Diffusion-controlled grain growth in liquid-phase sintering of W-Cu nanocomposites

The kinetics of IN grain growth during liquid-phase sintering (LPS) of W-15-25 wt.% Cu nanocomposite powder compacts was investigated in terms of microstructural development as well as the IN atom diffusion process in liquid Cu. It was found that IN grains grew rapidly while maintaining a round shape during LPS at 1623 K, being inversely proportional to the Cu matrix contents. This indicates that the diffusion-controlled Ostwald ripening (DOR) mechanism dominates the growth process in W-Cu nanocomposites. The result of this investigation on the kinetics of IN grain growth definitely identifies the occurrence of DOR growth. Namely, the time exponent of the growth equation was close to the value of 3 and the kinetic constant for IN grain growth decreased with decreasing volume fraction of the IN solid phase. This is basically due to the fact that the increase of a liquid matrix lengthens the diffusion path, as a result decreasing the growth rate. The diffusivity of the IN atoms in liquid copper was calculated from the growth kinetics to be lower within an order of magnitude than the self-diffusion of the liquid atoms. The presence of IN atom solubility in liquid Cu, as well as atom diffusivity, is thought to be responsible for diffusion-controlled growth of IN grains during LPS of W-Cu nanocomposite powder.