TiAl alloys are a new lightweight high temperature structural materials and have a broad application in aerospace, automotive and other fields for their low density, high specific strength, high modulus, good resistance to oxidation and excellent fatigue properties. In recent years, TiAl alloys are attracting world-wide attention and much work has been done. The major factors of restrain TiAl alloys to use are the lower room temperature ductility and fracture toughness, development of good performance of fine homogeneous organizations to explore the largest potential is to be the focus of TiAl alloys investigation. TiAl alloy materials with good performance can be made through hot extrusion, but there are component segregations in cast ingots, and fine homogeneous organizations can’t be obtained during extrusion processing. In this study, TiAl alloys are treated through powder metallurgy and hot extrusion to obtain fine homogeneous organizations with a view to be an excellent performance.
High purity pre-alloyed O-phase powders and γ-TiAl powders have been produced by Electrode Induction Melting Gas Atomization (EIGA) method. O-phase powders have been HIPped under the condition of 1000℃/130MPa/4h, and fine homogeneous equiaxed grain organizations are obtained, but some powder boundary still exists. γ-TiAl powders have been HIPped under the condition of 1100℃/130MPa/4h, and fine homogeneous equiaxed grain organizations are obtained with no powder boundary, which have good hot-working ability.
As HIP-compacted γ-TiAl alloy has been extruded under the condition of 1300℃, compared with extruded cast organizations, the organizations obtained are finer and more homogeneous, which have less component segregations, and it can be expected to have an excellent performance. After heat treatment under the conditions of 1340℃/10min/FC and 900℃/8h, the extruded γ-TiAl alloy has been tested for tensile performances. The tested tensile performances is good but worse than the performances of extruded cast γ-TiAl alloy. The reason is that the combining effect between powders is not good enough, during the tensile test, the crack resources can easily appear on the boundaries of combined powders, and they produce cracks which lead to fracture and make the tensile performance worse. The performance of extruded γ-TiAl alloy can be improved through improving powder capsulation and vacuum degassing technology, which makes the combining effect between powders better.
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