TEM characterization of Au-based alloys to join YSZ to steel for SOFC applications

The microstructures of two gold-based alloys with compositions (in wt.%) of 96.4Au–3Ni–0.6Ti and 97.5Au–0.75Ni–1.75V following oxidation at 850 °C for 200 min were characterized by analytical transmission electron microscopy with energy dispersive spectroscopy and by scanning electron microscopy. In the oxidized 96.4Au–3Ni–0.6Ti interlayer, a dense scale composed of nickel oxide (NiO) and nickel titanate (NiTiO3) formed at the alloy surface. No evidence of titanium oxide was found because there was not enough Ti present to form titanium oxide. In the oxidized 97.5Au–0.75Ni–1.75V interlayer, loose vanadium oxide (V2O5) and nickel vanadate (Ni2V2O7) formed and were distributed within the oxidized 97.5Au–0.75Ni–1.75V interlayer. Similarly, because of the low Ni content in the alloys, no NiO formed. The oxide products in the 96.4Au–3Ni–0.6Ti and 97.5Au–0.75Ni–1.75V interlayers after oxidation are consistent with the Pilling–Bedworth (PB) ratio considerations.