer A by reaction of the carbide-forming metal with carbon, which in addition to very high hardness has a good fracture toughness or damage tolerance. As a result, the harmful for multiple bombardment ceramic brittle fracture behavior is suppressed in an advantageous manner. The infiltration metal used is preferably an alloy containing at least a mass fraction of 50% silicon, with particular preference being given to technical silicon or pure silicon. In the infiltration with a silicon-containing alloy of metals, Fe, Cr, or Ni is preferably formed from the carbon contained in the precursor of the material layer A silicon carbide. When infiltrating with a titanium-silicon alloy, titanium carbide preferably forms in addition to silicon carbide from the carbon.

The particles of silicon carbide and nitrides contained in the material layer B are sintered together at the temperature of infiltration with the liquid metal at the points of contact, forming a loose structure with pores. The non-volatile pyrolysis products of the organic binder of the raw material mixture also contribute to the strength of the material layer B.

The material layer A preferably contains a mass fraction of at least 70% of SiC particles embedded in a matrix of free silicon. The mass fraction of SiC is preferably above 75% and particularly preferably above 85%. Here, the mass fraction of free silicon, which is to be understood as including all mixed silicon phases with other metallic elements, above 2.8%. The mass fraction of free silicon is preferably in the range from 3 to 21% and particularly preferably in the range from 3 to 15%. The Material layer A is constructed so that the highest possible hardness is achieved, which can be achieved, for example, by the highest possible density, ideally the theoretical density. Preferably, therefore, the porosity (volume fraction of the pores in the entire volume) of the material layer A is below 20% or the density at least 2.1 g / cm ^3, and more preferably the porosity is below 10% or the density above 2.2 g / cm ³ . Typically, the material A still free carbon, and optionally ceramic aggregates in mass fractions of about 0.5 to 15%. Particularly preferred ceramic additives used according to the invention are particularly hard nitride-based ceramics. These include in particular the nitrides of the elements Si, Ti, Zr, B and Al.

The average particle size of the SiC, which can be used for both the material layer A and for the material layer B, is typically in the range of 20 to 750 microns. Since, in general, a homogeneous green body (preliminary body of the metal infiltration) is generally produced from the ceramic powders for reasons of process, the particle sizes in the material layers A and B only differ insignificantly. Likewise, it is also possible to provide different particle sizes for the layers, in which case the material layer A preferably contains finer material than the material layer B. The average particle size in layer A is then more preferably below 50 μm and in layer B above 50 μm.

The material layer B is preferably constructed predominantly of SiC particles. The mass fraction of SiC particles is preferably above 70% and particularly preferably above 90%. The content of ceramic aggregates is also comparable to those in layer A. The material layer B preferably contains at least one of the nitrides of the elements Si, Ti, Zr, B and Al in mass fractions of 0.05 to 15%. Substantially different from the material A is the material in the material layer B, the ceramic, or their ceramic particles, not reaction bound by silicon, there is almost no matrix of silicon or a silicon alloy. The mass fraction of free silicon or of silicon / metal phases is typically below 5%, preferably below 2.5% and particularly preferably below 1%.

The ceramic particles in the material layer B are only weakly bound, partly via carbon binder phases, partly directly via sintered bridges with one another. The material layer B therefore has a comparatively high porosity, which typically ranges from 5% to 35%, and is preferably in the range of 12 to 27%.

The density of the material layer B is generally below 2.55 g / cm ³ , preferably below 2.05 g / cm ³ and more preferably below 1.96 g / cm ³ . Typically, the porosity in the material layer B is at least 7% higher than in the material layer A.

For the inventive effect of the material layer B, the only loose bond between the ceramic particles is essential. Among other things, this prevents the crack propagation typical of the brittle fracture through large areas of a contiguous workpiece part, while nevertheless utilizing the hardness of the ceramic particles. This effect is also achieved if the pores in this layer are filled by material which is much softer than the ceramic.

