Study on microstructure and high-temperature corrosion resistance to melt-salts of LDED High-Cr Ni-base alloy with low melting point

In view of the serious corrosion and wear failure of parts under harsh and high-temperature service conditions, low-melting nickel base alloy samples with different Cr content were prepared by laser directed energy deposition (LDED). The effects of Cr content on the microstructure and high-temperature corrosion resistance of the alloy were investigated. The microstructure of the alloy was analyzed by SEM, XRD and EPMA, and the relationship between the microstructure, hardness and resistance to high temperature molten salt corrosion was discussed. The results show that the microstructure of high Cr and low melting point nickel base alloy prepared by LDED is mainly composed of γ-Ni, CrB and Cr5B3. With the increase of Cr content, the boride content in the alloy increases correspondingly, and the coarse Cr5B3 phase changes from block to coarse strip gradually, The Daisy (γ-Ni+CrB) eutectic phase disappeared, and lamellar (γ-Ni+Cr5B3) eutectic phase appeared. The hardness of the alloy increases with the Cr content, reaching up to 360.8 HV, mainly due to the increase of matrix phase hardness and boride hard phase content. Compared with TP347H stainless steel, the new high Cr and low melting point nickel base alloy has better resistance to high temperature molten salt corrosion, with the increase of Cr content, the high temperature corrosion resistance of the alloy is obviously improved. Cr40 alloy samples show the best corrosion resistance, which is about 15 times higher than TP347H. During the high temperature corrosion process, a dense Cr-rich oxide film is formed on the alloy surface, which can effectively prevent the corrosion reaction from invading. On the other hand, Cr element can play the role of sulfur fixation, so that the high Cr low melting point nickel-based alloy shows excellent resistance to high temperature molten salt corrosion.