Thermal oxidation behavior of CoCrNi medium-entropy alloy bond coatings deposited using laser cladding process

Abstract The thermal oxidation behavior of CoCrNi coatings was investigated over different oxidation time at 750 ℃. Microstructure of oxide layers was analyzed in different regions. HR-TEM observation proved that the oxide layer mainly composed of Cr2O3. However, owing to atomic diffusion, the oxide layer near the fusion line was in the follows order: Cr2O3, NiO, FeCr2O4 and CoCr2O4. In addition, C atoms diffused into coatings during the oxidation process and were preferentially enriched near vacancies and grain boundary, forming Cr23C6 particles that were coherent with matrix (FCC). Cr23C6 phases hindered the outward diffusion of metal cations and oxygen ions into matrix.