Growth stresses in α-Cr2O3 thermal oxide films determined by <i>in situ</i> high temperature Raman spectroscopy

Abstract

Growth stresses have been investigated in relation with the microstructure in the case of α-Cr2O3 growing oxide films on NiCr30 alloy. The equibiaxial growth stresses have been measured thanks to a technique coupling Raman spectroscopy and in situ high temperature oxidation of the NiCr30 alloy in the temperature range (700−900 °C). It is established that the compressive growth stress in such oxide films can reach more than 2 GPa, before additional thermal stress arises on cooling. Moreover, the growth stress kinetics—subsequent establishment and relaxation—are highly microstructure sensitive: in particular, as the oxidation temperature rises, the chromia mean grain size also increases, and it consequently retards the occurrence of the creep relaxation phenomena which needs an additional stress level to start.