The thermal phase stability of plasma sprayed TBC is presented and discussed. TBC phase transformation after various isothermal heat treatment processes was studied via Xray diffraction (XRD) and Raman Spectroscopy methods. The YSZ-Gd-Yb and 20YSZ TBCs demonstrated superior thermal phase stability as compared with the high and standard purity 8YSZ TBCs, although higher purity also helps delay the tetragonal to monoclinic phase transformation. The phase transformation appears to be suppressed by cooling at higher rates. This data presents a qualitative phase stability comparison between the various coatings. However, cooling rate has to be taken into consideration in determining the extent of phase instability during the coating design of aero turbine applications.

Splats are the building blocks of thermal sprayed coatings, and thus the mechanical properties of such coatings are directly related to splat behavior. Elastic and elastoplastic properties of coatings have been measured on the macro-scale, but are not yet quantitatively predictable using process parameters as inputs. Coating mechanical properties represent contributions from intrinsic splat properties, splat-splat interfaces, and other microscopic defects. In this study, we investigated the intrinsic properties of Ni and Ni based alloy splats on substrates, for a variety of process methods and input parameters. Residual stresses were measured via X-ray microdiffraction and elastic and elastoplastic properties were studied via nano-indentation. From a purely scientific standpoint, splat studies provide insight into rapidly cooled small-volume structures that often exhibit extra ultrafine- or nano-crystalline structure. Thus, accordingly, nano-indentation response was also compared to the prediction for bulk counterparts of the splat materials.