Tribological characteristics of diamond-like films deposited with an arc-discharge method
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R. Lappalainen Cornell University, Department of Materials Science and Engineering, Ithaca, New York 14853
J. Koskinen and A. Anttila University of Helsinki, Department of Physics, 00170 Helsinki, Finland
T. R. Jervis and M. Trkula Los Alamos National Laboratory, Materials Science and Technology Division, Los Alamos, New Mexico 87545 (Received 12 April 1990; accepted 25 July 1990)
Using an arc-discharge method, we deposited a diamond-like carbon film 600 nm thick on hardened steel. Characterization of the film was carried out with Raman spectroscopy. In dry sliding wear and friction tests, with a hardened steel pin as a counterpart, we obtained a friction coefficient between 10000 and 20000 cycles, with the maximum value of 0.18. The value decreased to 0.12 after about 100000 cycles. We obtained a wear coefficient of 7 x 10~17 m3/mN. A transfer layer formed on the pin during sliding and probably had the dominating effect on the tribological behavior. We observed in nanoindentation measurements that the film softened in a wear track during the first 20000 cycles. Although fracture pits on the wear track occurred, fracture is not the dominant failure mechanism of these films. Degradation of good tribological properties was caused mainly by partial wear-through of the film after 370000 cycles and by a subsequent redeposition of the transfer film on the wear track during prolonged sliding.
I. INTRODUCTION
Although a plasma-assisted chemical vapor deposition (PACVD) technique is usually used in the deposition of diamond films,1 many methods produce diamond-like films. Cracking hydrocarbon molecules in plasma-assisted deposition systems was widely used in the past.2 Characteristic of these films was a high concentration of hydrogen, which could reach 50 at.%.3 Many properties, including mechanical and optical properties, as well as density, depended on the hydrogen concentration. Although hydrogen is necessary to tailor optical properties, it degrades the mechanical performance of these films.4 In recent years, processes that do not include hydrogen as an active participant have effected deposition of high-density diamond-like films. Two techniques based on energetic carbon ions have been successful. A direct, mass-analyzed ion beam method4"6 allows precise adjustment of deposition parameters, such as ion energy, ion current density, angle of incidence, and control of impurities at an isotopic level. Properties of the films depend on a nominal acceleration voltage ranging from 10 V to 2 kV.7 Density, hardness, and dc resistance possess the maximum value at about 2524
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J. Mater. Res., Vol. 5, No. 11, Nov 1990
Downloaded: 13 Mar 2015
500 V. The maximum density of these films is 1.6 x 1023 at ./cm3,7 which is close to that of crystalline diamond, 1.76 x 1023 at./cm3.8 The most serious disadvantage of direct deposition is a low growth rate, which depends on the ion source. Therefore, we are investigating an alternative technique based on an arc discharge, potentially a high-deposition-ra
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