Preparation of ta-C Coating by HiPIMS Technology with Reverse Positive Pulse and Study on Its Properties
HiPIMS technology is a magnetron sputtering technology that uses higher pulse peak power and lower pulse duty cycle to produces high sputtering ionization rate, which has significant advantages in the application of hard coatings. Due to the problems in the discharge during HiPIMS deposition process, the coating performance is poor. The ta-C deposition process is controlled by applying reverse positive pulse at the end of each pulse period. The deposition rate, film structure, hardness, binding properties and wear resistance of ta-C film are effectively improved.YG6 tungsten cobalt carbide (size 19 mm×19 mm×5.5 mm) was deposited as the test material ta-C film, and the reverse voltage range of 50-550 V and the frequency range of 200-5000 Hz were applied at the tail of each pulse cycle by high-power pulse magnetron sputtering technology. For other process conditions, the main gas source was argon, the power was 5 kW, the matrix bias was −150 V, the fixed pulse width was 50 µs, and the pulse frequency was set to 1500, 2400, 3200, 4000 Hz, respectively. Then the furnace was heated and vacuumed, and the target was cleaned by ion etching. Then the transition layer was deposited according to the set procedure and finally ta-C was deposited. Each experiment lasted for 10 hours, and finally the sample was cooled at room temperature. Then, the surface cross section morphology of the ta-C thin film was observed by ZEISS Gemini 300 field emission scanning electron microscope, the bond bonding in the ta-C thin film was analyzed by laser Raman spectrometer, and the surface structure of the thin film was analyzed by X-ray photoelectron spectrometer. The hardness of coating was obtained by nano-indentation and the wear resistance of coating was obtained by UMT multifunctional friction and wear testing machine.For the ta-C film prepared by HiPIMS technology with reverse positive pulse, the optimal experimental equipment parameters were to set the pulse frequency to 1500 Hz, reduce the frequency from 4000 Hz to 1500 Hz successively to prepare the coating under the condition of 4000 Hz frequency treatment. The thickness of ta-C film was 479.2 nm. The content of sp3 could reach 59.53％ by XPS. Its hardness was 32.65 Gpa and the resulting film failed at 12.7 N. At this time, the wear resistance was poor, and the friction coefficient was about 0.163. Under the treatment condition of 1500 Hz, all the properties of the coating were improved, and the thickness of ta-C film was 488.6 nm. The content of sp3 could reach 63.74％ by XPS. Its hardness was 40.485 Gpa and the resulting film failed at 14.9 N. At this time, the wear resistance was also relatively excellent, and the friction coefficient was about 0.138. The results show that the pulse frequency can effectively improve the deposition efficiency of ta-C films, improve the structure and properties of the films. As the deposition frequency of ta-C films decreases, the content of sp3 bond in the films increases. The friction coefficient is also reduced, which effectively improves the wear resistance of ta-C film.
high power impulse magnetron sputteringta-Cpulse frequencyadhesionhardnessabrasion resistance
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