Reactive air brazing of BaCe0.7Zr0.1Y0.1Yb0.1O3-δ proton conductive ceramic and stainless steel
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摘要: 针对质子陶瓷燃料电池堆中BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb)质子导电陶瓷与Crofer22APU不锈钢的连接难题展开研究，探究了Ag-CuO钎料在BCZYYb陶瓷表面的润湿性能，分析了CuO与陶瓷反应对钎料润湿的驱动作用. 研究了Ag-CuO钎料的空气反应钎焊工艺，在1010 ℃/20 min工艺条件下实现了质子导电陶瓷与不锈钢的无缺陷连接，分析了接头两侧界面连接特性以及接头元素分布规律. 结果表明，CuO与陶瓷基体中BaO的反应促进了钎料润湿，钎料扩散进入陶瓷基体形成了较厚的渗透层，CuO与不锈钢保护层 (Mn, Co)3O4的反应促进了保护层致密化，保护层在连接过程对不锈钢基体起到了良好的保护作用. 系统分析了CuO含量对接头组织与性能的影响规律，采用Ag-CuO(2%，质量分数)钎料获得了最高接头剪切强度(21.6 MPa)，综合评定了钎缝两侧界面反应对接头性能的影响.Abstract: In this study, the joining problem between the BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb) ceramic and Crofer 22 APU stainless steel in the protonic ceramic fuel cell stack was studied. The wettability of Ag-CuO braze on the surface of BCZYYb ceramic was explored. And the driving effect of the reactions between CuO and ceramic matrix on braze wetting was analyzed. The reactive air brazing process of Ag-CuO braze was studied, and the BCZYYb ceramic was soundly brazed to the stainless steel at 1010 ℃ for 20 min. The interfacial joining properties on both sides and the element distribution of joints were analyzed. It is showed that the wetting of Ag-CuO braze was promoted by the reactions between the CuO and BaO in the ceramic matrix. The braze could diffuse into the ceramic matrix, forming a thick fusion layer. The densification of the (Mn, Co)3O4 protective layer on the stainless steel could be densified by its reactions with the CuO from the braze, which played a key role in protecting the stainless steel from oxidization during reactive air brazing. Effects of CuO content on the microstructure and properties of joints were analyzed systematically. The highest shear strength of joints (21.6 MPa) was obtained by using Ag-2wt%CuO braze.
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0. 序言
搅拌摩擦焊(friction stir welding, FSW)作为一种固相焊接技术，具有焊缝质量高、变形小等优点[1-2]. 目前加工制造业对焊接智能化、高效化的要求日益上升，机器人搅拌摩擦焊得以更普遍的应用.在实际大型结构的FSW生产中，由于接头形式、板材加工精度以及工装夹具装配质量问题，焊接过程容易产生较大的间隙，对接头的成形和性能极为不利[3-4]，当工件之间的间隙超过工件厚度的10%时，很难获得无缺陷质量良好的接头[5]. 间隙的存在导致焊核区(weld nugget zone，WNZ)材料流动不充分，焊缝出现孔洞和隧道等缺陷[6]. 同时，工件被塑化的材料流入间隙，弥补材料缺失使得焊缝位置减薄严重，降低接头承载能力[7].
研究人员[8-9]采用粉末、焊丝或者补偿条作为填充材料对大间隙下的工件进行FSW，得到成形良好无缺陷的接头，接头与常规FSW接头力学性能吻合，然而，当焊接速度过快时，这些填充材料很容易飞出间隙，从而形成缺陷. 同时填充材料需要在焊前放置在间隙内，针对复杂结构间隙及焊接过程中产生的间隙，填充材料的尺寸以及填料的连续性受到限制.
基于传统搅拌摩擦焊方法，填充材料旁轴送料，将FSW与填料过程同时进行，实现大间隙机器人搅拌摩擦填丝焊，并对其接头进行盐雾腐蚀试验，分析搅拌摩擦填丝焊接头不同区域的腐蚀行为差异.搅拌摩擦填丝焊提高了FSW对工况条件的适应性，适用于高铁、船舶和飞机上大型及复杂结构焊缝，有望为工程实际应用提供理论依据和技术支撑.
1. 试验方法
试验材料为5A06铝合金轧制板材，尺寸为300 mm × 70 mm × 3 mm，填充材料为直径1.6 mm的5B06丝材. 机器人搅拌摩擦填丝焊焊接过程示意图及焊具尺寸如图1所示，对接板材焊接间隙为2 mm. 填充丝材经过高推力送丝系统从送丝孔连续输送到储料腔内部，高速旋转的螺杆将金属丝材剪切成粒状材料，粒状材料在自身重力及与螺杆侧壁的摩擦力的影响下，在储料腔内塑化从底部的缝隙流出. 轴向压力使储料腔与板材之间产生挤压效果，粒状材料发生变形堆积并被塑化. 在旋转的搅拌针的驱动作用下，塑化的填充材料发生流动并实现与基材的连接. 试验所采用的焊接工艺参数为转速3 000 r/min，焊接速度200 mm/min，送丝速度1.8 m/min，轴向压力5 000 N，倾角1.5°.
