A novel TWIP/TRIP near-α Ti alloy with multi-scale α-phase: The superior combination of strength and fracture toughness

Abstract

A novel near-α Ti–5Al–2Zr–1V–1Sn–1Mo alloy with Twining Induce Plasticity (TWIP) and Transformation Induce Plasticity (TRIP) effects was designed. The excellent combination of yield strength Rp0.2 ∼834 MPa and fracture toughness KIC ∼114 MPa m0.5 is achieved by tailoring multi-scale α phase, that includes micron primary α grains (αp), sub-micro α lath in the βtrans matrix (αlath) and nano-scale α platelets (αs) in the βlamellae. The high tensile strength mainly stems from the solution strengthening and αs precipitation strengthening. The βlamellae with the precipitation of αs can not only effectively block dislocation slip, but also decrease the mean free slip length from the size of αcolony (15 μm) to the width of αlath (1.2 μm). The {101¯2}⟨1¯011⟩ deformation twins in αp and hcp→fcc phase transformation in αlath were simultaneously activated to compensate for the concomitant decrease of fracture toughness with increase in strength. Furthermore, the hierarchical deformation of α phase with multi-scale distribution can cause more homogeneous strain partitioning, relieve stress concentration and delay crack initiation. This investigation provides a guideline for the composition design and microstructural regulation of other near-α Ti alloys with TWIP/TRIP effect and high damage tolerance.