Investigation of the effect of solid solution formation on creep kinetics of high-refractory oxides during sintering

Abstract

1. The characteristics of creep kinetics were studied during the formation of solid solutions with stabilization of zirconia and in mixtures of spinel with corundum. 2. It is shown that during the formation of solid solutions (even after the completion of these processes) the diffusion activity of the system determining the increase of creep rate at the initial and secondary stages of the process is not necessary and does not always increase. 3. It was found that an increase of self-diffusion during formation of solid solutions is related with their multiphase character. 4. If the formation of solid solutions causes the appearance and development of an additional network of interphase boundaries (as occurs upon stabilization of zirconia by calcium oxide and yttria, and also by magnesia and ceria above certain concentrations of the latter), this apparently increases the diffusion due to an increase of the portion of boundary (interphase) diffusion and involves an increase of the creep rates at the primary and secondary stages of the process. In this case the maximum values of diffusion creep rates correspond to the maximum degree of inhomogeneity of the system and development of interphase boundries, i.e., ∼50% content of the phases (for example, cubic and monoclinic solid solutions). 5. If the formation of the solid solution is not accompanied by the appearance and development of new interphase boundaries (for example, upon stabilization of zirconia by magnesia or ceria up to certain concentrations of these additives, and upon solution of corundum in spinel), activation of diffusion processes determining an increase of creep rates does not occur. 6. It is shown that the established regularties have a common character and extend to creep of materials with a formed microstructure.