High Strain Rate Superplastic Flow and Fracture Characteristics of a Fine-Grained Eutectic High Entropy Alloy

A fine-grained micro-duplex AlCoCrFeNi2.1 eutectic high entropy alloy exhibited high strain rate superplasticity with an elongation to failure of similar to 960 pct at 1173 K and a strain rate of 10(-1) s(-1). Optimum superplasticity was associated with a strain rate sensitivity of similar to 0.5, and there were transitions to non-superplastic flow with strain rate sensitivities of < 0.5 at both low and high strain rates. Superplasticity is attributed to grain boundary sliding with the observed retention of an equiaxed grain morphology, with some grain growth. Cavities with dimensions in the range of 1 to 5 mu m were observed in specimens pulled to failure. Although analysis revealed that cavity nucleation is likely under the experimental conditions, cavity growth was slow because of control by a plasticity growth rate that was proportional to the cavity size. [GRAPHICS] .