Effect of Ni additive on sintering and grain growth of tungsten

A number of mechanisms have been proposed in order for explaining the activated sintering of Ni-doped tungsten. Most of these mechanisms were developed without taking account of the exact physical and chemical state of nickel additive during the sintering process, especially in the initial stage. The present paper describes the dependence of sinterability of Ni-doped W-powder compact on the adding method of Ni-activator, on the contact size of the W-powders and on the chemical state of nickel, with an aim of providing some plausible explanation for the role of Ni-activator at the initial stage of sintering. In addition, the effect of Ni-additive on the grain growth in W-wire bundle model was examined, because the grain growth during the intermediate and final stage of the activated sintering is comparable to the Ni-induced recrystallization and grain growth of W-wire. The initial state of the nickel added will be a significant factor controlling the whole process of the activated sintering of W-powder compact. Also nickel diffuses quickly into W-wires through high diffusivity paths, inducing recrystallization at relatively low temperature