峰值温度和降温速率对TC4钛合金焊接热影响区组织与性能的影响

目的 通过Gleeble 540热模拟试验机模拟TC4钛合金的热影响区，探讨不同热循环条件下TC4钛合金组织性能的演变规律，为钛合金激光焊接工艺的优化提供指导。方法 利用Gleeble 540热模拟试验机对TC4钛合金焊接热影响区进行模拟试验，采用金相显微镜和扫描电镜观察不同热模拟参数下TC4钛合金的显微组织，运用数字式显微硬度计和拉伸试验机对热模拟试样进行硬度和拉伸测试。结果 当峰值温度低于相变温度时，热影响区组织呈块状α相，这种片层较厚且为块状组织的存在使硬度显著提高，拉伸强度大幅下降;当峰值温度升至完全相变温度以上时，热影响区组织逐渐转变为大量的针状α''马氏体，硬度和拉伸强度逐渐提高。当峰值温度为1 100 ℃时，抗拉强度显著高于母材拉伸强度，达到1 248 MPa。降温速率的增大导致针状α''马氏体增多，长针状马氏体破碎形成网篮状马氏体组织，虽然热影响区的硬度没有明显变化，但是拉伸强度略有降低。结论 在TC4钛合金实际焊接中，确保峰值温度高于钛合金组织的完全相变温度，可提高钛合金激光焊接接头的力学性能。

Effects of Peak Temperature and Cooling Rate on Microstructure and Properties in Heat-affected Zone of TC4 Titanium Alloy

The work aims to investigate the microstructure and property evolution of the TC4 titanium alloy through the thermophysical simulation of its heat-affected zone by Gleeble540 thermal simulation testing machine under different thermal cycling conditions, so as to provide guidance for the optimization of titanium alloy laser welding process. The HAZ of TC4 titanium alloy was simulated by Gleeble540 thermal simulation testing machine, the microstructure of TC4 titanium alloy under different simulation parameters was observed by metallographic microscope and scanning electron microscope, and the hardness and tensile properties of thermal simulation samples were tested by digital microhardness tester and tensile testing machine. When the peak temperature was below the phase transition temperature, the microstructure of the HAZ was composed of massive α phase, and the existence of the thick and massive α phase significantly increased the hardness and greatly reduced the tensile strength. When the peak temperature raised above the complete transformation temperature, the structure of the HAZ gradually transformed into a large amount of acicular α'' martensite, and the hardness and tensile strength also gradually increased, and the tensile strength at 1 100 ℃ was significantly higher than that of base metal, which was up to 1 248 MPa. The acceleration of the cooling rate increased the acicular α'' martensite, and the long needle-like martensite was broken and irregularly arranged, resulting in a basket-like martensite structure, but the hardness of the TC4 titanium alloy thermal simulation samples were not changed significantly, while the tensile strength decreased. In the actual welding of TC4 titanium alloy, it is necessary to ensure that the peak temperature is higher than the complete phase transformation temperature of titanium alloy structure to improve the mechanical properties of titanium alloy laser welded joints.