Fatigue behaviour of L-DED processed Ti-6Al-4V with microstructures refined by trace boron addition.

• A mixed equiaxed + columnar prior-β grain microstructure was achieved by 0.05 wt% boron addition. • High-cycle fatigue property was improved significantly in Ti-64-0.05B. • Fatigue crack propagation resistance was reduced due to the prior-β grain size reduction and the TiB particle precipitation. Boron is a powerful grain solute that promotes substantial microstructural refinement in titanium alloys produced by additive manufacturing. However, the fatigue performance of boron refined additive manufactured titanium alloys remained unknown. In this study, a thorough investigation into the high-cycle fatigue life and crack propagation rates of laser direct energy deposited Ti-6Al-4V with a trace boron addition was carried out. The high-cycle fatigue life was significantly improved, as the refined microstructure increased the crack initiation resistance. However, the crack propagation resistance estimated from spectrum loading was reduced, due to the refined prior-β grains and TiB particles. [ABSTRACT FROM AUTHOR]