Martensite nucleation site and grain refinement in duplex titanium alloy weldment by active flux with nanoparticle addition

The effects of activating flux containing nanoparticles on the welding microstructure and hardness distribution of titanium alloy were investigated. The fluxes, consisting of NaF with 1 wt-% of either nano-TiO₂ or nanodiamond, effectively yielded refined grain size and deep weld penetration. The hardness of the weldment was close to that of the base metal for 99 wt-% NaF plus 1 wt-% diamond, leading to a desirable uniform mechanical property in the weld design. In the meantime, the transmission electron microscopy images illustrate that the nanoparticles promote β phase coarsening and martensitic α′ phase formation at the β veins.