Browsing by Subject "-TiAl"

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    The effects of quaternary alloying additions on the TiAl alloy: Preferential site occupancy, interfacial energetics to physical parameters
    (2021-08) Mathabathe, Maria N; Modiba, Rosinah; Bolokang, Amogelang S
    The effect of Nb, Sn, Mn, and Si at a concentration of (0.3-2 at. %) on -TiAl based alloys’ preferential occupancy, interfacial energetics and mechanical properties were investigated by density functional theory (DFT) encompassed by the typical gradient estimation configuration and substantiated by experimental work. The site occupancies, elastic constants, shear and bulk modulus, B/G ratio, Poisson's ratio, hardness and universal anisotropy are systematically elucidated. The results indicated that Mn adamantly occupies Ti sites, while the Nb, Sn and Si occupy Al sites, with no significant influence on the alloy composition in-terms of their site preference. Interfacial energy of /a2-M system is the prerequisite energy to generate an interface from bulk materials. The stability criteria were satisfied attributable to Cij’s values greater than zero. The overall mechanical properties of the substitutional solid solution-TiAl alloy exhibited improved ductility. The alloy was produced by vacuum arc melting, with subsequent annealing to achieve homogeneity. The TEM results demonstrated that the a2/ interface boundaries yielded the -TiAl {111} <110>||a2-Ti3Al (0001)<110> orientation relationship.
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    In-situ LENS fabricated Ti–Al–Si alloy phase transformation and microstructural evolution after isothermal annealing heat treatments
    (2022-02) Raji, SA; Popoola, API; Pityana, Sisa L; Popoola, OM; Raji, NK; Tlotleng, Monnamme
    Gamma titanium aluminide ( -TiAl) alloys are lightweight materials with potential application for high-temperature components. But their ductility at room temperature impedes widespread production of parts via traditional processing routes. In this work, intermetallic Ti–Al–Si alloy was produced via laser in situ alloying from elemental powders by applying the laser engineered net shaping (LENS) technique. Isothermal annealing heat treatment was carried out at 1200, 1300, and 1400 °C for 1 h, followed by furnace cooling (FC). A second homogenization heat treatment was done at 850 °C for 6 h followed by FC. The microstructure was characterized by optical microscopy, (OM), scanning electron microscopy (SEM) equipped with an electron dispersion spectroscopy (EDS), and electron backscattered diffraction (EBSD) technique. The result shows precipitates of silicide ( -Ti5Si3) grains with lamellae microstructure in the as-built Ti–Al–Si samples, while dense columnar grains of fully lamellar (FL) microstructure comprising of a2-Ti3Al and -TiAl were observed for the 1300 °C/1 h/FC/850 °C/6 h/FC heat-treated sample with -Ti5Si3-phase at the grain boundaries. The high microhardness values of the samples were ascribed to the presence of -Ti5Si3-phase being formed. This study established that laser in-situ alloying with standard heat treatment is feasible for the development of TiAl-based alloys.