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Abstract
Specimens of the steels S 6-5-2 (AISIM2) and 100 Cr 6 (AISI 52100) were coated with TiN by a reactive DC-magnetron-sputtering process. The fatigue behaviour of coated and uncoated specimens was investigated under cyclic bending. The fatigue limit of the uncoated steel S 6-5-2 is mainly governed by internal defects like carbide clusters and micropipes. Therefore, a coating has no influence on the fatigue limit. At high stress amplitudes the failure of the uncoated material is initiated at the specimen surface. Thus, coating of the surface causes higher mean lifetimes. The fatigue behaviour of the uncoated steel 100 Cr 6 is mainly governed by crack initiation at the surface of the specimens. At low stress amplitudes, a coating may shift the crack initiation place to the interior of the specimens. Hence, a slight improvement of the fatigue limit by coating is observed. At high stress amplitudes the coating has no influence on crack initiation and no improvement of the lifetime can be achieved by coating.