On the Decomposition of TaC-WC Solid Solutions

Abstract

Powdered samples and sintered specimens of TaC-WC solid solutions containing up to 40 mol % WC as well as sintered alloys bonded with cobalt were heat-treated in vacuum at 1300-1500°C for 15-300 min. And the decomposition of solid solutions during heat treatment was studied. The results obtained are as follows.1) The sintered specimens of TaC-WC solid solutions containing up to 20 mol % WC were considerably stable against heat treatment. But the discontinuous precipitation by grain boundary reaction occurred in specimens containing more than 30 mol % WC. It seems that decomposition proceeds gradually to the solubility limit after the rapid decomposition at the first stage.2) Powdered samples of the solid solutions including those containing 10 mol % WC, however, decomposed very rapidly to the solubility limit.3) In alloys bonded with cobalt, the solid solutions decomposed to the solubility limit during sintering, as in powdered samples. But it was found that the microstructure of these alloys differed from that of WC-TaC-Co alloys to which TaC was added in the form of monocarbide, especially in the form of WC phase.