Self-Lubricating Nanoporous Hard Coatings

本课题旨在探索和论证一种新的自适应高温润滑方法。利用耐磨涂层内的自组织纳米孔引导润滑油流向滑动接触面。作为一个模型系统，该项目使用溅射沉积的CrN-Ag纳米复合涂层，其中纳米多孔CrN作为坚硬耐磨的基体，其中含有Ag，一种低温和高温固体润滑剂。该项目侧重于(a)基于原子阴影效应和表面扩散过程，通过研究纳米孔尺寸和银分布作为沉积角度、生长温度、离子辐照通量的函数，了解纳米孔的形成机制；(b)建立润滑油通过1纳米宽纳米孔扩散的动力学模型，包括涂层内运输和凝聚形成的几何约束。利用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的摩擦和磨损，研究高温下的自适应润滑机制。本研究项目将为研究新的自润滑方法提供基础的科学理解，包括涂层沉积、润滑剂输送和摩擦学机制。新方法使用自组装的1纳米宽的孔，这些孔形成于过渡金属氮化硬涂层中，作为引导固体润滑剂扩散传输的通道。在高温操作过程中，包含在坚硬基体中的固体润滑剂将通过孔隙移动，以补充润滑的表面层。这种新策略适用于一系列涂层系统，并有可能成为一项突破性技术，在各种环境和从0到~1000℃的多个温度循环中提供低摩擦表面，应用范围包括用于节油喷气式发动机和燃气轮机高温轴承的硬质耐磨润滑涂层，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的无油空气箔轴承。

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.