A study on thick coatings of tetrahedral amorphous carbon deposited by filtered cathode vacuum arc plasma
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Thick coatings of tetrahedral amorphous carbon (ta-C) have great existing and potential commercial importance for components such as automobile accessories. We confirmed the feasibility of depositing thick ta-C coating on Si wafer, WC, stainless steel (STS), and Al alloy substrates by a home-made filtered cathode vacuum arc. A ta-C coating of 800 nm thickness was successfully deposited over 20 min continuous coating. Interestingly, coatings with thicknesses exceeding 1 lm were easily delaminated by thermal and internal stress effects when the coating time exceeded 20 min. Varying the bias (0 V ↔ 500 V) was highly effective in controlling the internal stress relaxation of the ta-C. This method showed significant improvements in the stress relaxation of the ta-C coatings. By applying multicycle coating, the thickness and hardness of the ta-C coating could reach 9.3 lm and 45 GPa, respectively, at a coating speed of 3.0 lm/h on a fixed substrate.
I. INTRODUCTION
Diamond-like carbon (DLC) is an excellent coating material for many components in automobiles, mechanical machinery, and optical lenses. In many applications, DLC provides enhanced durability.1–4 For automobile applications, DLC coating films are subjected to antidelamination at high temperatures, thus requiring both the thermal stability and high performance such as low friction coefficients and strong adhesion. However, due to the high mechanical, thermal, and chemical stresses applied to the coated surface in practical use, the surface quality quickly degrades to an unacceptable level. Moreover, the thick coatings require high thickness to provide the necessary performance. Tetrahedral amorphous carbon (ta-C) is one candidate to replace coatings such as a-C and a-C:H. ta-C is a hydrogen-free carbon coating with sp3 phase, smooth surface, good thermal resistance, and high wear resistance. Moreover, ta-C can be synthesized through a convenient method with a much smoother surface than DLC, providing improved tribological performance over that of DLC. The filtered cathodic vacuum arc (FCVA) method is a particularly suitable technique for the mass-production of industrial ta-C coatings. Therefore, ta-C coatings have drawn considerable interest as potential commercially important components in applications such as automobile accessories, drills, and gears. Contributing Editor: Mohd Fadzli Bin Abdollah a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.78 J. Mater. Res., Vol. 31, No. 13, Jul 14, 2016
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The thickness of the ta-C coating must be considered in these applications; ta-C films of at least 3 lm in thickness are necessary for mechanical parts such as piston rings in automobile engine to provide sufficient performance and durability. Unfortunately, the high compressive stress in ta-C film limits the thickness of the material. Thick coatings are prone to easy delamination because of the high intrinsic stresses, which also decrease the adhesive strength between the film an
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