包覆热轧制备粉末冶金TiAl合金板材及热加工行为研究

Manufacturing of γ-TiAl Sheet by Hot Packed Rolling of Powder Metallurgy Preform

采用超声气体雾化法制备洁净的TiAl预合金粉末,再经粉末除气、封装、热等静压致密化等工序获得TiAl基合金热轧板坯,之后包覆热轧制备粉末冶金TiAl基合金板材。轧制过程中材料的应变、应力状态、温度场分布非常复杂,本实验采用Gleeble热模拟试验机和有限元(FEM)模拟相结合,确定热加工工艺窗口,优选出热轧工艺参数,并热轧得到组织均匀、性能良好、尺寸为220 mm×370 mm×2 mm的粉末冶金TiAl基合金板材。板材室温拉伸性能Rp0.2为608 MPa,Rm为668 MPa,A为2.56%;1 000℃拉伸性能Rp0.2为163 MPa,Rm为330 MPa,A为32.0%;焊接成形性良好,焊缝无缺陷及二次裂纹产生,焊缝区域显微组织与基体差别不大。

Sheets made of light high-temperature materials such as γ-TiAl alloys have a variety of applications in aerospace structures, and the demands for this alloy are increasing. The PM route offers an attractive alternative for the preparation of preforms for sheet rolling, because high-pressure gas atomization can be used to produce clean, fine, almost segregation-free prealloyed powders. Furthermore, the PM route enables the production of large dimension γ- TiAl-based alloy sheets. Thus compared to ingot metallurgy route, the powder metallurgy route has the advantages of compositional homogeneity and dimensional extensibility. This paper summarizes our successful effort of sheet rolling using atomized powder of gamma alloys. Emphasis will be placed upon impurity pick-up, control of the atomized powder, the influence of degassing/HIPing parameters on the soundness of perform, as welt as identification of optimal combinations of rolling parameters. Temperature distribution in the preform at different stage of the rolling operation was accurately simulated using a finite element method. Thermomechanical deformation map of the gamma alloys obtained on a Gleeble simulator proves to be an excellent guide to identifying the ＇ processing windows＇ in which sheets with satisfactory mechanical properties can be produced. The weldability of sheets is important in extending the applications of this advanced material. Our successful attempt at electron beam welding of the TiAI sheets will also be described.