EP1380809A2 - Ceramic composite bodies - 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, especially for protective armor, for civil and military Areas of application are suitable. In particular, the invention relates to a single body mainly multilayer composite material containing silicon carbide (SiC), with one essentially bonded in a matrix of free silicon (Si) SiC existing external material layer and an internal one Material layer containing loosely bound SiC ceramic powder, as well as a Process for their production and uses of these composite bodies.

Protective armor against the ballistic impact of projectiles are used Depending on the area of application, different requirements for the projectile Effect, multi-hit suitability, component geometry or component weight.

In the civilian sector, the focus is particularly on the Personal protection, armored limousines and protective vests. The requirements for The bullet-breaking effects are not as high, as they are rarely used in this area heavy weapons or medium and large calibers got to. Among other things, high demands are placed on component geometry and Component weight set. Complex shaped parts are required, coupled with the requirement for the smallest possible component thickness or installation depth and light weight. The distance to the threat is usually very short and can only be a few meters. This results in the case of the common one Multiple shots (referred to here as "multihit") are too close together Hits. This results in the highest requirements for multi-hit suitability the protective armor.

In the military field is threatened by high-speed and large caliber bullets and explosive bullets. Although the Component thickness and installation depth requirements are lower than in civilian applications Range, here too is a low specific weight of the armor material of crucial importance, because of the extremely high requirements the protective armor component in the generally run very thick.

The large distances to the target objects generally require long distances Hits distances. Therefore, there are fewer requirements for multi-hit suitability posed.

Flat plates are often used as armor for military purposes Additional armor for land and water vehicles as well as for helicopters, containers, Containers, shelters and field fortifications used.

Armor consisting of one or more armored steel plates is usually like this treats that at least the side facing the threat is extremely hard and so that the bullet breaks. The side facing away from the threat is more ductile or more visibly designed to withstand the energy of the projectile through a material deformation to absorb. This also results in that for armored plates from others Materials typical structure.

Compared to metals, ceramic materials have the advantage of being higher Hardness and lower specific weight. Since the monolithic ceramic at Shelling shows a typical brittle fracture behavior, ceramic plates burst (monolithic ceramics) with formation of many coarse to very fine fragments. The Use of ceramic plates without additional backing (support material and Fragmentation) on the side facing away from the entry of the projectile is due the splinter exit does not make sense when fired at. Due to the shelling in generally completely destroyed the respective ceramic plate. A multiple bombardment (multi-hit) can then no longer be held.

Armor with ceramic materials exists for these reasons preferably of two layers. The front plate made of monolithic ceramics has the task of deforming the remaining floor and, if necessary, the Breaking hard core. A deformable one attached behind the ceramic plate Armoring, the backing, has the task of projectile, bullet debris and Ceramic fragments to catch or absorb and the remaining ceramic plate to stabilize. It is also called the absorber layer below. 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 that Areas made of monolithic ceramics (bullet breakers) and fiber-reinforced Have ceramic (absorber layer), such as in EP-A 0 376 794 described. The disadvantage of these concepts is generally the high one Price and the low availability of suitable fibers for fiber-reinforced ceramics. So are for the commonly used sintering process for the production of fiber-reinforced ceramics only relatively expensive carbon fibers of technical Importance.

Another approach that uses the projectile and splinter-absorbing effect Reaching 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 one behind it Absorber plate consists of so-called chemically bound ceramics. The Chemically bonded ceramics consist of hard fillers such as Fibers or ceramic powder, and a binding phase (or matrix) made of with organic or inorganic polymers modified cements, which harden at low temperatures. The hard fillers lead to one Blunting, deflection and destruction of the projectile.

The production of multi-layer armor plates with complex geometry and solid chemical bond between the two layers of material is after this However, the process is very complex.

Compared to this prior art, it is an object of the invention, a Ceramic composite body with a bullet-breaking front layer and one with this connected absorber layer using an inexpensive Manufacturing process that also allows complex component geometries available do.

