Gas tungsten arc welding of CoCrFeMnNi high entropy alloy to 316 stainless steel

In this study, an as-annealed CoCrFeMnNi high entropy alloy (HEA) was successfully gas tungsten arc-welded (GTA-welded) to 316 stainless steel, resulting in a fully penetrated joint and free of visible macroscopic defects. In the heat-affected zone (HAZ) on the 316 stainless steel side, a phase transformation from δ-BCC to σ phase was detected. On the CoCrFeMnNi side, the base material (BM) primarily exhibited an FCC matrix phase, with a slight increase in Cr-Mn oxide content upon entering the HAZ. The formation of the BCC phase in the fusion zone (FZ) was mainly attributed to the mixing of Fe from the 316 stainless steel. This region exhibited the highest hardness, resulting from a combination of factors, including the BCC precipitates and minor incorporation of carbon introduced within the FZ, further aided by solid solution strengthening due to BMs mixing, but solid solution strengthening is the key factor. The BMs and the adjacent HAZs displayed highly similar equiaxed grain structure and size, and the hardness distributions, making it difficult to distinguish each region. However, the evolution of interplanar spacing obtained through synchrotron X-ray radiation effectively differentiated the various regions of the joint. Tensile testing revealed that the strength and hardness of this dissimilar joint were lower than those of both BMs, yet it still shows potential for structural applications. The fracture site of the joint occurred in the HAZ on the 316 stainless steel side, primarily due to the combined effects of localized large plastic deformation in the soft region and stress concentration caused by the presence of σ phase.