Effect of friction stir welding on the structure and mechanical properties of the CoCrFeNiMn-0.9%C alloy

CoCrFeNiMn-0.9%C high entropy alloy (HEA) was produced by self-propagating high-temperature synthesis. The as-sintered alloy was cold rolled and annealed at 900°C to produce refined microstructure before friction stir welding (FSW). The structure of the annealed alloy consisted of a recrystallized face-centered cubic (fcc) matrix with a grain size of 9.2 µm and fine M23C6 carbides with 2% volume fraction. Good quality of butt joints after FSW was observed. It was established that an increase of the tool rotation speed from 600 to 1000 rpm increased the average grain size from 3.2±0.7 µm to 4.6±2.4 µm, respectively. The structure of the stir zone contained M23C6 carbides in all conditions. Hardness and strength of the joints decreased with the increase of tool rotation speed due to higher grain size, while ductility increased.