This object is achieved by a composite body that comprises at least two layers, characterized in that one outside lying bullet-breaking ceramic layer (front panel) essentially a carbide and a carbide-forming metal, preferably SiC and Si (Material layer A) exists, and an internal one firmly connected to it Layer (material layer B), the weakly or loosely bound ceramic powder contains, which consists essentially of SiC.

Furthermore, a method for producing such a composite body specified, in which the multi-layer composite material by the Liquid infiltration of a porous green body made of ceramic particles and Carbon material through a carbide-forming metal, in particular silicon metal, is made by liquid metal infiltration in one common process step from both the outer ceramic layer Carbide and carbide-forming metal, preferably SiC and Si (material layer A), as also the inner layer of weakly or loosely bound ceramic powder predominantly SiC (material layer B) is formed, as well as both layers firmly are chemically linked together.

The invention is based on the knowledge that powdery or particulate Ceramic, similar to a sand fill, has a very favorable absorption behavior against ballistic effects, provided the powdery material is mechanical is stabilized or held together. This cohesion will according to the invention by the chemically firmly bonded ceramic layer (Material layer A), as well as by the during the metal melt infiltration sintering process of the ceramic mixture of the green body in the area of Material layer B reached.

The composite body according to the invention therefore comprises at least two layers, an outer material layer A, which contains phases made 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 a material layer B behind it, which through Sintering contains loosely bound SiC ceramic powder or particles, and optionally further layers arranged behind them, in particular made of material A or of fiber-containing backing. These additional layers further improve the energy-absorbing effect of the armor.
Loosely bound ceramic powder or particles is to be understood in particular as material whose strength is at least 20% below that of the material of material layer A.

In the preferred method of liquid metal infiltration, preferably with a Silicon melt - is in the material layer A by reaction of the carbide-forming Metal with carbon formed a ceramic, which in addition to very high hardness is a good one Exhibits fracture toughness or damage tolerance. This will make it for the Multiple bombardment harmful ceramic brittle fracture behavior in advantageous Suppressed way. An alloy is preferably used as the infiltration metal, which contains at least a mass fraction of 50% silicon, is particularly preferred is technical silicon or pure silicon. When infiltrating with a silicon-containing alloy of metals, Fe, Cr, or Ni forms from the im Carbon precursors of material layer A preferably contain silicon carbide. When infiltrated with a titanium-silicon alloy, the carbon forms preferably titanium carbide in addition to silicon carbide.

The particles of silicon carbide and nitrides contained in material layer B. are at the temperature of infiltration with the liquid metal to the Contact points sintered together, creating 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 which are embedded in a matrix of free silicon. The mass fraction of SiC is preferably above 75% and particularly preferably above 85%. The mass fraction of free silicon, which should also include all silicon mixed phases with other metallic elements, is 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 built up in such a way that the highest possible hardness is achieved, which can be achieved, for example, by the highest possible density, ideally the theoretical density. The porosity (volume fraction of the pores in the total volume) of the material layer A is therefore preferably less than 20% or the density is at least 2.1 g / cm ^3, and the porosity is particularly preferably less than 10% or the density above 2.2 g / cm ³ . Typically, material A still has free carbon and, if appropriate, ceramic additives in mass fractions of about 0.5 to 15%. According to the invention, particularly hard ceramics based on nitride are used as the preferred ceramic additives. These include in particular the nitrides of the elements Si, Ti, Zr, B and Al.

The average particle size of the SiC, which applies to both material layer A and material layer B can typically be used in the range of 20 to 750 µm. Since the process is generally a homogeneous one Green body (preform of metal infiltration) is made from the ceramic powders, the particle sizes in material layers A and B only differ immaterial. However, it is also possible to use different particle sizes for the Provide layers, in which case the material layer A is preferably finer Contains material as the material layer B. The is then particularly preferably average particle size in layer A below 50 µm and in layer B above 50 µm.