In a further advantageous embodiment of the invention, therefore, the spaces between the ceramic particles in the material layer B are filled with a soft material. Usually, a plastic or a metal is used as a soft material, wherein the metal has a hardness on the Mohs scale of at most 5. Particularly suitable are thermoplastic polymers, resins, adhesives, elastomers or aluminum. Preferably, then at least half of the space formed between the ceramic particles is filled with the soft material.

The application of the composite body according to the invention is in the field of protective armor, in particular against ballistic action. Due to the good thermal properties, in particular the high melting or decomposition point of SiC, the composite material also shows good suitability as armor material in safe and protective building construction.

Components of the composite bodies according to the invention are usually designed so that the total thickness of the material layers A and B is in the range of 6 to 300 mm. Other layers, in particular of the material A or fiber-containing backing can be arranged behind the layer of the material B. The layer thickness of the material A is usually above 1 mm, for armor plates preferably above 3 mm. The layer thickness ratio of the material layers A and B is typically below 1:50, preferably below 1:10, whereby only the front side of the material A facing the firing side and the subsequent layer of the material B are to be understood here.

The material layer A merges into the material layer B, wherein the transition is generally to be recognized by a significant decrease in the content of silicon in the matrix.

Fig. 1 shows a microscopic cross-section of the interface between the material layers A and B of a composite body according to the invention. The gray areas (1) are SiC particles which are distributed approximately uniformly over the entire area. In the upper half (A), which corresponds to the material A, the SiC regions are connected by a continuous light phase (2). This is the matrix of silicon. The lower half (B), which corresponds to the material B, has pores instead of the matrix (black areas, 3). The other constituents of carbon or nitride particles can not be distinguished in this illustration from the other materials.

Due to the process-related ease of manufacture of a material B surrounded on all sides by a material layer A, the layer sequence of a front plate made of the material A, an absorber zone made of the material B and back plate (or backing) made of the material A is particularly preferred for flat components.

According to the invention, the composite bodies are produced by the metal-liquid infiltration of SiC, carbon and nitride-containing porous green bodies.

• a) Herstellung eines porösen kohlenstoffhaltigen Grünkörpers, enthaltend Carbide, Nitride und Kohlenstoffmaterial
• b) Zuführung einer Schmelze eines carbidbildenden Metalls über mindestens eine Außenfläche des Grünkörpers
• c) Metallinfiltration und Reaktion zumindest eines Teiles der Metallschmelze mit Kohlenstoff zu Metallcarbid, wobei hierdurch die unterschiedlichen Werkstoffschichten A und B gebildet werden.

The method comprises the following essential process steps:

• a) Preparation of a porous carbon-containing green body containing carbides, nitrides and carbon material
• b) supplying a melt of a carbide-forming metal over at least one outer surface of the green body
• c) metal infiltration and reaction of at least a portion of the molten metal with carbon to metal carbide, whereby the different material layers A and B are formed.

In the preparation of the porous carbonaceous green body, a mixture of the solids containing silicon carbide, nitrides, optionally carbon and organic binder is first prepared. This mixture is shaped according to the usual methods of the ceramics industry (including pressing, injection molding, slurrying) in which the curing of the organic binder is responsible for the strength of the resulting body. The cured body is then carbonized by a temperature treatment in the range of about 650 to 1600 ° C, preferably 1000 ° C. According to the invention, the organic binder is carbonizable, that is, when heated under non-oxidizing conditions, the binder is not completely volatilized, but forms a carbon residue. The resulting body, the green body, now consists of the solids used, in particular the ceramic particles, which are held together by a binder phase of pyrolytically generated carbon.

The composition of the starting mixture is preferably selected such that the mass fraction of silicon carbide in the porous carbon-containing green body is at least 50%, preferably at least 65%. The mass fraction of carbon, of carbonized binder and solids used, is typically above 4% and preferably above 8%, the content by mass of nitrides above 1%, preferably above 3% and particularly preferably between 3 and 12%. The nitrides are in particular selected from at least one of the nitrides of the following elements: Ti, Zr, Si, B and Al.

