Effect of heat treatments on microstructure and corrosion resistance of laser-cladded Inconel 625 coatings

The influence of post weld heat treatment (PWHT) temperatures on the microstructure and corrosion resistance of laser cladded Inconel 625 coatings was investigated. The elements composition test indicates that the content of Fe changes sharply in the fusion zone between the coating and substrate, as well as overlap zone of coating layers. The microstructure observation shows that as welded Inconel 625 coating is mainly composed of columnar γ-Ni, Laves and seldom MC. The size of dendrites show an increase tendency with an increase in PWHT temperatures. There is no obvious difference in precipitates of the coating heat treated at 650℃ compared with the as welded. After heat treated at 750°C, a small amount of needle shaped δ phase precipitates. With a further increase in PWHT temperatures, a large number and continuous of δ phase forms, while the overall amount of δ phase seems to decrease when heat treated at 950°C. Electrochemical tests indicate that the ( R t ), self corrosion potential ( E corr ), and pitting potential ( E pit ) show increase tendency, while self corrosion density ( I corr ) shows opposite trend with an increase in PWHT temperatures less than 750℃. When the temperatures are larger than 850℃, R t , E corr and E pit decrease, while I corr increase. It is concluded that heat treated at temperatures not exceed 750℃ are benifit to improve resistance to initiate corrosion, uniform corrosion, and pitting.