Effect of Slurry Thickness on the Quality of Aluminized Coatings

Abstract

Diffusion aluminum coating is crucial to protect aero-engine turbine blades from high-temperature oxidation. Slurry aluminizing, as a commonly-used coating preparation technology, has variations in the process parameters that directly affect the quality of the coating. Therefore, this paper investigates the effect of slurry thickness on coating quality. Different forms of aluminized coatings were obtained by coating nine DZ22B nickel-based superalloy plates of the same size with different slurry thicknesses while keeping other parameters constant. These aluminized coatings were characterized using a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS), an X-ray diffractometer (XRD), and a surface gauge. The results show that the AlNi phase dominates the matrix of the aluminized coating, and the outer layer of the coating has white dotted precipitates of Cr. As the slurry thickness increases, the coating thickness increases, and the proportion of the outer layer in the overall coating increases. In contrast, the thickness of the interdiffusion layer does not change significantly. The thicker the slurry, the higher the Al content of the coating surface. A medium-thickness slurry can form a smooth aluminizing coating with a roughness Ra < 4.5 μm surface. The combined results show that a medium-thick slurry can produce a high-quality coating.

Recent Advances in the Deposition of Aluminide Coatings on Nickel-Based Superalloys: A Synthetic Review (2019–2023)

“…A similar tendency was found for the slurry-aluminizing [25,26,[29][30][31][32] and CVD technologies [1][2][3]5,[37][38][39][40][41][42][43]47,51,55], for which the deposition of NiAl coatings is still the main area of interest. Interestingly, the most frequently modified nickel-based alloys are those with the highest oxidation resistance, possessing high mechanical strength.…”

“…Due to these benefits, the slurry method is widely used in obtaining diffusion aluminide coatings for engine jet parts. Li et al [25] confirmed that smooth coating with a surface roughness Ra < 4.5 µm could be obtained on a nickel-based substrate by using slurry aluminizing. Besides the precise and uniform nature of these coatings, they are characterized by excellent high-temperature corrosion resistance either in molten NaCl-KCl at 700 • C [26], air [27,28] and in the absence of salt [29].…”

“…The slurry method offers several advantages as compared to other methods [25]. This involves a shorter thermal cycle during the coating preparation and the possibility of precise protection of large parts.…”

The Effect of Pulling Speed on the Structure and Properties of DZ22B Superalloy Blades

“…Nickel-based superalloys have been widely used in aero engines and gas turbines to produce turbine blades with excellent high-temperature tensile strength, stress fracture, and creep properties [1][2][3][4][5][6][7]. DZ22B nickel-based superalloy has good casting performance, hightemperature oxidation resistance, and corrosion resistance, and is a common material for directional column crystal blades of aero engines [8][9][10]. However, during the solidification process, the blade is often prone to casting defects such as holes, shrinkage, and hot cracks [11,12].…”