Effect of Ti-Si-Fe alloy on the nitriding behavior of Si powder

Abstract

Adding Ti-Si-Fe alloy to Si powder reduced the complete nitriding temperature of Si from 1450 °C to 1300 °C, greatly reducing the nitriding temperature of Si powder and the formation temperature of Si3N4 whiskers. At low temperature, Fe in Ti-Si-Fe alloy damaged the SiO2 film on the surface of Si and produced SiO (g), which was conducive for the indirect and direct nitridation of Si. The density functional theory (DFT) calculation results showed that the energy levels of SiO (g) molecules adsorbed by Fe broadened and moved towards lower energy levels, resulting in a decrease in the bonding strength and an increase in reaction activity of SiO (g) molecules. It was beneficial for the indirect nitridation reaction of 3SiO (g)+2N2 (g)=Si3N4 (s)+3/2O2 (g), and promoted the formation of α-Si3N4 whisker. The liquid phase formed by increasing temperature and Ti-Si-Fe alloy addition promoted the direct nitridation of Si. The activation energy of TiSi2 and Ti-Si-Fe alloy nitridation was 78.42 (KJ/mol) and 14.97 (KJ/mol), respectively. The nitridation of Ti-Si-Fe alloy was easier, and the pores and cracks generated by Ti5Si3 and TiSi2 step-by-step nitridation at low temperature in Ti-Si-Fe alloy provided pore channels for N2 transport and sufficient nitrogen for Si nitridation.