Hot-rolled heterostructured TiBw/TA15 composite: promoting pyramidal <c+a> slip and decoupling of uniform-grain and hetero-interface back stresses

Achieving high strength without sacrificing ductility remains challenging for HCP titanium alloys because limited room-temperature slip systems promote strain localization. This study proposes a combined strategy via low-energy ball milling, hot-press sintering, and 70% multi-pass hot rolling at 1000 ℃ to fabricate a multiscale soft-hard heterogeneous structure in TiBw/TA15 composite. This microstructure comprises soft coarse primary α and hard domains consisting of fine recrystallized α, α_s/β lamellae, and aligned TiBw. HR-DIC, TEM, and EBSD reveal strain gradients and GNDs pile-ups at hetero-interfaces, which raise local stresses and promote pyramidal <c + a> slip activation. The hot-rolled heterostructure composite reaches 1213 MPa yield strength and 1262 MPa ultimate tensile strength with 8.0% total elongation. Furthermore, based on a rule-of-mixtures approach coupled with the Taylor dislocation-strengthening model, the GNDs strengthening associated with incompatibility arising from uniform-grain is quantified as 226.9 MPa, while that arising from incompatibility at soft–hard hetero-interfaces are 363.4 MPa. The experimentally measured back stress is approximately 600 MPa (612 MPa at 4.0% global strain), and the predicted back stress is 590.3 MPa. The deviation between the predicted and measured values is below 5%, providing quantitative insight into heterostructure design.