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.