Effect of medium temperature precipitation phase and Mn element diffusion mechanism on high temperature oxidation process of repair and remanufacture CoCrFeMnNi high-entropy alloy cladding

Abstract

In order to study the effect of medium temperature precipitation phase and Mn element diffusion mechanism on the high temperature oxidation resistance of CoCrFeMnNi high-entropy alloy cladding layer, the high-entropy alloy cladding layers were prepared on Q235 substrate by micro-plasma arc process, which were annealed at different temperatures in atmosphere, and then subjected to high temperature oxidation at 900 °C for 100 h. Although the results showed that the microstructure of CoCrFeMnNi high-entropy alloy cladding layer was dendritic structure, the content of Fe, Co and Cr in dendrites was higher, while the content of Ni and Mn among dendrites was higher rather than the generally uniform elements compositions. As the annealing temperature increased, the crystal size in the layer grew slightly. The cladding layer of unannealed and annealed at 900 °C and 1160 °C for 4 h was a single FCC phase structure. However, the annealing cladding layer at 500 °C showed a small amount of Cr-rich BCC phase at the grain boundary, and the 700 °C annealing cladding layer appeared Cr–Fe-rich δ phase at the grain boundary. The alloy cladding layer annealed at different temperatures was subjected to high temperature oxidation experiments at 900 °C for 100 h. The oxidation kinetics curve was parabolic, the diffusion of Mn element controlled the entire oxidation process. The Mn element diffused faster than the other metal cations in the Cr2O3 oxide film and the grain boundary of the matrix, forming an intimate oxide film on the surface and a pore layer depleted in Cr and Mn at an interface portion between the substrate and the oxide film. With the increase of annealing temperature, the grain boundary effect and the interface of Cr and Mn were more favorable for the outward diffusion of Mn element, which formed an intimate oxide film, leading to the gradual severity of oxidation.