Doctor of Philosophy

dissertationThe present study focuses on the design and synthesis of titanium metal matrix composites (MMCs) based on the Ti-B-Fe system in which the Fe-stablized beta titanium phase serves as the matrix phase and the titanium boride (TiB) compound serves as the reinforcement phase. One of the principal objectives of this work is to use ternary CALPHAD calculations to determine the phase fields such that the optimum processing temperatures for Electric-Field-Activated-Sintering (EFAS) can be found. The second objective is to use EFAS to rapidly synthesize the selected compositions. Additionally, microstructures, phases, flexural strength, and fracture toughness properties of selected composites, which have been processed by EFAS, have been investigated. Ti-B-Fe phase diagram showed the isothermal section was generated by three elements as Ti, B, and Fe, and the titanium-rich corner showed the phase field of each MMCs compositions and the ternary phase diagram also matched accurately with HT-XRD results. In general, it is found that the hardness of the composites increases with an increase in the amount of TiB phase. These hardness levels are 530, 680, and 1080 kg/mm2, for volume fraction of boride phases as 0.22, 0.27, and 0.79, respectively. The composite with 30 mol. % of B composition showed a very interesting microstructure in which a uniform distribution of TiB phase (Vf = 0.79) separated by β-Ti phase with both phases forming in-situ under EFAS. The composite exhibited good mechanical properties with good combination of hardness. The flexural strength of this composite was found to be in the range of 556-727 MPa and the fracture toughness shows a moderate value of 10.3 MPa√m. Fractographic analysis revealed that the strength and fracture toughness are limited by the brittle behavior of the β-Ti phase. Additional research is planned to introduce alloying elements for β-Ti phase to enhance ductility and toughness of the composites