A comprehensive study on the microstructure evolution and oxidation resistance of conventional and nanocrystalline MCrAlY coatings

Abstract

Conventional and nanocrystalline MCrAlY coatings were applied by the high-velocity oxy-fuel (HVOF) deposition process. The ball-milling method was used to prepare the nanocrystalline MCrAlY powder feedstock. The microstructure examinations of the conventional and nanocrystalline powders and coatings were performed using X-ray diffraction (XRD), high-resolution field emission scanning electron microscope (FESEM) equipped with energy-dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS). Williamson–Hall analyzing method was also used for estimation of the crystalline size and lattice strain of the as-milled powders and sprayed coatings. Owing to the investigation of the oxidation behavior, the freestanding coatings were subjected to isothermal and cyclic oxidation testing at 1000 and 1100 °C under static air. The results showed that the conventional as-sprayed MCrAlY coating had a parabolic behavior in the early stage and prolonged oxidation process. On the contrary, in the case of the nanocrystalline MCrAlY coating, the long-term oxidation behavior has deviated from parabolic to sub-parabolic rate law. Moreover, the results also exemplified that the nanocrystalline MCrAlY coating had a greater oxidation resistance following the creation of a continuous and slow-growing Al2O3 scale with a fine-grained structure. The nucleation and growth mechanisms of the oxides formed on the nanocrystalline coating have also been discussed in detail.

Atomistic Origins of Reversible Noncatalytic Gas–Solid Interfacial Reactions

“…However, deviations from the parabolic kinetics during the steady-state oxide scale growth period have frequently been observed. Several interpretations have been used to explain such deviations, including a phase-boundary process as the rate-determining step of the reaction, , built-in electric field driven ionic diffusion, , doping effect in the oxide scale, − and microstructure evolution effect on the oxide scale growth. − The reverse reaction is often ignored to explain the deviations from the parabolic kinetics of the scale oxide growth. As shown from our results of the CO 2 -induced Ni oxidation, the reverse element of the reaction indeed exists and should be taken into account to understand the overall reaction rate.…”

High-Temperature Corrosion of Nickel-Based Coatings for Biomass Boilers in Chlorine-Containing Atmosphere

“…This essentially corresponds to a slow parabolic law, where the oxidation rate is controlled by the diffusion rate, which is reduced by the growth of oxides on the surface. However, in the case of thermally sprayed coatings, the initial rate of oxidation was accelerated by the large surface area of the samples, which were usually very coarse, and by their porosity [13,14].…”

“…the surface. However, in the case of thermally sprayed coatings, the initial rate of oxidation was accelerated by the large surface area of the samples, which were usually very coarse, and by their porosity [13,14]. However, these weight changes plummeted in time (after a rapid oxidation of the coarse surface layer), and further corrosion changes were extremely limited.…”

Research Progress and Development Trend of Amorphous and Nanocrystalline Composite Coatings: A Review

“…Ghadami et al 87,88 prepared nanostructured NiCoCrAlY coatings, and the slow rate formation of a relatively dense oxide layer prevents the interdiffusion of oxygen or the outdiffusion of metal ions. As a result, the oxidation resistance of nanostructured coatings is increased by 35% compared to conventional coatings.…”