Microstructure and failure mechanism of FGH96 solid-state diffusion bonding interface
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摘要: 对原始状态分别为锻态、固溶态和半时效态的FGH96合金固相扩散连接界面显微组织进行表征，并对连接界面的拉伸性能进行测试，对失效行为进行研究。结果表明，锻态、固溶态和半时效态试样经固相扩散连接后界面均实现了良好的冶金结合，连接界面无孔洞和缝隙等缺陷。锻态试样界面扩散更为充分，组织过渡更为平缓；固溶态和半时效态试样界面存在明显的连接影响区。锻态试样经固相扩散连接和标准热处理后，二次γʹ相细小、均匀且呈典型椭球状；固溶态和半时效态试样因固相扩散连接热循环的作用导致γʹ相发生长大和分化。二次γʹ相尺寸及形貌的不同决定了界面区域性能水平的差异。电子背散射衍射测试结果表明，连接界面处大晶粒的择优取向为{100}，距离固相扩散连接界面越近，晶粒的择优取向越明显。拉伸试验结果表明，锻态试样经固相扩散连接和标准热处理后，连接界面处的强度达到基体强度的99%以上。拉伸裂纹主要萌生于连接界面大晶粒及γʹ相粗化聚集区域，体现为穿晶的韧窝型断裂。Abstract: The microstructure on the solid-state diffusion bonding interfaces of the initially as-forged, as-solution, and sub-aging FGH96 was characterized, the tensile properties of the bonding interfaces were tested, and the failure behavior was studied. It is found that the good metallurgical bonding is achieved at the bonding interfaces of all the three primitive state specimens after the solid-state diffusion, and no cracks and cavities are found. The interfaces of the as-forged specimens show more sufficient diffusion of elements and smoother transition of microstructure, while the interfaces of both the as-solution and sub-aging specimens exhibit an obvious bonding effecting zone. After the solid-state diffusion bonding and the standard heat treatment, the second γʹ phases in the as-forged specimens are fine, uniform, and spherical. However, the second γʹ phases in the as-solution and sub-aging specimens grow up and split up because of the solid-state diffusion bonding thermal cycle. Different morphology of the second γʹ phases causes the difference of properties in the bonding interface regions. Results of the electron backscattered diffraction (EBSD) show that the preferred orientation of large grains is {100}, and the grain orientation is more obvious as the closer distance to the solid diffusion interface. The tensile test results show that the strength at the interfaces of the forged specimens after the solid-state diffusion bonding and the standard heat treatment is more than 99% of that of the matrix. The tensile cracks mainly initialize from the aggregated area of the large grains and the coarse γʹ phases, which show the transgranular dimple fracture behavior.
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Key words:
- FGH96 superally /
- solid-state diffusion bonding /
- microstructure /
- failure mechanism
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图 2 锻态试样连接界面金相组织（a）与元素扩散线扫描（b）
Figure 2. Microstructure (a) and element line scanning (b) of the as-forged specimens
图 4 不同原始状态试样距离固相扩散连接界面不同位置γʹ强化相：（a）锻态，Zone1；（b）固溶态，Zone1；（c）半时效态，Zone1；（d）锻态，Zone2；（e）固溶态，Zone2；（f）半时效态，Zone2；（g）锻态，Zone3；（h）固溶态，Zone3；（i）半时效态，Zone3
Figure 4. Microstructure of γʹ phases in the different distance from the solid-state diffusion bonding interface of specimens: (a) as-forged, Zone1; (b) as-solution, Zone1; (c) sub-aging, Zone1; (d) as-forged, Zone2; (e) as-solution, Zone2; (f) sub-aging, Zone2; (g) as-forged, Zone3; (h) as-solution, Zone3; (i) sub-aging, Zone3
图 5 固溶态试样连接界面处电子背散射衍射晶粒表征
Figure 5. Grains characterization by EBSD at the bonding interface of the solid solution specimens
图 6 固溶态试样连接界面区域电子背散射衍射晶粒取向分析：（a）连接界面处；（b）距连接界面100～200 μm处；（c）距连接界面200～300 μm处
Figure 6. EBSD analysis of the grain orientation at the bonding interface of the solid solution specimens: (a) bonding interface; (b) 100~200 μm away from the bonding interface; (c) 200~300 μm away from the bonding interface
图 7 不同原始状态试样室温拉伸性能：（a）抗拉强度；（b）屈服强度；（c）延伸率；（d）断面收缩率
Figure 7. Tensile properties at room temperature of the different specimens: (a) tensile strength; (b) yield strength; (c) elongation; (d) reduction of area
图 9 固溶态连接试样拉伸断口形貌：（a）室温宏观形貌；（b）室温扩展区形貌；（c）650 ℃宏观形貌；（d）650 ℃扩展区形貌
Figure 9. Tensile fracture morphology of the solid solution specimens: (a) macro morphology at room temperature; (b) extended region morphology at room temperature; (c) macro morphology at 650 ℃; (d) extended region morphology at 650 ℃
表 1 FGH96镍基粉末高温合金化学成分（质量分数）
Table 1. Chemical composition of the nickel-based powder metallurgy superalloy FGH96
% C Cr Co Mo W Al Ti Nb B Zr Ni 0.02～0.05 15.5～16.5 12.5～13.5 3.8～4.2 3.8～4.2 2.0～2.4 3.5～3.9 0.6～1.0 0.006～0.015 0.025～0.050 余量 
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