Fracture toughness and phase stability are crucial properties of thermal barrier coatings (TBC) during highly loaded thermomechanical operations in gas turbines. While several alternative TBC materials have exhibited excellent thermal resistance, their potential applicability has been limited due to poor endurance to cyclic stresses. The addition of TiO 2 to the non-transformable tetragonal t´-YSZ has been found to effectively enhance the fracture toughness and phase stability of YSZ at high temperature exposures. Thermal cycling tests in a burner rig were conducted on TBCs prepared from atmospheric plasma sprayed titania-doped YSZ to verify this phenomena. Exposure temperature was 1400°C at the surface and thermal gradient across the sample was provided by simultaneous back-cooling treatment. Cycling tests reveal that the slight increase in the tetragonality of the deposited coatings with increasing amount of dopant did not cause a significant effect to the lifetime of the TBCs. Moreover, increasing amount of Ti-substitution did not influence the fracture toughness of the bulk YSZ.

Processing of powder feedstock materials often influences the deposition behavior and ultimately, the properties of the atmospheric plasma spray (APS) deposited coatings. The necessity of materials design and the control of deposition parameters are therefore, of high importance. Feedstock from promising ceramic thermal barrier coating materials with Ba(Mg 1/3 Ta 2/3 )O 3 and La(Al 1/4 Mg 1/2 T 1/4 )O 3 perovskite structures (λ~ 2 W/m-K and α~11x10-6 /K at 1473 K) were prepared through solid state and conventional spray drying techniques. The powders were then deposited on metallic substrates by APS process. Monitoring of in-flight particle characteristics and splat formation as well as characterization of deposited coatings, were conducted. It was found that these types of perovskite materials tend to lose constituents during deposition by atmospheric plasma spraying. This paper reports on the challenges of powder feedstock design and the control of critical deposition parameters to prevent or minimize the non-stoichiometric deposition of decomposition-prone perovskite coatings by APS process.