| Summary: | 碩士 === 國立虎尾科技大學 === 機械與電腦輔助工程系碩士班 === 107 === In the era of metal industries and mass production sectors there are continuously increasing the demand and huge need for a highly efficient mechanical transmission components that requires high load sustaining and bearing capacity on the particular contact surfaces between two or more parts. High speed steel is highly alloyed tool steel capable of maintaining hardness even at elevated temperature. The word high speed tool steels are so named primarily because of their ability to machine materials at high cutting speeds. Widely used AISI H13 tool steel in the die casting molds as it’s among one of the hot-working die steel group and it has good corrosion resisting with high hardenability properties. In order to improve the properties of tools and molds. And the surface treatment. Thin film deposition is one of the most common surface treatment methods available today.
Physical vapor deposition (PVD) is the most widely used technology for depositing materials as a thin film onto a substrate. From metals, to semiconductor materials, to the most complicated optical film stacks, PVD is the most common deposition method to obtain excellent mechanical properties, high hardness, high temperature resistance, corrosion resistance and oxidation resistance.
A duplex treatment, i.e. plasma nitriding followed by cathodic arc evaporation, is used to strengthen the bonding of AlCrSiN coatings to H13 Tool steels. A nitride layer is first formed on H13 steel samples by plasma nitriding and then the CrN transition layer is prepared on the surface of the nitrided H13 steels using cathodic arc evaporation to extend the life time of molding dies in mass production and to protect from delamination of coatings.
In this study, gradient and AlCrSiN Coatings were synthesized by cathodic-arc evaporation. Before deposition a nitride layer is first formed on H13 steel samples by plasma nitriding. The plasma nitriding process is carried out in industrial furnace with the proper parameters like process temperature, nitrogen/hydrogen ratio and voltage with duty cycle. During the coating process of AlCrSiN, AlCrN was deposited as an interlayer to enhance adhesion strength between the coatings and nitrided substrates. By controlling the temperature and mixture of N2/H2 at atmosphere. The plasma nitrided duplex treated AlCrSiN coated tool steels possessed different microstructures and mechanical properties. The microstructure of the deposited coatings were investigated by field emission scanning electron microscope (FE-SEM) equipped with an energy-dispersive X-ray analysis spectrometer (EDS), Glancing angle X-ray diffraction was used to characterize the microstructure and phase identification of the films. The hardness of coatings was evaluated using nanoindention and Vickers hardness measurement.
To evaluate the impact fracture resistance of the coatings, an impact test (200K, 300K and 400K times) was performed using a cyclic loading device with a tungsten carbide indenter as an impact probe at room temperature and high temperature (500°C).the impact fatigue results shows for AlCrSiN coated sample at room temperature after 400K of impacts that the surface has no any iron signal however cohesive failure can be found on the surface of AlCrSiN sample. The PN+AlCrSiN coated samples shows better wear performance even after 400K of impacts and there is no any kind of surface failure can be seen. The high temperature impact test for AlCrSiN coated sample resist the impacts of 200K, after that the surface showed iron signals, but in case of PN+AlCrSiN there is no any iron signal even after 200K of impacts at high temperature. That means PN+AlCrSiN sample shows the significant change because of pre-treated nitrided process which supports the substrate surface from any external applied loads. The results show that the adhesion strength and wear resistance for duplex-treated coatings increase significantly due to a gradient-hardness support. The combination of plasma nitriding and hard coatings may increase the life of molding dies and metal forging dies in mass production.
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