Optimization of Si3n4 Fiber and Bn Interface for High Mechanical Properties and Thermal-Shock Resistance of Si3n4/Bn Composites

Abstract

This work demonstrates a strategic approach to enhance the thermomechanical performance of Si3N4/BN composites through interface optimization and granulometric control. By tailoring the MgO sintering additive at BN interfaces coupled with 0.5 μm Si3N4 fiber precursor, we achieved full densification with concurrent mechanical strengthening - attaining a density of 3.19 g·cm-3, remarkable flexural strength of 627.36 MPa, and fracture toughness of 13.48 MPa·m1/2. The composites exhibit exceptional thermal shock resistance, retaining 586.19 MPa (93.44% retention) after 1000 ℃ thermal shocking, facilitated by in situ formation of a continuous SiO2 glass barrier that effectively passivates oxidation pathways. Intriguingly, residual strength evolution reveals a distinctive two-stage response: an initial decline followed by strength recovery at extreme thermal gradients. At ΔT=1500 ℃, the composite maintains the residual strength of 469.46 MPa (74.83% retention), outperforming conventional monolithic ceramics through a self-healing mechanism enabled by viscous flow of the glass phase. Microstructural evolution analysis coupled with fractography studies establishes direct correlations between the interface architecture, mechanical properties, and thermal-shock resistance. These findings provide fundamental insights into designing composites with excellent thermal-shock resistance for ultrahigh-temperature structural applications.

Keywords: Sintering additives, Si3N4/BN composites, mechanical properties, Thermal shock resistance, Residual strength.