激光线能量对TC17钛合金焊接接头组织和疲劳性能的影响

Effect of Laser Heat Input on Microstructure and Fatigue Behavior of TC17 Titanium Alloy Laser Welded Joint

摘要:

在不同的激光线能量条件下对TC17钛合金进行了焊接，采用光学显微镜、扫描电镜、透射电镜、拉伸和疲劳试验机对接头的宏观形貌、微观组织和力学性能进行了对比研究。结果表明：随着激光线能量的增加，焊缝宏观形貌由Y型转变为X型、焊缝中气孔缺陷数量先增加后减少，气孔缺陷主要分布在焊缝的中下部。焊缝由柱状晶粒组成，柱状晶内部存在条形枝晶，枝晶间距随着线能量的增加而逐渐增大。热影响区由尺寸较小的等轴晶组成，随着激光线能量的增加，α相晶粒逐渐细化，而β相逐渐粗化。在拉伸和疲劳试验中，TC17激光焊接接头均断裂在焊缝。受焊缝内部枝晶尺寸的影响，抗拉伸强度随线能量的增加而降低。气孔是导致疲劳断裂的主要原因，气孔缺陷数量越少，则疲劳寿命越长。

Abstract:

TC17 titanium alloy was weld under different laser heat input conditions. Optical microscope, scanning electron microscope, transmission electron microscope, tensile and fatigue tests were used to compare the macroscopic morphologies, microstructures, and mechanical properties of the welded joints. The results show that with the increase in heat input, the morphology of weld changes from Y- to X-shaped. The number of pore defects in the weld increases first and then decreases. The pore defects are mainly distributed in the middle and lower part of the weld zone. The weld is composed of coarse columnar grains with strip dendrites inside, and the spacing of dendrite increases gradually with the increase in heat input. The heat affected zone comprises finer equiaxed grains, and the increase in heat input leads to the refinement of α phase and coarsening of β phase. Moreover, the TC17 laser welded joints all fracture at the weld zone in the tensile and fatigue tests. Under the influence of dendrite size, the tensile strength decreases with the increase in heat input. The welding pore is the main reason for the fatigue fracture, and the fatigue life peaks when the number of pore defect is the lowest.