Transformation induced plasticity in ceramics

Transformation induced plasticity was investigated in a model ceramic. The effect upon toughness of the martensitic transformation from the cubic (paraelectric) to the tetragonal ( ferroelectric) phase in BaTiO3 was determined. The K1C fracture toughness, as measured by the hardness indentation technique, exhibits a maximum within a temperature range approximately 50°C above the stress-free transformation temperature. Unlike the martensitic transformation associated with partially stabilized zirconia, there is no volume change during the cubic-to-tetragonal phase change in BaTi03. In addition, no evidence of microcracking was observed. The enhanced toughness in the vicinity of the transition temperature was attributed to limited plasticity at crack tips provided by the transformation shear strains. The effective strains at the crack tips required to produce the observed fracture toughness values are consistent with transformation strains calculated using the phenomenological theory of martensite.