Overcoming the strength and ductility trade‐off in a metastable β‐Ti alloy by coupling heterostructure strengthening and transformation‐induced plasticity

Abstract To improve the yield strength of metastable β‐Ti alloys with transformation‐induced plasticity (TRIP) and twinning‐induced plasticity effects, a novel strategy combining heterostructure strengthening with the TRIP effect was developed. A metastable β‐Ti alloy with a nominal composition of Ti–4Mo–3Cr–1Fe–1Al was used as the base alloy. By adjusting the annealing temperature after cold rolling, heterostructured samples comprising soft recrystallized β‐grains and hard un‐recrystallized β‐grains and α‐phase were prepared. Compared with the homogeneous coarse‐grained sample, the yield strength of the heterostructured sample significantly increased from 610 to 905 MPa, while maintaining excellent plasticity (32.7%), overcoming the traditional trade‐off between strength and ductility. The observed high yield strength is attributed to significant back‐stress strengthening caused by the accumulation of a large number of geometrically necessary dislocations at the interfaces between the soft and hard regions. Meanwhile, the exceptional plasticity is attributed to the activation of stress‐induced martensite (SIM) within the metastable β matrix. The sequential activation of dislocation slips and SIM is achieved through the construction of a heterostructured structure. This work provides a new strategy for designing metastable β‐Ti alloys with high strength and plasticity by coupling heterostructure strengthening and transformation‐induced plasticity.