New Mechanism for Toughening Ceramic Materials

Abstract : A 14 month study by Ceramatec, with a subcontract to the University of Utah, was initiated in order to determine if ferroelastic switching contributes to toughening in ceramic materials. Domain switching in ZrO2 single crystals (heat treated to minimize transformation) at 1400 C was used to show that ferroelastic switching is a process which occurs at temperatures in excess of the monoclinic to tetragonal transformation temperature. These data, coupled with fracture toughness measurements of 8 MPa.m 1.2 at 1000 C, show that ferroelastic toughening has the potential for toughening at temperatures in excess of that possible by transformation toughening. Experiments on PZT, SrZrO3 and Gd2 (MoO4) 3 were used to show that ferroelastic switching can contribute to toughening. The time dependence of switching was demonstrated using PZT ceramics. Dopants were added to polycrystalline TZP materials in order to substantially increase their fracture toughness. In the case of SrO additions, strontium aluminate platelets, formed in-situ during sintering, contributed to toughness. Keywords: Zirconium oxides, Ceramic materials, Polycrystalline lead Zirconate titanate, (P2T, Tetragonial Zirconate Polycrystalline, (T2P).