Investigating the influencing variables on the aluminizing process on the metals by chemical vapor deposition method

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Investigating the influencing variables on the aluminizing process on the metals by chemical vapor deposition method

ارائه دهنده: Provider: نگار احمدی - مهندسی مواد

اساتید راهنما: Supervisors: Hassan Elmkhah -Hamid Esfahani

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Mohsen Sheykhi- Esmaeil Damavandi

زمان و تاریخ ارائه: Time and date of presentation: 2024

مکان ارائه: Place of presentation: Faculty of Engineering

چکیده: Abstract: The primary objective of this research is to enhance the hot corrosion and high-temperature oxidation resistance of Inconel 738 LC superalloy through the process of aluminizing the surface. The application of protective coatings is crucial for shielding metals from harsh thermal environments, a necessity in the aerospace and gas turbine industries. The effectiveness of these coatings relies on the formation of a stable Al2O3 oxide layer on the metal surface, which acts as a protective barrier against corrosion. Although numerous studies have focused on optimizing the aluminizing process, the effect of temperature with a fixed powder composition in the out-of-pack cementation method has been less explored. In this study, an aluminum coating was applied to the nickel-based superalloy using the out-of-pack cementation method. The powder mixture used consisted of aluminum, NH4Cl activator, and alumina in a weight ratio of 18, 3, and 79 percent, respectively. The coating process was carried out at three temperatures: 950°C, 1000°C, and 1050°C in a tube furnace under an argon atmosphere to maintain a neutral environment. Results indicated that increasing the aluminizing temperature from 950°C to 1050°C led to an increase in the diffusion layer thickness from 32 micrometers to 52 micrometers, with a corresponding increase in the intensity of the NiAl phase, which is desirable for improving corrosion and oxidation resistance. Following the coating application, hot corrosion and high-temperature oxidation tests were conducted to evaluate the performance of the coatings. The hot corrosion test was performed for 30 hours at 900°C using corrosive salts Na2SO4, NaCl, and V2O5. Additionally, the high-temperature oxidation test was conducted for 80 hours at 950°C in a furnace environment. To assess the microstructure of the coatings, scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) was utilized, and phase compositions were identified using X-ray diffraction (XRD) analysis. The hot corrosion test results demonstrated that uncoated samples were severely degraded, whereas the aluminized samples exhibited significantly lower degradation. Among the aluminized samples, the one coated at 1050°C showed the least degradation and weight change. Furthermore, the high-temperature oxidation test results confirmed the formation of a stable oxide layer on the surface of the aluminized samples. This improved behavior can be attributed to the higher percentage of the NiAl phase present at 1050°C.

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