The effect of SiO2 on high-temperature deformation and strength of zirconia-toughened alumina

At room temperature, SiO₂ additions may increase the fracture toughness, K _IC, by diminishing the tetragonal phase contents to about 50%, but with ground surfaces the influence on strength is small. A pronounced decrease in strength is observed with rising temperature in the high toughness region from 20°C to M _s, the starting temperature for martensitic transformation. Beyond M _s at lower toughness, the strength behaviour is very similar to nontransforming alumina ceramics, and an even modest increase of the silicate concentration intensively promotes propagation-controlled failure in the brittle creep region (> 900°C) and inelastic deformation. With less than 1% amorphous grain boundary phases, damage-free superplasticity is restricted to small strains of less than 10%. The significance of high-temperature data for tool applications is considered by cutting tests with high feeding rates.