Influence of thermal exposure on the stability of metastable microstructures of sputter deposited nanocrystalline 304 and 310 stainless steel coatings

The effect of thermal exposure on the stability of the microstructures of magnetron sputter deposited 304 and 310 stainless steel (SS) coatings have been investigated. The coated 304SS samples were exposed to thermal cycling between 750 °C and room temperature and aged at 500 °C and 650 °C. X-ray diffraction (XRD) results revealed that the microstructures of the as-deposited 304SS and 310SS coatings consisted of αFe + σ and γFe + αFe, respectively. Thermal exposure at 500 °C and 650 °C resulted in the dissolution of σ and partial transformation of αFe into γFe in the 304SS coating and led to the precipitation of σ phase particles, at the expense of αFe, in the 310SS coating. The amount of σ phase in the 310SS coating increased with exposure time. However, both coatings showed no σ phase after thermal cycling to 750 °C for approximately 500 cycles.