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

Nhung Thi-Cam Nguyen,Alireza Zargaran,Praveen Sathiyamoorthi,Hyoung Seop Kim,Peyman Asghari-Rad,Chong Soo Lee

doi:10.1038/s41467-020-16601-1

Nhung Thi-Cam Nguyen, Alireza Zargaran + Show 4 more

Open Access

https://doi.org/10.1038/s41467-020-16601-1

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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.

Highlights

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
The fine grain size accompanied by high-strain-rate sensitivity and Grain Boundary Sliding (GBS) accommodation by plastic deformation lead to an ultra-high superplasticity of 2000% at a high-strain rate of 5 × 10−2 s−1 in the present alloy
The XRay Diffraction (XRD) patterns of the as-annealed and as-high-pressure torsion (HPT) specimens show the peaks of Face-Centered Cubic (FCC) and B2 phases (Fig. 1b), we can see peak broadening occurs after HPT due to grain refinement and lattice distortion

Summary

Introduction

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 is generally observed in fine-grained materials at low strain rates (10−4–10−3 s−1) and high homologous temperatures (>0.5 Tm), where Tm is the melting temperature[1,2,3]. We fabricate an Al9(CoCrFeMnNi)[91] HEA with nanosized FCC grains and B2 phase in the range of a few hundred nanometers to micrometers through thermo-mechanical treatment followed by high-pressure torsion (HPT) processing.

Results

Conclusion