Tailoring planar slip to achieve pure metal-like ductility in body- centred-cubic multi-principal element alloys

L Wang and J Ding and SS Chen and K Jin and QH Zhang and JX Cui and BP Wang and B Chen and TY Li and Y Ren and SJ Zheng and KS Ming and WJ Lu and JH Hou and G Sha and J Liang and L Wang and YF Xue and E Ma, NATURE MATERIALS, 22, 950-+ (2023).

DOI: 10.1038/s41563-023-01517-0

Uniform tensile ductility (UTD) is crucial for the forming/machining capabilities of structural materials. Normally, planar-slip induced narrow deformation bands localize the plastic strains and hence hamper UTD, particularly in body-centred-cubic (bcc) multi-principal element high-entropy alloys (HEAs), which generally exhibit early necking (UTD < 5%). Here we demonstrate a strategy to tailor the planar-slip bands in a Ti-Zr-V-Nb-Al bcc HEA, achieving a 25% UTD together with nearly 50% elongation-to-failure (approaching a ductile elemental metal), while offering gigapascal yield strength. The HEA composition is designed not only to enhance the B2-like local chemical order (LCO), seeding sites to disperse planar slip, but also to generate excess lattice distortion upon deformation-induced LCO destruction, which promotes elastic strains and dislocation debris to cause dynamic hardening. This encourages second-generation planar-slip bands to branch out from first-generation bands, effectively spreading the plastic flow to permeate the sample volume. Moreover, the profuse bands frequently intersect to sustain adequate work-hardening rate (WHR) to large strains. Our strategy showcases the tuning of plastic flow dynamics that turns an otherwise- undesirable deformation mode to our advantage, enabling an unusual synergy of yield strength and UTD for bcc HEAs. This work shows that by designing appropriate alloying elements in a body-centred-cubic high- entropy alloy, local chemical order and lattice distortion can be tuned, which influences the evolution of planar-slip bands, realizing pure- metal-like tensile ductility at gigapascal yield strength.

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