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

Ti-rich body-centered cubic (BCC, β) high-entropy alloys having compositions Ti(35)Zr(27.5)Hf(27.5)Nb(5)Ta(5), Ti(38)Zr(25)Hf(25)Ta(10)Sn(2), and Ti(38)Zr(25)Hf(25)Ta(7)Sn(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′).