Microstructure-Dependent Local Fatigue Cracking Resistance of Bimodal Ti-6Al-4V Alloys

The fatigue crack growth behavior of the bimodal Ti-6Al-4V alloys with two different volume fractions of the primary phase (alpha(p)) of 76 and 36% is investigated by the in situ testing technique. The experimental results show that the crack growth rate of the alpha(p) = 36% Ti-6Al-4V alloy is lower than that of the alpha(p) = 76% one. The local fatigue crack growth rate is evidently decreased by the various boundaries including alpha(p) grain boundaries, boundaries between the alpha(p) phase and basketweave microstructure, and alpha/beta lamellar interfaces. A criterion associated with the boundary characteristics is obtained to evaluate the grain boundary resistance to the fatigue crack growth in the engineering alloys.