Effect of vapor grown carbon fiber content on microstructure and tensile properties of Ti64/TiC composite fabricated by powder metallurgy method

Ti-6%Al-4%V (Ti64) alloy powder coated with vapor grown carbon fibers was consolidated to fabricate titanium matrix composites by spark plasma sintering, followed by hot extrusion process. Four compositions of the additive vapor grown carbon fibers were 0.1, 0.2, 0.3 and 0.4 wt. %. The microstructure was changed from the full lamellar of monolithic Ti64 alloy to the bimodal structure by addition of vapor grown carbon fibers to Ti64 alloy. The changing of microstructure was attributed by an α-stabilize effect of carbon (vapor grown carbon fiber). Almost all the vapor grown carbon fibers reacted with Ti and result in formation of Ti ₆ C _3.75 carbide phases detected by x-ray diffractometer and energy dispersive spectrometer. Hardness was improved by effect of solid solution strengthening of carbon in the Ti matrix and reached the maximum value of 495.8 Hv. 0.2%YS and UTS were significantly increased by addition of 0.1 wt. % vapor grown carbon fiber. However, they were not much improved when more vapor grown carbon fiber content was applied. Ductility of the sample was affected by a change in microstructure when 0.1 wt. % of vapor grown carbon fibers was added because the bimodal structure shows higher ductility compared to the full lamellar structure. The carbide precipitation in TMCs was not much contributed in improving of strength and decreased a ductility of material.