Abstract:
In one embodiment, a composition (10) to be mixed with a molten metal to make a metal matrix composite, the composition characterized by: a ceramic reinforcing filler (12), the ceramic reinforcing filler not being wettable by molten aluminum and/or not being chemically stable in molten aluminum, the ceramic reinforcing filler being coated with a ceramic material, the ceramic material being wettable by and chemically stable in molten aluminum. In a related embodiment, a composition (20) to make a porous preform to be infiltrated by molten metal to make a metal matrix composite, the composition characterized by: a ceramic reinforcing filler (23), the ceramic reinforcing filler not being wettable by molten aluminum, the ceramic reinforcing filler being coated with a ceramic material (22) and optionally with a metal (21) such as nickel, the ceramic material being wettable by molten aluminum. The ceramic material can be coated on the ceramic reinforcing filler by a vacuum deposition technique such as vacuum sputtering.
Abstract:
A hard drive disk substrate is formed of a multi-phase ceramic-based material having at least two phases with amorphous phases being present in an amount less than about 1 volume percent based on the volume of the ceramic-based material or at least one phase being free metal. A process for producing the ceramic-based disk substrate is produced by forming a flat disk of a porous ceramic and then infiltrating the porous ceramic with a metal whereby a multi-phase ceramic-based computer hard drive disk is produced. Additionally, a step of passivating the porous ceramic by elevating it to a temperature of about 1300.degree. to about 1800.degree. C. before the infiltrating step may be performed, such that the surfaces are passivated and the reaction kinetics can be controlled during the infiltrating step. A preferred composite material is made of a multi-phase boron carbide composite material including grains having peaks with an average roughness value, Ra, of between about 1 to about 200 .ANG., the roughness value being formed in situ by causing a micro hardness gradient of between about 19 and about 3200 Kg/mm.sup.2 in the various phases of the multi-phase boron carbide composite material.
Abstract:
Densified boron carbide-aluminum, ceramic-metal composites that are substantially free of AlB.sub.12, AlB.sub.12 C.sub.2 and Al.sub.4 C.sub.3 result from a two stage process. Admixtures of boron carbide are densified under pressure in stage one, In stage two, the densified admixture is heat treated. In both stages, the temperature is less than 800.degree. C. If the temperatures do not exceed 600.degree. C., the resultant densified cermet has only three phases: a) boron carbide; b) Al.sub.4 BC; and c) aluminum.
Abstract:
Infiltrate a porous, self-reinforced .beta.-Si.sub.3 N.sub.4 preform with a metal or a crystallizable glass to yield a composite material. The preform possesses a low glass phase and has a density of from about 50 to about 70 percent of theoretical density. Prepare the .beta.-Si.sub.3 N.sub.4 preform by subjecting a porous body formed from an .alpha.-Si.sub.3 N.sub.4 powder composition to two sequential heat treatments. The first heat treatment occurs below the .alpha.- to .beta.- conversion temperature and results in a strengthened body that can be machined. The second heat treatment occurs above that temperature and yields the self-reinforced .beta.-Si.sub.3 N.sub.4 preform. Conventional infiltration procedures with an infiltrant that is a metal or a glass results in a Si.sub.3 N.sub.4 /metal or Si.sub.3 N.sub.4 /glass composite material that has 50 to 70 percent of its volume occupied by .beta.-Si.sub.3 N.sub.4 whiskers.
Abstract translation:用金属或可结晶玻璃渗透多孔,自增强β-Si3N4预成型体,得到复合材料。 预制棒具有低玻璃相,并且具有理论密度的约50至约70%的密度。 通过将由α-Si 3 N 4粉末组合物形成的多孔体进行两次连续的热处理来制备β-Si 3 N 4预型体。 第一次热处理发生在α至β转化温度以下,并导致可加工的加强体。 第二次热处理发生在该温度以上,并产生自增强的β-Si 3 N 4预制件。 具有金属或玻璃的渗透剂的常规渗透程序导致Si3N4 /金属或Si3N4 /玻璃复合材料,其具有其β-Si 3 N 4晶须占据其体积的50%至70%。
Abstract:
A dense, self-reinforced silicon nitride ceramic prepared by pressureless sintering or low pressure gas sintering. The composition comprises (a) silicon nitride, at least 20 percent of which is in the form of .beta.-silicon nitride whiskers having a high average aspect ratio, (b) from about 2 to about 10 weight percent of a glassy grain boundary phase containing magnesium oxide, yttrium oxide, silica, zirconia, and optionally, one oxide selected from the group consisting of calcium, gallium, indium and hafnium oxides, and (c) a second crystalline phase in an amount ranging from 0.5 to about 5.0 weight percent comprising zirconium oxide, and (d) optionally, crystalline phases of metal zirconium silicide and/or metal zirconium silicon nitride in a combined amount from 0.1 to 3.0 weight percent, wherein the metal is tantalum, calcium, hafnium, gallium or indium, and wherein when the metal is calcium, hafnium, gallium or indium, the same metal occurs as the metal oxide in the glassy phase. The ceramic exhibits high fracture toughness and high fracture strength and has a density of at least 98 percent of theoretical.
