Microstructure and Formation Mechanism of Aluminized Coatings on Nickel-Based Superalloys
Aluminized coatings prepared on nickel-based superalloys can provide good protection against high temperature oxidation and hot corrosion. This study investigated the simple aluminized and silicon-aluminized coatings on nickel-based superalloy K4104. The simple aluminized coating was prepared by pack cementation and the Al-Si coating was prepared by slurry aluminizing, respectively. The microstructure of simple aluminized and Al-Si coatings was analyzed by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and electron probe microanalysis (EPMA). And the formation mechanism of simple aluminized and Al-Si coatings was discussed. The results showed that the simple aluminized coating was about 49 um thick and consisted of three layers. The outer layer mainly consisted of Al-rich β-NiAl. The intermediate layer consisted of Ni-rich β-NiAl and Cr-rich. The inner diffusion layer consisted of Cr-rich and γ’-Ni3Al. The microstructure of Al-Si coating showed that the coating was about 70 um thick and consisted of five layers. The Al-Si coating consisted of CrxSiy, Al-rich β-NiAl, Ni-rich β-NiAl, Cr-rich and γ’-Ni3Al. The microstructure of simple aluminized coating was compared with that of Al-Si coating in order to find out the effect of Si. Owing to the effect of Si, there was a Transition layer in Al-Si coating. The Al-Si coating was thicker than simple aluminized coating. The declining trend of the aluminum concentration in the Al-Si coating was smoother than that of the simple aluminized coating.
M.K. Lei, X.P. Zhu, K.W. Xu and B.S. Xu
J. B. Pei et al., "Microstructure and Formation Mechanism of Aluminized Coatings on Nickel-Based Superalloys", Key Engineering Materials, Vols. 373-374, pp. 204-207, 2008