The concepts and properties of nanoskin materials and components created by ultrasonic nanocrystal surface modification Young Shik Pyoun1, Qingyuan Wang2, Muhammad Kashif Khan3, Ravil Kayumov4, *, Junhyong Kim4 1Dept. of Mechanical Engineering, Sun Moon University, Asan, 336-708, South Korea 2Dept. of Civil Engineering and Mechanics, Sichuan University, Chengdu, 610065, China 3Dept. of Mechanics and Engineering Science, Sichuan University, Chengdu, 610065, China 4Dept. of Mechanical Engineering, Graduate School, Sun Moon University, Asan, 336-708, South Korea *ravilkayumov@yahoo.com Abstract Material surface and immediate subsurface layers can be called “skin”. A novel Ultrasonic Nanocrystal Surface Modification (UNSM) technology produces uniformed micro dimples on the top surface and nanometer grain in the subsurface, increases surface hardness and induces compressive residual stress. This way mechanical characteristics related to fatigue, wear, friction, etc. can be improved. The concepts and properties of nanoskin materials and components are proposed with their potential application. Keywords: Nano grain materials; Nano skin materials; Ultrasonic Nanocrystal Surface Modification. 1. Introduction. Concept of Nanoskin Materals and Components Friction and wear, low, high and very high cycle fatigue, rolling contact fatigue and some other characteristics of machine components are influenced by the surface characteristics of material. The top surface and immediate subsurface layers can be called “skin”. When subsurface grain dimensions reach nanometer range and top surface acquire micro or nano scale roughness and texture, these properties are much different from those of the ordinary structure. The hardness, compressive residual stress and grain size of subsurface are major factors that determine fatigue, friction, wear and fatigue characteristics. Therefore, nanoskin materials and components can be defined as top surface of material consisting of nano scale roughness and nano and/or micro scale texture, and subsurface nanoscale grain size with improved hardness and compressive residual stress. Lowest roughness of 10 - 200 nm is usually achieved through various forms of abrasive surface finish [1]. However, manufacturing costs rise exponentially with decreasing of the surface roughness. Surface texturing can reduce friction and wear characteristics, but there is no general rule yet to explain its effects on wear and friction. Besides, the size of the pattern is usually bigger than several dozen micro millimeters [2, 3, 4]. Grain size refinement is usually achieved through conventional heat treatment and deformation processes like forging, rolling, drawing and extrusion. However, 1μm (for steels) is a limit for the grain size refinement [5]. The severe plastic deformation process such as ECAP (Equal Channel Angular Process) is a novel technology which refines the grain size of bulk rod into nano scale [6]. But from the view point of nano skin of materials and components, there is still a lot more research to do.
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