Residual stresses in high-temperature ceramic eutectics

This paper explores residual thermal stresses in directionally solidified c eramic eutectics, a class of materials that has much promise for high-tempe rature structural applications. Residual strain tensors of both phases in a eutectic composite are measured by single crystal X-ray diffraction techni ques. In the analysis the material is treated as fully anisotropic and the strain tensors, subsequently converted to stress tensors, are measured Resu lts are presented for two oxide eutectics, NiO-cubic ZrO2 and YAG-Al2O3, th e former having a large thermal expansion mismatch between the two phases a nd the latter having similar thermal expansion properties. It is discovered that large residual stresses (of the order of 1 GPa) can be present at roo m temperature in as-processed eutectic materials unless the thermal expansi on behaviors of the constituent materials are very similar. Ultimately thes e measurements not only elucidate the stress state but, when compared to th eory, give information about the degree of interfacial constraint between t he two phases. (C) 1999 Elsevier Science Ltd. All rights reserved.