”Fabrication of chromium carbide coatings by reactive sputtering - roles of power supply system and target poisoning”
Jyh-Wei Lee 1,2,3, Zheng-Long Li4, Yen-Yu Chen1, Chaur-Jeng Wang4
1 Department of Materials Engineering, Ming Chi University of Technology, New Taipei, Taiwan
2 Center for Plasma and Thin Film Technologies, Ming Chi University of Technology, New Taipei, Taiwan
3 Department of Mechanical Engineering, Chang Gung University, Taoyuan, Taiwan
4 Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
The potential use of chromium carbide coatings has been a great interest to academia and industry due to their outstanding properties such as chemical stability, low coefficient of friction, adequate hardness and high wear resistance. In this study, the chromium carbide coatings were fabricated by a magnetron sputtering using three different power supply systems, including direct-current (DC), pure high power impulse magnetron sputtering (HiPIMS), and superimposed HiPIMS- middle frequency (MF). The Cr target poisoning status was controlled using a plasma emission monitoring (PEM) system by adjusting the gas flow ratios of Ar and acetylene (C2H2). The morphology and microstructure of coatings were evaluated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The crystallinity of films was studied using an X-ray diffractometer (XRD). The electron probe micro analyzer (EPMA) and X-ray photoelectron spectroscope were used to determine the chemical compositions and binding structures of thin films, respectively. The hardness, adhesion and tribological properties of coatings were explored. The CrC or Cr3C2 nanocrystallites within the column structures imbedded in the amorphous CrCx matrix were observed in the coating deposited by superimposed HiPIMS-MF or by pure HiPIMS power supply, whereas the amorphous coatings were grown by the DC power supply. The appearance of these CrC or Cr3C2 nanograins in the columnar structure of the coatings may enhance the mechanical property due to the Hall-Petch effect. The chromium carbide coating with the highest hardness of 27.5 GPa, upper critical load of 30.7 N, a coefficient of friction of 0.35, and an adequate deposition rate of 17.6 nm/min was grown by the superimposed HiPIMS-MF power supply at the target poisoning degree of 70% in this work.