(华中科技大学 材料成形与模具技术国家重点实验室，武汉430074)
摘 要: 通过对Ti-6Al-4V合金板材预制一定深度的疲劳裂纹，研究母材与焊缝区疲劳裂纹尖端的TEM显微形态。结果表明：经历疲劳循环后，位错密度大大增加，α/β相界面位错密度高，易成为位错形核的源区；在周期性疲劳载荷的作用下，位错以源区为原点呈放射状向四周发散运动；在焊缝区马氏体板条之间的细碎相之间，位错聚集严重，说明细碎相也易成为位错萌生的源区，从而成为疲劳裂纹形核的源区；在焊缝区马氏体板条宽度越窄，位错聚集密度越高，易成为疲劳裂纹萌生的位置。此外，TEM观察证实了裂纹尖端存在一定尺寸的塑性变形区。通过焊接接头分区的TEM对比分析，获得焊缝区比母材区更易萌生疲劳裂纹的相关证据。
关键字: Ti-6Al-4V合金；电子束焊接；疲劳；裂纹尖端；显微形态
Ti-6Al-4V electron beam welding joints
（State Key Laboratory of Material Processing and Die and Mould Technology,
Huazhong University of Science and Technology, Wuhan 430074, China）
Abstract:Ti-6Al-4V sheet alloy specimens were precracked in different regions of electron beam welded joints. Transmission electron microscopy (TEM) observations were carried out at fatigue crack tip of base metal and welded joint. The microstructure observations reveal that the experiencing fatigue crack growth, the dislocations which emit from α/β interfaces reach so densely that they incline to become a source of the fatigue cracks, from which the dislocations are diverged radioactively under the cyclic stress. Dislocations accumulate seriously among the fine phases which lay between two martensite lathes, indicating that these small fatigue phases tend to become the source of fatigue crack. In addition, the narrower the width of martensite lathes is, the more easily the dislocations accumulate to become the fatigue source. The plastic zone is also observed at the fatigue crack tip. By comparing the TEM images of different regions, the corresponding evidence that welded joints are more liable to become the source fatigue cracks is found.
Key words: Ti-6Al-4V alloy; electron beam welding (EBW); fatigue; crack tip; micromorphologies
