Influence of minor addition of boron on tensile and fatigue properties of wrought Ti–6Al–4V alloy

Abstract

Abstract Addition of boron to cast Ti–6Al–4V alloy leads to significant refinement in grain size, which in turn improves processibilty as well as the mechanical properties of the as-cast alloy. Room temperature tensile and fatigue properties of Wrought Ti–6Al–4V–B alloys with B up to 0.09 wt.% are investigated. Thermo-mechanical processing at 950 °C caused kinking of α lamellae and alignment of TiB particles in the flow direction with a negligible change in prior β grain and colony sizes, indicating the absence of dynamic recrystallisation during forging. Characterisation with the aid of X-ray and electron back scattered diffraction reveal a strong basal texture in B free alloy which gets randomised with the 0.09B addition in the forged condition. Marginal enhancement in tensile and fatigue properties upon forging is noted. B free wrought Ti–6Al–4V alloy exhibits better tensile strength as compared to B containing alloy, due to the operation of 〈 c + a 〉 slip on pyramidal planes with high value of CRSS as compared to 〈 a 〉 slip on basal and prismatic planes. Decrease in fatigue strength of Ti–6Al–4V–0.04B in as-cast and the wrought state is observed due to increase in the volume fraction of grain boundary α phase with B addition, which acts as a crack nucleation site. No significant effect of TiB particles on tensile and fatigue properties is observed.