Dual Atmosphere Isothermal Aging and Rapid Thermal Cycling of Ag-Ni and Ag-CuO Stainless Steel to Zirconia Braze Joints

Abstract

Silver-copper oxide brazes are commonly used to bond zirconia to stainless steel (SS) for Solid Oxide Fuel Cell (SOFC) and other high temperature joining applications. In fact, conventional Ag-CuO compositions (where Cu segregates to the surface, oxidizes, and reduces the silver wetting angle on zirconia from ∼85 to ∼40°) allow brazing to be performed in air. Unfortunately, the relatively high ∼40°wetting angles of these reactive air brazes, and the ability of SOFC anode gases to reduce the CuO in them, produce pores during SOFC manufacturing and operation that reduce joint strength, impermeability, and longevity. Recently, Ag brazes utilizing transient porous nickel layers, instead of CuO additions, have been shown to produce high quality braze joints between SS and yttria stabilized zirconia (YSZ). Here, the microstructural and compositional evolution of SS|Ag-3CuO|YSZ and SS|Ag-Ni|YSZ braze joints exposed to air on one side and humidified 4%H 2 -96%N 2 on the other side for either ∼300 hours of ∼750°C aging or ∼300 25°C/min 35-830°C rapid thermal cycles are compared. While both brazes display considerable microstructural and compositional evolution, only the Ag-Ni brazes remain pore free and well bonded, indicating that Ag-Ni brazes may be more suitable for long term SOFC operation.

Joining the BaZr0.1Ce0.7Y0.1Yb0.1O3-δ Electrolyte to AISI 441 Interconnect for Protonic Ceramic Fuel Cell Applications: Interfacial Microstructure and Long-Term Stability

“…According to the XRD patterns shown in Figure b and the elemental distribution in Figure d, it can be considered that the metal-side oxide consists of two layers: the (Cu, Cr, Fe) 3 O 4 layer (close to Ag) and the Cr 2 O 3 -rich layer (close to AISI 441). The previous studies on the RAB of stainless steel also reported similar oxide layers. − …”

Temperature-Dependent Sheet and Contact Resistivity Measurements on Ag and Ag-Ni Circuit Pastes

“…In these applications, electrical contacts with low electronic sheet resistance, low electronic contact resistance, and high adhesion strength are desired. Recently, a new Particle-Interlayer-Directed Wetting and Spreading (PIDWAS) technique has been developed that utilizes a) the low wetting angle of silver on nickel (10,11), and b) the high work of adhesion between nickel and various oxides (12), to fabricate well-adhered silver patterns on substrates not normally wet by silver (5,(13)(14)(15)(16)(17)(18). However, the full electrical performance (i.e.…”