The material layer B is also preferably predominantly made of SiC particles built up. The mass fraction of SiC particles is preferably above 70% and particularly preferably above 90%. Also the content of ceramic Aggregates are in comparable proportions as in layer A. Preferred contains the material layer B at least one of the nitrides of the elements Si, Ti, Zr, B and Al in mass proportions of 0.05 to 15%. The main difference to Material A in material layer B is ceramic, or its Ceramic particles, not bonded by silicon, it is almost no matrix made of silicon or a silicon alloy. The mass fraction of free Silicon or silicon / metal phases is typically below of 5%, preferably below 2.5% and particularly preferably below 1%.

The ceramic particles in the material layer B are only weakly bound, some over Carbon binding phases, sometimes directly with each other via sinter bridges. The Material layer B therefore has a comparatively high porosity typically ranges from 5% to 35%, and preferably in the range from 12 to 27% lies.

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

For the effect of the material layer B according to the invention, the only loose bond is between the ceramic particles essential. Among other things, this is for the Typical crack propagation through large areas of a brittle fracture coherent workpiece part prevented, while the hardness of Ceramic particles is used. This effect is also achieved when the pores in This layer is filled with material that is significantly softer than the ceramic.

In a further advantageous embodiment of the invention, therefore Spaces between the ceramic particles in the material layer B with a soft material filled. A plastic or is usually used as the soft material a metal is used, the metal having a hardness on the Mohs scale of at most 5 has. Thermoplastic polymers, resins, Adhesives, elastomers or aluminum. Then at least half of the Space that is formed between the ceramic particles with the soft Material filled.

The application of the composite body according to the invention is in the range of Protective armor, especially against ballistic effects. Due to the good thermal properties, especially the high melting or Decomposition point of SiC, the composite material also shows good suitability as Armor material in the vault and protective building.

Components from the composite bodies according to the invention are usually so designed that the total thickness of the material layers A and B in the range of 6 up to 300 mm. Also other layers, in particular from material A or fibrous backing can be placed behind the layer of material B. his. The layer thickness of material A is usually above 1 mm, for Armor plates preferably above 3 mm. The layer thickness ratio of Material layers A and B are typically below 1:50, preferably below 1:10, here only the front layer facing the bombardment side from material A and the subsequent layer from material B. are understand.

Material layer A merges into material layer B, the transition in generally due to a significant decrease in the silicon content in the matrix is recognizable.

Fig. 1 shows a microscopic micrograph of the interface between the Material layers A and B of a composite body according to the invention. The gray ones Areas (1) are SiC particles which are approximately uniform over the entire Neckline are distributed. In the upper half (A), which corresponds to material A. the SiC areas connected by a continuous bright phase (2). this is the Silicon matrix. The lower half (B), which corresponds to material B, takes place of the matrix pores (black areas, 3). The other ingredients In this representation, carbon or nitride particles cannot be separated from the differentiate other materials.

Because of the process-related ease of manufacture, one with all sides Material layer A surrounding material B is for flat components Layer sequence of a front panel made of material A, an absorber zone made of Material B and back plate (or backing) made of material A in particular prefers.

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

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 process has the following essential process steps:

a) Production of a porous carbon-containing green body, containing carbides, nitrides and carbon material

b) supplying a melt of a carbide-forming metal via at least one outer surface of the green body

c) metal infiltration and reaction of at least part of the metal melt with carbon to metal carbide, the different material layers A and B being formed as a result.

In the manufacture of the porous carbon-containing green body, one is first Mixture of the solids containing silicon carbide, nitrides, if appropriate Carbon and organic binder made. This mixture is made according to the usual processes in the ceramic industry (including pressing, injection molding, Slip) brought into shape, the curing of the organic binder for the Strength of the resulting body is responsible. The hardened body will followed by a temperature treatment in the range of approx. 650 to 1600 ° C, preferably 1000 ° C, carbonized. According to the invention, the organic binder carbonizable, that is, when heated under non-oxidizing conditions the binder does not evaporate completely, but it forms Carbon residue. The resulting body, the green body, exists now from the solids used, especially the ceramic particles held together by a binding phase made of pyrolytically produced carbon become.

