Thermomechanical Processing of a Near-α Ti Matrix Composite Reinforced by TiB_w

To further improve the mechanical properties of the as-cast 7.5 vol.% TiB_w/Ti-6Al-2.5Sn-4Zr-0.7Mo-0.3Si composite, multi-directional forging (MDF) and subsequent heat treatments were carried out to adjust TiB whiskers (TiB_w) and matrix characteristics. The effect of various microstructures on the tensile properties and fracture toughness of the composites was analyzed in this paper. After MDF, the TiB_w are broken into short rods with a low aspect ratio and display a random distribution. Moreover, distinct microstructures were obtained after thermomechanical processing and different heat treatments. Both room-temperature and high-temperature tensile strength and ductility are improved after thermomechanical processing. By increasing the solution-treatment temperature, the microstructures transform from equiaxed to fully lamellar. A simultaneous improvement of the room-temperature and high-temperature properties is associated with the microstructural changes. In addition, the fracture toughness exhibits an increasing trend as the volume fraction of equiaxial α phases decreases. The lamellar microstructure demonstrates excellent fracture toughness due to deflection of the crack propagation path.