Ordering and Plastic Deformation in Zirconia Based Ceramics

摘要

Various aspects of phase transformations and deformation of Xr02-CaO and ZrO2-Y2O3 ceramics have been studied. The kinetics of precipitation of both tetragonal (t-Zr02) and CaZr409 (Phi 1) from cubic Zr02-CaO solid solutions have been studied. The precipitation and growth of the precipitates proceed by nucleation and growth and quantitative analysis shows good agreement with data on diffusion rates and interfacial energies. Phi 1 is found to be metastable with respect to Phi2-Ca6Zr19044 after aging. Phi 2 has much higher coherency strains than Phi 1. Plastic deformation of single crystals of Zr02-CaO has been studied at high temperatures. The primary slip system is (001)<110> and the secondary system is (111)<110>. Both hypo- and hypereutectoid compositions showed precipitation hardening when aged. Dislocation substructures have been examined by transmission electron microscopy and observations include channels devoid of precipitates which are induced to dissolve by dislocation motion. Zr02-Y203 has also been studied for comparison. Single crystals are found to be almost 100% tetragonal; this metastable t' phase has a higher Y203 content than the normal t phase and is believed to form by a massive transformation from the cubic phase. Annealing causes the T7 to decompose into colonies of two t variants plus cubic. (Author)