坡口形式对TC18钛合金厚板焊接接头组织及性能的影响

Effect of Groove Form on Microstructure and Properties of TC18 Titanium Alloy Thick Plate Welded Joints

将15 mm的TC18钛合金厚板分别加工成U型、V型及X型坡口,采用惰性气体钨极氩弧焊的方法实现对接焊。利用光学显微镜、扫描电子显微镜对接头的宏观形貌、显微组织及断口特征进行分析,用硬度计测量焊缝区、热影响区及母材区的显微硬度,并用电子万能试验机测试不同坡口形式下接头的拉伸性能。结果表明,U型及V型坡口的焊缝组织基本相同,均得到柱状β相和针状及颗粒状α相。X型坡口组织为柱状β相上弥散分布着等轴状及针状α相,且X型坡口中晶粒尺寸最小。与母材及焊缝区相比,热影响区晶粒粗化,硬度最低。U型坡口的接头抗拉强度及伸长率最低,X型坡口最高。U型坡口断口呈现出脆性断裂为主的特征,X型坡口断口表现出准解理断裂的特征。

The 15 mm TC18 titanium alloy thick plate was machined into U, V and X type grooves, respectively. The butt welding was realized by tungsten inert gas welding. The macroscopic morphology, microstructure, and fracture characteristics of the joints were analyzed by using optical microscope and scanning electron microscope. The hardness of the weld zone, the heat affected zone and the base material zone was measured by hardness meter, and the tensile properties of joints under different groove forms were tested by electronic universal testing machine. The results show that the weld zone structures of U and V grooves are basically same, and the columnar β phase, acicular and granulate α phase are obtained. The structure of X groove is columnar β phase with dispersed equiaxed and acicular α phase, and the grain size in the X groove is the smallest.Compared with the parent material and the weld zone, the grain of the heat affected zone is coarse and the hardness is the lowest. The tensile strength and elongation of the joint of U groove are the lowest, and those of X groove are the highest. The fracture of U groove is mainly characterized by brittle fracture, and the fracture of X groove shows the characteristic of quasi cleavage fracture.