Wear debris and electrical resistance in textured Sn-coated Cu contacts subjected to fretting

Fretting wear is the most common failure mechanism in electrical connectors for automotive applications. In this study, the fretting wear behavior of laser-textured tin-coated copper contacts has been investigated, focusing on the temporal evolution of wear debris formation and its relation to the electrical contact resistance. The dot-like pattern was produced on the samples by interfering laser beams with a period of 7.5 µm. A fretting apparatus was used for testing, applying two different normal loads (2.5 and 5.0 N). The fretting-induced chemical and topographical changes were studied by scanning electron microscopy, focused ion beam, Raman spectroscopy, and X-ray diffraction. This analysis revealed the formation of oxide particles (SnO and CuO) and of a closed intermetallic layer (Cu6Sn5). For CuO, the transition from loosely-packed wear particles to a dense layer is observed. During the entire experiment, the SnO particles remain as compact agglomerates without showing any layer formation. Based upon these observations, a model for the non-textured reference was developed, describing the processes taking place during fretting wear. Furthermore, it can be concluded that under the studied conditions the laser interference pattering reduces the coefficient of friction and the contact resistance by up to approx. 12% and 71%, respectively.