聚晶金刚石表界面摩擦效应及其微观磨损机制

The demand for exploration of unconventional energy, stored in the deep within the earth, ocean and polar region, become more and more urgent. The polycrystalline diamond (PCD) material with excellent tribological performances is being put forward to new and higher requirements. Until now, the research on PCD has been only paid attention to the forms of macro-failure, which indirectly presents the mechanical properties during the drilling progress. However, the relationships among the actual service environments, the tribological effects of surface and interface and the micro-failure mechanisms have not yet been systematically set up. Therefore, the laws of surface and interface tribological effects and microscopic wear mechanisms in different environmental conditions are proposed. A series of tribotests will be performed under conditions of different relative humidities, PH values in water lubrication and high temperature heat treatments. It aims to explore the function laws of surface and interfacial tribological effects caused by the theories of the dangling-bonds surface chemical combination state, surface adsorption characteristics, surface graphitization and transfer film structures. The intrinsic interactions and the corresponding models of microscopic wear mechanisms among the parameters of environmental factors of humidity, PH values and high temperature - surface and interfacial tribological effects - the graphitization, chemical passivation and transfer film formations theories - tribological behaviors - microscopic wear mechanism will be revealed and established. The expected results will provide more adequate theoretical basis and technical support for designing PCD material used in exploration with high efficiency, long life and excellent tribological performances.

随着对地球深部、海洋和极区等非常规能源探索需求的日益增加，对具有优异摩擦学性能的聚晶金刚石（PCD）材料提出了新的和更高的要求。目前对PCD的研究只是注重其宏观失效形式，间接地反映在钻削过程中PCD的机械性能，尚未系统建立起实际服役环境因素、PCD摩擦表界面效应以及微观失效机理之间的联系。为此，本项目提出深入研究环境因素对PCD表界面摩擦效应及微观磨损机理的影响规律，通过模拟不同相对湿度、水润滑PH值、高温热处理条件下的摩擦学实验，探索表面悬键化学结合状态、表面吸附特性、表面石墨化和转移膜结构对PCD表界面摩擦效应的影响规律，揭示湿度、高温、PH值环境因素——表界面摩擦效应——石墨化、化学钝化、转移膜理论——摩擦学性能——微观磨损机制之间的内在关系，建立相应的微观磨损机制模型。为设计高效率、长寿命、优异摩擦学性能的勘探用PCD材料提供更为充分的技术支撑和理论依据。

根据聚晶金刚石材料实际服役工况，本项目模拟并设计了在潮湿、真空、高温、复杂液体等多种环境因素的摩擦学实验。探究聚晶金刚石材料摩擦学行为的规律及其机理。在真空环境下，PCD对磨氮化硅表现出与大气环境下完全不同的摩擦学行为，大气条件下最低至0.08的摩擦系数，PCD在真空中的摩擦系数最高可达0.97，且摩擦系数曲线波动剧烈，磨损严重。这是由于在真空环境下对磨副界面处悬键键合导致的高粘附作用导致的。高温热处理工艺可有效降低PCD在真空环境中的摩擦系数，其中700°C热处理工艺最佳，热处理产生的石墨化与氧化物层阻止界面间键合。而粉体镀硅能够有效提升聚晶金刚石的热稳定性能，初始氧化温度提高了12°C。探究了湿度环境对PCD摩擦学性能的影响，随着湿度的增高，摩擦系数不断增大，当湿度为85%时摩擦系数达到最大0.125，而水润滑条件下摩擦系数最小为0.07，湿度环境下摩擦诱导界面化学反应是控制PCD摩擦学行为的主要因素。而当环境处于液体环境时，液体pH值对摩擦界面化学反应及粘附的影响对PCD液体环境摩擦学行为有重要作用，当pH值为0.5时，PCD对磨氮化硅材料达到最低摩擦系数为0.009。PCD摩擦学性能对气氛条件同样具有依赖性，处于干燥Ar条件下时，摩擦系数达到最低0.04。转移膜机制是影响气氛环境下PCD摩擦学行为的主要因素。针对不同配副材料，PCD表现出不同的摩擦学行为，其中摩擦系数大小依次为SiO2＞Si3N4＞SiC＞Al2O3，这与摩擦界面处碳的重杂化以及配副材料的硬度等有关。本研究总结了不同条件下聚晶金刚石的摩擦学行为及其微观磨损机理，为聚晶金刚石材料高效长寿服役提供了技术支持与理论基础。