Effects of rare earth dopants on grain boundary bonding in alumina–silicon carbide composites

Effects of trace rare earth impurities on grain boundary bonding in Al2O3–5 vol.% SiC composites were investigated. It was found that doping of 800 ppm different rare-earth impurities (Y3+, Nd3+ and La3+) led to a fracture-mode change from transgranular in dopant-free composites to intergranular in rare-earth doped composites. The fracture toughness of rare-earth doped composites was higher than that of the composites without dopants, due to an increased crack deflection in doped composites caused by the intergranular fracture. Boundary chemistry analyses showed that rare-earth impurities and Si4+ ions both segregated at the Al2O3 grain boundaries and resulted in a weak grain boundary bonding.