Shape memory behaviour in partially stabilized zirconia ceramics

Abstract

Shape memory behaviour has been observed in a variety of metallic alloys. It is usually associated with specific materials which on being deformed to various degrees of inelastic strain, return to their original shape on heating. The essential requirement is that they undergo reversible martensitic (diffusionless) phase transformations on heating and cooling. The past decade has seen considerable scientific and technological interest in ceramics containing zirconia (ZrO₂), a material that exhibits such martensitic transformations. This interest has arisen because of the high strengths and toughness that can be achieved in such materials by a stress-induced volume-expanding phase transformation about the crack tip¹. Observations are reported here of shape memory behaviour in a zirconia alloy partially stabilized with magnesia, at temperatures a few hundred degrees higher than reported for metallic alloys. The reversible deformation strains are relatively small, 0.5%, and are limited by the brittleness of the ceramic material. In the MgO–PSZ material the phase exhibiting the martensitic behaviour is the minor phase and occurs as precipitates in a stable matrix.