The solid carbon material is selected from coal, coke, natural graphite, engineering graphite, carbonized organic material, carbon fibers, glassy carbon and coking products. Particularly suitable are natural graphite or synthetic graphite.

An essential advantage of the invention is that expensive carbon fibers can be dispensed almost completely or completely.

According to the invention, it is also possible to produce a multilayer green body from different starting mixtures. For this purpose, preference is given to compositions in which the region corresponding to the later material layer B has a higher content of nitrides. This advantageously influences the ballistic behavior of the multilayer composite body.

In step b), the feeding of a molten metal, a carbide-forming metal is infiltrated into the porous green body. The infiltration is assisted by the capillary action and the chemical reaction between the free carbon of the green body with the carbide-forming metal taking place during the infiltration. In general, the infiltration is carried out at reduced pressure or vacuum, at temperatures of about 150 ° C above the melting temperature of the infiltration metal.

As infiltration metal silicon alloys, typically of Si and at least one of the elements Ti, Fe, Cr and Mo, and particularly preferably technically pure Si are preferably used.

By liquid metal infiltration, the pores of the green body are filled with infiltration metal and its reaction products with carbon in the outer region, while the inner region remains substantially free of infiltration metal and / or its reaction products with carbon. The mass fraction of infiltration metal supplied by the infiltration inside the composite material according to the invention, corresponding to the material layer B, is typically below 1%, and the mass fraction of metal carbide newly formed by the infiltration metal is below 3%.

According to the invention, the chemical composition and the porosity of the green body and the infiltration metal offer are selected so that the green body is only partially infiltrated. In particular, by the ratio of carbides, carbon and nitrides, the depth of infiltration can be controlled specifically.

The nitrides worsen the wetting of the green body with the molten silicon. In particular, this reduces the infiltration depth of the silicon-containing melt and controls the degree of conversion of the green body.

In step c), the reaction of at least part of the free carbon with the infiltration metal takes place. In particular, the temperature and process duration of the turnover can be controlled. In this step, the material layers A and B are formed. In the material layer A, a dense ceramic of reaction-bonded metal carbide, in the preferred case of infiltration with liquid silicon, ie SiSiC, is formed. In the material layer B, where almost no infiltration metal reaches, a sintering reaction takes place between the ceramic particles at the temperature of step c), which inter alia leads to a mechanical stabilization of the material layer. The strength (breaking strength) must only be so high that the material B is manageable and does not readily decay. The actual mechanical stabilization of the material layer B, however, takes place via the firmly bonded material layer A. The strength of the layer B can be increased if sintering aids which preferably contain Si compounds or powder are added to the mixture for the green body.

The molten metal is usually supplied via wicks or metal powder spills. Typically, the metal infiltration takes place substantially over the entire surface, so that the material layer A results in a closed material surface. If plate-shaped green bodies are used, the result is a component which, in the direction of the surface normal, the preferred direction of the ballistic threat, has the layer sequence of the material layers ABA.

This simple procedural approach to achieve this preferred layer structure is one of the significant advantages of the method according to the invention.

The mechanical stability of the material layer B can be improved without losing the typical properties of a loose powder bed similar properties of the invention, if the pores of the material B are additionally filled by a soft material. This can be achieved, for example, by melt infiltration with a thermoplastic polymer or by liquid infiltration with a polymer resin. Preferably, the pores are filled with polyolefins or epoxy resins at least 30%.
In a further advantageous embodiment of the invention, the pores are infiltrated with adhesives, which are particularly suitable for bonding with a backing. In this case, backing materials made of aramid fibers are particularly suitable.

In a further advantageous embodiment of the invention, the composite body, in particular the material layer B, with a light metal, in particular Al, infiltrated.

If the pores are filled by a soft material, the residual porosity of the layer B is preferably below 15%.

The filling of the pores of the material layer B with a polymer can be used particularly advantageously for bonding with a backing, in particular a backing made of fiber mats or fabrics.

