Effect of nano-crystals at surfaces induced by ion beam irradiation on the tribological behaviour in microforming

To realize the effect of surface topography on tribological behaviour in microforming, the surface of a copper thin sheet was modified using ion beam irradiation equipment to change the micro-topography of the surface. The surface quality was evaluated by the surface roughness using SEM and AFM. A serial of strip drawing experiments were carried out to analyse the effect of surface modification on the tribological behaviour. Then, the modified specimens were applied to micro-cup deep drawing process of 1.1 mm in diameter. The results show that the surface roughness (Ra) decreases and many nano-crystals are induced by ion beam irradiation. The surface with many nano-crystals is helpful for storage of lubricant oil to bear high pressure. With the modified specimen, the punch load in micro-deep drawing process is lower than that with original sheet. This can be analysed by the hypothesis of the Wanheim/Bay model. The results indicate that surface modification using ion beams can be used to decrease friction in small contact area.