Static grain growth in a microduplex Ti–6Al–4V alloy

The grain growth behavior of the microduplex titanium, 6% aluminum, 4% vanadium alloy is addressed. Although there has been considerable work done on second phase particle coarsening, there is limited research on coarsening in a two-phase material with nearly equal phase ratios. In this study, coarsening parameters were determined for the temperature range of 850–925°C, where α and β phase ratios are approximately 50 percent. Experimentally determined grain growth data for the Ti alloy are found to follow classical particle-stabilized grain growth kinetics with a temperature dependent coefficient and a constant exponent. On the basis of these observations a grain boundary pipe diffusion model is proposed which has the desired features of incorporating both the faster kinetics of the grain boundary diffusion and the unidirectional exponent q=5, which is often observed in microduplex alloys. The model appears to resolve a previously reported dilemma that the time exponent suggests pipe diffusion but the kinetics associated with the triple boundary is too slow. The concept proposed should have applicability to other two-phase alloys containing approximately equal volume fractions of each phase.