Wear analysis in fretting of hard coatings through a dissipated energy concept

Fretting situations are becoming increasingly important for industrial applications. Numerous studies have been undertaken to understand the damage created by low-amplitude reciprocating motion, particularly in the case of a ball on flat contact in dry conditions. The loading condition of materials can be characterized by a ''running condition fretting map'' which describes, in a graph of normal load versus displacement amplitude, the various domains of sliding: partial or gross slip. By considering the time evolution of sliding conditions, various regimes can be defined: a partial slip regime when partial slip is observed throughout the test, a gross slip regime for gross slip, and a mixed regime when both partial and gross slip are observed. The response of the material is, of course, dependent on the sliding regime: crack initiation and propagation are related more to the mixed regime, while surface transformations and loss of matter are related more to the gross slip regime. This paper analyzes the fretting gross slip situation and describes the loss of matter in the case of hard coatings deposited on high-speed steel. Two aspects are considered: (i) the wear volume measurements are usually performed using 3D topography, whereas modeling of the wear scar morphology indicates that valuable estimates of the worn volume can be obtained by 2D profilometry, which is much less time-consuming than 3D topography; and (ii) the wear volume observed in experiments is related to the energy dissipated in the contact at both the global scale and the local scale where the wear depth is an important parameter. With this energy approach, the wear behaviour of a TiN-coated and uncoated high-speed steel can be compared quantitatively. (C) 1997 Elsevier Science S.A.