Interfacial and mechanical characterization of yttria-stabilized zirconia (YSZ) to stainless steel joints fabricated using Ag–Cu–Ti interlayers

An Ag–26.7Cu–4.5Ti metallic interlayer was used to join yttria-stabilized zirconia (YSZ) and stainless steel for solid oxide fuel cell (SOFC) applications. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) were used to characterize the joint microstructure. The bond strength and hermeticity of steel/metallic interlayer/YSZ joints were also evaluated. TEM analysis revealed that the Fe from the steel reacted with Ti of the interlayer to form Fe2Ti near the steel/Ag–26.7Cu–4.5Ti interface. At the Ag–26.7Cu–4.5Ti interlayer/YSZ interface, Ti2O3 and Fe2Ti4O reaction layers formed near the YSZ and the interlayer, respectively. While titanium reacted with oxygen from YSZ to form titanium oxide (Ti2O3), Fe diffused toward the YSZ to react with titanium oxide to form the Fe2Ti4O layer. The tensile and shear strengths of the joints, evaluated according to “ISO 13124” test method, were 16.7±4.8 and 40.2±8.2 MPa, respectively. Nano-indentation hardness was characterized across the steel/Ag–26.7Cu–4.5Ti interlayer/YSZ joint. The hermeticity of the joint was measured by using He leakage tests. The leak rate of the joined assembly was 1.5±1.1×10–9 mbar ℓ/s, indicating good hermeticity of joints.