TC25G钛合金高温变形组织演变及强塑性研究

Study on Microstructure Evolution and Mechanical Property of TC25G Titanium Alloy during High Temperature Deformation

摘要:

对比研究了网篮组织TC25G钛合金棒材在不同变形量下的组织演变及其550℃热暴露和蠕变性能变化。结果表明：随变形量的增加，合金热暴露后拉伸塑性逐渐增加，而高温抗蠕变性逐渐减弱，两种性能在变形量100%时达到良好匹配，均可满足工程应用要求。变形量的增加对应显微组织中片层α相的球化过程，在片层α相充分球化前，显微组织中多层级结构的界面强化效应使得合金具有良好的高温抗蠕变性；而α相充分球化后，等轴组织为主的显微组织使得合金具有较好的塑性。随变形量的增加，热暴露后拉伸断口韧窝尺寸逐渐变得细小均匀，且韧窝深度增加，表明合金热暴露后塑性提升。纳米显微硬度测试结果表明，合金中初生α相的显微硬度高于β转变组织，通过固溶温度调整合金中α相的含量和分布，可提升抗蠕变性，但其效果不及变形量的调控显著；为获得最佳的高温强塑性匹配，可通过控制片层α相球化程度来实现。

Abstract:

The microstructure evolution of TC25G titanium alloy bar with basket microstructure after different deformation degrees were studied and the changes of its thermal stability and creep resistance at 550 ℃ were compared. The results show that the tensile plasticity after thermal exposure increases and the creep resistance decreases with the increase of deformation degree. The two mechanical properties match well at 100% deformation degree and can meet the requirements of engineering application. The increase of deformation degree corresponds to the spheroidizing process of lamellar α phase. Before the lamellar α phase is fully spheroidized, the interface strengthening effect of multi-layer structure makes the alloy have good creep resistance at high temperature. However, after α-phase spheroidization, the alloy has better plasticity because of the microstructure dominated by equiaxed microstructure. With the increase of deformation degree, the size of the fracture dimples becomes smaller and more uniform, and the dimple depth increases, which indicates that the plasticity after heat exposure increases . The results of nano-hardness test show that the microhardness of primary α phase is higher than that of β transforms, and the creep resistance can be improved by adjusting the content and distribution of α phase in the alloy by solution temperature, in order to obtain the best matching of strength and plasticity at high temperature, the extent of lamellar α phase spheroidization can be controlled.