Grain refinement of Ti-15V-3Cr-3Sn-3Al metastable β titanium alloy welds using boron-modified fillers

Highlights: • Boron in CP-Ti filler refined fusion zone grain size in Ti-15-3 GTAW welds. • TiB at grain boundaries impeded grain boundary migration in welds. • Boron rejection resulted in constitutional supercooling and equiaxed grains. • CP-Ti-0.5 B fillers improved mechanical properties by microstructural modification. Metastable beta (β) titanium alloy welds typically exhibit low strength and hardness due to their coarse fusion zone (FZ) microstructure. Efforts to improve the mechanical properties of these alloys have been confined to the use of various heat treatment processes as the means to promote α precipitation in the β matrix. The present study employs a novel method of using boron-added commercial pure-Ti fillers in gas tungsten arc welding (GTAW) of the Ti-15V-3Cr-3Sn-3Al metastable β titanium alloy. Microstructural analysis of boron-added welds showed refined prior-β grains and equiaxed dendritic grains with nonlinear grain boundaries. The formation of TiB and consequent microstructural modification of the FZ in the welds prepared using 0.5 wt% boron-added CP-Ti filler contribute to the improvement in the mechanical properties.