초록 ▼

Polycrystalline sintered bodies are provided consisting of at least 66% by weight of a crystalline Si3N4 phase, of which at least 90% by weight is in the beta-modification, and of up to 34% by weight of secondary intergranular grain boundary phases of oxide, carbide and/or nitride. At least 25% by w

Polycrystalline sintered bodies are provided consisting of at least 66% by weight of a crystalline Si3N4 phase, of which at least 90% by weight is in the beta-modification, and of up to 34% by weight of secondary intergranular grain boundary phases of oxide, carbide and/or nitride. At least 25% by weight of the secondary grain boundary phases consists of a quasi-ternary crystalline compound in the E1－E2－E3 triangle of the Ga2O3－La2O3-Al2O3 ternary system called “Gala”, the “Gala”compound being prepared from gallium oxide, lanthanum oxide and aluminum oxide prior to producing the sintered bodies. The polycrystalline sintered bodies are produced by sintering with and without application of pressure from silicon nitride powders having a portion of impurities not exceeding 4.0% by weight, sintering additives of oxides and optionally other refractory admixtures of carbides and/or nitrides. Powders of a quasi-ternary crystalline compound (Gala compound) are employed as at least one sintering additive prepared, prior to mixing with the remaining components and to sintering, from gallium oxide, lanthanum oxide and aluminum oxide by heating to temperatures from 1500°C. to 1850°C. When using at least 70% by weight of silicon nitride powder, there can be used up to 30% by weight of a crystalline “Gala”compound alone or mixed with other admixtures of oxides, carbides or nitrides, but altogether at least 1% by weight of a crystalline “Gala”compound must be present. The sintered bodies are especially tough and very hard and can be used for the machining of iron materials at high cutting speeds.

대표청구항 ▼

Polycrystalline sintered bodies of great fracture toughness and hardness consisting essentially of at least 66% by weight of a crystalline silicon nitride phase, of which at least 90% by weight is present in the beta-modification, and up to 34% by weight of secondary, intergranular grain boundary ph

Polycrystalline sintered bodies of great fracture toughness and hardness consisting essentially of at least 66% by weight of a crystalline silicon nitride phase, of which at least 90% by weight is present in the beta-modification, and up to 34% by weight of secondary, intergranular grain boundary phases based on oxides, carbides and/or nitrides, of which at least one is crystalline, and wherein at least 25% by weight of the intergranular, secondary grain boundary phases consists essentially of a quasi-ternary crystalline compound of Ga2O3－La2O3－Al2O3, the quantitative portions of which in % by mole in the ternary system Ga2O3－La2O3－Al2O3 are determined by the triangular surface with the corners E1=5%Ga2O3－5%La2O3－90%Al2O3 E2=90%Ga2O3－5%La2O3－5%Al2O3 E2=5%Ga2O3－90%La2O3－5%Al2O3 of the FIGURE, and the quasi-ternary crystalline compound is prepared from gallium oxide, lanthanum oxide and aluminum oxide prior to producing the polycrystalline sintered bodies and wherein at least 1% by weight of the sintered body is the quasi-ternary crystalline compound.