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图 1 焊接过程示意图及焊具结构Figure 1. Welding process and the welding tool structure. (a) schematic illustration of wire-feeding friction stir welding; (b) dimensions of the welding tool2. 试验结果与分析
2.1 焊缝成形
图2为机器人搅拌摩擦填丝焊接头焊缝表面形貌. 焊缝表面光滑成形良好，无沟槽缺陷，在搅拌针的驱动作用下，塑化的填充材料发生流动后沉积弥补了间隙位置材料缺失，同时焊缝有一定程度的增厚，提高了接头的承载能力.
2.2 焊缝微观组织
图3为焊缝整体微观形貌及不同区域的微观组织. 焊接接头填充材料与基体母材结合良好，焊缝无孔洞及隧道缺陷，由于搅拌针的存在，搅拌针促进塑化的丝材和基材发生流动，提高了填充材料与基材的结合效果. 丝材经过螺杆的剪切及静轴肩的挤压作用，与焊核区受到搅拌针的搅拌作用一样，填充材料也经历了大塑性变形，发生动态再结晶，形成细小的等轴晶.
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图 3 搅拌摩擦填丝焊接头微观组织Figure 3. Microstructures of wire-feeding friction stir welding. (a) microstructures of the cross-section; (b) top interface; (c) thermo-mechanically affected zone interface; (d) filler materials zone2.3 焊缝腐蚀性能
搅拌摩擦填丝焊接头经过7天盐雾腐蚀试验后接头各区域腐蚀形貌如图4所示. 接头表面均发生了点蚀坑的萌生, 表面出现腐蚀产物；焊核区及填充材料区域的点蚀坑尺寸较小，且分布较为均匀；母材点蚀坑分布不均匀，尺寸较大.热力影响区(thermo- mechanically affected zone，TMAZ)的点蚀坑随晶粒分布特征呈流线分布，热影响区(heat-affected zone，HAZ)的点蚀坑尺寸较大，且出现一定的聚集现象，点蚀坑发生扩展.焊核区和填充材料区表现出更好的耐腐蚀性能.
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图 4 不同区域盐雾腐蚀形貌Figure 4. Salt spray corrosion morphologies in different zones. (a) WNZ; (b) filler materials zone; (c)TMAZ; (d) HAZ; (e)BM第二相分布及尺寸对点蚀坑的形成有巨大影响，第二相和基体之间形成微电偶会导致腐蚀现象发生.焊核区经过塑性变形后第二相颗粒被打碎，尺寸较小分布也更均匀，进而发生腐蚀现象后点蚀坑分布均匀细小；填充材料区域拥有更小且弥散分布的第二相颗粒，填充材料的加入增强了焊核区的耐蚀性.经过轧制后的母材中第二相颗粒尺寸较大且分布不均匀，耐蚀性较差易形成较大的点蚀坑；热力影响区点蚀坑呈流线分布，而热影响区第二相颗粒发生聚集长大，发生点蚀后有利于点蚀坑的扩展,导致热影响区的耐蚀性较差.
图5为热影响区点蚀坑SEM图及附近元素分布.发现在第二相Al6(FeMn)附近产生了明显的腐蚀现象, 点蚀坑发生扩展. 在盐雾环境中，铝合金表面虽然存在一层氧化膜，但是随着溶液中Cl−的侵入，Cl−破坏了表面氧化膜，促进点蚀现象发生. 同时热影响区第二相颗粒Al6(FeMn)与铝基体之间存在腐蚀电位差形成原电池，由于Al6(FeMn)电位高于铝基体[10]，第二相颗粒在腐蚀过程中充当阴极，促使周围基体发生腐蚀，因此在第二相附近形成环形腐蚀区域产生腐蚀坑并向四周扩展. 当第二相尺寸较大时，周围基体溶解的范围增大，点蚀坑的尺寸也会更大. 基于元素分布图可以看出，在腐蚀坑附近Al元素含量减少，点蚀坑内金属发生溶解，点蚀孔内阳离子浓度升高，Cl−就会不断侵入以维持平衡.随着Cl−浓度的升高发生水解，导致点蚀坑内部氢离子浓度升高，溶液酸化，促使基体进一步溶解，点蚀坑发生扩展.
