Foil Bearing Solid Lubrication Of The Design, Fabrication And Performance Of The Dlc Films

Foil bearings are compliant, self-acting hydrodynamic bearings which use air as their lubricant. However, they rely upon solid lubricants to reduce friction and minimize wear during sliding which occurs at start-up and shut down period, when surface speeds are too low to allow the formation of a hydrodynamic air films. But, the researchs about the solid lubricant coatings for foil bearings are relatively backward in domestic, which are thought as one of the main reasons that restricted development and application of foil bearings in china.This dissertation aims at overcoming this problem.In this dissertation, we tried to use a new kind of coating material (Diamond like carbon film, or named DLC film) as the coating for foil bearing. The main contents of this dissertation are as follow:1) The major problems for DLC films in applications are their high internal compressive stress and relative low adhesion on metallic substrates. In order to overcome these problems and furthermore, enhance the film properties, we have developed a novel diamond-like carbon film design, which introduced doping metal technology and interlayer technology to reduce internal stress of the films and increase adhesion strength of the films on metallic substrates.2) The mathematics principle of Gauss fitting for Raman spectrum of diamond-like carbon films is studied, and the arithmetic of Gauss fitting is given. This method of Gauss fitting was used in analysis the Raman spectrum of diamond-like carbon films in this study.3) A mid-frequency magnetron sputtering technique was used to deposit diamond-like carbon films. Three kinds diamond-like carbon films were deposited in this research, they are titanium doped diamond-like carbon(Ti-DLC) films, Chromium doped diamond-like carbon(Cr-DLC) films, and non-doped diamond-like carbon(C-DLC) films. These films were characterized by various methods or instruments and compared. The results indicated that interlayer and doping metal can significantly reduce internal stress and increase adhesion strength of DLC films. Among these three kinds diamond-like carbon, Ti-DLC films exhibited best combination properties such as:high adhesion strength (-29N), thickness more than 1.5μm, low initernal stress (<1.0Gpa), and excellent friction and wear properties.4) The difference of friction and wear performances when coated on different one of or both of the contact surfaces of the foil bearing friction pairs were studied by using a ball-on-disk tribometer with coated or uncoated steel balls and little size beryllium bronze foils. Based on the results, the final coating solution was discussed.5) The bench tests were performed on a foil bearing bench tester with a DLC coated shaft coupled with a DLC coated foil. It was found that the bench test result was vary different from the test results on ball-disk tribometer, this difference was explained by considering the thermal stability of DLC films at high temperature.