Microstructural characterization of Ni-201 weld cladding onto 304 stainless steel

Ni-201(ERNi-1), a cladding layer which is resistant to the corrosion of molten salts, was deposited on 304SS substrate by Gas Tungsten Arc Welding (GTAW). Microstructure characterization showed that the cladding interface was obviously divided into three zones from microstructures along depth, weld metal (WM), unmixed zone (UZ) and heat affected zone (HAZ). Element distribution presented that elements Ti, N, Si were segregated into interdendritic region of WM and formed the TiN precipitates during the solidification. The element distribution of UZ was similar to that of HAZ. A large quantity of vermicular delta-ferrite phases were precipitated in laminar UZ. Grain coarsening in HAZ was evident compared with the grains in base metal, and no precipitates were found in HAZ. The hardness of cladding layers was decreased from interface to surface. The cladding layer exhibited excellent corrosion resistance to molten FLiNaK salts.