(華中科技大學 材料成形與模具技術國家重點實驗室，武漢430074)
摘 要: 通過對Ti-6Al-4V合金板材預制一定深度的疲勞裂紋，研究母材與焊縫區(qū)疲勞裂紋尖端的TEM顯微形態(tài)。結果表明：經(jīng)歷疲勞循環(huán)后，位錯密度大大增加，α/β相界面位錯密度高，易成為位錯形核的源區(qū)；在周期性疲勞載荷的作用下，位錯以源區(qū)為原點呈放射狀向四周發(fā)散運動；在焊縫區(qū)馬氏體板條之間的細碎相之間，位錯聚集嚴重，說明細碎相也易成為位錯萌生的源區(qū)，從而成為疲勞裂紋形核的源區(qū)；在焊縫區(qū)馬氏體板條寬度越窄，位錯聚集密度越高，易成為疲勞裂紋萌生的位置。此外，TEM觀察證實了裂紋尖端存在一定尺寸的塑性變形區(qū)。通過焊接接頭分區(qū)的TEM對比分析，獲得焊縫區(qū)比母材區(qū)更易萌生疲勞裂紋的相關證據(jù)。
關鍵字: Ti-6Al-4V合金；電子束焊接；疲勞；裂紋尖端；顯微形態(tài)
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
