Enhancement of tensile properties of gas tungsten arc welds using Cu-coated CoCrFeMnNi filler and post-weld heat treatment

This study investigated the gas tungsten arc (GTA) weldability of cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) using Cu-coated HEA filler, specifically through the application of various post-weld heat treatment (PWHT) temperatures. The GTA weldability of cold -rolled HEA was evaluated by applying the optimum condition of full penetration, and the effect of PWHT was investigated in the temperature range of 973-1173 K. No macro-defects were detected in the weld metal (WM) to which the Cu coated HEA filler was applied. All the PWHT-applied specimens, including the as-welded specimens, were composed of the FCC phase. The Cu component was solid-solutionized over the entire area of the WM and did not form a precipitate. The tensile properties of the as-welded specimens deteriorated in the presence of CrMn oxides. As the PWHT temperature increased, the grain size in the base metal (BM) increased and inclusions in the WM were re-dissolved. Furthermore, by increasing the PWHT temperature, the hardness of the BM decreased significantly by grain growth, and the WM softened slightly owing to the re-dissolution of inclusions. Therefore, the WMs improved the tensile strength and elongation with increasing PWHT temperature. The application of PWHT significantly improved the weldability of the Cu coated CoCrFeMnNi welds.