2.4 接头力学性能
图6为经过7天盐雾腐蚀接头、未腐蚀接头及母材的拉伸测试结果.未腐蚀接头抗拉强度为388.9 MPa ± 1.4 MPa，断后伸长率为20.5% ± 0.4%，分别达到母材的99%及94%. 经过7天盐雾腐蚀后接头抗拉强度降低到356.6 MPa ± 1.2 MPa，断后伸长率为18.1% ± 0.9%，盐雾腐蚀后接头强度降低了8.3%，断后伸长率下降了11.7%，盐雾腐蚀试验后接头仍保持较优的力学性能. 盐雾腐蚀环境造成焊缝表面出现点蚀坑，而富Cl−环境使基体金属进一步溶解，点蚀坑发生扩展，减少了接头有效承载面积，在承受载荷时其易成为薄弱位置，裂纹在点蚀坑位置产生，降低了接头承载能力.
3. 结论
(1) 实现了大尺寸间隙下机器人搅拌摩擦填丝焊，焊接过程与填料过程同时进行，提高了搅拌摩擦焊对接头间隙的容忍性，消除了焊缝减薄问题.
(2) 填充材料与基材实现了良好的冶金连接，经过剧烈塑性变形后，焊核区和填充材料发生动态再结晶，表现为细小的等轴晶粒.
(3) 未腐蚀接头抗拉强度达到388.9 MPa ± 1.4 MPa，断后伸长率为20.5% ± 0.4%，分别达到母材的99%及94%. 在腐蚀过程中焊核区和填充材料区耐腐蚀性能优于热影响区与母材，点蚀坑细小且均匀分布，7天盐雾腐蚀后接头保持优异的耐蚀性能.
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图 1 接头剪切强度测试加载示意图
Figure 1. Schematic diagram of loading for shear strength test of joints
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图 2 BCZYYb质子导电陶瓷断口形貌及元素分布
Figure 2. Fracture morphology and EDS maps of BCZYYb protonic ceramic. (a) Fracture morphology; (b) Ba; (c) Ce; (d) Zr; (e) Y; (f) Yb; (g) O
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图 3 Ag-CuO钎料在BCZYYb陶瓷表面润湿性
Figure 3. Wettability of Ag-CuO braze on the surface of BCZYYb ceramic. (a) Ag; (b) Ag-CuO (1%); (c) Ag-CuO (2%); (d) Ag-CuO (4%)
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图 4 Ag-CuO钎料在BCZYYb陶瓷表面润湿过程示意
Figure 4. Schematic of the wetting processes of the Ag-CuO braze on the BCZYYb ceramic surface
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图 7 焊后接头元素面分析
Figure 7. Analysis of elemental surface scanning of as-brazed joint. (a) Ag; (b) Cu; (c) Mn; (d) Fe; (e) Cr; (f) Ba
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图 8 钎料成分对接头组织的影响
Figure 8. Effects of braze composition on the joint microstructure. (a) Ag; (b) Ag-CuO (1%); (c) Ag-CuO (4%); (d) Ag-CuO (8%)
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图 9 钎料成分对接头剪切强度的影响
Figure 9. Effect of braze composition on the shear strength of joints
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图 10 BCZYYb侧断口形貌及成分分析[Ag-CuO (4%)]
Figure 10. Fracture morphology from BCZYYb side [Ag-CuO4%]
位置 Fe Cr Mn Co Ag Cu Ba Ce O Yb A 72.3 22.5 0.7 0.9 − − − − 3.6 − B 11.4 36.0 3.3 5.9 − 0.8 − − 42.6 − C 1.0 0.5 22.0 22.3 − 7.2 − − 47.0 − D − − 3.8 4. 1 5. 8 45.2 − − 41.1 − E − − − − 5. 5 45. 7 − − 48.8 − F − − − − 95.1 2.6 − − 2.3 − G − − − − 2.2 55.7 − − 42.1 − H − − − − − 7.6 24.3 17.5 49.2 1. 4 I − − − − 2.0 2.9 25.7 19.0 49.0 1.4 
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表 2 BCZYYb侧断口成分分析(原子分数, %)
Table 2 Composition analysis from BCZYYb side
Ba Ce Zr Y Yb Cu O 23.7 17.3 2.6 2.8 2.4 7.8 43.4
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[1] Bian W J, Wang B M, Tang W, et al. Revitalizing interface in protonic ceramic cells by acid etch[J]. Nature, 2022, 604: 479 − 485.
