Microstructural evolution and mechanical property optimization of TC11 alloy fabricated by coaxial wire-fed laser directed energy deposition

TC11 alloy fabricated by laser directed energy deposition (LDED) commonly suffers from coarse columnar β grains, strong crystallographic texture, and martensitic α′ phase, resulting in pronounced anisotropy and limited ductility. In this study, a six-beam coaxial wire-fed laser directed energy deposition (CWL-DED) technology was employed to fabricate TC11 alloy, and the synergistic effects of laser power, scanning speed, and wire feeding rate on microstructural evolution and mechanical properties were systematically investigated. The results demonstrate that the optimized parameter matching under the P3120 condition effectively suppresses the epitaxial growth of coarse columnar β grains and promotes a columnar-to-equiaxed transition, leading to a fully equiaxed β-grain structure with an average grain size of 322.45 ± 100.99 μm. Meanwhile, the enhanced cyclic thermal effects promote α′ martensite decomposition and α-phase spheroidization, accompanied by a substantial reduction in texture intensity. Repeated α↔β phase transformations induce dislocation accumulation, subgrain boundary formation, and interface evolution, thereby facilitating lamellar breakup and spheroidization of the α phase. The P3120 specimen exhibits the optimal comprehensive mechanical performance, achieving a maximum ultimate tensile strength of 1154.14 ± 16.12 MPa. The enhanced mechanical performance is mainly attributed to the synergistic effects of grain boundary strengthening, α colony interface strengthening, and dislocation strengthening. Furthermore, the near-annular heat source distribution generated by the six-beam coaxial configuration effectively homogenizes melt pool thermal conditions and improves deposition stability. This study establishes the process-microstructure-property relationship for CWL-DED-fabricated TC11 alloy and provides theoretical support for the microstructural regulation and performance optimization of multi-laser-beam coaxial directed energy deposition titanium alloys.