Cooperative strengthening and toughening of titanium alloy weld joints by solute atom W and TiC ceramic particles

The strength-ductility trade-off remains a significant challenge in alloy welding. This study introduces an in-situ alloying design strategy for weld seams, achieving a strength-ductility synergy in welded joints through the simultaneous incorporation solute atoms and heterogeneous nucleating agents . In this study, W and TiC particles are selected as representatives, and this system is not limited to these two. The W solute atoms enhance the compositional undercooling of the molten pool while promoting TiC nucleation. The nano-TiC particles amplify the solid-solution strengthening effect of W and provide low-energy-barrier heterogeneous nucleation sites . These synergistic effects facilitate the transformation from columnar to equiaxed grains, significantly reducing texture intensity and decreasing the average grain size from 243.63 μm to 123.16 μm—a reduction of 49.4 %. Additionally, the needle-like martensite within β-Ti grains transforms into low-aspect-ratio martensite. Compared to the Ti64 joint , the welded joint with W and TiC exhibits a tensile strength of 1106 MPa and an elongation of 7.2 %, representing increases of 21 % and 36 %, respectively, with a mixed ductile-brittle fracture characteristic . The W and in-situ-generated nano-TiC particles obstruct dislocation motion , triggering multiple strengthening mechanisms (grain boundary strengthening, solid solution strengthening, dislocation strengthening, Orowan strengthening and load transfer strengthening.). Furthermore, these particles inhibit crack propagation , enhancing strain-hardening capability and improving elongation without sacrificing strength . • A coaxial powder feeding laser welding method for weld alloying was adopted. • The design idea of alloy co-doped with solute atoms W and TiC ceramic particles was proposed. • The strength-plastic synergy of the joint was achieved by component undercooling and heterogeneous nucleation effect.