置氢量对TC4钛合金激光焊接头组织相变及硬度的影响

采用光学显微镜(OM)、扫描电镜(SEM)和X射线衍射(XRD)等研究了置氢量分别在0%、0.05%、0.16%和0.37%时的TC4钛合金激光焊接头的显微组织及相变,并用数字显微硬度计分析置氢后接头硬度的变化规律,阐述其影响机制。结果表明:随着置氢量的增加,母材中的α相减少,β相增加;焊缝组织由针状马氏体α′相转变为片层状组织,且母材和焊缝组织向同一方向转变。接头显微硬度随置氢量的增加逐渐降低,且母材和焊缝的硬度差值逐步缩小,当置氢量为0.37%时,焊缝和母材的硬度差最小,为13 HV。置氢量影响TC4钛合金接头硬度的原因是接头中软化相β、氢化物δ和氢的固溶强化等引起的多种相变的作用。

Effect of hydrogen content on microstructure phase transformation and hardness of TC4 titanium alloy laser welded joint

Microstructure and phase transformation of TC4 titanium alloy laser welded joint with hydrogen content of 0%, 0.05%, 0.16% and 0.37% were studied by means of optical microscope(OM), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The change of hardness of the TC4 titanium alloy joint after hydrogen addition was analyzed by digital microhardness tester, and the influence mechanism was expounded. The results show that with the increase of hydrogen content, the α phase in the base metal decreases and the β phase increases, and the microstructure of the weld changes from acicular martensite α′ phase to lamellar structure, and the base metal and weld microstructure change in the same direction. The microhardness of the joint decreases with the increase of hydrogen content, and the hardness difference between the base metal and the weld decreases gradually. When the hydrogen content is 0.37%, the hardness difference between the weld and the base metal is the smallest, which is 13 HV. The effect of hydrogen content on the hardness of the TC4 titanium alloy joint is due to the effects of various phase transformation caused by softened phase β, hydrogenated δ and solid solution strengthening of hydrogen in the joint.