Evolution of the microstructure in a W alloy during sintering before the formation of a liquid phase

Partial densification in W-based alloy sintering occurs before liquid phase formation by solid phase diffusion. During this step W diffuses in the second phase and tungsten grains connect between them to constitute a skeleton. A dilatometric study permits to follow the shrinkage during heating. The second phase, a Ni-based alloy NiFeCo, forms with tungsten a NiFeCoW alloy. The structure is that of nickel and the lattice parameter increases with increasing W content. Sintering tests are made from 500°C to 1,400°C to know the solid phase range of W during liquid phase sintering. Limits of W% are determined until 1,400°C and are used to define the diffusion temperature range. The observation of fracture surfaces gives the evolution of the microstructure during the sintering and can be correlated to diffusion results.