通道偏析对Ti45Nb合金丝材组织及力学性能的影响

Effect of Channel Segregation on Microstructure and Mechanical Properties of Ti45Nb Alloy Wire

摘要:

研究了通道偏析对Ti45Nb合金丝材宏观/微观化学成分、显微组织、硬度及拉伸变形行为的影响。结果表明，存在大量通道偏析的丝材，其宏观化学成分与无偏析丝材一致，三维X射线成像也未发现异常。退火后，2类丝材均呈现等轴单相组织，晶粒尺寸相近，表明通道偏析对宏观成分及晶粒尺寸无明显影响。金相组织显示通道偏析在丝材横截面呈现为斑点状组织；纵截面呈现为条带状结构。能谱分析显示通道偏析为富Ti偏析，其Ti含量较基体高出约4.42wt%。与无偏析丝材相比，存在大量通道偏析的丝材抗拉伸强度和屈服强度分别高了15.5%和12.3%，但延伸率和断面收缩率分别低了19.8%和18.9%，且存在通道偏析的丝材性能波动大。断口分析显示，存在通道偏析丝材断口截面面积大，位错在偏析区界面处严重塞积，诱发了微裂纹形核，促使裂纹源快速扩展，导致材料塑性及断面收缩率显著下降。

Abstract:

The effects of channel segregation on the macro- and micro-scale chemical composition, microstructure, hardness, and tensile deformation behavior of Ti45Nb wires were investigated. The results show that wires with severe channel segregation exhibit a macroscopic chemical composition identical to those without segregation, and 3D X-ray imaging result also reveals no abnormalities. After annealing, both types of wires exhibit an equiaxed single-phase microstructure with comparable grain sizes, suggesting that channel segregation has negligible influence on the macroscopic composition and grain size. Metallographic examination reveals that channel segregation manifests as spot-like features in the transverse section and band-like structures in the longitudinal section. EDS analysis identifies these regions as Ti-enriched segregations, with a Ti content higher than that of the surrounding matrix by approximately 4.42wt%. Compared to segregation-free wires, those containing extensive channel segregation demonstrate a 15.5% increase in ultimate tensile strength and a 12.3% increase in yield strength, but suffer a reduction in elongation and reduction of area by 19.8% and 18.9%, respectively. Furthermore, the mechanical properties of wires with segregation show significant fluctuations. Fractographic analysis reveals a larger fracture surface area in segregated wires. Severe dislocation pile-ups occur at the interfaces of these segregated regions, initiating microcrack nucleation. This promotes rapid crack propagation of the Ti45Nb wire, leading to a significant decrease in plasticity and reduction of area.