This study investigates a new zirconia-based ceramic for potential use in thermal barrier coatings. In the experiments, Sc 2 O 3 -Gd 2 O 3 -Yb 2 O 3 -ZrO 2 (SGYZ) powder was synthesized by coprecipitation and calcination, then agglomerated and sintered to facilitate spraying. The structure, morphology, and phase stability of the powder and plasma-sprayed SGYZ coatings were analyzed and thermal conductivity was measured. Test results show that the powders and coatings have good phase stability even after 500 h at 1400 °C and do not undergo tetragonal-to-monoclinic phase transition upon cooling. Plasma-sprayed SGYZ also has a lower thermal conductivity than YSZ, which is currently used in gas turbine engines.

In cold spraying, several theories have been presented to explain the bonding between the substrate and coatings. In this work, finite element simulations were performed to obtain the minimal bonding strength to overcome rebounding at different initial velocities. The correlation with critical deposition velocity is also discussed.

TiAl 3 -Al composite coating on γ-TiAl alloy was prepared by cold spray and subsequent heat-treatment. The Oxidation test, which was carried out at 950 °C in air, indicated that the bare alloy exhibited poor oxidation resistance, significant weight loss was observed after oxidation for 70 h. The oxides formed were the mixture of TiO 2 /Al 2 O 3 . For the specimen with the TiAl 3 –Al coating, great improvement in oxidation resistance was observed. Approximate parabolic oxidation kinetics was observed for the oxidation period. The microstructure analysis showed a dense TiAl 2 interlayer and a reticular Cr rich phase formed between the composite coating and the substrate. The oxides in the oxidized coating were mainly alumina, with only trace of titanium dioxide and titanium nitrides after oxidation up to 1000 h. A certain amount of TiAl 3 phase in the coating remained unoxidized and unconsumed. The EPMA analyses of the coated samples showed that no trend of oxygen or nitride diffusion into the substrate and no oxide formed beneath the TiAl 2 interlayer.