MICROSTRUCTURAL CHARACTERIZATION OF PLASMA-SPRAYED ZIRCONIA THERMAL BARRIER COATINGS BY X-RAY-DIFFRACTION FULL PATTERN-ANALYSIS

Thick two-layered thermal barrier coatings made of Ni-Co-Cr-Al-Y and y ttria-partially stabilized zirconia were plasma sprayed at controlled deposition temperature onto stainless steel substrates. During the spr aying of the top coat, the deposition temperature was kept as constant as possible using a front air or liquid-argon-cooling system. The cor relation between process parameters and microstructure was investigate d by scanning electron microscopy and X-ray diffraction (XRD) analysis . The application of a new procedure for XRD data processing, based on the Rietveld method, made it possible to obtain good accuracy in the phase determination and quantitative evaluation of zirconia polymorphs . Moreover, the crystallite size and microstrain were refined simultan eously to phase percentages. Also the preferred orientation in the coa ting could be taken into account, adding useful information and increa sing the reliability of all the other results. The influence on the co ating microstructure of changing the deposition temperature and enviro nment is also discussed.