Interfacial phase transformation and element diffusion mechanism of high-speed laser cladding Inconel 625 in high-temperature environment

It is essential to reveal the phase transformation and element diffusion mechanism at the interface between the Inconel 625 coating prepared by high-speed laser cladding and the Q245R substrate to meet the requirement of high-temperature service environment. A banded area formed at the bottom of the laser cladding layer after being heated at 700 °C. The banded area thickened as the duration of high-temperature treatment increased. The cellular and columnar crystals in the banded area were not visible. Laves phase at the banded area dissolved, and M23C6 precipitated and accumulated significantly. The main reasons for phase transformation in the banded area could be attributed to C diffusion from the substrate to the laser cladding layer. Additionally, the lamellar structure contained α-Fe and Fe3C, which formed in the substrate beneath the interface due to the C enrichment at the interface. Simultaneously, element diffusion and phase transformation led to the increase of lattice misfit, dislocations, and vacancies at the interface. Ultimately, element diffusion and phase transformation led to an increase in the microhardness at the bottom of the laser cladding layer and a decrease in the microhardness at the heat affect zone.