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

Growth stresses have been investigated in relation with the microstructure in the case of alpha-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 degrees 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. (C) 2007 American Institute of Physics.