Claims (21)

1. A composite body containing silicon carbide particles and a carbonized binder, wherein an outer region A of the composite body is infiltrated with a carbide-forming metal in such a way that this outer region contains phases of this metal and its reaction product with carbon, characterized in that
   an inner region B of the composite body, free of infiltrating metal, contains a loose structure of silicon carbide particles bound by sinter bridges and the non-volatile pyrolysis residues of the carbonized binder, this structure having a pore content of 10% to 35% by volume,
   the outer region A and the inner region B merge together, and
   the strength of the material in region B is at least 20% lower than the strength of the material in region A.
2. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that region A has a pore content below 20% by volume and region B has a pore content of 5 to 35% by volume.
3. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that region B has a pore content of 12% to 27% by volume.
4. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that region A has a density above 2.1 g/ccm and region B has a density below 2.55 g/ccm.
5. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that it is infiltrated with the carbide-forming metal from several sides so as to comprise three regions, the outer regions A being infiltrated with metal and the inner region B being substantially free of infiltrating metal.
6. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that region B has a silicon carbide content of at least 70 wt.%.
7. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that at least region B contains nitrides of at least one of the elements silicon, titanium, zirconium, boron and aluminium.
8. A composite body containing silicon carbide particles and a carbonized binder according to Claim 7, characterized in that regions A and B have the same nitride content by weight.
9. A composite body containing silicon carbide particles and a carbonized binder according to Claim 7 or 8, characterized in that the nitride content of region A and/or B is 0.05 to 15 wt.%.
10. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that region A has a silicon carbide content of at least 70 wt.%.
11. A composite body containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that at least part of the volume of region B that is not filled with SiC is filled with plastics, synthetic resins, elastomers, adhesives or metals with a hardness of at most 5 on the Mohs scale.
12. A process for the production of composite bodies containing silicon carbide particles and a carbonized binder according to Claim 1, characterized in that
    in a first step a green body is produced which contains silicon carbide and metal nitride in powder form and a carbonizable organic binder,
    in the second step this green body is carbonized to a porous carbon body by heating in a non-oxidizing atmosphere to temperatures ranging from 650°C to 1800°C, and
    in the third step the carbon body is infiltrated with a silicon-containing molten metal from one or more sides, the temperature being chosen so that at least part of the carbon reacts with the metal and/or silicon to form carbides, and the amount of molten metal and metal nitride being chosen so that the inner region of the body remains substantially free of metal and/or silicon.
13. A process according to Claim 12, characterized in that the silicon-containing molten metal has a silicon content of at least 25 wt.%.
14. A process according to Claim 12, characterized in that the metal nitrides in the green body are selected from titanium nitride, zirconium nitride, silicon nitride, boron nitride and aluminium nitride.
15. A process according to Claim 12, characterized in that the green body additionally contains carbon in the form of coke, natural graphite, synthetic graphite, carbonized organic material or vitreous carbon.
16. A process according to Claim 12, characterized in that the porosity remaining in the composite body after infiltration with a silicon-containing molten metal is at least partially filled with plastic, synthetic resin, elastomers, adhesive or metal with a hardness of at most 5 on the Mohs scale.
17. Use of composite bodies containing silicon carbide particles and a carbonized binder according to Claim 1 in the form of plates as protective shielding.
18. Use according to Claim 17, characterized in that the total thickness of the plates comprising regions A and B ranges from 6 to 300 mm.
19. Use according to Claim 17 or 18, characterized in that the thickness ratio of region A, which faces towards the direction of stress, to region B is at most 1:20.
20. Use according to Claim 18, characterized in that plates are used in which, in the direction of ballistic threat, a region A infiltrated with carbide-forming metal is followed by a region B substantially free of infiltrating metal and by a region A infiltrated with carbide-forming metal.
21. Use according to Claim 18 or 20, characterized in that the side of the plates that faces away from the direction of stress is reinforced with a layer of fibrous material or textiles.

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