加工熱処理により組織制御されたγ+α_2 型 Ti-Al 系金属間化合物の高温特性 [in Japanese] High Temperature Properties of Thermo-mechanically Treated γ+α_2 Type Titanium Aluminides [in Japanese]
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The effects of microstructure morphorgy and the rolls of α_2(Ti_3Al) secondary phase on high temperature tensile property and creep rupture strength was investigated in structure controlled titanium aluminides. Three types of microstructure such as equi-axed, duplex and nearly lamellar were obtained by thermo-mechanical treatments performed in the α+γ phase field. As the volume fraction of α_2 phase increased from Ti-50.8at%Al to Ti-48.5at%Al, with decreasing Al content tensile strength at high temperature was improved by the strength of the α_2 phase itself and the stabilized lamellar structure which severely obstructed deformation. On the other hand, specimens with the stabilized lamellar structure in Ti-48.5at%Al showed little tensile elongation as little as 5% even at 1173K. The stabilized lamellar structure by α_2 phase also interferes with recrystalization during deformation, leading to a significant increase in creep rupture strength.