The Ultrasonic Nano-crystal Surface Modification Technology And It's Application To Improve Fatigue Strength, Wear Resistance

Author:  Pyoun, Suh, IH Cho, Kim, IS Cho, Lee, Park, Jung
Source:  Conf Proc: ICSP-10 Tokyo, Japan 2008
Doc ID:  2008103
Year of Publication:  2008
Abstract:  
ABSTRACT The ultrasonic nano-crystal surface modification (UNSM) technology utilizes the ultrasonic vibration energy to maximize coverage and stress-field density; during the process, a tool-steel, tungsten carbide, or ceramic ball attached to an ultrasonic device strikes the surface of a workpiece 20,000 to 40,000 times per second and 1,000 to 10,000 shots per square millimeter. These strikes produce severe plastic deformation and induce a nano-crystalline microstructure in the near surface layer. The nano-structuring of the surface layer can simultaneously improve hardness and toughness of the workpiece according to the well-known Hall-Petch relationship. UNSM treatment induces deep compressive residual stresses comparable to DR, LSP and LPB, increases surface hardness, decreases surface roughness, and produces also a uniform "dimpled" surface. The effect of UNSM treatment on the fatigue and tribology characteristics was discussed in terms of rotary bending fatigue, rolling contact fatigue, and friction torque and friction coefficient in typical bearing steels. The field test results of trimming knives were also introduced. KEY WORDS Ultrasonic nano-crystal surface modification (UNSM), High cycle fatigue (HCF), Wear, Friction, Rolling contact fatigue (RCF).