2.1.2 modified aluminide coating
Adding a small amount of Si, Cr, Pt and other elements into the simple aluminizing coating can obviously improve the performance of the coating. The improved aluminide coating mainly includes the following types:

(1) CR modified aluminide coating
Adding CR into the coating can significantly improve the thermal corrosion resistance of the coating and slow down the degradation caused by the mutual diffusion between the coating and the substrate. The coating can be prepared by one-step and two-step methods. Due to the huge difference in the thermal stability of the halides of Al and Cr, it is very difficult to achieve Al and Cr co penetration by embedding pure metal powder. Therefore, in the early stage, the two-step method is usually used to prepare the chromium modified aluminide coating, that is, pre depositing the chromium layer on the metal matrix, which can be used by embedding, slurry and electroplating, and then embedding the thermal diffusion aluminizing. By using CR Al Binary Alloy, the vapor pressure of halide with relatively high Al can be reduced, and Al and Cr co penetration on nickel base alloy can be realized. The coating is mainly NiAl phase, Cr is solid solution in NiAl phase, or α - Cr phase precipitates.

(2) Si modified aluminide coating
Adding a proper amount of Si in the coating can slow down the degradation caused by the mutual diffusion between the coating and the substrate, and also improve its thermal corrosion resistance. Moreover, compared with Al Cr infiltration, it has better high temperature oxidation resistance, but the content of Si should not be too high, because at high temperature, Si and Ni will form harmful low melting point phase, which will make the coating brittle and easy to peel off in the oxidation process. Slurry method is the most commonly used method to prepare Al Si coating. The main phase of the coating is β - NiAl, and the second phase particles rich in Si are distributed in the coating.

(3) Pt modified aluminide coating
Among the modified aluminide coatings, Pt Al coating has the most obvious modification effect. PT improves the anti peeling and self-healing ability of α - Al2O3 film, increases the structure stability of aluminide coating, and reduces the mutual diffusion between coating and matrix. PT Al coating is usually prepared by two steps. First, a layer of Pt is electroplated on the alloy substrate, and then annealed. After annealed, the powder is embedded and aluminized. The coating is usually a two-layer structure, the outer layer is a two-phase structure of ptal2 and NiAl or a single-phase layer of Pt rich (PT, Ni) al, and the inner layer is a single-phase layer of NiAl.

The improved aluminide coating has been widely used in the hot end parts of gas turbine.