Microstructure, hardness, and fracture toughness evolution of hot-pressed SiC/Si3N4 nano/micro composite after high-temperature treatment

Abstract

Abstract The grain boundary phases in SiC/Si3N4 nano/micro-composite changes with time of high temperature treatment at 1750°C in nitrogen atmosphere. Stable phases were obtained after 26 hours of annealing. Moreover, the average grain diameter distribution was significantly changed. The hardness and fracture toughness of the SiC/Si3N4 nano/micro-composites decreased with the duration of the high-temperature treatment. Both findings can be explained by the different secondary crystalline phases formed during the high-temperature treatment. Phases Si2N2O, Y2SiO5, and Y2Si2O7, typical for the samples treated up to 4 h, were replaced by the YNSiO2 phase in the samples treated longer than 26 h. Anisotropy of the measured mechanical properties in different sample cross-sections caused by the Si3N4 grain alignment become negligible after long term high-temperature treatment.