CHEMICALLY-INDUCED INSTABILITY AT INTERFACES OF CUBIC ZRO2-Y2O3 GRAINS IN A LIQUID MATRIX

The grain boundary migration, grain surface corrugation, and recrystallization occur in cubic 90ZrO2-10Y2O3 (mol%) grains in a liquid CuO-rich matrix when MgO and Y2O3 are added. When a powder mixture of 50(90ZrO2-10Y2O3)-50CuO is sintered at 1450-degrees-C, spherical grains of cubic Y2O3-stabilized ZrO2 form in a CuO-rich liquid matrix. The specimen is heat-treated again after adding MgO and Y2O3, which are, respectively, expected to produce tensile and compressive diffusional stresses, at varying concentration ratios to the liquid matrix. At a low MgO to Y2O3 concentration ratio, grain boundary migration and surface corrugation occur with the coherency strain estimated to be compressive. When the MgO to Y2O3 ratio is slightly increased, no change occurs at the interfaces with the coherency strain estimated to be very small. When the MgO to Y2O3 ratio is increased much, the grain boundary migration and surface corrugation occur again with an estimated tensile strain. When the MgO to Y2O3 ratio is increased further, recrystallization occurs with the lattice parameter change estimated to be relatively large. These observations are essentially identical to those observed in Mo-Ni alloy and show that the driving force arises from the size misfit between the solvent and solute ions. The space charge effect which can be present at the boundaries appears to be negligible in this oxide system.