Fracture-mode change in alumina-silicon carbide composites doped with rare-earth impurities

Al2O3-5 vol% SiC particle composites doped with 800 ppm rare-earth impurities (Y3+, Nd3+, and La3+) were fabricated by hot-pressing at a temperature of 1550degreesC. Doping of rare-earth impurities in Al2O3-SiC composites led to a fracture-mode change from transgranular in dopant-free composites to intergranular in rare-earth-doped composites. The fracture mode change obviously increased the crack deflection so that the fracture toughness of rare-earth-doped composites was higher than that of the composites without dopants, especially for the Nd3+- and La3+-doped composites. It was found that the fracture-mode change originated from a weak grain-boundary bonding caused by co-segregation of the rare-earth dopants and Si4+ ions dissolved from the SiC particle surfaces.