Study on Y-Mg-Si alloy additives to improve the thermal conductivity of Si3N4 by efficient deoxygenation

Abstract

Using Y-Mg-Si alloy as a sintering additive, Si₃N₄ ceramics were prepared by hot-pressing sintering combined with atmospheric pressure heat treatment. The effects of alloy additive content on the densification, microstructure, thermal conductivity, and mechanical properties of hot-pressed sintered Si₃N₄ ceramics were studied. Si₃N₄ ceramics with a density greater than 96% can be prepared by hot-pressing sintering at 1750°C for 2 h with an alloy as a sintering additive. With the increase of additive content, the density increases first and then decreases, and the grain size increases gradually. By preferentially reacting with the inherent SiO₂ on the surface of Si₃N₄, the alloy additive improves the N/O ratio of the sintered liquid phase and reduces the effect of lattice oxygen on the thermal conductivity. Finally, the thermal conductivity of 52.7 W·m⁻¹·K⁻¹ was achieved at the content of 6 wt% alloy additive, which was 22% higher than that of 43.2 W·m⁻¹·K⁻¹ of pure oxide additive; It's hardness and fracture toughness are 16.1 GPa and 9.63 MPa·m^1/2, respectively. After heat treatment at 1850°C for 5 h, the thermal conductivity increased to 67.2 W·m⁻¹·K⁻¹. Using Y-Mg-Si alloy as a sintering additive is an effective method to prepare high strength and high thermal conductivity Si₃N₄ ceramics, which provides a new idea for the preparation of high thermal conductivity Si₃N₄ ceramics.