TRIBOLOGICAL PROPERTY ANALYSES OF DLC FILMS ON CERAMIC BALL SURFACES WITH 3-D FEA METHOD AND EXPERIMENTS

摘要

Diamond-like carbon (DLC) films are excellent candidates to improve tribological properties of silicon nitride (Si_3N_4) ceramic elements. Particular attentions have been paid to the preparation and analysis of DLC films on rings and discs. However, few researches on fabrication of DLC films on ball surfaces were carried out, especially on ceramic ball surfaces, because it is hard to achieve uniform coatings on ball surfaces.In this paper, DLC films on ceramic ball surfaces were studied with both experiment and FEA method. DLC films were deposited on Si_3N_4 ceramic ball and disc surfaces with plasma immersion ion implantation and deposition techniques (PIII-D). Surface topography of ceramic balls before and after coated with DLC films showed that DLC films on ceramic ball surfaces were uniform. Tribological tests under dry friction were conducted with a ceramic ball sliding against ceramic disc and, alternatively, one of the two surfaces was coated with DLC films. The tests demonstrated that DLC films on disc surfaces were worn, while ball surface films were partly flaked.3-D FEA models of ceramic ball sliding against ceramic disc were built and the ceramic ball/disc was coated with DLC films alternatively. DLC films were supposed to be bonded with ceramic substrates. The FEA stress fields in DLC films and on film/substrate interface showed that DLC films had great effects on stress distribution due to the low frictional coefficient and material difference from substrates. The friction force caused an increment of the stress near surfaces during sliding process, and the material difference leaded to discontinuous stress distribution on film/substrate interface. The shear stress on film/substrate interface was very slightly different between DLC films coated on ceramic balls and discs. Under almost the same shear stress, the flakes and wear of DLC films were mainly determined on the adherence of DLC films to ceramic substrates.