The composition of the starting mixture is preferably chosen so 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, from carbonized binder and solids used, is typically above 4% and preferably above 8%, the mass fraction nitride content above 1%, preferably above 3% and particularly preferably between 3 and 12%. The nitrides are particularly selected from at least one of the nitrides of the following elements: Ti, Zr, Si, B and Al.

The carbon material used as a solid is selected from the group Coal, coke, natural graphite, technical graphite, carbonized organic material, Carbon fibers, glassy carbon and coking products. Particularly suitable are natural graphite or synthetic graphite.

A major advantage of the invention is that almost on expensive carbon fibers can be completely or completely dispensed with.

According to the invention, it is also possible to make a multilayer green body different starting mixtures. Are preferred for this Compositions in which the area of the material layer B corresponds, has a higher content of nitrides. This will make the ballistic Behavior of the multilayer composite body advantageously influenced.

In step b), the supply of a molten metal, a carbide-forming metal is in infiltrates the porous green body. The infiltration is caused by the capillary action and the chemical reaction between the free one that occurs during infiltration Carbon of the green body supported with the carbide-forming metal. in the in general, the infiltration takes place at reduced pressure or vacuum, at Temperatures of approx. 150 ° C above the melting temperature of the Infiltration metal.

Silicon alloys, typically made of Si, are preferred as the infiltration metal and at least one of the elements Ti, Fe, Cr and Mo, and particularly preferred technically pure Si used.

Due to the liquid metal infiltration, the pores of the green body in the Outside with infiltration metal and its reaction products with Carbon filled, whereas the inner area is essentially free of Infiltration metal and / or its reaction products with carbon remains. 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 by that Infiltration metal newly formed metal carbide below 3%.

According to the chemical composition and the porosity of the Green body and the infiltration metal range chosen so that the green body only is partially infiltrated. In particular through the ratio of carbides to carbon and nitrides, the depth of infiltration can be specifically controlled.

The nitrides wetting the green body with the molten Silicon deteriorates. In particular, the depth of infiltration of the silicon-containing melt reduces and the degree of implementation of the green body controlled.

In step c) the conversion of at least part of the free carbon takes place the infiltration metal instead. Especially about temperature and process time sales are controlled. In this step, the material layers A and B. A dense ceramic is formed in material layer A. reaction-bound metal carbide, in the preferred case of infiltration with liquid Silicon thus SiSiC, formed. In material layer B, where almost none Infiltration metal arrives at the temperature of step c) Sintering reaction takes place between the ceramic particles, which among other things leads to a mechanical stabilization of the material layer leads. The firmness (Breaking strength) only has to be so high that material B can be handled and does not disintegrate easily. The actual mechanical stabilization of the Material layer B, however, takes place via the firmly attached material layer A. The Strength of layer B can be increased if the mixture for the green body Sintering aids are added, preferably Si compounds or powders contain.

The molten metal is usually over wicks or over Metal powder fillings fed. Typically, the metal infiltration takes place in the essentially over the entire surface, so that the material layer A a closed material surface results. Become plate-shaped green bodies used, results in a component that in the direction of the surface normal, the preferred direction of the ballistic threat, the layer sequence of the Material layers A B A has.

This simple procedural approach, this preferred Reaching layers is one of the main advantages of the inventive method.

The mechanical stability of the material layer B can be improved without the properties according to the invention, which are similar to a loose powder bed, being lost if the pores of the material B are additionally filled with a soft material. This can be achieved, for example, by melt infiltration with a thermoplastic polymer or by liquid infiltration with a polymer resin. The pores are preferably filled at least 30% with polyolefins or epoxy resins.
In a further advantageous embodiment of the invention, the pores are infiltrated with adhesives which are particularly suitable for bonding to a backing. Backing materials made from 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 with a soft material, the residual porosity lies in the Layer B preferably below 15%.

