Ultrahigh high-strain-rate superplasticity in a nanostructured high-entropy alloy

Abstract

Superplasticity describes a material’s ability to sustain large plastic deformation in the form of a tensile elongation to over 400% of its original length, but is generally observed only at a low strain rate (~10⁻⁴ s⁻¹), which results in long processing times that are economically undesirable for mass production. Superplasticity at high strain rates in excess of 10⁻² s⁻¹, required for viable industry-scale application, has usually only been achieved in low-strength aluminium and magnesium alloys. Here, we present a superplastic elongation to 2000% of the original length at a high strain rate of 5 × 10⁻² s⁻¹ in an Al₉(CoCrFeMnNi)₉₁ (at%) high-entropy alloy nanostructured using high-pressure torsion. The high-pressure torsion induced grain refinement in the multi-phase alloy combined with limited grain growth during hot plastic deformation enables high strain rate superplasticity through grain boundary sliding accommodated by dislocation activity.

Superplasticity at high strain rates is challenging to achieve in high strength materials. Here, the authors show superplastic elongation in excess of 2000% in a high entropy alloy nanostructured by high-pressure torsion.