Abstract:In this work, the effect of water vapour on a new thermal barrier coating system synthesised from a slurry containing Al microparticles was studied under isothermal regime at 1100 °C for short oxidation times (50 h). Both dry air and argon gas atmospheres were investigated with increasing water vapour contents (0, 5, 10% RH, relative humidity) and the oxidation mechanisms and growth kinetics of the oxide scales were compared to conventional aluminide coatings up to 50% RH. The phase transformations occurring i… Show more
“…The Raman spectra shown in Figs. 6. a. and b. let appear a doublet at 1400 cm -1 which is characteristic of the presence of α-Al 2 O 3 [31,32] but no signal was observed in the Raman domain ( Fig. 6.…”
Section: Influence Of Pressure -1 Vs 300 Bar -5000 H Of Exposurementioning
B2-FeAl-based aluminide coatings were elaborated on P92 ferritic-martensitic steels by slurry. Under atmospheric pressure of steal and 650°C, a thin protective α-Al 2 O 3 oxide layer formed and was maintained until 5000 h. With increasing pressure to 300 bar, the morphology of α-Al 2 O 3 changed markedly. Iron oxide clusters started to appear at the surface of the scale after 5000 h of exposure and kept on growing till 10000 h. It appears that pressure increased the outward diffusion of Fe through the coating and through the oxide scale and fostered the propagation of the tensile cracks of the coating.
“…The Raman spectra shown in Figs. 6. a. and b. let appear a doublet at 1400 cm -1 which is characteristic of the presence of α-Al 2 O 3 [31,32] but no signal was observed in the Raman domain ( Fig. 6.…”
Section: Influence Of Pressure -1 Vs 300 Bar -5000 H Of Exposurementioning
B2-FeAl-based aluminide coatings were elaborated on P92 ferritic-martensitic steels by slurry. Under atmospheric pressure of steal and 650°C, a thin protective α-Al 2 O 3 oxide layer formed and was maintained until 5000 h. With increasing pressure to 300 bar, the morphology of α-Al 2 O 3 changed markedly. Iron oxide clusters started to appear at the surface of the scale after 5000 h of exposure and kept on growing till 10000 h. It appears that pressure increased the outward diffusion of Fe through the coating and through the oxide scale and fostered the propagation of the tensile cracks of the coating.
“…Indeed, for the same coating thickness, the number of interfaces increases with decreasing the size of the particles. Therefore, and because interfaces are known to scatter heat in ceramic coatings [9][10][11], the greater the number of interfaces, the lower the thermal diffusivity. In addition, the HS microparticles whose shells are thicker than those of the DS ones will lead to higher heat conduction because the ratio of material vs. void is more significant.…”
Section: Discussionmentioning
confidence: 99%
“…However, this thin foam did not display sufficient resistance to erosion by grit blasting because of the thin oxide shell of the alumina hollow spheres [6]. Previous studies that investigated the role of the microparticles' properties [7], the mechanisms of coating formation [8] or the influence of the annealing gases [9,10] on the formation of such coatings showed that it was possible to obtain different foam top coatings by varying the parameters of the annealing conditions or the microparticles of the slurry itself. In an attempt to thicken the shell and enhance the sintering of the hollow spheres, hence to improve the mechanical strength of the insulative foam, previous research aimed at controlling the annealing atmosphere to promote the growth of the oxide shells of the original microparticles while enabling enough Al to react with the Ni substrate to form the diffusion coating [11].…”
In this study, the mechanical resistance and the thermal insulation potential of novel thermal barrier coatings (TBCs) made of a foam of hollow alumina particles are assessed through scratch testing, micro-indentation and thermal diffusivity measurements using laser-flash. The thermal diffusivity of the foam coatings ranges between 0.6 × 10−7 and 5 × 10−7 m2·s−1 and is thus comparable with the thermal insulation potential of the standard plasma-sprayed (PS) and electron beam–physical vapour-deposited (EB-PVD) TBCs made of yttria-stabilised zirconia (YSZ). The coatings annealed in more oxidative atmospheres exhibit greater mechanical resistance due to the thickening of the alumina shells and the increased sintering of the foam. However, when the oxidation is poorly tailored, the adhesion of the foam to the substrate decreases due to the presence of unwanted oxide that grows at the substrate/coating interface.
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