The Effect of Si₃N₄Addition on Nitriding and Post-Sintering Behavior of Silicon Powder Mixtures

Abstract

Nitriding and post-sintering behavior of powder mixture compacts were investigated. As mixture compacts are different from simple Si compacts, the fabrication of a sintered body with a mixture composition has engineering implications. In this research, in specimens without a pore former, the extent of nitridation increased with Si 3 N 4 content, while the highest extent of nitridation was measured in Si 3 N 4-free composition when a pore former was added. Large pores made from the thermal decomposition of the pore former collapsed, and they were filled with a reaction product, reaction-bonded silicon nitride (RBSN) in the Si 3 N 4-free specimen. On the other hand, pores from the decomposed pore former were retained in the Si 3 N 4-added specimen. Introduction of small Si 3 N 4 particles (d 50 = 0.3 µm) into a powder compact consisting of large silicon particles (d 50 = 7 µm) promoted close packing in the green body compact, and resulted in a stable strut structure after decomposition of the pore former. The local packing density of the strut structure depends on silicon to Si 3 N 4 size ratio and affected both nitriding reaction kinetics and microstructure in the post-sintered body.