Enhancement of damage tolerance in Ti-6554 alloy through twinning and hetero-deformation induced strengthening synergy

Abstract

Heterogeneous structure exhibits superiority in improving mechanical properties, whereas their effects on fatigue damage properties have rarely been studied. In this work, we employed a high-throughput gradient heat treatment method (757–857 °C) to rapidly acquire the solution microstructure of the Ti-6554 alloy with different recrystallization degrees (0%, 40% and 100%), followed by the same aging treatment. The results showed that the β-hetero structure exhibited a yield strength (σ_YS) of 1403 MPa, an increase of 6.7%, and a remarkable improvement in uniform elongation (UE) of 109.7%, reaching 6.5%, compared to the homogeneous structure. Interestingly, introducing a heterogeneous structure not only overcame the traditional trade-off between strength and ductility but also enhanced fatigue crack propagation (FCP) performance. During FCP process, β-hetero structure, through hetero-deformation induced (HDI) strengthening effects, promoted the accumulation of geometric necessary dislocations (GNDs) within coarse α_S phase, enabling faster attainment of the critical shear stress of twinning and increasing twinning density. This facilitated stress relief, improved plastic deformation in the crack tip zone, and increased the critical fast fracture threshold from 30.4 to 36.0 MPa·m^1/2 showing an enlarged steady state propagation region. This study provides valuable insights on tailoring fatigue damage tolerance through heterogeneous structure for titanium alloys.

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