The synergistic effect of Si and Ce addition on the oxidation resistance of a pack cementation aluminide coating applied on a Ni-based IN738LC superalloy substrate was investigated in this study. The structural and thermal influences of both Si and Ce, focusing on morphology, oxidation behavior, and scale spallation tendency, are accordingly discussed based on the experimental results using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analyses (EDX). For this purpose, the oxidation resistance of the modified coatings was evaluated by measuring the weight gain of the coated samples after 16 h for each cycle at 1100 °C for a total of 50 cycles of the oxidation process. The investigations indicated that Si addition to the modified aluminide coating improves the oxidation resistance through the formation of β-NiAl and δ-Ni2Al3 phases, and also δ-Ni2Si phases. Furthermore, the addition of 1% Ce to the modified aluminide coating enhances the formation of the fine-grained microstructure of the β-NiAl and δ-Ni2Al3 and reduces the outward/inward diffusion of elements (so-called blocking effect), which significantly modifies the cyclic oxidation resistance. The oxidation enhancement also may be attributed to synergistic effects of Ce and Si addition during the deposition process that reduce the inward oxygen diffusion and reduce the growth rate of α-Al2O3 during oxidation tests.

The synergistic effect of silicon and cerium addition on the oxidation resistance of pack cementation aluminide coating applied on Ni-based superalloy substrate was investigated. The effect of cerium and silicon on the scale morphology, oxidation behavior, and scale spallation tendency are discussed based on the experimental results, using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analyses (EDX). In addition, the oxidation resistance was evaluated by measuring the weight of samples after each 16-hour cycle at 1100˚C for 50 cycles. The experiments indicated that silicon addition to aluminide coating improves the oxidation resistance through the formation of β-NiAl1-nSin and δ-Ni2Al3-nSin and δ-Ni2Si phases. Furthermore, the addition of 1% cerium to modified aluminide enhances the formation of the fine-grained microstructure of the β-NiAl and δ-Ni2Al3 and reduces the outward/inward diffusion of elements (so-called blocking effect) which significantly modifies the hot oxidation resistance. The addition of 2% cerium, owing to the distortion of the β-NiAl and δ-Ni2Al3 phases, strictly decreases the hot oxidation resistance and the coating is exfoliated after 450 h at 1100 °C. The cyclic oxidation tests showed that the samples containing 1% cerium and 6% silicon possess the highest hot oxidation resistance in which 2 mg/cm2 weight loss of Ce-Si-aluminide was reported after 800 h. This is attributed to the simultaneous effect of cerium and silicon during the deposition process which reduces the oxygen diffusion and reduces the growth rate of α-Al2O3 during oxidation tests. The α-Al2O3 oxidation layer morphology showed that finer grains are formed in samples containing optimum ratios of cerium and silicon which indicates that these elements improve the coating adhesion and oxidation resistance simultaneously.