SEM原位观察BT20钛合金激光焊接头的断裂行为

In-Situ SEM Observation on Fracture Behavior of Laser Welded BT20 Titanium Alloy Joints

采用单边缺口试样用扫描电镜原位观察了BT20钛合金激光焊接头焊缝的裂纹萌生与扩展特征。焊后态试样裂纹一经萌生随即失稳断裂。焊后热处理试样经历了较长的裂纹亚稳扩展阶段,在切应力与正应力共同作用下,微裂纹沿滑移带萌生;裂纹扩展过程中遇到滑移带时发生偏转;新的微裂纹在裂纹尖端的滑移带相交处萌生,并随后与主裂纹相连。焊后热处理可显著提高激光焊接头的韧塑性。

The fracture characteristics of laser welded BT20 titanium alloy joints have been investigated through in-situ tensile tests in scanning electron microscope using a single-edge notched specimen. For as-welded specimens, they would fracture as soon as the crack initiated. The specimen after post-weld heat treatment experienced a long metastable stage before fracture. Microcrack initiated along slip band under the combination action of shear stress and normal stress. The crack would deflect when it came across slip bands. New microcrack would initiate at the position of slip bands intersecting each other ahead of the main crack, and converged with the main crack subsequently. Post-weld heat treatment can improve the toughness and plasticity of laser welded joints markedly.