Microstructure influence on residual stresses in growing chromia oxide films as determined by in situ high temperature Raman spectroscopy

In this work, 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°C-900°C]. The low acquisition time necessary to obtain a Raman spectrum allows to follow the chromia growth kinetic with sufficient accuracy. It is demonstrated that the growth stress in such oxide films can attain more than 2 GPa, before additional thermal stress arises on cooling. Moreover, the growth stress kinetic - subsequent establishment and relaxation - are highly microstructure sensitive: in particular, as the oxidation temperature rises, the chromia grain size also increases, and it consequently retards the occurrence of the creep relaxation phenomena which needs an additional stress to start