热循环对TC4钛合金窄间隙焊接接头组织和性能的影响

Effect of Thermal Cycling on Microstructure and Properties of TC4 Titanium Alloy Narrow-Gap Welded Joints

摘要:

热循环对钛合金厚板窄间隙焊接接头的组织和性能具有重要影响，本工作采用摆动送丝磁控电弧窄间隙焊接技术完成60 mm厚TC4钛合金焊接接头，借助数值模拟研究了典型热循环下的显微组织演变（α相、β相和晶界α_GB）、显微硬度变化及拉伸性能变化。结果表明，高温热循环发生完全的α→β转变，将有利于α相择优生长，形成粗大且方向一致的α群落；相比之下，后续低温热循环发生不完全α→β转变，较低的冷却速率及温度梯度将削弱择优取向，板条α相得以细化。经过整个热循环后，板条α相的厚度由0.910.09 μm增加至1.020.18 μm，残余β相比例由0.02%增加至1.89%。得益于细晶强化作用，焊接接头打底层显微硬度最高；打底层拉伸强度最高，盖面层延伸率最高，接头均表现为韧性断裂。

Abstract:

Thermal cycling has a significant impact on the microstructure and properties of narrow-gap welded joints in titanium alloy thick plates. In this study, a 60 mm-thick TC4 titanium alloy welded joint was fabricated using oscillating-wire magnetic-controlled arc narrow-gap welding technique. The evolution of the microstructure (α phase, β phase, and grain boundary α_GB), as well as changes in microhardness and its tensile properties under typical thermal cycling conditions were investigated through numerical simulation. The results show that high-temperature thermal cycling induces a complete α→β transformation, promoting the preferential growth of the α phase and forming coarse and uniformly-oriented α colonies. In contrast, subsequent low-temperature thermal cycling causes an incomplete α→β transformation, where lower cooling rate and temperature gradient weaken the preferential orientation, leading to the refinement of lamellar α phase. After the entire thermal cycling process, the thickness of lamellar α phase increases from 0.910.09 μm to 1.020.18 μm, and the proportion of residual β phase increases from 0.02% to 1.89%. The weld root layer exhibits the highest microhardness, attributed to grain refinement strengthening. The root layer also demonstrates the highest tensile strength, while the cap layer shows the highest elongation. The joints exhibit ductile fracture behavior overall.