Microstructure, interfaces and creep behaviour of Al2O3–Sm2O3 (ZrO2) eutectic ceramic composites

Abstract

New compositions in the melt-grown eutectic ceramics field are investigated for thermomechanical applications. This paper is focused on the Al2O3–Sm2O3–(ZrO2) system. The studied compositions give rise to interconnected microstructures without anisotropy along the growth direction. At variance with the binary eutectic Al2O3–SmAlO3, the homogeneity of the microstructure of the Al2O3–SmAlO3–ZrO2 ternary eutectic is less sensitive to the growth rate. Interfaces between the alumina and perovskite phases are investigated by high-resolution transmission electron microscopy (TEM). They are semi-coherent. In stepped interfaces, the facets are parallel to dense planes of each phase. The steps have a dislocation character and may accommodate both misfits. The ternary eutectic displays a very good creep behaviour with strain rates very close to those obtained on other previously studied eutectics in the Al2O3–RE2O3(RE = Y, Gd, Er)–ZrO2 systems. The deformation micromechanisms are analysed by TEM in the three eutectic phases. After creep, dislocations are present in every phase. The activation of unusual slip systems (pyramidal slip in the alumina phase) shows that high local stresses can be reached. The presence of dislocation networks with low energy configurations is consistent with predominance of dislocation climb processes controlled by bulk diffusion.