In situ determination of growth and thermal stresses in chromia scales formed on a ferritic stainless steel

International audienceIn situ Raman spectroscopy experiments have been performed to determine both growth and thermal stresses of chromia scales formed at 750°C in oxygen on a stabilized ferritic stainless steel Fe-18Cr-TiNb. The measured growth stresses were shown to be highly compressive, near - 2 GPa. Cooling down and reheating cycles under inert gas showed that the thermal stresses were slightly compressive when cooling down (- 0.2 GPa), and reversible when heating up, showing their perfect thermo-elastic origin. Measurements, with temperature changes, of the deflection of oxidized samples after removal of one side oxide confirmed the Raman measurements and allowed to derive the actual value of the thermal expansion coefficient of the oxide scale: αox = 10.75 × 10-6 K-1