Microstructure and high temperature mechanical properties of liquid-phase-sintered $\alpha$-SiC with Y$_2$O$_3$-Al$_2$O$_3$ additions

Abstract

Samples of $\alpha$-SiC have been sintered with liquid phase (LPS) to 1950 $^\circ$C, in atmosphere of argon and processing times between 1 and 7 hours. Using scanning electron microscopy (SEM) the microstructure of the samples has been characterized, being obtained average grain size that grows with the processing time from 0.64 to 1.61 $\mu$m. These samples have been deformed in compression under constant load, to temperatures between 1450 and 1625 C, stresses between 25 and 450 MPa and strain rate between $4.2\times 10^{-8}$ and $1.5\times 10^{-6}$ s$^{-1}$. The creep parameters have been determined, obtaining for n values between 2.4 0.1 and 4.5 0.2 and Q=680 35 kJ.mol$^{-1}$ in samples sintered during 1 hour and n between 1.2 0.1 and 2.4 0.1 and Q=710 90 kJ.mol$^{-1}$ for samples sintered during 7 hours. These results have been correlated with the microstructure, being the grain boundary sliding (GBS) accommodated by lattice diffusion and the movement of dislocations the possible deformation mechanisms, operating both in a simultaneous way.