Tensile properties and microstructure evolution during two-stage tensile testing of CoCrFeMnNi high-entropy alloy

The tensile properties of a CoCrFeMnNi high-entropy alloy, obtained by isothermal tensile testing and two-stage non-isothermal tensile testing, were compared. During the two-stage tensile testing, a tensile sample with the as-cast microstructure was loaded at 22 degrees C up to a strain level of 15%. Subsequently, the tensile specimen was re-loaded until it fractured at 500 degrees C and 700 degrees C. Formation of several steps was observed at the point where grain boundaries and deformation twin boundaries intersect after the two-stage tensile testing at 500 degrees C. The local deformation at the steps results in the fragmentation of the twin lamellae grains, which leads to the formation of an ultra-fine-grain structure. A high density of deformation twins was detected inside the ultra-fine grains. Furthermore, the grain fragmentation mechanism is discussed. (C) 2020 The Author(s). Published by Elsevier B.V.