Role of Second Phase Powders on Microstructural Evolution During Sintering

The influence of second phase fine powders on solid state sintering was investigated in situ by synchrotron radiation X-ray computed tomography (SR-CT). The evolutions of microstructure during sintering of pure SiO2 powders and SiO2 powders mixed with Si3N4 powders were observed from reconstructed SR-CT images. Typical sintering parameters, which determine mechanical properties, were extracted from the experimental data, and the effects of the second phase powders were quantitatively analyzed. The experimental results showed that with second phase powders, 1) the specific surface area decreases more efficiently; 2) pore shape evolution is accelerated; 3) sintering necks grow faster and 4) densification process is notably accelerated. It was indicated that the Si3N4 fine powders enhanced the sintering of the original SiO2 powders rather than hindering the process. A qualitative explanation based on the experimental results and existing powder sintering theory is provided.