Microstructures and properties of Zr-4 alloy diffusion bonding joint with Nb interlayer
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摘要:
为提高Zr-4合金扩散焊接头强度，降低有效连接温度，采用不同厚度的Nb中间层在760 ℃/30 min/7 MPa条件下扩散连接Zr-4合金，分析了Nb中间层的加入及其厚度对接头界面组织和性能的影响. 结果表明， 在扩散连接过程中，界面处Zr和Nb原子相互扩散形成由(Zr, Nb)固溶体构成的扩散层，且扩散层厚度随着中间层厚度的增加基本不变，靠近Nb侧的扩散层中观察到Zr(Cr, Fe)2和Zr(Fe, Nb)2第二相的生成. 在760 ℃条件下，Zr-4合金直接扩散焊接头抗拉强度仅为75 MPa，存在大量未连接区域，添加Nb中间层可显著提高界面结合率，接头抗拉强度达到450 MPa，接头抗拉强度和断后伸长率随着Nb中间层厚度的增加稍有下降，在添加20 μm中间层时最大，分别为450 MPa和13.1%，且断裂位置由Zr-4合金基体(20 μm)转变为界面扩散层(50 μm和80 μm). Zr-4合金扩散焊接头在经历400 ℃，10.3 MPa的过热蒸气腐蚀后，扩散层发生明显腐蚀现象，腐蚀深度最大达到108.39 μm，接头抗拉强度和断后伸长率下降至415 MPa和5.1%，断裂位置在连接界面处，断口中发现Zr(Fe, Nb)2相.
Abstract:To improve the strength of Zr-4 alloy diffusion bonding joints and reduce the effective bonding temperature, different thicknesses of Nb interlayer were used for the Zr-4 alloy diffusion bonding at 760 °C/30 min/7 MPa. The effect of the Nb interlayer and its thickness variation on the microstructures and properties of the joints was investigated. During the diffusion bonding process, the diffusion layer was formed by the mutual diffusion of Zr and Nb, which was composed of (Zr, Nb) solid solution, and its thickness was constant with the increase of the Nb thickness. Secondary phases of Zr(Cr, Fe)2 and Zr(Fe, Nb)2 were observed in the diffusion layer near the Nb interlayer. The tensile strength of the joints was only 75 MPa at 760 ℃ and many unbonded areas existed. The tensile strength and elongation of the joints decreased slightly with the increase of Nb thickness, and reached the maximum of 450 MPa and 13.1%, respectively, with the 20 μm Nb interlayer. The fracture position was changed from the Zr-4 matrix (20 μm) to the diffusion layer (50 μm, 80 μm). After superheated steam corrosion of 400 ℃ and 10.3 MPa, obvious corrosion occurred at the diffusion layer of the Zr-4/Nb/Zr-4 joint. The maximum corrosion depth was 108.39 μm, and the tensile strength and elongation of the joints decreased to 415 MPa and 5.1%. The Zr(Fe, Nb)2 phases were found on the fracture surface.
