Microstructure Investigation and Cyclic Oxidation Resistance of Ce-Si-Modified Aluminide Coating Deposited by Pack Cementation on Inconel 738LC

Abstract

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.