High temperature compliance test: A new methodology to characterize visco-elastic, anelastic and plastic behaviour

High temperature compliance testing in four-point bending geometry were performed at various temperatures in air to understand visco-elastic behaviour of SiC ceramics sintered with R2O3–AlN (R = Y, Lu) and YAG–AlN additives. The stiffness, calculated from the slope of the loading–unloading curve, essentially characterises the elastic and fast recoverable anelastic components of the material's behaviour. The slow anelastic and plastic behaviour can be determined from the loop area. Excellent visco-elastic behaviour were observed for SiC sintered with Lu2O3–AlN additives as compared to that of with Y2O3–AlN or commercial SiC (Eka-SiC T). Substitution of Y3+ by Lu3+ modifies the grain boundary composition and thickness which governs the high temperature mechanical behaviour. HRTEM investigation on grain-boundary elucidate the property-microstructure correlation.