| Summary: | 碩士 === 國立清華大學 === 工程與系統科學系 === 100 === The purpose of this study is to solve the wettability issue by growing ZrO2 from heat treatment of the ZrN thin films on stainless steel substrate and investigate the oxidation mechanism of ZrN films in different atmospheres. ZrN thin films were deposited on Si and 304 stainless steel substrates using hollow cathode discharge ion-plating (HCD-IP), and were annealing at temperatures ranging from 700 to 1000°C and over durations ranging from 1 to 4 hours. Vacuum (510-6 Torr) and forming gas (N2/H2=9) environment were selected to prevent sever oxidation. As the annealing temperature was higher than 800°C, the specimens were totally oxidized in the forming gas within one hour. However, ZrN still remained as the major phase in the films even annealing at 1000°C for 4hr in vacuum. The microstructure and composition also revealed different behaviors in two annealing atmosphere. The difference may be derived from the surface structure in different annealing environments. The surface oxide was non-protective in the forming gas so that the oxygen in the system can easily reacted with ZrN, and the volume expansion during oxidation would lead to the formation of blisters and cracks on the sample surface. Once cracks appeared on the surface, oxygen could penetrate through the oxide layer and react with ZrN and accelerate the oxidation rate; on the other hand, since the surface oxide was protective in vacuum, the diffusion of oxygen was hindered and remained an intact surface. Retained ZrN could be observed on the surface layer in stainless steel-based specimens even annealed at 800°C for 4hr after vacuum annealing. The ratios of corrosion area for all the oxidized ZrN films were less than 0.2% after 500hr salt spray test indicating an excellent corrosion resistance. Thus, by selecting a proper environment, ZrO2 can be grown from ZrN without peeling and crack formation, which may provide good corrosion protection. Moreover, the stress could be relieved without significant change in properties as the specimens were annealed at 1000°C for 1hr in vacuum.
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