The filling of the pores of the material layer B with a polymer can be special advantageous for gluing with a backing, in particular a backing Fiber mats or fabrics can be used.

Claims (22)

Ceramic composite body comprising at least two layers A and B, characterized in that one layer A contains phases made of a metal and the carbide of this metal, and in that the other layer B contains particles of silicon carbide bound partly via carbon binding phases, partly directly via sintered bridges and has a volume fraction of pores of 10% to 35%. Ceramic composite body according to claim 1, characterized in that the material layer A has a volume fraction of pores below 20% and the material layer B has a volume fraction of pores of 5 to 35%. Ceramic composite body according to claim 1, characterized in that the layer B has a volume fraction of pores of 12% to 27%. Ceramic composite body according to claim 1, characterized in that the material layer A has a density above 2.1 g / ccm and the material layer B has a density below 2.55 g / ccm. Ceramic composite body according to claim 1, characterized in that the silicon alloy contains a mass fraction of at least 25% silicon. Ceramic composite body according to claim 1, characterized in that it comprises three layers, the outer layers being made of material A and the inner layer being a material layer B. Ceramic composite body according to claim 1, characterized in that the material layer B contains a mass fraction of at least 70% silicon carbide. Ceramic composite body according to claim 1, characterized in that at least the material layer B contains nitrides at least one of the elements silicon, titanium, zirconium, boron and aluminum. Ceramic composite body according to claim 8, characterized in that the material layers A and B have the same mass fraction of nitrides. Ceramic composite body according to claim 8 or 9, characterized in that the mass fraction of the nitrides in the material A and / or B is 0.05 to 15%. Ceramic composite body according to claim 1, characterized in that the material layer A has a mass fraction of at least 70% of silicon carbide. Ceramic composite body according to claim 1, characterized in that at least part of the volume of the material layer B not filled by SiC is filled by plastics, synthetic resins, elastomers, adhesives or metals with a hardness of at most 5 on the Mohs scale. A method for producing ceramic composite bodies according to claim 1, characterized in that in a first step a green body is produced which contains silicon carbide and metal nitride in the form of a powder and a carbonizable organic binder, this green body in the second step by heating in a non-oxidizing atmosphere is carbonized to temperatures in the range from 650 ° C. to 1800 ° C. to form a porous carbon body, and in the third step the carbon body is infiltrated from one or more sides with a silicon-containing molten metal, the temperature being chosen such that at least part of the carbon reacts with the metal and / or silicon to form carbides, and the amount of the metal melt and the metal nitride is selected such that the inner region of the body remains essentially free of the metal and / or silicon. A method according to claim 13, characterized in that the silicon-containing molten metal contains a mass fraction of at least 25% of silicon. A method according to claim 13, characterized in that the metal nitrides in the green body are selected from titanium nitride, zirconium nitride, silicon nitride, boron nitride and aluminum nitride. A method according to claim 13, characterized in that the green body additionally contains carbon in the form of coke, natural graphite, synthetic graphite, carbonized organic material, carbon fibers or glassy carbon. A method according to claim 13, characterized in that the prosthesis remaining after infiltration with a silicon-containing metal melt in the composite body is at least partially filled with plastic, synthetic resin, elastomers, adhesive or metal with a hardness of at most 5 on the Mohs scale. Use of ceramic composite bodies according to claim 1 in the form of two- or multi-layer panels as protective armor. Use according to claim 18, characterized in that the total thickness of the plates made of the material layers A and B is in the range from 6 to 300 mm. Use according to claim 18 or 19, characterized in that the layer thickness ratio of the material layer A facing the direction of stress and the material layer B is at most 1:20. Use according to claim 18, characterized in that three-layer plates with the layer sequences of a material layer A, a material layer B and a material layer A are used. Use according to claim 18 or 21, characterized in that the side of the two-layer or multilayer plates facing away from the direction of stress is reinforced with a layer of fiber material or textiles.

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