Substrate grain boundary effect on residual stress distribution at micrometer scale in chromia oxide thin films

Residual stresses in chromia oxide films formed at 700 degrees C on NiCr30 have been investigated with confocal Raman spectroscopy. The high lateral resolution allows us to determine stress distribution in the oxide growing above both substrate grains and grain boundaries. It is demonstrated that the magnitude of the equibiaxial compressive stress is related to local oxide microstructure evolution: during the initial oxidation, stress is smaller in the chromia located above substrate grain boundaries as compared to that above substrate grains. Subsequently, this gap in stress magnitude progressively vanishes due to the occurrence of oxide grains forming bridges across depressions in the oxide scale above substrate grain boundaries. (C) 2008 American Institute of Physics.