PRODUCTION OF ZIRCONIUM HAFNIUM AND ZIRCONIUM NIOBIUM CARBIDES.

Many workers have looked for substitutes for TaC in hardmetal tools because of the restricted availability and high cost of tantalum. The authors investigated compositions which would be in solid solution when made but would decompose spinodally at lower temperatures during tool manufacture to give fine dispersions of carbides in the final tool. This should emulate the grain growth inhibiting action of TaC. Pre-alloyed powders of zirconium hafnium carbide or zirconium niobium carbide have been produced using a two-stage route. The first was carbothermic reduction in a vacuum furnace at 2200C; the pre-alloy was then milled with tungsten and titanium carbides before undergoing a second vacuum furnace treatment at 2200C to produce the final single phase alloy of the four carbides.