Abstract:

In order to improve the surface properties of the burnished copper,a gradient nano- grained surface layer was fabricated by means of a multi- pass burnishing process with a large burnishing force,which can cause a severe plastic deformation.The fretting wear tests were then performed under a dry condition on the burnished copper and the coarse- grained (CG) copper in the forms of ball- on- plane,so as to reveal the influences of burnishing on the microstructure,the surface structure,the friction and wear properties as well as the wear mechanisms of nanocrys-talline copper.The results show that (1) for the burnished samples,the grain size in the topmost burnished surface ranges from 4 nm to 18nm,with an average value of about 9 ～10nm; (2) as compared with the CG copper,the burnished copper is of a significantly- decreased surface roughness,which is from 1.50μm to 0.55μm,and its mi-crohardness greatly increases from 52.2 to 120.0; (3) the friction and wear performance of the burnished copper under the whole range of load is better than that of the CG copper; and (4) the wear forms of the burnished copperare mainly abrasive wear and fatigue wear under low loads and turn to be mainly abrasive wear and adhesive wear under high loads.

Key words: burnishing, copper, gradient nano- grained structure, fretting wear