外加直流电场对DLC/PAO固液复合润滑体系摩擦学行为的影响

本文中利用球-盘式载流摩擦试验机研究了DLC/PAO固液复合润滑体系在外加直流电场中的摩擦学行为,考察摩擦副滑动速度、加载电压以及回路电流的影响,结果表明:外加直流电场对复合润滑体系摩擦磨损行为的影响与摩擦副的滑动速度密切相关,这源于不同润滑状态时DLC薄膜的电气损伤行为以及薄膜的结构、成分变化.根据润滑状态和外加电压的不同,DLC薄膜的电气损伤可以表现为线状隆起或烧蚀坑,其中线状隆起型损伤源于载流摩擦界面的焦耳热,烧蚀坑损伤则源于摩擦对偶之间的拉弧放电及PAO油膜的击穿.Raman光谱显示电气损伤区DLC薄膜发生显著的石墨化转变,且石墨化程度取决于回路电流的大小.外加电场条件下DLC薄膜的石墨化转变虽然在一定条件下可使复合润滑体系的摩擦系数降低,但削弱了DLC薄膜的抗磨性能,使薄膜的磨损表现为电气损伤和机械磨损的耦合.

The Tribological Behavior of PAO Lubricated DLC Contacts Under DC Electric Field

The tribological behavior of PAO-lubricated DLC contacts under DC electric field was investigated on a designed tribo-meter with a ball-on-disk configuration, and the effects of sliding speed, applied voltage and electric current were studied. The results show that the influence of applied DC electric field on the friction and wear of DLC strongly depended the sliding speed, which could be ascribed to the different electrical damage and corresponding changes in the microstructure of DLC coating under different lubrication regime. According to the lubrication regime of DLC contacts and applied voltage, the electrical damage of DLC coating could be liner bulges or ablated pits. It is found that the liner bulges were caused by the high joule heat generated at the sliding interface with electric current, while the ablated pits were produced by the arc discharge and breakdown of PAO oil film between friction pairs. The Raman spectra showed that the DLC suffered of electrical damage exhibited high graphitization degree, and the extent of graphitization was correlative with the electric currents. Although the graphitization of DLC under electric filed lowered friction in certain conditions, the wear resistance of DLC coating was weakened, so the DLC coating failed in a short time under the combined effects of electrical damage and mechanical wear.