MANUFACTURE OF OXIDATION-RESISTANT TUNGSTEN-BASE SINTERED ALLOY

摘要

PURPOSE:To obtain a W-base sintered alloy maintaining low coefficient of thermal expansion and sufficient ductility and having superior oxidation resistance, by sintering a green compact consisting of W powder and a powder mixture of Ni and Fe in which the weight ratio between Ni and Fe is specified and then by diffusing Cr and Mo into the resulting sintered compact. CONSTITUTION:A powder mixture consisting of 85-95wt.% W powder and the powders of Ni and Fe in which the weight ratio of Ni to Fe is regulated to 1:1-4:1 is compacted. The green compact is sintered in a reducing atmosphere at a temp. higher than the melting temp. of an Ni-Fe phase by 20-60 deg.C. The resulting sintered compact is buried in a powder mixture of powdered Cr, powdered Mo, and powdered Al2O3, to which heat treatment is applied at 1,420-1,500 deg.C to form a diffusion layer of Cr-Mo on the surface of the sintered alloy. This Cr-Mo diffusion-treated W-base sintered alloy has superior oxidation resistance even at high temp., so that it is applicable to a member for high-temp. forming, such as die for die casting.