Characterization of Aluminized Layers on Inconel‐738 Alloy: Microstructure, Modeling of Aluminizing Kinetics, and Thermal Behavior

In the present study, kinetics and thermal behavior of the Inconel 738 alloy were studied by the low‐temperature thermoreactive aluminizing process, which was carried out at 625°C, 650°C, 675°C, and 700°C for 2, 4, and 6 h. The coating layer formed on the surface of the Inconel 738 alloy substrate was characterized by X‐ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and EDS‐attached SEM. XRD analysis revealed that the dominant compounds formed during the thermoreactive aluminizing process are Al ₃ Ni ₂ , AlNi, and AlCr ₂ . SEM examinations showed that the aluminized layer formed on the surface of the Inconel 738 alloy has a compact nature with different contrast due to the presence of various elements. Depending on the process temperature and duration, the aluminide layer thickness and hardness values were found to be in the range of 6–68 μm and 390–1200 HV, respectively. A kinetic model employing the mass balance equation was considered in the multiphased aluminized layer formed on the Inconel 738 alloy. In this model, the diffusivity of aluminum (Al) in the Ni matrix was accounted for under a transient diffusion regime, and the distribution of Al concentration within the aluminized layer was linear. It enabled us to assess the activation energy for Al diffusion in the aluminized layer on the Inconel 738 alloy. In addition, the sample coated at 650°C for 4 h was exposed to oxidation at 700°C, 800°C, and 1000°C. It was found that the activation energy of oxidation was 296 kJ mol ⁻¹ for the coated sample, whereas it was 113 kJ mol ⁻¹ for the bare alloy.