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.

Recent Advances in the Deposition of Aluminide Coatings on Nickel-Based Superalloys: A Synthetic Review (2019–2023)

“…Furthermore, it was also characterized by an extended service life. It was stressed that while specimens after simple aluminide lost their scale, the Si-modified aluminide coatings retained their protective capabilities even after 300 h. Such behavior was also reported for Inconel 738LC protected with a Ce-Si-modified NiAl coating obtained by using PC [11]. It was found that the simultaneous addition of 1% cerium and 6% silicon led to the formation of Ce 1 Si 6 , which limits the oxygen diffusion, promotes the growth of the continuous Al 2 O 3 layer, and further enhances the hot-oxidation resistance of the coating.…”

“…Interestingly, the most frequently modified nickel-based alloys are those with the highest oxidation resistance, possessing high mechanical strength. These involve Rene 80 [8,18,63], Inconel 625 [13,57,58], Inconel 713 [39,40,52], Inconel 718 [41], Inconel 738L [11,19,22,36,45,59,61,65,68] and CMSX-4 [17,30,42,44,46]. One should highlight that the research involving conventional nickel-based superalloys is mainly dedicated to future high-temperature applications.…”

A Comparative Study on Characterization and High-Temperature Wear Behaviors of Thermochemical Coatings Applied to Cobalt-Based Haynes 25 Superalloys

“…Numerous studies have been conducted to form carbide precipitates to improve the mechanical properties of cobalt, nickel, or iron superalloys [4,5,[7][8][9]. While some of these studies aimed to form regional carbides throughout the alloy's microstructure [4,5,[7][8][9], others focused on forming aluminide nitride, boride, carbide, etc., on the surface of these alloys [10][11][12][13]. These advanced surface coatings often offer a more cost-effective approach to increasing service life.…”

“…However, cobalt-based superalloys have many applications in high-temperature abrasive environments such as gas turbines, nuclear power plants, high-temperature furnaces, and the oil and gas industry [1,2,22]. When thermomechanical coatings are applied to the surfaces of these superalloys, they improve surface hardness and chemical inertness and provide a thermal barrier effect, resulting in enhanced oxidation, corrosion, and wear resistance at high temperatures [10][11][12][13][14][17][18][19][20][21]. These advantages enhance the performance of cobalt-based superalloys, enabling their use in more challenging operating conditions.…”

“…Depending on the specific application requirements and the desired coating properties, various thermomechanical coating methods can be applied to cobalt-based superalloys, such as nitriding, aluminizing, boriding, carburizing, and so on [10,14]. However, the high hardness and stability of boride layers up to 1000 • C [17], as well as the high coating thickness and oxidation resistance of aluminide coatings at high temperatures [18], have highlighted the need for further investigation of these methods.…”