t-ZrO2 toughened Al2O3 free-standing films and as oxidation mitigating thin films on silicon nitride via colloidal processing of flame made nanopowders (NPs)

Zirconia toughened aluminas (ZTAs) are one of the most important engineering ceramics with high melting points, excellent mechanical strength, and chemical stability, and are commonly used as wear resistant and high-temperature components, as prosthetic implants, and electric circuit substrates. In this work, we explore methods of processing fine-grained, dense, thin, free-standing (ZrO₂)_x(Al₂O₃)_1?x films (x = 0-50 mol%, ~40 μm thick) by sintering flame made nanopowders (NPs) to optimize the t-ZrO₂ content, sinterability, and microstructures under select conditions (1120°C-1500°C/5 h in O₂ or 95%N₂/5%H₂). In all cases, the final sintered products retain t-ZrO₂ with average grain sizes (AGSs) of 0.1-1 μm. ZTA film thicknesses were increased to ~200 μm to assess potential as electronic substrates. Excellent fracture toughness (24 MPa m^1/2) and small AGSs of 0.7 μm were found for ~200 μm thick ZTA films sintered at 1500°C/5 h/N₂/H₂ using a three-step binder burnout process. Furthermore, we show that homogeneous ZTA thin films (<5 μm thick) can be sintered on Si₃N₄ substrates (thickness ≈ 300 μm) to provide physical protection against oxidation under extreme conditions (1500°C/1 h/O₂), offering additional practical utility for high-temperature ceramics and power electronic substrates.