Investigation on the microstructure, room and high temperature mechanical behaviors and strengthening mechanisms of the (TiB+TiC)/TC4 composites

A hybrid of (TiB+TiC) reinforced Ti-6Al-4V (TC4) matrix composite was produced by solution ball milling and spark plasma sintering process. The reinforcements were uniformly dispersed into the β grain boundary of the TC4 matrix. The size of β-grain is markedly reduced from more than 300 μm to about 23 μm after adding 9.5 vol % reinforcements to the matrix. The room-temperature tensile test results show that yield strength of the composites was enhanced and eventually saturated with the addition of reinforcements. Among all the strengthening mechanisms, grain-refinement effect plays the most important role and contributes 58.5–76.3% increment of the room-temperature yield strength. TiC-particles contribute 15.9–32.2% and TiB-whiskers share the rest contribution. However, the existence of TiB_w clusters weakens the load-bearing effect of TiB. The high-temperature yield strength of the composites was improved with increasing volume fraction of the reinforcements and decreased with increasing test temperature. The grain-refinement strengthening efficiency decreases with increasing temperature, while by contrast, the strengthening efficiency of TiC particles goes up. Owing to the combination effect of matrix softening and dynamic recovery process, no saturation of high-temperature yield strength is observed even when the maximum volume fraction of reinforcements (9.5 vol %) were added to the composites.