Effects of extrusion ratio on microstructural evolution and mechanical behavior of in situ synthesized Ti-6Al-4V composites

TiB whiskers and TiC particles reinforced Ti-6Al-4V composites (TMCs) were synthesized by in situ method and then extruded with different extrusion ratios (λ=7, 10 and 16) at 1258 K. The effects of extrusion ratio on the microstructural evolution and mechanical behavior have been systematically investigated. The room temperature tensile results indicate that the strength, elastic modulus and ductility of the TMCs are simultaneous to be improved after extrusion. With the increase of extrusion ratio, the yield strength of the TMCs increases and the fracture strain of the TMCs decreases, respectively. Meanwhile, the elastic modulus almost keeps as a constant during the extrusion process. The mechanical properties of the TMCs are found to be determined by the interplay of reinforcements and the metal matrix. With the increase of extrusion ratio, the aspect ratio of TiB whiskers decreases from ~4.3 to ~3.5. Nevertheless, the volume fraction of dynamic recrystallization of the matrix shows positive correlation with the extrusion ratio. It is up to about 72% of dynamic recrystallized grains at the extrusion ratio of 16. EBSD and TEM observations are used to study the texture evolution during extrusion process, which indicate that the type of the deformation texture is similar with the recrystallization texture, while its intensity is higher than the latter one.