An internal synthesis method for mullite-chromium carbide composite in a vacuum system

Abstract

In situ formation of chromium carbide in a mullite matrix through reaction of Cr2O3, SiC and A2O3 has been studied. Three different chromium compounds, Cr3Si, Cr3C2, Cr7C3, and mullite were formed. In a vacuum environment, the Cr3Si particles formed first and were retained below 1550 °C, while the Cr7C3 phase was only dominant above 1600 °C. The Cr3C2 phase was the dominant dispersed phase at temperatures of 1450–1500 °C. In an argon environment, the Cr3C2 phase was the main product component at temperatures ranging from 1450 to 1550 °C. The mullite phase formed concurrently through the diffusion of the SiO2 phase into the Al2O3. SiO2 was the product of the reaction between Cr2O3 and SiC. The composite hot-pressed at 1450 °C in vacuum gave a flexural strength and fracture toughness of up to 457 MPa and 4.1 MPa m1/2, respectively.