The elevated-temperature fatigue behavior of boron-modified Ti–6Al–4V(wt.%) castings

This work investigated the effect of nominal boron additions of 0.1 and 1.0 wt.% on the elevated-temperature (455 °C) fatigue deformation behavior of Ti–6Al–4V(wt.%) castings for maximum applied stresses between 250 and 450 MPa (R = 0.1 and 5 Hz). Boron additions resulted in a dramatic refinement of the as-cast grain size, and larger boron additions resulted in larger titanium-boride (TiB) phase volume percents. The boron-containing alloys exhibited longer average fatigue lives than those for Ti–6Al–4V, which was suggested to be related to the reduced as-cast grain size and the addition of strong and stiff TiB phase. The Ti–6Al–4V–0.1B alloy exhibited the longest average fatigue lives. The TiB phase cracked during the fatigue experiments and this resulted in a decreasing Young's modulus with increased cycle number. Each alloy exhibited α-phase cracking and environmentally assisted surface edge cracking.