Shape Memory and Superelastic Properties Of Small-Scale Zirconia Ceramics

Ceramics are technologically interesting as shape memory materials because of their high transformation stresses and high operating temperatures. However they have received little research interest as shape memory materials due to intergranular cracking that leads to failure after only several load cycles.  Cracking happens as a means of accommodating the large transformation mismatch stresses between grains, and can be mitigated by reducing the sample size and controlling the grain size so that it is on the same order as the sample dimensions. This creates an “oligocrystalline” structure where each grain has access to a free surface, thereby alleviating internal stresses.  Micro-pillar compression tests were carried out on ceria-doped zirconia ceramics under both shape memory and superelastic conditions. Shape memory recovery was induced at 500°C with higher temperatures possible by controlling the dopant concentration. Superelastic results show transformation stresses of ~1500 MPa, recoverable compression strains up to 8%, and dozens of repeatable cycles measured.  The improved cyclic behavior opens up the possibility of robust shape memory ceramics that can be deployed in high temperature applications.