Relationship among Thermodynamic, Growth Kinetics, and Microstructure Characterization of the Simple and Silicon‐Modified Aluminide Coating on Ni‐based Superalloy.

This research investigates the effects of pack cementation parameters on the thermodynamics, growth kinetics, and microstructure of the simple and silicon‐modified aluminide coatings on the IN718 superalloy. The growth kinetic modelling of the aluminide coating, activated by NH4Cl, is established as h=174252.02T12WAl12WNH4Cl12t12exp-8306.5T ${h={{174252.02}\over{{T}^{{{1}\over{2}}}}}{W}_{Al}^{{{1}\over{2}}}{W}_{NH4Cl}^{{{1}\over{2}}}{t}^{{{1}\over{2}}}exp\left({{-8306.5}\over{T}}\right)}$. further optimizing the kinetics modelling that includes both CaCl2 activator or the mixture of CaCl2 and NH4Cl. The results showed that NH4Cl as an activator generated a higher equilibrium partial pressure of halides, which enhanced the deposition efficiency of active Al atoms and facilitated the significant precipitation of Cr‐rich carbides. Additionally, part of the CaCl2 substitute NH4Cl could maintain a high coating growth rate and reduce the hazards. Adding Si element preferentially combines with Cr formed the Cr9.1Si0.9 phase along grain boundaries, which blocked the inner‐diffusion channels of Al atoms and reduced the thickness of the silicon‐modified aluminide coating compared to simple aluminide coating. These researches revealed the relationship among the thermodynamics, growth kinetics, and microstructure of simple and silicon‐modified aluminide coatings. The thickness and microstructure of coatings can be effectively regulated by adjusting the powder composition, content, and process parameters to achieve precise control. [ABSTRACT FROM AUTHOR]