Phase boundary plasticity and spatial distribution mediated high‑temperature deformation inhomogeneity and damage in laser additively manufactured Ti‑6Al‑4 V titanium alloy

Randomly oriented α phases cause heterogeneous plastic deformation in laser powder directed energy deposition (LP-DED) Ti-6Al-4V alloy components under 400°C tensile loading, leading to premature stress concentration and failure. To address this issue, this study integrates 400 °C in-situ scanning electron microscopy‑electron backscatter diffraction (SEM‑EBSD) with a microstructure‑based crystal plasticity‑phase field (CP‑PFM) model, revealing the dominant role of phase boundary plasticity and its spatial distribution in deformation inhomogeneity and damage evolution at high‑temperature. Results show that low‑angle grain boundaries (LAGBs) trigger early stress concentration through preferential dislocation multiplication, whereas dislocation accumulation at other types of phase boundaries is governed by the geometric compatibility between slip systems. Notably, the high‑temperature condition significantly lowers the threshold required for slip system compatibility, and this compatibility undergoes substantial changes during deformation. In addition, α colonies oriented perpendicular to the tensile axis enhance grain boundary strengthening by effectively impeding dislocation motion. In addition, the CP-PFM model accurately captures the deformation-damage evolution process, soft-oriented α colonies alleviate stress concentration through lattice rotation and activation of non-basal slip systems, whereas hard-oriented α colonies are prone to rapid stress buildup due to low Schmid factors and restricted slip system activation. This study provides critical theoretical support for the microstructural optimization of additively manufactured titanium alloys, thereby improving their damage tolerance in high-temperature application scenarios.