Investigation on cryogenic TRIP/TWIP effects in metastable β-Ti alloy with complex deformation behavior

The cryogenic properties and deformation mechanisms were systematically investigated in a ternary beta-metastable alloy of Ti-8.5Cr-1.5Sn in this work. Owing to the complex deformation behavior observed at 77 K, the very superhigh tensile strength of -1840 MPa and large elongation-to-failure of -16.4% was successfully achieved. Detailed microstructural analysis showed that deformation process involves the occurrence of stressinduced {332}<113> twins together with the stress-induced omega transformation, leading to a complex deformation microstructural network with very specific synergistic characteristics. To accommodate plastic deformation caused by progressively forming of {332}<113> twins and omega phases, the dynamic Hall-Petch effect was induced, thus improving the strength and plasticity at low temperature. More importantly, the introduction of numerous heterogeneous beta/twin, omega/twin and twin/twinnano interfaces leads to mechanical incompatibility and strain gradients near these interfaces, thereby generating remarkable hetero-deformation induced (HDI) stress, which could induce additional strain-hardening (HDI hardening). Therefore, the combined effects of the above factors bring about outstanding combinations of strength and plasticity at 77 K.