高Nb-TiAl合金的高温变形行为及其板材的性能

对高Nb-TiAl合金进行多步热压缩，研究其高温变形行为及其板材的性能。结果表明，热压缩变形后高Nb-TiAl合金的组织中等轴γ晶粒和α晶粒的增多、层片晶团的体积分数和尺寸降低，使其变形能力提高。根据这些结果确定了最优轧制工艺为应变速率低于0.5 s-1、道次变形量前期应不高于25%、变形温度高于1150℃。选用上述工艺对其其进行5道次大变形量轧制，制备出表面质量良好、无缺陷的高Nb-TiAl合金板材，其尺寸为600 mm×85 mm×3 mm。这种板材具有双态组织，平均晶粒尺寸小于5μm，其室温屈服强度、抗拉强度和塑性分别为948 MPa、1084 MPa和0.94%,800℃下抗拉强度为758 MPa。

High-temperature Deformation Behavior and Properties of High Nb Containing TiAl Alloy

The high-temperature deformation behavior of high Nb containing TiAl alloy during step-by-step hot compression process was studied. Results show that the workability of high Nb containing TiAl alloy was improved after one hot compression deformation due to the increased volume fraction of equiaxed γ grains and α grains, as well as the decreased volume fraction and size of lamellar colony. Accordingly, based on the processing map and microstructure optimization, the optimal rolling process can be acquired as: the rolling process with strain rate lower than 0.5 s^-1, deformation strain less than 25% in the early deformation stage and deformation temperature higher than 1150℃ was determined. Correspondingly, a large size of 600 mm×85 mm×3 mm high Nb containing TiAl alloy sheet with good surface quality and defect-free was successfully fabricated by hot pack rolling with 5 passes of large deformation rolling. The microstructure of the as-rolled high Nb containing TiAl alloy presented fine duplex microstructure with mean grain sizes of less than 5 μm. At room temperature, the as-rolled alloy exhibited yield strength, ultimate tensile strength and ductility as 948 MPa, 1084 MPa and 0.94%, respectively. The tensile strength at 800℃ also remained as high as 758 MPa.