Exceptionally high strain-hardening and ductility due to transformation induced plasticity effect in Ti-rich high-entropy alloys

Abstract

Ti-rich body-centered cubic (BCC, β) high-entropy alloys having compositions Ti ₃₅Zr _27.5Hf _27.5Nb ₅Ta ₅, Ti ₃₈Zr ₂₅Hf ₂₅Ta ₁₀Sn ₂, and Ti ₃₈Zr ₂₅Hf ₂₅Ta ₇Sn ₅ (in at%) were designed using bond order (Bo)-mean d-orbital energy level (Md) approach. Deformation mechanisms of these alloys were studied using tensile deformation. The alloys showed exceptionally high strain-hardening and ductility. For instance, the alloys showed at least twofold increment of tensile strength compared to the yield strength, due to strain-hardening. Post-deformation microstructural observations confirmed the transformation of β to hexagonal close packed (HCP, α′) martensite. Based on microstructural investigation, stress–strain behaviors were explained using transformation induced plasticity effect. Crystallographic analysis indicated transformation of β to α′ showed strong variant selection (1 1 0) _β //(0 0 0 1) _α′ , and [1 − 1 1] _β //[1 1 − 2 0] _α′ .