Characterization and Growth Kinetics Modelling of Nickel Silicides Formed on Inconel 738 Alloy

In this study, the growth kinetics of the silicide layer on Inconel 738 alloy were reported. The powder mixture containing NH₄Cl as an activator and Al₂O₃ as an inert filler, and metallic silicon was used for the siliconizing process on the Inconel 738 alloy for 2, 4, and 6 h at 800, 900 and 950 °C. The morphologies and types of silicides that developed on the surface of Inconel 738 alloy were examined using energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). The thickness of the siliicide layer varied between 20 ± 7 and 280 ± 20 μm. The temperature and duration time of treatment had an impact on the hardness of the silicides formed on the samples, ranging from 400 to 1500 HV. With the siliconizing process, a layer with high mechanical properties is created on the alloy surface. In nanoindentation tests, there was an increase in reduced elastic modulus from 212 to 241 GPa and in hardness from 6.7 to 16 GPa. A decrease of up to 84% was observed in the wear losses of siliconized Inconel 738 alloy at 950 °C–6 h due to the presence of silicide layer. Furthermore, the Taylor expansion model was utilized to assess silicon diffusivities within Ni silicide layers, incorporating the silicon diffusion coefficient within the Ni matrix. The activation energy for silicon was determined and compared with data available in the literature. Finally; a comparison was done between the predicted layers’ thicknesses and the experimental measurements.

Graphical Abstract