Inconel 600 is widely used as the steam generator tubing in pressurized water reactor.In order to investigate the fretting behaviors of Inconel 600 at different displacement amplitudes,fretting test on Inconel 600 alloy at different displacement amplitudes was conducted at room temperature in air using a SRV IV fretting test rig.The effect of displacement amplitude on the ratio of tangential force to normal load and wear volume were analyzed.The worn surfaces and cross-sectional morphologies were subsequently investigated using optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and transmission electron microscopy(TEM).The results indicated that fretting wear behaviors were strongly dependent of the displacement amplitude.With increase of fretting amplitude,the ratio of tangential force to normal load and wear volume increased,and the fretting regime gradually transformed from partial slip to gross slip.Correspondingly,the wear mechanism transformed from local adhesive damage to the combination damage of oxidation and delamination wear.Microcracks in the wear scar were strongly depended on fretting regime.They were usually found in the slide zone and the junction of slide and adhesion zone,but no microcracks were observed in the adhesion zone.The shape of the worn scar changed from round to ellipsoidal complied with the formation of delamination cracks in the subsurface as the result of ploughing effect on the edge of the wear scar.Fretting created a gradient strain in subsurface of worn scar,and resulted in formation of nanocrystalline in tribological transformed structure layer under the worn scar.