显微组织对低成本Ti-6Al-4V合金拉伸性能及高周疲劳行为的影响

Effect of Microstructure on Tensile Properties and High-Cycle Fatigue Behavior of a Low-Cost Ti-6Al-4V Alloy

摘要:

利用电子束冷床熔炼技术重熔TC4合金返回料并结合短程热轧工艺制备的低成本Ti-6Al-4V（TC4）合金为研究对象，采用去应力退火与固溶时效2种热处理制度，系统研究了显微组织对合金拉伸性能和高周疲劳性能的影响。结果表明：去应力退火后，合金主要呈现网篮状α+β片层组织；经固溶时效处理后，组织由粗化α片层、等轴α及β转变组织组成。与退火态相比，固溶时效态合金在保持较高强度的同时塑性显著提高，实现了较好的强塑性匹配。这主要归因于粗化α片层与等轴α的协同变形能够有效协调位错滑移并促进高阶滑移系的激活，从而提高材料的塑性变形能力。高周疲劳测试结果表明，退火态合金具有更高的疲劳强度，其原因在于网篮状片层组织能够促进疲劳裂纹偏转并延长裂纹扩展路径，从而提高疲劳裂纹的扩展阻力。

Abstract:

A low-cost Ti-6Al-4V (TC4) alloy fabricated by remelting TC4 scrap using electron beam cold hearth melting (EBCHM) combined with a short-process hot-rolling route was investigated. Two heat treatment conditions, namely stress-relief annealing and solution treatment followed by aging were adopted to study the influence of microstructure on the tensile properties and high-cycle fatigue (HCF) performance of the alloy. The results indicate that the stress-relieved alloy exhibits a typical basketweave α+β lamellar microstructure. After solution treatment and aging, the microstructure transforms into a heterogeneous structure consisting of coarsened α lamellae, equiaxed α grains, and transformed β. Compared with the annealed condition, the solution-aged alloy shows a significant improvement in ductility while maintaining relatively high strength, leading to a favorable strength-ductility synergy. This enhancement is primarily attributed to the cooperative deformation of coarsened α lamellae and equiaxed α grains, which effectively accommodate dislocation slip and promote the activation of higher-order slip systems, thereby improving the plastic deformation capability of the alloy. High-cycle fatigue tests reveal that the annealed alloy exhibits a higher fatigue strength. This behavior is associated with the basketweave lamellar microstructure, which facilitates crack deflection and prolongs the fatigue crack propagation path, thereby improving resistance to fatigue crack growth.