Coordinated deformation mechanisms in a trimodal microstructure for achieving strength–toughness synergy in powder-metallurgy near-α titanium alloys

Microstructural optimization of powder metallurgy (PM) titanium alloys to simultaneously achieve high strength, good ductility, and excellent impact toughness remains highly challenging. Here, equiaxed, bimodal, and trimodal microstructures were produced through a route integrating powder metallurgy, hot deformation, and heat treatment, yielding refined grain sizes of 5.24, 5.36, and 4.55 μm, respectively. The equiaxed and bimodal microstructures showed reasonable quasi-static tensile ductility, but limited impact toughness (< 25 J) due to stress localization and the development of preferential crack propagation paths. In contrast, the trimodal microstructure exhibited substantially improved impact resistance. Its hierarchical architecture, composed of discontinuous equiaxed primary α at grain boundaries, intragranular short rod-like secondary α, and retained β t matrix, facilitates cooperative deformation and strain partitioning under high-rate loading. This deformation mode enhances plastic dissipation and impedes unstable crack advance. Consequently, the trimodal alloy exhibits an outstanding combination of properties, with a yield strength of ∼950 MPa, an elongation of 12%, and an impact energy of 43 ± 5 J, representing an improvement of more than 50% over the equiaxed and bimodal counterparts. The present findings highlight trimodal microstructural engineering as a promising strategy to break the conventional strength–ductility–toughness trade-off in PM titanium alloys.