Deformation mechanisms study of heterostructured Ti-80 alloy based on crystal plasticity theory

: To enhance the strength–ductility synergy of titanium alloys under extreme service conditions, heterogeneous structures have been increasingly adopted in materials design and processing. To systematically elucidate the mechanisms and governing principles by which heterogeneous structures affect the strength and ductility of titanium alloys, a crystal-plasticity finite-element method (CPFEM) was employed to investigate the underlying deformation and hardening mechanisms of heterostructured Ti-6Al-3Nb-2Zr-1Mo (Ti80). A realistic representative volume element (RVE) was constructed from EBSD data, and non-local hardening induced by plastic incompatibility across grain boundaries was characterized through geometrically necessary dislocations (GNDs) and back stress. The simulation results indicate that back stress contributes approximately twice the strengthening (incremental hardening) of GNDs at the same strain level. Compared with the homogeneous model (HM), which tends to develop a diffuse shear-band structure penetrating the entire field at larger strains, the heterogeneous structure (HS) promotes shear-band deflection within coarse-grained regions. Slip-activity statistics show that fine-grain (FG) regions in HS activate a large number of pyramidal and pyramidal slip systems at an engineering strain of 15%, resulting in substantial GND accumulation and effective regulation of deformation heterogeneity. Meanwhile, compared with the homogeneous model and the fine-grain region, the principal stress direction in the coarse-grain (CG) region of the heterogeneous structure deviates more markedly from the global loading direction, thereby promoting pronounced activation of basal slip systems.