Self-Lubricating Nanoporous Hard Coatings

该研究项目旨在探索和展示一种自适应高温润滑的新方法。耐磨涂层内的自组织纳米孔被用来引导润滑剂流向滑动接触表面。作为一个模型系统，该项目使用溅射沉积的CrN-Ag纳米复合材料涂层，其中纳米多孔CrN作为硬耐磨基体，其中含有Ag，一种低温和高温固体润滑剂。该项目的重点是：（a）通过研究纳米孔尺寸和Ag分布作为沉积角度、生长温度、离子辐照通量的函数，了解基于原子遮蔽效应和表面扩散过程的纳米孔形成机制，（B）开发润滑剂通过1 nm宽纳米孔扩散的动力学模型，包括涂层内传输和团聚体形成的几何约束，通过退火实验和成分映射，以及（c）通过映射温度、接触压力和滑动速度空间上的摩擦和磨损来研究高温下的自适应润滑机制，该研究计划将为所研究的自润滑新方法提供基础科学理解，包括涂层沉积、润滑剂传输和摩擦学机制。这种新方法使用自组装的1 nm宽的孔，形成在过渡金属氮化物硬涂层中，作为引导固体润滑剂扩散运输的通道。在高温操作期间，包含在硬基质中的固体润滑剂将移动通过孔隙以补充润滑表面层。这种新的策略适用于一系列涂层系统，并有可能成为一项突破性的技术，在各种环境中和从0到~1000 ℃的多个温度循环期间提供低摩擦表面。应用包括用于燃料效率高的喷气发动机和燃气涡轮机的高温轴承的硬耐磨润滑涂层，用于空间应用的循环空气真空环境中的固体润滑，以及用于燃料电池的气体压缩机中的无油翼型轴承。

This research project proposes to explore and demonstrate a new approach to adaptive high-temperature lubrication. Self-organized nanopores within wear-resistant coatings are exploited to guide lubricant flow to the sliding contact surface. As a model system, this project uses sputter deposited CrN-Ag nanocomposite coatings where nanoporous CrN acts as a hard wear-resistant matrix which contains Ag, a low- and high-temperature solid lubricant. The project focuses on (a) understanding the nanopore formation mechanism, based on atomic shadowing effects and surface diffusion processes, by studying nanopore dimensions and Ag distribution as a function of deposition angle, growth temperature, ion-irradiation flux, (b) developing a kinetic model for lubricant-diffusion through 1-nm-wide nanopores, including geometrical constraints for transport and agglomerate formation within the coating, using annealing experiments and compositional mapping, and (c) studying the adaptive lubrication mechanisms at elevated temperatures, by mapping friction and wear over a space of temperature, contact pressure, and sliding speed.This research program will provide a fundamental scientific understanding, including coating deposition, lubricant transport, and tribological mechanisms, for the investigated new approach for self-lubrication. The new approach uses self-assembled 1-nm-wide pores, that form in transition-metal nitride hard-coatings, as channels that guide the diffusive transport of solid lubricants. During high-temperature operation, a solid lubricant which is contained in the hard matrix will move through the pores to replenish a lubricious surface-layer. This new strategy is applicable to a range of coating systems and has the potential to become a breakthrough technology by providing low friction surfaces in various environments and during multiple temperature cycles ranging from 0 to ~1000 C. Applications include hard wear-resistant lubricious coatings for high-temperature bearings in fuel-efficient jet-engines and gas-turbines, solid-lubrication in cyclic air-vacuum environments for space applications, and oil-free air-foil bearings in gas compressors for fuel cells.