Microstrucrure of Multi-phase Ti_5Si_3 Base Intermetallic Compounds Fabricated by Adding Ternary Element and Improvement of Their Ductility

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Ti_5Si_3 exhibits low density, high melting temperature and adequate oxidation resistance. However, the compound is very brittle due to the complex crystal structure, D88. Hence, many cracks are introduced during ingot metallurgical fabrication process by anisotropic thermal expansion coefficient. Therefore, I tried to form ductile second phase, beta-Ti, by adding ternary element, and make clear the effect of that on mechanical properties. It is impossible that Ti-Si system realizes (Ti_5Si_3+beta-Ti) dual phase alloy. V and Mo were chosen as additives, as those were strong beta former of Ti alloy. The addition of 10mol%V (Ti-3Omol%Si-lOmol%V) or 5mol%Mo (Ti-32mo1%Si-5mol%Mo) was able to stabilize beta-Ti at room temperature after stabilization treatment at 1473K for 86.4ks. Chemical compositions of each phase in the samples were obtained by EDS analysis. Using the results of quantitative observations and X-ray diffraction to identify the phases. Ti-Si-V and Ti-Si-Mo isothermal section at the area around (Ti_5Si_3+Ti) dual phase composition at room temperature were able to illustrated. D88 phase can dissolve over 20mol%V and 14vol%Mo in Ibis investigation. D88 phase in the Ti-37.Smol%Si-20mol%V alloy showed enhanced fracture toughness of 185MPa・m^<1/2> compared to the value of 1.17 of stoichiometric D88 phase (Ti-37.5mol%Si). Mo addition had an effect of microstructure refinement that was decreasing aspect ratio of primary Ti_5Si_3 grain and spheroidizing of eutectic structure (especially Ti_5Si_3 phase). This microstructural effect had prevented to introduce cracks during cooling after melting.