Effects of heating rate on the alloy element partitioning and mechanical properties in equiaxed α+β Ti-6Al-4V alloy

Abstract The effects of heating rate on the alloy element partitioning and mechanical properties during the phase transformation of α→β in Ti-6Al-4V alloy under solution treatment have been investigated by the experiments and phase field simulations, which reveal the evolutions of microstructure and compositions at the non-equilibrium state and well verify the experimental results. The specific results indicate that the compositions measured through electron probe micro-analysis (EPMA) under a lower heating rate are close to the equilibrium ones corresponding to the solution temperature. Heating up to the target solution temperature, as the heating rate increases, the Al content decreases and V increases in the primary α (αp) grain with a larger size, the volume fraction of αp increases and the composition gradient between αp and β phases gets steeper. The interrelated relationship among the diffusion, compositions, solution temperature and free energy of the system has been discussed in detail. Moreover, increasing the heating rate (∼20.0 K/min) may help to improve the mechanical properties of the alloy by mainly adjusting the αp/βt volume fractions, αp particle size and secondary α (αs) size during the process of heating up to the solution temperature. These results may shed some light on the optimization of the knowledge-based heat treatment route.