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Keywords:
- diffusion bonding /
- Zr-4 alloy /
- Nb interlayer /
- corrosion behavior
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图 1 扩散焊的装配示意图及试样取样示意图
Figure 1. Schematic of the diffusion bonding assembly and location of test samples. (a) assemblies; (b) location of the test samples
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图 2 不同温度下Zr-4合金直接扩散焊接头的显微组织
Figure 2. Microstructures of Zr-4 alloy diffusion bonding joints at different temperatures. (a) 760 ℃; (b) 780 ℃; (c) 800 ℃
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图 3 添加80 μm厚度Nb中间层Zr-4/Nb/Zr-4扩散焊接头界面显微组织
Figure 3. Interface microstructures of Zr-4/Nb/Zr-4 diffusion bonding joint with 80 μm Nb interlayer. (a) low magnification microstructure of the joint; (b) microstructure of one side of the joint; (c) high magnification microstructure of the Zr-4/Nb interface
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图 4 Nb中间层厚度对Zr-4/Nb/Zr-4扩散焊接头界面显微组织与成分分布的影响
Figure 4. Influence of Nb interlayer thickness on interface microstructures and content profiles of Zr-4/Nb/Zr-4 diffusion bonding joints. (a) interface microstructures of 20 μm interlayer; (b) interface microstructures of 50 μm interlayer; (c) interface microstructures of 80 μm interlayer；(d) content profiles of 20 μm interlayer；(e) content profiles of 50 μm interlayer； (f) content profiles of 80 μm interlayer
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图 5 Nb中间层厚度对Zr-4/Nb/Zr-4扩散焊接头拉伸性能的影响
Figure 5. Influence of Nb interlayer thickness on tensile properties of Zr-4/Nb/Zr-4 diffusion bonding joints
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图 6 Nb中间层辅助扩散连接Zr-4接头断口形貌 (20 μm)
Figure 6. Nb interlayer assisted diffusion bonding of Zr-4 joints facture morphologies (20 μm). (a) low magnification fracture morphology; (b) high magnification fracture morphology
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图 7 Nb中间层辅助扩散连接Zr-4接头断口形貌 (50 μm)
Figure 7. Nb interlayer assisted diffusion bonding of Zr-4 joints facture morphologies (50 μm). (a) low magnification fracture morphology; (b) high magnification fracture morphology on b area；(c) high magnification fracture morphology on c area；(d) high magnification fracture morphology on d area
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图 8 Nb中间层辅助扩散连接Zr-4接头腐蚀前后界面显微组织 (50 μm)
Figure 8. Nb interlayer assisted diffusion bonding of Zr-4 joints microstructures before and after corrosion (50 μm) .(a) before corrosion; (b) after corrosion
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图 9 Nb中间层辅助扩散连接Zr-4接头腐蚀后横截面显微组织 (50 μm)
Figure 9. Nb interlayer assisted diffusion bonding of Zr-4 joints cross-section microstructures after corrosion(50 μm). (a) low magnification microstructure; (b) high magnification microstructure
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图 10 Nb中间层辅助扩散连接Zr-4接头腐蚀后断口形貌 (20 μm)
Figure 10. Nb interlayer assisted diffusion bonding of Zr-4 joints facture morphologies after corrosion (20 μm). (a) low magnification morphology; (b) high magnification fracture morphology on b area；(c) high magnification fracture morphology on c area；(d) high magnification fracture morphology on d area; (e) high magnification fracture morphology on e area；(f) high magnification fracture morphology on f area
表 2 图3各点的化学成分(原子分数，%)
Table 2 Chemical composition of the points labeled in Fig. 3
位置 Zr Nb Fe Cr Sn 物相 1 61.04 25.53 9.88 2.27 1.26 α-Zr 2 71.31 21.92 4.53 1.63 0.59 (Zr, Nb) 3 69.58 24.22 3.00 1.58 1.62 (Zr, Nb) 
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表 3 图8和图9中各点的化学成分(原子分数，%)
Table 3 Chemical composition of the points labeled in Fig. 8 and Fig. 9
位置 Zr Nb O Fe Cr Sn 物相 1 36.05 4.85 56.30 1.88 0.43 1.44 ZrO2 2 58.40 11.62 27.18 1.49 0.77 0.54 Zr，ZrO2，NbO2 3 1.82 44.41 52.77 0.57 0.42 0.00 Nb，Nb2O5，NbO2 4 60.89 8.60 27.49 1.11 0.58 1.34 Zr，ZrO2，NbO2 5 34.81 6.55 56.71 0.84 0.53 0.55 ZrO2，NbO2 6 9.39 23.62 63.62 2.60 0.59 0.18 Zr，ZrO2，NbO2 7 76.13 9.13 12.41 0.52 0.45 1.35 Zr基体
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