Ti-6Al-4V alloy is the most commonly employed titanium alloy due to its good combination of excellent properties, such as high specific strength, high fatigue strength, good ductility and weldability, and excellent stress corrosion cracking resistance. However, Ti-6Al-4V alloy shows low stiffness and poor wear resistance. To further increase the strength properties and improve the stiffness and wear resistance, many researchers have studied Ti-6Al-4V alloy matrix composites (TMCs) using ceramic reinforcements, such as TiB (Gorsse, et al., 2003, Panda, et al., 2003, Giannopulos, et al., 2007, Nandwana, et al., 2012, Huang, et al., 2012, Ropars, L., et al., 2015, WC (Chen, et al., 2009), TiC (Rastegari, et al., 2013, TiAl (Decker, et al., 2016), and SiC (Sivakumar, et al., 2017).The reinforcements usually need to be stiffer and harder than the matrix and to be chemically stable. For pure titanium matrix composites, TiB is currently recognized as one of the most compatible and effective reinforcements (Ravi Chandran, et al., 2004, Moris, et al., 2007. The reasons are as follows: first, there is no intermediate phase between Ti and TiB; second, TiB forms as long, pristine single-crystal whiskers which are thermodynamically and mechanically stable in the Ti matrix; and third, the relatively low temperatures involved in solid-state composite processing (under 1000 °C) offer manufacturing ease. Furthermore, TiB offers increases in strength and stiffness without increasing density or generating residual stresses, because the density and thermal expansion coefficient of TiB are comparable to those of titanium.Although some research on TiB-reinforced Ti-6Al-4V alloy matrix (TiB/Ti-6Al-4V alloy) composites has been published, such as those mentioned above, the effect of the TiB volume fraction on the mechanical properties and Hiroshi IZUI* and Tsubasa SHINOHARA* * Department of Aerospace Engineering, Nihon University 7-24-1 Narashinodai, Funabashi, Chiba 274-8501, Japan E-mail: izuihi@aero.cst.nihon-u.ac.jp AbstractTi-6Al-4V alloy exhibits a good combination of excellent properties, such as high specific strength, high fatigue strength, good ductility and weldability. However, Ti-6Al-4V alloy shows low stiffness and poor wear resistance. To further increase the strength properties and improve the stiffness and wear resistance, TiB reinforced Ti-6Al-4V alloy matrix (TiB/Ti-6Al-4V) composites were fabricated by a spark plasma sintering (SPS) process. The TiB/Ti-6Al-4V alloy composites with 4.2 vol.% TiB, which were fabricated at a sintering temperature of 900 °C and for a holding time of 30 min, had the highest tensile strength of 1174 MPa. The Young's modulus and Vickers microhardness of the composites increased with increasing TiB volume fraction, and the composite with 16.7 vol.% TiB exhibited values of 159 GPa and 517 HV, respectively. The tensile strength of the composite with 4.2 vol.% TiB at 400 °C was higher than that of the mild annealed Ti-6Al-4V alloy. The fatigue limits (over 10 7 cycles) at room temperature and ...