Characterization of Reactive Air Brazed Ceramic/Metal Joints with Unadapted Thermal Expansion Behavior
Characterization of Reactive Air Brazed Ceramic/Metal Joints with Unadapted Thermal Expansion Behavior
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DOI：
10.1002/adem.201400311
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发表时间：
2014-12-01
影响因子：
3.6
通讯作者：
Broeckmann, Christoph
中科院分区：
文献类型：
--
作者：
Bobzin, Kirsten;Oete, Mehmet;Broeckmann, Christoph
反应空气钎焊（RAB）是一种很有前途的、经济的陶瓷与金属、陶瓷与陶瓷连接方法。混合接头在诸如气体分离或固体氧化物燃料电池等具有挑战性的应用领域中变得重要。虽然由于其功能性，通常直接选择陶瓷配合物，但需要仔细选择金属配合物，以避免由于热膨胀系数的差异而产生的高残余应力。这导致限制了大量潜在加入伙伴的使用。通过RAB连接具有不适应的热膨胀行为的陶瓷/金属部件（Ba0.5Sr0.5Co0.8Fe0.2O3-delta /Crofer 22 H和3 YSZ/AISI 314）。使用含Cu以及不含Cu的Ag基填充金属。钎焊样品的横截面的分析表明，样品的微观结构特别取决于所使用的填充金属。在差示扫描量热测量中可以观察到熔化过程以及导致明显反应区的放热反应。虽然接头的微观结构不受基体材料的显著影响，但BSCF/Crofer 22 H试样的强度比具有适当热膨胀系数的试样（BSCF/AISI 314和3 YSZ/Crofer 22 H）的强度低近四倍。其原因是不同的热膨胀系数引起的残余应力。假设粘塑性材料模型的有限元模拟显示，可以通过银基钎焊内的松弛来减少应力量。但BSCF/Crofer 22 H接头的高残余应力体积仍大于BSCF/AISI 314接头，导致其断裂强度较低。
Reactive air brazing (RAB) is a promising and economic method for joining ceramic to metal as well as ceramic to ceramic. Hybrid joints gain importance in the field of challenging applications such as gas separation or solid oxide fuel cells. While the ceramic partner is often directly chosen due to its functionality, the metallic partner needs to be chosen carefully in order to avoid high residual stresses due to the differences in the thermal expansion coefficients. This leads to the restriction of the usage of a significant number of potential joining partners. Ceramic/metals components with unadapted thermal expansion behavior (Ba0.5Sr0.5Co0.8Fe0.2O3-delta /Crofer 22 H and 3YSZ/AISI 314) were joined by RAB. Cu-containing as well as Cu-free Ag-based filler metals were used. Analysis of the cross-section of brazed samples showed that the microstructure of the samples depends especially on the used filler metal. The melting process as well as the exothermic reactions leading to a distinct reaction zone could be observed in the differential scanning calorimetric measurements. While the microstructure of the joints is not significantly influenced by the base material, the strength of the BSCF/Crofer 22 H specimens is nearly four times lower than the strength of the specimens with the adapted thermal expansion coefficients (BSCF/AISI 314 and 3YSZ/Crofer 22 H). The reasons are residual stresses caused by the different thermal expansion coefficients. Finite element simulations assuming a visco-plastic material model show that an amount of stress can be reduced by relaxation within the silver based braze. But the volume of the high residual stresses is still larger in the BSCF/Crofer 22 H joints than that of the BSCF/AISI 314 joint resulting in a lower fracture strength.