Surface and Interface Designs for Friction Control

Abstract

Modern engineering surfaces are cut, grind, and polished to create surfaces that are isotropic, uniform, and homogeneous to enable easy assembly and manufacture. Commonly used surface descriptors such as Ra are based on these characteristics. In the 1990s, the magnetic hard disk drive storage industry began to use multiscale directionally aligned roughness to achieve its lubrication requirements successfully, and this leads to the concept of designed surface topography and textures to enable additional functionalities. The design and fabrication of surface topography to impart directionality, uniform reactivity, and patterned geometric dimples or protrusions can enhance or expand the surface properties to meet specific desirable application needs. Adding thin films, coatings, multilayer nanocomposites on the surface can alter the surface physical and chemical characteristics and enhance durability. Properly designed surface textures (dimples, grooves, and discrete shapes) can reduce friction, create drag reduction, as well as control the real area of contact and heat transfer characteristics. In terms of designing friction reducing surfaces for an application, the dominant friction mechanisms need to be understood and proper surface designs applied to reduce the dominant friction generation. Generally, roughness perpendicular to the sliding direction will increase frictional resistance while increasing the interfacial temperatures. Multiscale roughness parallel to the sliding direction, depending on the speed and load of the contact, will reduce scuffing and reduce friction. In this paper, we use surface textures coupled with diamond-like-carbon thin films and bonded chemical layer to effect friction reduction of piston ring-cylinder liner friction.