12 mm厚TC4钛合金激光-MIG复合焊接头疲劳裂纹扩展行为研究  

Study on Fatigue Crack Growth Behavior of 12mm Thick TC4 Titanium Alloy Laser-MIG Hybrid Weld Joint

作　　者：王洪潇 王春生 邓钢 朱宗涛[2] 陈辉[2] WANG Hongxiao;WANG Chunsheng;DENG Gang;ZHU Zongtao;CHEN Hui(CRRC Changchun Railway Vehicles Co.,Ltd.,Changchun 130062,China;School of Material Science and Engineering,Southwest Jiaotong University,Chengdu 610031,Chnia)

机构地区：[1]中车长春轨道客车股份有限公司,吉林长春130062 [2]西南交通大学材料科学与工程学院,四川成都610031

出　　处：《电焊机》2024年第10期17-31,共15页Electric Welding Machine

摘　　要：为探究12 mm厚TC4钛合金激光-MIG复合焊接头在不同区域的疲劳裂纹扩展行为,并分析微观组织与裂纹扩展之间的相互作用。利用体式显微镜、相显微镜、扫描电子显微镜和电子背散射衍射技术分别对接头不同部位的裂纹扩展速率,裂纹扩展路径的变化,接头不同区域的显微组织与裂纹扩展的交互作用和裂纹尖端周边组织的变形特征进行了深入探究。结果表明,在裂纹稳定扩展阶段,母材区域的裂纹扩展速率最大,分别是热影响区和焊缝区域裂纹扩展速率的1.16倍和1.81倍。当ΔK=20 MPa·m^(1/2),母材裂纹扩展速率为3.39×10^(-4)mm/cycle。裂纹尖端的IPF图表明,在焊缝区中存在的50°~70°的大角度晶界占比为36.36%,高于母材的11.91%和热影响区的11.65%,大角度晶界的存在使裂纹沿晶界偏转或消耗更多能量穿过晶界,增大裂纹扩展阻力,表现出较好的裂纹扩展抗性。母材和热影响区表现出沿晶脆性断裂和韧性断裂的混合断裂模式,而焊缝区主要呈韧性断裂模式。此外,EBSD分析结果表明,焊缝区裂纹尖端附近具有更高的几何位错密度,位错在马氏体边界聚集,导致裂纹沿晶界发生偏转,进一步阻碍了裂纹的扩展。施密特因子分析也表明,焊缝区组织间的取向差差异较大,导致其裂纹扩展门槛值较高。综上,焊缝区中存在的大量大角度晶界和高位错密度是焊缝区具有较高裂纹扩展抗性的主要原因。The study aims to investigate the fatigue crack growth behavior in different regions of a 12 mm thick TC4 titanium alloy laser-MIG hybrid welded joint and to analyze the interaction between microstructure and crack growth.Volume microscopy,phase microscopy,scanning electron microscopy,and electron backscatter diffraction(EBSD)techniques were used to explore the crack growth rates in different parts of the joint,the changes in crack growth paths,the interaction between microstructure and crack growth in different joint regions,and the deformation characteristics of the tissue around the crack tip.The results show that in the stable crack growth phase,the crack growth rate in the base metal area is the highest,which is 1.16 times and 1.81 times that of the heat-affected zone and the weld zone,respectively.WhenΔK=20 MPa·m^(1/2),the crack growth rate in the base metal is 3.39×10^(-4)mm/cycle.The IPF map at the crack tip indicates that the proportion of large-angle grain boundaries in the weld zone is 36.36%,which is higher than the 11.91%in the base metal and the 11.65%in the heat-affected zone.The presence of large-angle grain boundaries causes the crack to deflect along the grain boundaries or consume more energy to pass through the grain boundaries,increasing the crack growth resistance and showing better crack growth resistance.The base metal and heat-affected zone exhibit a mixed fracture mode of intergranular brittle fracture and ductile fracture,while the weld zone mainly shows a ductile fracture mode.In addition,EBSD analysis results show that the weld zone near the crack tip has a higher geometric dislocation density,and dislocations accumulate at the martensite boundary,causing the crack to deflect along the grain boundary,further hindering crack growth.Schmidt factor analysis also shows that the difference in orientation between the weld zone tissues is large,resulting in a higher crack growth threshold.In conclusion,the presence of a large number of large-angle grain boundaries and high dislocation den

关 键 词：钛合金 疲劳裂纹扩展 激光-MIG复合焊接 断裂模式 裂纹尖端 裂纹扩展行为 

分 类 号：TG456.7[金属学及工艺—焊接]