摘要
Abstract
The study aims to investigate the fatigue crack growth behavior in different regions of a 12 mm thick TC4 tita-nium 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 be-tween 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.When ΔK=20 MPa·m1/2,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 density in the weld zone is the main reason for the higher crack growth resistance in the weld zone.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Key words
titanium alloy/fatigue crack growth/laser-MIG hybrid welding/fracture mode/crack tip/crack growth behavior分类
矿业与冶金
