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选区激光熔化成形Inconel 625合金的激光焊接头组织及高温蠕变性能

Microstructure and high temperature creep properties of Inconel 625 alloy by selective laser melting

  • 摘要: 采用光学显微镜、扫描电镜、X射线衍射仪和能谱仪等对选区激光熔化 (SLM) 成形Inconel 625合金的激光焊接头组织特征及高温蠕变性能进行研究分析. 结果表明,SLM成形Inconel 625合金的激光焊接头质量良好,无明显的制造缺陷存在. SLM成形Inconel 625合金激光焊焊接试样的组织主要由母材区的等轴奥氏体组织以及焊缝区的柱状枝晶组成. 高温蠕变试验结果显示,试样的蠕变时间随着应力的增大急剧下降. 较高的应力水平(200 MPa)对合金在同一温度下的蠕变性能影响很大,会导致蠕变变形直接进入蠕变第三阶段——加速阶段,引发试样较早发生断裂. 断口分析表明,所有试样断裂均发生在母材区或近热影响区,母材区观测有大量二次裂纹,熔覆区未观察到明显裂纹. 蠕变断口形貌呈冰糖块状特征,表明断裂模式主要为沿晶断裂. 高温下晶界滑移引发的形变位移是晶界空洞形核的主要机制.

     

    Abstract: Microstructure and high temperature creep properties of laser welded joints of Inconel 625 alloy fabricated by selective laser melting (SLM) method were investigated using optical microscope, scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometer. The results show that the quality of laser welded joints of Inconel 625 alloy by SLM is superior, and no obvious manufacturing defects are found. The microstructure of the laser welded Inconel 625 alloy by SLM specimen is mainly composed of the austenitic in the base metal and columnar dendrites in the fusion zone. High temperature creep test results show that the creep time of the alloy drops sharply with the increase of the applied stress level. The higher stress level (200 MPa) has a great influence on the creep property of the alloy at the same temperature, which will lead to the creep deformation directly entering the third stage of creep - acceleration stage, and cause the sample to fracture earlier. The mechanism of creep failure was discussed by analyses of the fracture surface. It is found that the fracture of all specimens occurred in the base metal or near the heat-affected zone. A large number of secondary cracks were observed in the base metal, while no obvious cracks were found in the fusion zone. Also, the fracture morphology is characterized by a rock candy pattern, indicating the intergranular fracture mode. The deformation displacement induced by the grain boundary slipping at elevated temperature is the principal mechanism of the cavity nucleation.

     

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