铜-钢电子束焊接材料的疲劳特性

Fatigue characteristics of copper-steel electron beam welding materials

异种金属焊接构件的疲劳性能对于航天器的服役可靠性具有重要影响。探索了Cr0.8铜合金和1Cr21Ni5Ti不锈钢异种金属焊接接头的疲劳寿命和疲劳断裂机制,采用合理的电子束焊接工艺制备得到铜-钢复合板。利用金相显微镜表征和分析焊缝处的组织与成分,使用电子拉伸试验机和疲劳试验机对焊接接头进行力学性能测试,利用扫描电镜观察不同周次断裂下的疲劳断口。结果显示:两种金属整体冶金结合情况良好,但是钢侧局部熔合区面积较大且由钢基体伸入到焊缝中;铜-钢电子束焊接接头的拉伸试样均断裂于焊缝最小截面处,疲劳试样的平均疲劳极限值为48.04 MPa,且均起裂于焊缝最小截面处;高周疲劳试样在焊缝上表面端点处观察到单一裂纹源,低周疲劳试样观察到较多裂纹源分布于焊缝上下表面及内部,两者的最终断裂区均位于铜合金基体。可见在疲劳断裂过程中,焊接试样在高周和低周断裂下的裂纹源数量存在差异,但是裂纹均易萌生于焊缝最小截面处,且向铜合金基体进行扩展。

The fatigue performance of dissimilar metal welded components has an important influence on the service reliability of spacecraft.The fatigue life and fatigue fracture mechanism of dissimilar metal welded joints of QCr0.8 copper alloy and 1Cr21Ni5Ti stainless steel were investigated.The copper-steel composite plate was properly prepared by electron beam welding.The microstructure and composition of welding seam were characterized and analyzed by metallographic microscope.Mechanical properties of welded joints were tested using electronic tensile testing machine and fatigue testing machines.Scanning electron microscopy was used to observe the fatigue fracture in different cycles.The results show that the overall metallurgical bonding of the two metals is good,however,the local fusion zone on the steel side has a large area and extends into the weld from the steel base.The tensile specimens of the copper-steel electron beam welding all fracture at the minimum section of the weld,and the average fatigue limit of the fatigue specimens is 48.04 MPa and they all fracture at the minimum section of the weld.In the high cycle fatigue sample,a single crack source is observed at the endpoint of the weld top surface,while in the low cycle fatigue sample,more crack sources are observed on the top and bottom surface and inside of the weld.The final fracture zone of both samples is located in the copper alloy matrix.It can be seen in the process of fatigue fracture,the number of crack sources is different between high and low cycle fracture,but in both cases,the cracks are easy to initiate at the minimum section of the weld and spread to the copper alloy matrix.