| Summary: | 碩士 === 國立臺北科技大學 === 材料科學與工程研究所 === 104 === V4E high vanadium tool steel possesses superior mechanical properties. It combines high wear resistance, high toughness and good stability suitable for cold work tools. On the other hand, oxynitriding treatment can form several kinds of nitrides and oxides. A complex oxide layer, with Fe2O3 and Fe3O4 structures, is formed on the surface, improving the corrosion and erosion properties of the steel. Moreover, the oxynitriding layer not only improves wear resistance but also adhesive strength as an intermediate layer. DLC (diamond-like carbon) films have many excellent properties, such as a high level of hardness, a low friction coefficient and a high corrosion resistance. It can significantly improve the adhesion and properties of DLC films by the DC pulse PECVD (plasma chemical vapor deposition) method. Therefore, our research utilized PECVD and oxynitriding duplex treatment to study the behaviors of DLC films, as well as to increase the tool life of V4E high vanadium tool steel.
In this study, DLC films were prepared by DC-pulsed PECVD after oxynitriding treatment of V4E high vanadium tool steel. The experimental parameters included various power densities (200, 400, 600 and 800 mW•cm-2) and CH4 gas flows (5, 15, 25 and 35 sccm) with an unbalanced bipolar-pulsed voltage (-15+10%). In order to compare the properties of the DLC films for oxynitriding/DLC treated V4E high vanadium tool steel, Raman spectroscopy analysis, wear tests, scratch tests, hardness tests, Rockwell indentation and corrosion resistance inspections were performed.
The experimental results show that 27 μm of oxynitriding layer and 2-4 μm of DLC thin film could be successfully obtained after V4E high vanadium tool steel was treated by the oxynitriding/DLC duplex treatment. As CH4 gas flow increased to 35 sccm, the deposition rate became faster and the DLC thickness was rapidly enhanced to 4.4 μm. However, this obviously resulted in poor adhesion. Consequently, the duplex coating layers had optimal properties when DLC films were treated by a unipolar negative-pulsed voltage and with an appropriate power density (400 mW•cm-2). Meanwhile, the deposition time was 90 min, and the CH4 gas flow was maintained at 5 sccm, respectively. As a result, it possessed the lowest wear volume loss (when the load of 1.96 N and 4.9 N was 6.23 × 10-3 mm3 and 1.19 × 10-2 mm3, respectively). In this study, increasing the DLC thickness effectively improved corrosion resistance. When the CH4 gas flow increased to 35 sccm, it had the lowest corrosion current (Icorr = 1.36 × 10-4 A•cm-2) and highest polarization resistance (Rp = 5.64 × 102 Ω•cm2) in 3.5 wt% NaCl solutions. The study results confirm that optimal wear and corrosion resistance followed the oxynitriding/DLC duplex treatment of V4E high vanadium tool steel.
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