Role of grain boundaries in sintering

Abstract

The effect of the presence of grain boundaries on the sintering rate was investigated by measuring the growth of necks between three twisted wires as a function of time and temperature. It was found that, in the presence as well as absence of the grain boundary in the neck, volume diffusion controls the process. The measured rate of neck growth was in good agreement with that calculated from the theory. The rate of approach of centers of wires was also studied. In the absence of grain boundaries no approach of centers was observed. In the presence of grain boundaries, the centers did approach at a rate which was measured. This study allowed distinction between grain boundary and surface sinks of vacancies during sintering; in the absence of grain boundaries, the diffusion flux of vacancies is from the region just beneath the neck to the adjacent free surface; in the presence of grain boundaries, vacancies migrate from the region just beneath the neck to the grain boundary.