Microstructure refinement and strengthening mechanisms of network structured TiBw/Ti6Al4V composites by TIG remelting

In order to further strengthen TiB whiskers reinforced Ti6Al4V (TiBw/Ti6Al4V) composites with a network microstructure, tungsten inert gas (TIG) remelting was performed on the composites with different reinforcement volume fractions to tune microstructure. The results showed that the size of network unit and TiB whisker reinforcement of the composites were significantly refined from 150 μm to 20 μm in diameter and 3 μm to 0.5 μm in width after remelting, respectively. Moreover, the α phase of Ti6Al4V matrix was transformed into a refined α′ phase due to the rapid air-cooling process. It is also revealed that the refinement of network microstructure was resulted from the hypoeutectic reaction of the Ti–B system. However, the network microstructure disappeared when the reinforcement volume fraction rises to 10 vol.%, and then coarse primary TiBw appeared when to 20 vol.%. After remelting, the hardnesses of 3.4 vol.%, 10 vol.%, 15 vol.% and 20 vol.% TiBw/Ti6Al4V composites were increased to HRC 36, HRC 40, HRC 43 and HRC 50 from HRC 32, HRC 37, HRC 40, HRC 47, respectively. The tensile strength at 600 °C was increased by 10%–20% while remaining the similar tensile ductility. The strengthening mechanisms can be mainly attributed to microstructure refinement and α’ martensite formation.