Abstract:
A process for preparing a self-reinforced silicon nitride ceramic body of high fracture toughness comprising hot-pressing a powdcer mixture containing silicon nitride, a densification aid such as sodium oxide, a conversion aid such as lanthanum oxide and a compound, such as gallium oxide, which enhances growth of .beta.-silicon nitride whiskers-under conditions such that densification and the in situ formation of .beta.-silicon nitride whiskers having a high aspect ratio occur. A novel silicon nitride ceramic of high fracture toughness and high fracture strength is disclosed comprising a .beta.-silicon nitride crystalline phase wherein at least about 20 volume percent of the phase is in the form of whiskers having an average aspect ratio of at least about 2.5; a glassy second phase containing the densification aid, the conversion aid, the compound which enhances growth of .beta.-silicon nitride whiskers, and an amount of silica; and not greater than about 10 weight percent of the total weight as other phases. The glassy phase may also include a minor amount, e.g., up to 5.0 weight percentg, based upon total weight of the ceramic, of aluminum nitride or boron nitride. The glassy phase optionally includes an amount of a secondary reinforcing material such as silicon carbide whiskers.
Abstract:
A fully densified, self-reinforced silicon nitride ceramic body of high fracture toughness and high fracture strength is disclosed comprising (a) .beta.-silicon nitride in the form of whiskers having an average aspect ratio of at least about 2.5, and (b) a crystalline grain boundary phase having an oxynitride apatite structure, as determined by X-ray crystallography.A process for preparing the above identified silicon nitride body comprising hot-pressing a powder mixture containing silicon nitride; silica; a densification aid including strontium oxide; a conversion aid, such as, yttrium oxide; and a compound, such as, calcium oxide which enhances growth of .beta.-silicon nitride whiskers, under conditions such that densification and the in situ formation of .beta.-silicon nitride whiskers having a high aspect ratio occur, and thereafter annealing the densified composition for a time sufficient to produce a crystalline grain boundary phase having an oxynitride apatite structure.
Abstract:
Substantially dense, void-free ceramic-metal composites are prepared from components characterized by chemical incompatibility and non-wetting behavior. The composites have a final chemistry similar to the starting chemistry and microstructures characterized by ceramic grains similar in size to the starting powder and the presence of metal phase. A method for producing the composites requires forming a homogeneous mixture of ceramic-metal, heating the mixture to a temperature that approximates but is below the temperature at which the metal begins to flow and presssing the mixture at such pressure that compaction and densification of the mixture occurs and an induced temperature spike occurs that exceeds the flowing temperature of the metal such that the mixture is further compacted and densified. The temperature spike and duration thereof remains below that at which significant reaction between metal and ceramic occurs. The method requires pressure of 60-250 kpsi employed at a rate of 5-250 kpsi/second.
Abstract:
A process is described for making a composite article without shrinkage, particularly of ceramic and metal wherein the article includes complex internal surfaces or cavities. The process requires forming an insert body that includes an external surface that corresponds to an internal cavity of the article. The insert body consists of a material having a melting temperature less than that of the article. The process further requires forming a porous compact about the insert body wherein the compact is formed into the substantially the net shape of the article. The compact is made of a material that is wetted by liquid insert material and has a sintering temperature greater than the wetting temperature of the insert material. The process further requires heating the article to a temperature such that the inserts substantially melts and infiltrates the porous compact forming the finished composite article. The process produces products including complex internal surfaces without the necessity of costly and sometimes technically difficult internal machining operations.