Proceedings of the Korean Vacuum Society Conference (한국진공학회:학술대회논문집)

The Korean Vacuum Society (한국진공학회)
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Tribological study on the thermal stability of thick ta-C coating at elevated temperatures

  • Lee, Woo Young (Surface Engineering Department, Process Implementation Center, Korea Institute of Materials Science) ;
  • Ryu, Ho Jun (Surface Engineering Department, Process Implementation Center, Korea Institute of Materials Science) ;
  • Jang, Young Jun (Surface Engineering Department, Process Implementation Center, Korea Institute of Materials Science) ;
  • Kim, Gi Taek (Surface Engineering Department, Process Implementation Center, Korea Institute of Materials Science) ;
  • Deng, Xingrui (Advanced Materials and Manufacturing Laboratory, Department of Mechanical Science and Engineering, Nagoya University) ;
  • Umehara, Noritsugu (Advanced Materials and Manufacturing Laboratory, Department of Mechanical Science and Engineering, Nagoya University) ;
  • Kim, Jong Kuk (Surface Engineering Department, Process Implementation Center, Korea Institute of Materials Science)
  • Published : 2016.02.17
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Abstract

Diamond-like carbon (DLC) coatings have been widely applied to the mechanical components, cutting tools due to properties of high hardness and wear resistance. Among them, hydrogenated amorphous carbon (a-C:H) coatings are well-known for their low friction properties, stable production of thin and thick film, they were reported to be easily worn away under high temperature. Non-hydrogenated tetrahedral amorphous carbon (ta-C) is an ideal for industrial applicability due to good thermal stability from high $sp^3$-bonding fraction ranging from 70 to 80 %. However, the large compressive stress of ta-C coating limits to apply thick ta-C coating. In this study, the thick ta-C coating was deposited onto Inconel alloy disk by the FCVA technique. The thickness of the ta-C coating was about $3.5{\mu}m$. The tribological behaviors of ta-C coated disks sliding against $Si_3N_4$ balls were examined under elevated temperature divided into 23, 100, 200 and $300^{\circ}C$. The range of temperature was setting up until peel off observed. The experimental results showed that the friction coefficient was decreased from 0.14 to 0.05 with increasing temperature up to $200^{\circ}C$. At $300^{\circ}C$, the friction coefficient was dramatically increased over 5,000 cycles and then delaminated. These phenomenon was summarized two kinds of reasons: (1) Thermal degradation and (2) graphitization of ta-C coating. At first, the reason of thermal degradation was demonstrated by wear rate calculation. The wear rate of ta-C coatings showed an increasing trend with elevated temperature. For investigation of relationship between hardness and graphitization, thick ta-C coatings(2, 3 and $5{\mu}m$) were additionally deposited. As the thickness of ta-C coating was increased, hardness decreased from 58 to 49 GPa, which means that graphitization was accelerated. Therefore, now we are trying to increase $sp^3$ fraction of ta-C coating and control the coating parameters for thermal stability of thick ta-C at high temperatures.

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