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

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 Cr 2 O 3 . However, owing to atomic diffusion, the oxide layer near the fusion line was in the follows order: Cr 2 O 3 , NiO, FeCr 2 O 4 and CoCr 2 O 4 . In addition, C atoms diffused into coatings during the oxidation process and were preferentially enriched near vacancies and grain boundary, forming Cr 23 C 6 particles that were coherent with matrix (FCC). Cr 23 C 6 phases hindered the outward diffusion of metal cations and oxygen ions into matrix. • The thermal oxidation behavior of CoCrNi coatings was investigated at 750 ℃. • The coherent relationship of Cr 23 C 6 and matrix (FCC) improves the oxidation resistance of CoCrNi coatings. • The Cr 23 C 6 surrounds the hole to grow, which hinders the outward diffusion of cations and oxygen ions into the matrix.