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

Richard Laine

Xinyu Zhang, Xiaopo Cheng, Monika Jansohn, Matthias Niedermaier, Thomas Lenk, Stefan Britting, Karsten Schmidt, and Richard Laine (2020)

Journal of the American Ceramic Society, 104(3):1281-1296.

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 m1/2) 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.

Thin film, ceramics, flame spray pyrolysis, nanopowders

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