Microstructure analyses and thermophysical properties of nanostructured thermal barrier coatings

Abstract

Nanostructured 8 wt% yttria partially stabilized zirconia coatings were deposited by air plasma spraying. Transmission electron microscopy, scanning electron microscopy, and X-ray diffraction were carried out to analyze the as-sprayed coatings and powders. Mercury intrusion porosimetry was applied to analyze the pore size distribution. Laser flash technique and differential scanning calorimetry were used to examine the thermophysical properties of the nanostructured coatings. The results demonstrate that the as-sprayed nanostructured zirconia coatings consist of the nonequilibrium tetragonal phase. The microstructure of the nanostructured coatings includes the initial nanostructure of powder and columnar grains. Moreover, micron-sized equiaxed grains were also exhibited in the nanostructured coatings. Their evolution mechanisms are discussed. The as-sprayed nanostructured zirconia coating shows a bimodal pore size distribution, and has a lower value of thermal conductivity than the conventional coating.

High temperature mechanical characterization of plasma-sprayed zirconia–yttria from conventional and nanostructured powders

“…As also reported elsewhere in the literature [32,33,43] this observation could depend on the fact that this kind of Fig. 12.…”

Comparison of the hot corrosion of nanostructured and microstructured thermal barrier coatings

“…The corrosion resistance of nano‐TBC is better than the micro‐TBC, which can be attributed to that the nanostructure leads to lower defects, such as pores or cracks, excellent smooth surface and component homogeneity . Under the corrosive conditions, it is more difficult for the molten salt to penetrate into zirconia coating in nano‐TBC than in micro‐TBC.…”

Nanocomposite coatings: thermal spray processing, microstructure and performance

“…290 Comparing nanostructured thermal spray coatings to their conventional counterparts, nanostructured coatings exhibit a lower thermal conductivity and diffusivity because of their small grain size and homogeneous pore distributions. 291,292 The attenuation length decreased when the grain size decreased, hence effectively reducing grain boundary scattering and thermal conductivity; 290 Fig. 37a.…”

“…The smaller and more homogeneously distributed pores and thinner splats in nanostructured coatings provided a larger boundary volume for effective phonon scattering and stronger interfacial thermal resistance, which consequently reduced the thermal conductivity. 292 The equiaxed grains in nanostructured coatings with tortuous zigzag-like boundaries also contributed to a greater thermal resistance compared to conventional coatings, which exhibit columnar grains that are aligned parallel to the direction of heat flow. 292 The thermal conductivity of plasma sprayed conventional ZrO 2 -7wt-%Y 2 O 3 coatings was reported to be almost twice that of nanostructured coatings.…”