Elastic constants of plasma-sprayed yttria-stabilized zirconia coatings determined via resonant ultrasound spectroscopy coupled with laser-Doppler interferometry

Abstract

Plasma-sprayed yttria-stabilized zirconia (YSZ) coatings exhibit five independent elastic constants with transverse isotropy owing to splat-based layered structures, including numerous preferentially oriented defects. In this study, we measure all the elastic constants of free-standing YSZ coatings in both as-sprayed and thermally treated conditions from 800 °C to 1300 °C for 2 h. The YSZ coatings were produced via atmospheric plasma spraying under one typical processing condition. The elastic constants are determined using resonant ultrasound spectroscopy coupled with laser Doppler interferometry . This approach allows us to overcome the difficulty of resonant-mode identification caused by the high internal friction of plasma-sprayed YSZ coatings; hence, reliable elastic constant data are obtained. We discovered that the splat-based layered structures provide strong elastic anisotropies in both the shear and longitudinal moduli. In addition, our measurements in the as-sprayed condition suggest that the as-sprayed YSZ coatings exhibit degenerate (elliptic) transverse isotropy with inter-splat pores that tend to be perpendicular to the spraying direction. The dependence of the elastic constants on the heat-treatment temperature shows that the elastic anisotropy of the plasma-sprayed YSZ coatings increases slightly and then decreases as the heat-treatment temperature increases. This finding is supported by the different effective sintering temperatures of the inter-splat pores and intra-splat cracks. • All the elastic constants of free-standing YSZ coatings were determined precisely. • YSZ coatings exhibited degenerate transverse isotropy with inter-splat pores. • Elastic constants provided appropriate information on the coating microstructures.