한국주조공학회

In this study, the variations of microstructures and tensile properties of Ti-(44-54)at.% Al binary alloys were investigated. The heat-treated microstructure depended greatly on their solidification structure and annealing temperature. We measured the variations of volume fractions of primary and secondary lamellar structure as a function of the heat treatment temperature in a Ti-47at.%Al alloy. The variation of ductility as a function of Al content was in good agreement with the change of fracture mode in the tensile fracture surface. It can be inferred that the variations of yield stress and hardness of γ phase in a single γ-phase field region are enhanced by anti-site defects created by deviations from the stoichiometric composition. In a Ti-47at.%Al alloy within the (α2+γ) two-phase field, the yield stress tended to be the maximum at a near equal volume fraction of lamellar and γ grains. The ductility depended sensitively on the overall grain size and Al content. The calculation of fracture strain using Chan’s model indicated that the change of ductility as a function of annealing temperature was primarily determined by the variations in the overall grain size and lamellar volume fraction.

Ti-(44-54)at.%Al alloys, Tensile properties, Cast Ti-Al binary alloys, Heat-treated cast microstructures, Tensile fracture mode