Experimental and Finite Element Simulation of Milling Process for γ-TiAl Intermetallics
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Gamma titanium aluminide (γ-TiAl)intermetallic compounds are spotlighted as lightweight heat-resistant materials, and have been investigated extensively to aiming commercial use.Fundamental approaches in which phase diagrams of Ti -Al -Cr and TiAl -Nb have been studied based on the experimental data and calculations , have been performed in the national project For industrial approach, ingot process and direct casting process have been developed to provide sheet form of TiAl. By these approaches, γ-TiAl base ,intermetallic compounds show a great possibility to apply in the variety of fields .However, a more detailed understanding of phase equilibrium in Ti-Al -X and the relationship between the mechanical properties and microstructure will be necessary
Titanium aluminide
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Titanium alloy
Aluminide
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TiAl alloys undergo cyclic temperature changes during use, the process of which can be simulated by the thermal shock test. A systematic investigation of the thermal shock behavior of four Mo‐containing TiAl alloys is conducted. The increase in Mo content from 1.0% to 4.0% causes the gradual decrease in the volume fraction of γ / α 2 lamellar colony, while the volume fraction of equiaxed γ and β o phases gradually increases. At the same time, the thermal shock resistance of the TiAl alloys decreases as the Mo content increases. After thermal shock, cracks often occur within the lamellae and extend in a zigzag manner for TiAl−1.0Mo and TiAl−1.5Mo alloys. Their thermal shock resistance is enhanced by crack deflection, bridging, and microcrack shielding. For TiAl−2.0Mo and TiAl−4.0Mo alloys, cracks occur at the grain boundaries or within the γ phase and extend straight, with the result that these two alloys have worse thermal shock resistance than the other two alloys due to the limited effect of microcrack shielding. In addition, the microstructure stability of TiAl alloys after thermal shock is discussed, and there is a critical value of Mo content between 3.13% and 5.67%, which inhibits the β o → ω phase transition.
Thermal shock
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Compression creep behavior was investigated on a Ti-53.4 mol%Al intermetallic compound which was prepared by ingot casting. The material was made into a single gamma (TiAl) phase by vacuum annealing, though it still retained a columnar structure whose dimensions were about 100 μm in diameter and about 1 mm long. Constant true stress compression creep tests were performed under 80∼400 MPa at 1000∼1150 K in an argon atmosphere.Normal creep curves were obtained at the higher stress, but the shape of the creep curves gradually changed into sigmoidal-like one with decreasing stress. Stress- and temperature-dependence of the creep rate was evaluated by comparing the creep rates at a fixed true strain. Both the stress exponent and the apparent activation energy decreased with straining and reached constant values, n\fallingdotseq4.3, Q\fallingdotseq330 kJ/mol at around 0.3∼0.5 strain. Minimum creep rates were close to those reported on equi-axed samples and were characterized by nm\fallingdotseq5 and Qm\fallingdotseq380 kJ/mol in the high stress region.
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