利用局部過渡液相接合法以鈦/鎳/鈦金屬箔層接合316L不鏽鋼與釔安定氧化鋯之界面反應與氧化測試

Abstract

本研究利用局部過渡液相接合法，以Ti/Ni/Ti金屬箔層為活性焊料，分別在950°C與1050°C下持溫0.5小時，接合固態氧化物燃料電池的連接板材料316L不鏽鋼與固態氧化物電解質8 mol.% 釔安定氧化鋯（8YSZ），並仿其工作環境，於大氣氣氛中分別以600°C和800°C各持溫10小時與25小時進行氧化測試，以附加能量分散光譜儀的掃描式電子顯微鏡分析接合及氧化試片的微觀結構，探討其界面及氧化反應機構，以氦氣測漏儀檢測其氣密性。

本研究發現在950°C與1050°C均能夠有效地接合8YSZ與316L不鏽鋼，在陶瓷側產生鈦氧化合物與鈦鎳相，鈦鎳界面因kirkendall effect產生不連續空孔，在不鏽鋼側則主要生成層狀鈦鐵鎳化合物生成相。950°C/0.5h反應後，試片會有殘存鈦箔，1050°C/0.5h反應後鈦箔則會完全耗盡。經過600°C與800°C氧化處理後，從Ti2Ni反應層產生焊料與陶瓷側的剝離，造成接合失敗，為了增加焊料在高溫抗氧化性，必須設法減少較脆的Ti2Ni相。此外，氧化試片的鈦氧化物在冷卻時會剝離，因此在微觀結構中並沒有觀察到明顯的氧化層，只有氧化800°C/25h鈦側的TiNi反應層觀察到氧化產生的Ni(Ti)和TiNi3。在接合溫度1050°C時，因鈦箔反應耗盡，鎳箔持續擴散到反應層中，生成富鎳相的TiNi，並在緩慢冷卻、氧化持溫的過程中，造成時效的效果，使鈦鎳介穩相亦析出在TiNi基質中。

本研究以漏氣率來檢測接合效果，發現未氧化試片都具備良好的氣密性，然而氧化試片氣密性極差，歸因陶瓷側與焊料分離，雖然Ti/Ni/Ti夾層箔片能夠成功接合母材，仍無法應用在高溫氧化氣氛當中。

In this study, partial transient liquid phase (PTLP) bonding with Ti/Ni/Ti foils interlayer was used to join 8 mol% Yttria-Stabilized Zirconia (8YSZ) and 316L stainless steel at 950°C and 1050°C for the application of solid oxide fuel cell (SOFC). According to SOFC working conditions, the bonding was also subjected to the oxidation environment at 600°C and 800°C for 10 and 25 hours. The interfacial reaction and hermeticity were characterized and investigated by scanning electronic microscopy and energy dispersive spectroscopy (SEM/EDS) and helium leak detector, respectively.

This method has been successfully developed to joint 8YSZ and 316L stainless steel. Titanium oxide and Ti-Ni compounds were formed at the ceramic side, while Ti-Ni-Fe compounds dominated at stainless steel side. Kirkendall voids were found between the interface of Ti and Ni foils. Ti foils were totally consumed at the brazing temperature of 1050°C; on the other hand, there were residual Ti foils at 950°C. Oxidation would result in the separation of 8YSZ and brazing interlayer, fracture surfaces were all located in the Ti2Ni reaction layer. Brittle phase Ti2Ni has to reduce in order to enhance the ability of anti-oxidation at high temperature. Moreover, the oxide layer was hardly observed after oxidation in most samples due to the spallation during cooling process, except for the sample oxidation at 800°C/25h which TiNi reaction layer evolved into Ni(Ti) and TiNi3. While brazing at 1050°C, metastable Ti-Ni phases precipitated in the matrix owing to the depletion of Ti foils, continuos diffusion of Ni, long reaction time and low cooling rate, which brought about the reaction layer of Ni-rich TiNi matrix and the effect of aging.

The leakage test showed that bonding with Ti/Ni/Ti foils as interlayer provided good hermeticity. However, they could not remain their reliability in the oxidation atmosphere at high temperatures.