| Summary: | 碩士 === 國立虎尾科技大學 === 機械與電腦輔助工程系碩士班 === 105 === PVD coatings are today frequently used in order to improve the tribological performance of cutting tools, forming tools and machine components. In this study, optical emission spectroscopy (OES) was employed to identify the species present in the plasma and to correlate them with the properties of the deposited thin films. VN-based coatings are known to show a combination of high hardness and toughness and the possibility to form a low friction Magnéli phase, promoting low friction coefficient in sliding contact, and consequently these coatings are of interest for sliding contact tribosystems.
In this study, TiVN coatings were synthesized by cathodic arc evaporation (CAE). Pure Ti and TiV alloy cathodes were used for the deposition of TiVN coatings. By controlling the different bias voltage, the deposited monolayered TiVN coatings possessed different mechanical properties and plasma characteristics of TiVN hard coatings. Plasma characteristics were observed by optical emission spectroscopy (OES). The microstructure of the deposited coatings was investigated by a field emission scanning electron microscope (FE-SEM), equipped with an X-ray energy dispersive spectrometer (EDS). Glancing angle X-ray diffraction was used to characterize the microstructure and phase identification of the films. A field emission transmission electron microscope (FE-TEM) to characterize the microstructure and phase identification of TiVN-200V coating after oxidation at 500˚C. The information of surface element distribution and chemical bonding of wear tracks is measured by X-ray photoelectron spectrometer (XPS). Mechanical properties, such as the hardness, were measured by means of Vickers indentation. The adhesion strength and impact fatigue performance of the coatings were evaluated by Rockwell indentation and dynamic impact fatigue device. Ball-on-disk wear test at room temperature and high temperature was conducted to evaluate the tribological properties of the deposited coatings. Finally, a field end milling test of SUS 304 stainless steel was conducted to investigate the tool performance by employing the TiVN coatings. Flank wear of the coated end mills and the surface roughness of the machined workpieces were measured.
The experimental result showed that monolayered TiVN-200V coating possessed the B1-NaCl structure and the fewest microparticles. It possessed the highest hardness (25.8GPa) and the best adhesion (class 0). Besides, the TiVN-200V coating showed good impact resistance (higher than 4×105 impacts). The residual stress of TiVN coatings increased as bias voltage increased. The best tribological performance of TiVN coatings is TiVN-200V. It possessed low friction coefficient (0.38) and low wear rate (7.5×10-7mm3/Nm). A field end milling test also showed TiVN-200V coating possessed the lowest flank wear (40.7µm) and the best surface roughness (Ra：0.5µm) of the machined workpieces. Finally, it can be concluded that vanadium incorporation provided self-lubricous abilities achieving low friction coefficient due to oxide formation at elevated temperatures.
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