Diffusion-Controlled Grain Growth in Liquid-Phase Sintering of W–Cu Nanocomposites

Abstract

Abstract The kinetics of W 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 theWatom diffusion process in liquid Cu. It was found that W 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 W 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 forWgrain growth decreased with decreasing volume fraction of the W 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 W 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 Watom solubility in liquid Cu, as well as atom diffusivity, is thought to be responsible for diffusion-controlled growth of W grains during LPS of W–Cu nanocomposite powder.