Correlation study of Fatigue Behavior and Microstructure of Metallic Materials Coated with a Glass-Forming Metallic Thin Film
| Autor: | Zhe-Zhi Liang, 梁哲誌 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 The glass-forming metal films, Cu51Zr24Hf18Ti7 and Cu31Zr47Al13Ni9 (atomic percent, at.%) deposited respectively on the two substrates of 316L stainless steel (316L) and Ni-based alloy (C2000) using magnetron sputtering, have been investigated by using high reso?lution transmission electron mi?croscopy (HRTEM) coupled with nanobeam energy dis?persive x-ray (EDX). The substrates were first carried out electrical polishing before depositing to the smooth surface. The as-deposited specimens were following proceeded fatigue test controlled by a computer in the Material Test System (MTS). Accordingly, the fatigue strength and life of the specimens coating with each glass-forming metal film are all much better than those without coating. It was found that 316L substrate coated with a 200 nm glass-forming Cu51Zr24Hf18Ti7 film shows the highest fatigue life improvement, which was considerably improved up to 4,490 %. The 316L substrate coated with a 200 nm glass-forming Zr47Cu31Al13Ni9 film shows the next-highest fatigue life improvement, which was also improved up to 3,224 %. However, the Ni-based substrate coated with a 200 nm glass-forming Zr47Cu31Al13Ni9 film shows the worst fatigue life improvement, which was just up improved up to 390 %. To further study the relationship between fatigue property improvement and microstructure, these specimens were sequentially characterized by using HRTEM coupled with nanobeam EDX. The results are divided into two groups: I). Both 316L and Ni-based coated with a 200 nm glass-forming Zr47Cu31Al13Ni9 film ; and II). 316L substrate coated with a 200 nm glass-forming Zr47Cu31Al13Ni9 film but 316L substrate coated with a 200 nm glass-forming Cu51Zr24Hf18Ti7 film. It was clear that 316L substrate coated with a 200 nm glass-forming Zr47Cu31Al13Ni9 film exhibited the better fatigue strength and life improvement than that of Ni-based substrate coated with the film of the same thickness and composition. Very likely, it was due to the improvement of surface roughness of the substrate. From the HRTEM cross-sectional images, 316L substrate coated with a 200 nm glass-forming Zr47Cu31Al13Ni9 film shows a thicker oxygen-rich interlayer (~ 5 nm) which offer a smoother surface formed on the 316L substrate before the film coating, thereby resulting in a good adhesion ability to enhance fatigue limit. Moreover, 316L substrate coated with a 200 nm glass-forming Cu51Zr24Hf18Ti7 film shows the better fatigue strength and life improvement than the substrate coated with a 200 nm glass-forming Zr47Cu31Al13Ni9 film. The main reason for the better performance of Cu-based BMG film is due to the formation of amorphous matrix involved nano-crystal, while the Zr47Cu31Al13Ni9 film composed of amorphous matrix involved coarse crystal pecipitates. It is well known that the coarse crystal would cause the “transgranular” behavior, on the contrary, the nano-crystal could reinforce the strength of the thin film. Consequentially, 316L substrate coated with a 200 nm glass-forming Cu51Zr24Hf18Ti7 film shows the highest fatigue life improvement. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|