Operation of solute-drag creep in an AlCoCrFeMnNi high-entropy alloy and enhanced hot workability

Abstract

Strong evidence for creep controlled by solute-drag processes, such as the yield-drop phenomenon, a stress exponent of 3 and a sluggish tendency to form subgrains, was found during hot compressive deformation of a cast BCC AlCoCrFeMnNi high-entropy alloy with coarse grains; these characteristics are typically observed in conventional metals that exhibit solute-drag creep. These three features were not observed in the FCC CoCrFeMnNi alloy with coarse grains, indicating that the addition of aluminum causes solute-drag creep to arise as the rate-controlling deformation mechanism. Compared with the FCC Al0.5CoCrFeMnNi matrix (with a small amount of BCC phase), the AlCoCrFeMnNi exhibited more distinct characteristics of solute-drag creep. This is likely because the Al concentration in the matrix of AlCoCrFeMnNi is notably higher than that in the matrix of Al0.5CoCrFeMnNi (17.8 vs. 6.5 at.%). Also, the solute-drag creep extended to an increased strain rate and a decreased temperature in AlCoCrFeMnNi because the critical stress for dislocations to break away from the solute atmospheres increases as the Al solute concentration in the matrix increases. This outcome improves hot workability of AlCoCrFeMnNi according to the processing maps because the power dissipation efficiency increases and the flow instability regime shrinks at high strain rates and low temperatures.