Distinct strain transfer and co-deformation mechanisms at α/β interfaces with different orientation relationships in metastable β Ti-7333 alloy

The interface characteristics and strain transfer behavior between equiaxed α phase (α_e) and β phases in metastable β Ti-7Mo-3Al-3Cr-3Nb alloy were investigated through micropillar compression. The finding reveals that there are two deviation angles from the Burgers orientation relationship (BOR) between α_e and < 001 > β grain that occur most frequently, namely 5° and 30°, which can be defined as α₁/β and α₂/β, respectively. A dislocation slip region within the β matrix, which also functions as a deformation transition zone, was observed at both types of interfaces. It is identified as the βᵢ (interfacial β) region and is driven by compositional effects. Although deformation transfer between stress-induced α" martensite in the β phase and dislocation slip in the α phase is dominant at both types of interfaces, {11̅01}_α nanotwin-assisted deformation is additionally activated at the α₁/β interface. Furthermore, the geometric compatibility factor (m′) between the slip systems of the two phases is higher at the α₁/β interface, indicating that dislocation transfer across the interface is more effective. This results in a more continuous and stable plastic flow behavior, as evidenced by the compressive stress–strain curve. More importantly, in the micropillar containing α₁/β phases, plasticity initiates in the α phase, which contributes the onset of yielding, and is subsequently transferred to the β phase, leading to a significant increase in the corresponding yield strength compared to the micropillar containing α₂/β phases. These findings provide novel insights for the design of microstructures and deformation mechanisms in metastable β titanium alloys.