Effects of boron addition on microstructures and mechanical properties of Ti-6Al-4V manufactured by direct laser deposition

Highlights: • Microstructures, including prior-β and α grains, are significantly refined in DLDed Ti-6Al-4V through addition of boron. • Boron addition also reduces the solidification texture, and leads to weak α texture. • Mechanical property anisotropy is greatly reduced due to the microstructure refinement and texture weakening -- Abstract: Large columnar grains with strong texture in direct laser deposited (DLDed) Ti-6Al-4V (Ti-64) is widely reported to cause issues like strong mechanical property anisotropy and poor tensile strength, which make this material unsuitable for many uses in the aerospace industry. In this study, a microstructure refinement investigation was carried out by adding various amounts of boron from 0.05 wt% to 1.0 wt%. The effects of boron additions, even with 0.05 wt%, are very strong on the microstructure refinement. The presence of large columnar grains was eliminated along with the α lath refinement, the grain boundary α elimination and the texture weakening. β reconstruction results showed that boron is very effective in the β grain refinement and the β texture weakening, which contributes to the transformed α lath refinement and the α texture weakening, respectively. Furthermore, the tensile strength of DLDed Ti-64 with different boron additions is improved. A good balance of the tensile strength and ductility, with considerably reduced anisotropy, was achieved by adding 0.05 wt% boron. A comprehensive understanding between the boron additions, microstructure refinement and tensile performance improvement was fully established, which could enable greater usage of DLDed Ti-64 in the aerospace industry.