In situ Raman monitoring of chromium oxide scale growth for stress determination

Raman spectra of a growing chromia(Cr2O3) layer generated by oxidation of pure chromium at 730 degreesC under 150 mbar of oxygen were recorded in situ every 5 min. The wavenumber evolution of the main Raman band versus oxidation time was interpreted in terms of mechanical stress development. Comparison with Raman spectra of a fully relaxed spalled chromia layer submitted to high-pressure and high-temperature treatments showed that internal compressive stresses develop during the growth, varying from -2.1 GPa when the scale is very thin to -2.4 GPa when the scale reaches a thickness of 0.6 mum. Relaxation phenomena seem to take place during isothermal oxidation. During cooling, thermal stresses are induced, which are purely elastic according to the perfect reversibility of cooling-heating cycles. Copyright (C) 2001 John Wiley & Sons, Ltd.