In this paper, the pure MCrAlY coating and nano-Al2O3 particles reinforced MCrAlY graded coating were prepared on TiAl base intermetallic alloy substrates by laser cladding process. Furthermore, the microstructure characterization, microhardness and wear resistance of the two kinds of MCrAlY coating were comparatively investigated with scanning electron microscope (SEM), HXD-1000TC hardness tester and MM-200 block-on-ring dry sliding wear tester. The results show that the laser-clad pure MCrAlY coating has a dendrite crystals characteristic. However, the graded composite MCrAlY coating consists of fine equiaxed grains because of addition of nanometer ceramic particles. Moreover, the grain size becomes small with increasing the nano-Al2O3 content in the coating. The microhardness and wear resistance of the composite coating is higher than that of the pure coating. The mainly wear mechanism of the pure MCrAlY coating is abrasive and delamination, while the mainly wear mechanism of the composites graded MCrAlY coating is abrasive.
This paper deals with the microstructure and thermal shock behavior of laser remelting of yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) deposited by plasma spraying. The microstructures of the coatings were analyzed by scanning electron microscopy (SEM). It was found that the as-sprayed ceramic coating had laminated structure with high porosity. However, the coating exhibited a dense lamellar-like layer with segment cracks on the remained plasma-sprayed porous layer. Thermal shock experiments for the two kinds of TBCs were performed by water quenching method. Testing result showed that the laser-remelted TBC had better thermal shock resistance than the as-sprayed one. The damage mode of the as-sprayed TBC was great-size whole spalling. In contract, the failure mechanism of the laser-remelted one was mainly local pelling. Segmented cracks of the top ceramic coatings caused by laser remelting improved the stress accommodation and were mainly attributed to the enhancement for thermal shock life of TBC.
Abstract. In this work, conventional and nanostructured Al2O3-13wt.%TiO2coatings were deposited by the plasma spraying technique. The microstructures of the two types of coatings were analyzed, and the solid particle erosion behaviors of the two coatings were comparatively researched in an erosion tester. Meanwhile, the erosion failure mechanisms of the coatings were discussed. The results show that the traditional coating has laminated structure and some pores. However, the nanostructured coating possesses a denser structure and not obviously lamellar-like structure, and exhibits a bimodal microstructure consisted of fully melted regions and partially melted regions. Owing to the compact microstructure and remained nano-particles, the nanostructured coating had a better erosion wear resistance than the conventional coating. Eroded morphology analysis indicates the main erosion mass loss of the coatings is attributed to lamellar spalling of the sprayed splats and fracture of brittle ceramic particles. In addition, the nanostructued coating has some impact craters and plough marks. In terms of the erosion mechanism, the conventional ceramic coating is dominated by brittle erosion, while the nanostructured ceramic coating is dominated by brittle erosion as well as ductile erosion to some extent.
In this study, conventional and nanostructured MCrAlY/ZrO2-7wt.%Y2O3 double-layer thermal barrier coatings (TBCs) were fabricated on TiAl base intermetallic alloy substrates by the plasma spraying technique. The microstructural characterization and thermal insulation capability of the two types of coatings were comparatively researched. The results show that the conventional ceramic coating has a typical lamellar stacking characteristic. However, the nanostructured coating exhibits a bimodal microstructure, which is composed of both fully melted regions and partially melted regions (remained nanoparticles). The nanostructured TBCs has higher thermal barrier effect than the traditional one. The temperature drops of the nanostructured TBCs at 1100 °C increases 53% compared with that of the conventional TBCs.
Based on the single-layer thin film theory, we calculated transmittance of ITO thin film. The reflectivity arrive a maximum or a minimum according to whether the refractive index of film is greater or smaller than the refractive index of the glass substrate. we obtain the same maximum of transparence which is above 95% and the minimum value which decrease to 76.5% with the increase of refractive index.
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