摘要:
Aluminum nitride powder, aluminum nitride platelets, powdered solid solutions of aluminum nitride and at least one other ceramic material such as silicon carbide, and composites of aluminum nitride and transition metal borides or carbides are prepared by combustion synthesis at low gaseous nitrogen pressures. Porous bodies of aluminum nitride or composites of aluminum nitride and transition metal borides or carbides are also prepared by combustion synthesis at these pressures. The porous bodies are suitable for infiltration, either as formed or after being coated with at least one layer of a silicate material, by polymers or metals.
摘要:
A method of forming a low level carbon high-density tungsten carbide-containing material includes sintering a preform which contains tungsten carbide powder and has a composition such that the resulting sintered material has at most 6.05 weight percent tungsten-bound carbon based on the total weight of tungsten and tungsten-bound carbon. This low level of carbon may be achieved by, prior to the sintering step, oxidizing the tungsten carbide powder sufficiently to achieve the desired substoichiometric carbon level in the sintered product or by adding a carbon-lowering material selected from the group consisting of tungsten, ditungsten carbide, and tungsten oxide. Optionally, other materials can be present in the preform such as carbon-getter metals and compounds thereof. The carbon-getter metals are those metals of which the carbides thereof are more thermodynamically stable than monotungsten carbide.
摘要:
Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.
摘要:
A method for making submicrometer metallic carbides and submicrometer solid solution metallic carbides from sources of at least one metallic oxide and carbon involves the rapid heating of a reactive particulate mixture of at least one metallic oxide and carbon in order to achieve a resulting particulate size of less than 1 micrometer. Submicrometer sized metallic carbides and solid solution metallic carbides have found great use in commercial ceramic applications. It has been found that the smaller sized particles produce a product having superior toughness and hardness. In addition, the submicrometer sized solid solution metallic carbide resulting from this method is also disclosed.
摘要:
Aluminum nitride powder, aluminum nitride platelets, powdered solid solutions of aluminum nitride and at least one other ceramic material such as silicon carbide, and composites of aluminum nitride and transition metal borides or carbides are prepared by combustion synthesis at low gaseous nitrogen pressures. Porous bodies of aluminum nitride or composites of aluminum nitride and transition metal borides or carbides are also prepared by combustion synthesis at these pressures. The porous bodies are suitable for infiltration, either as formed or after being coated with at least one layer of a silicate material, by polymers or metals. The powders are also suitable for preparing dense sintered bodies. The aluminum nitride powder is also used to prepare AlN sintered bodies.
摘要:
Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.
摘要:
A method for forming monotungsten carbide, comprising heating a solid, non-elemental tungsten-containing material in a flowing atmosphere containing molecular hydrogen and molecular methane for a time sufficient to convert substantially all of the tungsten-containing material to monotungsten carbide, The heating brings the temperature of the tungsten-containing material to a first elevated temperature of from about 520 to about 550.degree. C. and, subsequently, at a rate of from about 3 to about 10.degree. C. per minute, the heating brings the temperature from the first elevated temperature to a second elevated temperature of about 800 to about 900.degree. C. Thereafter the temperature is held at the second elevated temperature for at least about 15 minutes. At least about 50 weight percent of the monotungsten carbide formed is formed while holding the temperature at the second elevated temperature.
摘要:
Ceramic-metal composites (cermets) are made by a combination of self-propagating high temperature combustion synthesis and molten metal infiltration. Solid-gas, solid-solid and solid-liquid reactions of a powder compact produce a porous ceramic body which is infiltrated by molten metal to produce a composite body of higher density. AlN-Al and many other materials can be produced.
摘要:
A multi-phase cemented ceramic article, method of making same, and the material thereof is disclosed which is useful for machining and forming of metals, including ferrous metals, titanium, aluminum and other metals. The article and its material preferably includes novel microstructures including platelets, a range of grain sizes which yields superior hardness and other characteristics, and a lower tungsten concentration within the binder phase than has been seen in the prior art. The preferred composition includes ultrafine WC, an ultrafine solid solution of (Ti, Ta, W)C, and a cobalt binder. Platelets are formed in-situ, eliminating the need to add them during manufacture for improving toughness.
摘要:
Densified refractory carbide and solid solution carbide materials that have an average grain size of less than 1.1 .mu.m, a density of at least 98% of theoretical may be prepared by any conventional densification procedure. Pressure densified tungsten carbide ceramic materials exhibit a simultaneous increase in Vickers hardness and a toughness (K.sub.IC) with decreasing average grain size.