Tribological properties of metals modified by ion-beam assisted deposition of silicone oil
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Aichi-gun,
(Received 21 June 1989; accepted 3 January 1991)
Silicone oil vapor deposition and Ar + ion irradiation can form an adhesive carbonaceous film on a steel substrate. The friction coefficient /u, of the coated substrate is found to be very low for sliding against a steel ball both in air (^ ~ 0.04) and in N2 gas (p < 0.02). The duration of the low friction state is comparatively long and is 5 x 103-1.5 x 104 cycles for a film 0.15 fim thick. X-ray photoemission spectroscopy, infrared reflection spectra, and Raman measurements indicate that the film mainly consists of amorphous carbon containing Si and O.
I. INTRODUCTION
Recently, Ion Beam Assisted Deposition (IBAD) coatings with thin metal film processing and ion beam irradiation, such as TIN1 or A1N,2 have been increasingly studied due to low process temperature, strong adhesion to substrate, and direct controlability of film composition. IBAD coatings with organic materials, however, have scarcely been reported. In previous papers, we reported that an adhesive, solid, carbonaceous film can be formed on ceramic substrates by vapor deposition of a silicone oil and energetic Ar + ion irradiation.3'4 The ceramic substrates coated with the carbonaceous film were found to show friction coefficient as low as 0.04 for sliding against both ceramic and metal pins.3'4 Braun also reported that N + ion-irradiated silicone oil reduced the friction coefficient of a bearing steel from 0.94 to 0.12.5 In this paper, we report on the characterization and tribological property of metals coated with the IBAD carbonaceous film. II. EXPERIMENTAL
Hardened and prehardened SUJ2 (AISI 52100) disks (30 mm in diameter, 3 mm thick) were used for the IBAD substrates and for pin-on-disk type friction tests. The Knoop hardnesses of the disks were 822 (hardened) and 181 (prehardened). Their surface roughness was 0.1 /im Rz. Hardened SUJ2 balls (5 mm in diameter) were used as the pins for the friction tests. The organic material for IBAD was a silicone oil, pentaphenyle-trimethyl-trisiloxane [(Si3O2C33H32)B]. The structure of the silicone oil molecule and the system used for IBAD are shown in Fig. 1. The disk samples were mounted on a liquid-nitrogen cooled sample holder in a vacuum chamber where the base pressure was 5-7 x 10"4 Pa. The silicone oil was vaporJ. Mater. Res., Vol. 6, No. 4, Apr 1991 http://journals.cambridge.org
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deposited onto the disks from an oil reservoir by ohmic heating. The reservoir temperature during the deposition was about 170 °C. By measuring the weight increase of the disk, the deposition rate of the silicone oil molecules at this temperature was obtained to be 6.5 x 1012 molecules/cm2 s. Because the substrate temperature is low (77 K), the deposition rate is considered to be equal to the impinging rate of the silicone oil molecules. The film thickness was varied by changing the period for which a shutter in front of the oil reservoir was open. As the shutter was opened, the disk sample was simultaneously irradiated with 1.5 MeV Ar
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