Tensile properties of low-stacking fault energy high-entropy alloys

An equiatomic NiFeCrCoMn alloy, two non-equiatomic NiFeCrCoMn alloys optimized for low stacking fault energy, and an equiatomic NiFeCrCo alloy were produced by arc melting. Samples were homogenized, cold rolled, and annealed at temperatures between 575 and 1100 degrees C. Samples annealed at a moderate temperature near their recrystallization temperature (625-675 C) and 1100 degrees C were cut into flat tensile samples and tested at a strain rate of 7.3 x 10(-4) s(-1). Equiatomic NiFeCrCo had the highest ductility and toughness after annealing at both temperatures, followed by Ni18.5Fe18.5Cr15.5Co26Mn18.5. Ni14Fe20Cr26Co20Mn20 exhibited poor thermal stability, forming a-phase intermetallics at temperatures below 1100 degrees C. Observation of the fracture surfaces suggested that the high performance of NiFeCrCo might be due to the absence of oxide particles that form in the Mn-containing alloys. The strain-hardening rate and exponent were calculated from the results, showing a large deviation from typical behavior and significant grain size dependence. (C) 2015 Elsevier B.V. All rights reserved.