Applying high-entropy AlCrSiTiZr-based coatings and investigating their tribological and electrochemical behaviors

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Applying high-entropy AlCrSiTiZr-based coatings and investigating their tribological and electrochemical behaviors

ارائه دهنده: Provider: Erfan Lotfi Khojasteh

اساتید راهنما: Supervisors: Dr. Hasan Elmkhah and Dr.Meisam Nouri

اساتید مشاور: Advisory Professors: Dr. Masoud Atapour

اساتید ممتحن یا داور: Examining professors or referees: Dr. Mohsen Sheikhi and Dr. Hamid Esfahani

زمان و تاریخ ارائه: Time and date of presentation: 2023/10/7

مکان ارائه: Place of presentation: Class 10 located in materials engineering department

چکیده: Abstract: In this research, high-entropy AlCrSiTiZr-based coatings were successfully applied to ۳۰۴ stainless steel substrates using the cathodic arc evaporation (CAE-PVD) method. The coatings were divided into two categories: single-layer high-entropy alloy (named HEA) and multilayer high-entropy nitride (named HEN). A number of samples for both coatings were subjected to annealing heat treatment in an air atmosphere at a temperature of ۸۰۰°C. This process resulted in the transformation of the coatings into annealed single-layer high-entropy alloy coatings (named HEAO) and annealed multilayer high-entropy nitride coatings (named HENO). The calculated mixing entropy parameter (ΔSmix) indicates that both the deposited HEA and HEN coatings fall within the high entropy range. Furthermore, X-ray diffraction (XRD), grazing incident X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the coatings. Consequently, the HEA coating exhibits a predominantly amorphous structure with a low density of HCP nanocrystalline islands, while the HEN coating features a nanocomposite structure with FCC nanocrystalline islands. The results obtained indicated that the HEN coating exhibited superior oxidation resistance compared to the HEA coating. This implies that the HEN coating has a lower propensity for forming an oxide layer due to the presence of stable nitrides bondings in its structure, unlike the HEA coating. It has been observed that the annealing treatment resulted in the formation of TiO۲ and SiO۲ phases and bondings within the HEAO coating, while the HENO coating exhibited the formation of SiO۲ phases and bonding. Additionally, the results of the wettability test indicated that all three HEA, HEN, and HENO coatings exhibited hydrophobic properties. However, the HEAO coating demonstrated superhydrophobic characteristics. The nano-indentation test revealed that the HEN coating, with the inclusion of reactive nitrogen gas, exhibited a hardness up to ۱.۵ times higher than that of the HEA coating. Furthermore, the HEAO coating demonstrated a hardness that was ۲.۸ times higher than that of the HEA coatings after undergoing annealing heat treatment. Additionally, the HEAO coating exhibits the highest H/E and H۳/E۲ ratios, whereas the HEA coating displays the lowest values for these ratios. Furthermore, the ball-on-disk wear test was conducted in dry and a ۳.۵ wt.% NaCl solution. In both environments, the HEAO coating demonstrated superior wear resistance attributed to its high hardness and the presence of solid lubricant phases on the surface. Furthermore, the corrosion resistance of these coatings was evaluated in ۳.۵ wt% NaCl and ۰.۱ M H۲SO۴ electrolytes. The results indicated that the HEAO coating exhibited the highest corrosion resistance, followed by the HENO, HEN, and HEA coatings in descending order. The superior corrosion resistance of the HEAO coating can be attributed to factors such as the presence of a dense oxide layer on its surface, closure of surface pores, existence of corrosion-resistant surface phases, and superhydrophobic behavior

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