Microstructure-sensitive damage in dual-phase Ti-5553 alloy: Effects of stress state and α/β interfacial mechanics

This study presents a comprehensive microstructure-sensitive investigation of deformation and failure in dual-phase Ti-5Al-5Mo-5V-3Cr (Ti-5553) alloy using crystal plasticity finite element methods coupled with experimental characterisation. Material parameters governing elastic–plastic behaviour and damage evolution (void nucleation, growth, and coalescence) were calibrated via inverse modelling using stress–strain data and EBSD-informed microstructures from heat-treated samples. Representative volume elements systematically capture realistic α/β morphologies, including embedded, grain boundary, triple junction, and elongated grain configurations. Simulations explore how stress triaxiality ( X = 1/3 to 3), Lode parameter ( L = −1 to 1), Burgers orientation relationship (BOR) variants, crystal orientation, α phase volume fraction, and phase-boundary geometry govern slip localisation and damage evolution. Key findings reveal stress-state dependent optimal microstructural parameters: (1) at moderate triaxiality ( X = 1/3), α volume fractions near 10% suppress strain localisation and delay damage onset; (2) under elevated triaxiality ( X = 1), lower α fractions (∼5%) become more damage-resistant; (3) crystallographic compatibility across α/β interfaces, determined by BOR variant selection and boundary orientation, directly controls interfacial stress concentrations and void nucleation sites; (4) orientation-dependent slip transfer at interfaces is found to be critical, favourable crystal alignments (e.g. 60° rotation of α grain) promote homogeneous strain distribution, whereas unfavourable alignments (0°, 30°) localise deformation at boundaries. SEM fractography from tensile-tested samples validates predicted void nucleation and coalescence patterns near fracture surfaces. This work establishes quantitative, mechanistic links between microstructure (phase-morphology, crystallographic relationships, volume fractions) and damage under complex loading states, providing new insights for rational alloy design and process optimisation in high-performance dual-phase titanium aerospace components.