Yielding nature and Hall-Petch relationships in Ti-6Al-4V alloy with fully equiaxed and bimodal microstructures

Hall-Petch relationships were studied in Ti-6Al-4V alloy with fully equiaxed and two different bimodal microstructures obtained by intercritical annealing at 850 degrees C (BM850) and 950 degrees C (BM950). The Hall-Petch coefficient of the BM850 microstructure composed of harder primary alpha grains and softer transformed beta areas was identical to that of the fully equiaxed microstructure, indicating the same nature of yielding behavior determined by the resisting ability of equiaxed alpha grain boundaries against slip transfer in both microstructures. The BM950 microstructure having smaller amount of primary alpha, however, showed a yielding nature like a particle-strengthened composite, leading to the different Hall-Petch relationship.