Improvement of Tribological Properties of Mos 2 Films by Forming Interlayers and/ or Bombarding with Ions
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IMPROVEMENT OF TRIBOLOGICAL PROPERTIES OF MoSa FILMS BY FORMING INTERLAYERS AND/OR BOMBARDING WITH IONS AKIHIKO MATSUI and YOSHIMI KAGIMOTO Mitsubishi Heavy industries LTD., Nagasaki R&D Center, 1-1, Akunoura-machl, Nagasaki 850-91, Japan
ABSTRACT The effects of forming interlayers and/or bombarding with ions on the tribological properties of the sputter-deposited MoS a films were investigated. The MoS 2 films on substrates of Ti-alloy, martensitic stainless steel and high speed tool steel with TiN interlayers were evaluated by ball/disk sliding tests under ultra-high vacuum condition. Furthermore, nitrogen- or sulfer-ion-bombarded MoS 2 films tested too. The test results showed correlation between the surface hardness of substrates and the wear life of MoS 2 films. The wear life of the ionbombarded MoS 2 films was improved by mixing film/substrate interface.
INTRODUCTION Solid lubricant film should be low in shear strength and strong in adhesion to the substrate to ensure low friction and long wear life [1]. Tribological properties of the film vary with the coating conditions, which affect the film structure, crystallinity, etc., as well as with the friction conditions and service environment. The sputter-deposited MoS 2 film is commonly used in vacuum and opace applications. The effects of its morphology and crystallinity on tribological properties [2,3,4,5], improvement by co-deposition (6,7,8], multi-layers [9,10,11,12], and ion-bombardment (13,14,15] have been reported [16,17]. It however remains unclarified what is useful for the improvement of tribological properties of MoS 2 film. In the present study, the authors explored the effects of forming interlayers and/or bombarding with ions on triobological properties of the sputter-deposited MoS 2 films.
EXPERIMENTAL The MoSp films were deposited by the rf-sputtering technique to the thickness of about li•m on the martensitic stainless steel (SUS440C), high speed tool steel (SKH2) and Ti-alloy (Ti6Al4V) with a electric power of 200 W in 2.7 Pa argon. SUS440C and SKH2, high in hardness, are employed as bearing materials. Ti6Al4V features the high strength-to-weight ratio. Some substrates were nitrogen-ion-bombarded or coated with TiN by ionplating. Also, some MoS 2 films were nitrogenor sulfer-ion-bombarded under the conditions shown in Table I . The films were evaluated by ball/disk sliding tests under ultra-high vacuum condition. An uncoated SUS440C ball( 0 7.9 mm) was slid on the rotating disk ( 0 43 mm X t 7 mm) coated MoS. film. The test conditions are shown in Table]] . The wear life of MoS 2 film was evaluated in terms of the number of sliding cycles repeated until the coefficient of friction reached 0.15. Optical Microscopy(OM), Scanning Electron Microscopy(SEM), Rutherford Back Scattering method(RBS), and X-Ray Diffractlometry (XRD) were employed for the analysis of wear scar, film structure, concentration depth profile and crystallinity. The wear track was profiled using the profilometer and through line analysis by Electron Probe Micro Analysis
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