本研究目的在探討硬焊填料和金屬連接板間的接合強度及破壞模式，所使用的硬焊填料為核能研究所開發適用於金屬支撐固態氧化物燃料電池的銀基合金，金屬連接板則是使用代號為Crofer 22 H的商用肥粒鐵系不銹鋼。藉由製作兩款三明治接合件試片，分別量測接合件在室溫與750 °C下的剪力及張力強度，並評估接合時間和在750 °C、1000小時熱時效處理對接合件強度的影響。另外，亦建立硬焊封裝多層電池堆的有限元素模型，並求解各階段的熱應力分布。 實驗結果顯示，接合時間30分鐘可以產生較佳的接合件室溫張力強度，並選為後續各項試驗試片之接合時間。1000小時熱時效試片與未時效試片相比較，其張力強度在常溫下降約38.1%，而剪力強度在常溫下降23.8%。1000小時熱時效試片其張力強度與剪力強度在750 °C下與未時效試片相比，其強度相差有限。此乃熱時效處理過程中，部分硬焊密封劑擴散至Crofer 22 H側，並在高溫測試條件下增強了接合件的延展性，以吸收更多的應力，使得時效前後的高溫接合強度並沒有很大的改變。 試片在高溫接合與熱時效處理的過程中，會形成一氧化層 (Cr2O3) 主導破壞機制。由破斷面分析結果發現未時效張力試片不管在高溫與室溫環境下，破裂皆發生在硬焊填料與Cr2O3氧化層的介面，偶爾發生在Cr2O3氧化層之間。而熱時效張力試片不管在高溫與室溫環境下，破裂皆發生在Crofer 22 H側的硬焊填料與Cr2O3氧化層的介面。當未時效剪力試片的測試溫度從室溫升至高溫環境，破裂發生的位置從硬焊填料與Crofer 22 H的介面改變至硬焊填料與Cr2O3氧化層的介面。當測試溫度從室溫升至750 °C，時效剪力試片破裂位置從Crofer 22 H側的硬焊填料與Cr2O3氧化層的介面改變至硬焊填料與Ag2CrO4氧化層的介面，並且部份發生在Cr2O3氧化層內部。 由模擬結果得知，本研究中所使用的平板式SOFC電池堆，其PEN板和金屬連接板在各階段的最大等效應力皆小於該材料所能承受的臨界應力；而玻璃陶瓷密封膠在完成組裝階段及電池停機階段的最大等效應力在其邊角處皆有些大於臨界應力；銀基硬焊填料除了在高溫長時間運作階段外，其他階段所產生的最大等效應力值皆大於臨界應力值。 ;The aim of this study is to investigate the mechanical strength of the braze sealant/metallic interconnect joint. The braze sealant used is a silver-based alloy developed at the Institute of Nuclear Energy Research (INER) for metal-supported solid oxide fuel cell (MS-SOFC). The metallic interconnect used is a commercial ferrite stainless steel (Crofer 22 H). Two types of sandwich-like joint specimens are made to determine the shear and tensile joint strength at room temperature (RT) and 750 °C. The effects of bonding time in the joining process and thermal aging treatment (1000 h at 750 °C) on the joint strength are also investigated. In addition, a finite element model for a planar SOFC stack is also established to solve the thermal stress distribution at different stages. Experimental results indicate that a bonding time of 30 min can produce better tensile strength of the joint at RT, and it is thus selected as the bonding time for each specimen used in the subsequent tests. After 1000-h thermal aging, the tensile and shear strength is decreased by 38.1% and 23.8% at RT, respectively, compared to the unaged counterparts. The tensile strength and shear strength of the 1000 h-aged specimens tested at 750 °C are comparable to the counterparts of the unaged specimens. The braze sealant formed on the Crofer 22 H side after thermal aging enhances the ductility of the joint under mechanical loading at high temperature such that the joint strength is not significantly reduced at 750 °C as compared to the unaged condition. During the process of bonding and thermal aging treatment, an oxide layer (Cr2O3) is formed and associated with the failure mechanism. Fractography analysis reveals that regardless of testing temperature, fracture of the unaged tensile specimens occurs at the interface between the braze sealant and the Cr2O3 oxide layer and occasionally within the Cr2O3 oxide layer. For the 1000-h aged tensile specimens tested at both 750 °C and RT, cracking occurs at the interface between the braze sealant on the Crofer 22 H side and the Cr2O3 oxide layer. When the testing temperature of the unaged shear specimens is increased from RT to 750 °C, the location of rupture changes from the interface between the braze sealant and Crofer 22 H to the interface between the braze sealant and the Cr2O3 oxide layer. The fracture path of the aged shear specimens changes from the interface between the braze sealant on the Crofer 22 H side and the Cr2O3 oxide layer at RT to the interface between the braze sealant and the Ag2CrO4 oxide layer or partly to the interior of the Cr2O3 oxide layer at 750 °C. Simulation results indicate the maximum equivalent stress in cell assembly and interconnect/frame at each stage of the SOFC operation conditions is less than the critical value. However, the maximum equivalent stress in glass-ceramic sealant at the after-assembly and shutdown stages is greater than the critical value, which occurs at the corners of the bonding region. The maximum equivalent stress in the brazing filler at all stages is greater than the critical stress except at the long-term high-temperature operation stage.
