Superior-tensile property of CoCrFeMnNi alloys achieved using friction-stir welding for cryogenic applications

Abstract

The friction-stir weld (FSW) was investigated based on the relationship between microstructural and mechanical properties at room and cryogenic temperatures for rolled and cast Co0.2Cr0.2Fe0.2Mn0.2Ni0.2 high entropy alloys (HEAs). The rolled and cast HEA welds exhibited good weldability without welding defects. The grain size (GS) of the stir zone (SZ) for rolled and cast HEAs was smaller than that of the base metal (BM). The W, Cr, and C particles caused by the wear of the WC-Co tool formed fine M23C6 carbides, due to the heat generated during the FSW, and accelerated the recrystallization via the particle stimulated nucleation (PSN) effect. Therefore, the area with M23C6 carbide exhibited a finer grain size compared with the area without M23C6 carbide. The rolled HEA was fractured in the SZ owing to the thinning phenomenon, and the cast HEA was fractured in the BM owing to the GS of the SZ, which was much finer than the GS of the BM. However, both HEA welds had larger room temperature strength than BM, and the cryogenic strength was also improved owing to the primary twin, secondary twin, and tangled dislocation. The PSN effect due to the carbides contributed to the increase in strength. Therefore, the FSW of the rolled and cast HEAs produced in this study is suitable for cryogenic applications.