Achieving superior strength-ductility combination in the heterogeneous microstructured Ti64 alloy via multi-eutectoid elements alloying with CoCrFeNiMn during laser powder bed fusion

The formation of coarse needle-shaped α′-Ti within columnar β-Ti grains in additively manufactured titanium alloy components is nearly unavoidable, and it can lead to unforeseeable service failures. This study employs a multi-component eutectoid alloying strategy, integrating CoCrFeNiMn high-entropy alloy particles within Ti64 alloy. By varying laser parameters, the resulting microstructure transitions from β-dominated to a metastable β + nanoscale α′ microstructure. The coarse needle-shaped α′-Ti and columnar β-Ti grains are significantly refined. Concurrently, the multi-component eutectoid alloying strategy successfully suppresses the formation of detrimental intermetallic compounds by promoting the uniform distribution and solubility of the alloying elements. The Ti64-(4.5%) CoCrFeNiMn alloy demonstrates exceptional mechanical properties, including high tensile strength (1333.8 MPa), uniform elongation (9.3%), and a work-hardening capacity (>390.0 MPa). These are attributed to the continuous variation of Co, Cr, Fe, Ni, and Mn concentrations within the ultrafine α′ and metastable β-phase regions, providing a progressive transformation-induced plasticity effect.