[2] Duan C, Tong J, Shang M. et al. Readily processed protonic ceramic fuel cells with high performance at low-temperatures[J]. Science, 2015, 349: 1321 − 1326. doi: 10.1126/science.aab3987
[3] Duan C, Kee R J, Zhu H, et al. Highly durable, coking and sulfur tolerant, fuel-flexible protonic ceramic fuel cell[J]. Nature, 2018, 557: 217 − 222. doi: 10.1038/s41586-018-0082-6
[4] Le L Q, Hernandez C H, Rodriguez M H, et al. Proton- conducting ceramic fuel cells: Scale up and stack integration[J]. Journal of Power Sources, 2021, 482: 228868. doi: 10.1016/j.jpowsour.2020.228868
[5] Kaletsch A, Pfaff E M, Broeckmann C. Effect of aging on microstructure and mechanical strength of reactive air brazed BSCF/AISI 314-joints[J]. Advanced Engineering Materials, 2014, 16: 1430 − 1436. doi: 10.1002/adem.201400102
[6] Fabbri E, Bi L, Pergolesi D, et al. Towards the next generation of solid oxide fuel cells operating below 600 ℃ with chemically stable proton-conducting electrolytes[J]. Advanced Materials, 2012, 24: 195 − 208. doi: 10.1002/adma.201103102
[7] Lin C K, Lin T W, Wu S H, et al. Creep rupture of the joint between a glass-ceramic sealant and lanthanum strontium manganite-coated ferritic stainless steel interconnect for solid oxide fuel cells[J]. Journal of European Ceramic Society, 2018, 38(5): 2417 − 2429. doi: 10.1016/j.jeurceramsoc.2018.01.016
[8] Chou Y S, Thomsen E C, Williams R T, et al. Compliant alkali silicate sealing glass for solid oxide fuel cell applications: thermal cycle stability and chemical compatibility[J]. Journal of Power Sources, 2011, 196(5): 2709 − 2716. doi: 10.1016/j.jpowsour.2010.11.020
[9] Kuhn B, Wetzel F J, Malzbender J, et al. Mechanical performance of reactive-air-brazed (RAB) ceramic/metal joints for solid oxide fuel cells at ambient temperature[J]. Journal of Power Sources, 2009, 193(1): 199 − 202. doi: 10.1016/j.jpowsour.2008.10.117
[10] 司晓庆, 李淳, 郑庆伟, 等. Ag-CuO-Al2O3复合钎料空气反应钎焊SOFC及服役性能[J]. 焊接学报, 2020, 41(5): 1 − 6. doi: 10.12073/j.hjxb.20190907001 Si Xiaoqing, Li Chun, Zheng Qingwei, et al. Reactive air brazing of SOFC using Ag-CuO-Al2O3 composite braze and the service performance study[J]. Transactions of the China Welding Institution, 2020, 41(5): 1 − 6. doi: 10.12073/j.hjxb.20190907001
[11] 蒋文春, 张玉财, 关学伟. 平板式SOFC钎焊自适应密封热应力与变形分析[J]. 焊接学报, 2012, 33(11): 55 − 58. Jiang Wenchun, Zhang Yucai, Guan Xuewei. Thermal stress and deformation in bonded compliant seal design for planar SOFC[J]. Transactions of the China Welding Institution, 2012, 33(11): 55 − 58.
[12] Zhou Q, Bieler T R, Nicholas J D, et al. Transient porous nickel interlayers for improved silver-based solid oxide fuel cell brazes[J]. Acta Materials, 2018, 148: 156 − 162. doi: 10.1016/j.actamat.2018.01.061
[13] Cao J, Si X Q, Li W J, et al. Reactive air brazing of YSZ- electrolyte and Al2O3-substrate for gas sensor sealing: interfacial microstructure and mechanical properties[J]. International Journal of Hydrogen Energy, 2017, 42: 10683 − 10694. doi: 10.1016/j.ijhydene.2017.01.105
[14] Wang X Y, Si X Q, Li C, et al. Joining the BaZr0.1Ce0.7Y0.1Yb0.1 O3-δ electrolyte to AISI 441 interconnect for protonic ceramic fuel cell applications: interfacial microstructure and long-term stability[J]. ACS Applied Energy Materials, 2021, 4: 7346 − 7354. doi: 10.1021/acsaem.1c01491
[15] 苏毅. 用于质子陶瓷燃料电池的不锈钢/BCZY-Yb 电解质空气下连接机理[D]. 哈尔滨: 哈尔滨工业大学, 2021. Su Yi. Research on air brazing of BCZY-Yb ceramic to strainless steel in protonic ceramic fuel cell[D]. Harbin: Harbin Institute of Techonligy, 2021.
[16] Si X Y, Wang D, Li C, et al. Exploring the role of Mn-Co spinel coating on Crofer 22 APU in adjusting reactions with the Ag based sealant during reactive air brazing[J]. Journal of Materials research and technology, 2022, 16: 608 − 618. doi: 10.1016/j.jmrt.2021.12.032
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