ULTRASONIC SURFACENANOCRYSTALLIZATION (USN) TREATMENT

Ultrasonic Surface Nanocrystallization (USN) Treatment is a new method for developing a nanostructure surface layer on metal alloys. In this process, simultaneous preload and high frequency impacts were applied on the surface of work piece and the consequence of this loading was local severe plastic deformation at the surface. The severe plastic deformation created a new layer on the surface, which had a different microstructure in compare to the initial microstructure of sample. In this research, USN treatment applied on an annealed AISI S1 steel shaft. The original microstructure of work piece consisted of ferrite and pearlite with average grain size 20 m. Microstructure observations showed that after USN treatment, nanostructure layer is resulted with grain size 70 nm. at the surface. The Grain size increased from surface of new layer to bottom of it and the thickness of this layer was 100 um. Before applying the USN process, the hardness of surface had been 180 Hv. After ultrasonic impacts, the hardness of surface increased up to 350 Hv. Enhancement of hardness was observed up to depth 400 p.m.

Keywords:

Ultrasonic , Surface Nano crystallization , Severe Plastic Deformation , Surface Treatment , Hardness