极端工况下聚晶金刚石摩擦学行为及其影响机制

Recently, the development of the unconventional energy (such as ultradeep drilling, tight-rock, outer space ect.) exploration technology urgently needs to use the polycrystalline diamond (PCD) materials with lower wear loss and friction under extreme conditions such as high temperature, vacuum and water lubrication. The researches on the tribology of PCD are mainly focused on the intrinsic physical characteristics and wear performances. While the friction behaviors and the effects of the surface and interface physical or chemical characteristics are usually ignored. In this project, the tribological influencing factors and mechanisms of the PCD will be investigated systematically under different extreme conditions. Several series of tribotests are proposed and planned to carry out under high temperature, atmosphere, vacuum and water lubrication conditions. It aims at to further understand the single and complex effects of surface graphitization, oxidation and hanging bond passivation on the tribological behaviors of the PCD. The impact mechanism among the service conditions - the friction surface layer structural evolution and chemical passivation - the tribological performance will be revealed and deeply discussed. The theoretical prediction and experimental control of the tribology performances of the PCD under the extreme conditions will be realized. The expected results will provide a theoretical and practical guidance to the selection and design of the superhard material PCD and the relative applied technique for the demand working in the extreme conditions.

非常规能源勘探(如超深部、致密岩、外太空等)开发技术的发展，对高温、真空、水润滑等极端工况下具有低磨损、优异摩擦性能的聚晶金刚石（Polycrystalline Diamond，PCD）材料提出了更高和迫切的要求。目前PCD的摩擦学研究过多地强调固有物理属性和磨损性能，而忽视全面摩擦性能及表面界面材料物理化学特性的作用。因此，本项目提出系统深入研究极端工况对PCD摩擦学性能的影响因素和作用机理，通过设计在高温、大气、真空、水润滑工况下的摩擦学试验，深入了解摩擦表面的石墨化、表面氧化和表面悬键钝化效应单独和复合作用的规律，揭示工况条件--摩擦表面结构演化和化学钝化--摩擦学性能之间的作用机制，实现对极端工况下PCD摩擦学性能的理论预测和控制，为设计满足极端工况要求的PCD超硬材料及应用技术提供理论和技术支持。

非常规能源的勘探开发对极端工况下超硬钻具材料聚晶金刚石（Polycrystalline Diamond，PCD）的摩擦磨损性能提出了更高的要求。本项目全面探索了PCD在高温、大气、真空、水润滑工况下的摩擦学行为，揭示了石墨化、表面氧化、表面悬键钝化、热损伤、摩擦化学等摩擦表面效应对其摩擦学行为的影响机制。制备了一种新型超硬聚晶金刚石（UHPCD），其硬度高达120 GPa，较普通PCD提高了41%，耐磨性显著提高。研究了高温环境下PCD的热损伤机制及其摩擦学机理，发现大气600℃及以下热损伤的PCD摩擦学行为由金刚石颗粒诱导转移膜机制控制，600℃以上热损伤时则由表面粗糙度、金刚石表层石墨化及部分金刚石颗粒诱导转移膜机制共同控制，PCD几乎无磨损。真空热损伤PCD的摩擦系数随着热处理温度升高而逐渐增大，磨损主要由表面细小金刚石颗粒的剥落及其引起的磨粒磨损所导致。淬火工艺可有效控制PCD的表面形貌及化学成分，进而影响其摩擦学性能。水淬工艺可去除PCD表面的细小金刚石颗粒，增强其抗磨损性能，但摩擦系数略有提高，而在炉冷工艺下则相反。考察了PCD的真空摩擦学行为，PCD与SiC和Si3N4材料对磨时发生黏着磨损，摩擦系数较高，磨损严重；而与GCr15和Al2O3材料对磨时则磨损轻微，摩擦系数较低。PCD表面σ键的钝化程度导致其摩擦系数随真空度增加而逐渐增大，且磨损加剧。高温热处理可显著减轻PCD的真空黏着现象，700℃热处理效果尤为显著。探究了湿度环境下PCD的摩擦学行为及其机理，结果表明在5%-50% RH条件下碳质转移膜与悬键钝化竞争机制控制PCD的摩擦学行为，而在55%-85% RH及水润滑条件下摩擦诱导氮化硅球的氧化水解反应起主导作用。700℃热处理可促进低湿度环境下配副表面碳质转移膜的形成，并实现高湿度环境下PCD几乎零磨损的状态。本研究成果可对PCD在极端工况下的摩擦学行为进行理论预测和控制。