Abstract: The radial fretting behavior of ion plated TiN coating on AISI 1045 steel substrate sliding against AISI 52100 steel was investigated on a radial fretting test rig developed in our laboratory. The deformation characteristics of the coating was compared with that of AISI 1045 steel substrate at maximum normal load from 200 N to 800N and cycle numbers from 1 to 10 5. As the results, TiN coating is superior to AISI 1045 steel substrate in resisting radial fretting and plastic deformation. SEM observation of the fretted surface morphology indicates that TiN coating is characteristic of delamination during the radial fretting and AISI 1045 steel of adhesion. EDAX analysis of wear debris components shows that oxidation was involved during the radial fretting process of the two materials, which is similar to what has been observed with conventional horizontal fretting. Thus the newly developed test rig is capable of simulating radial fretting satisfactorily.