Fretting behaviour of W–Si coated steels in vacuum environments

This study was focused on the effects of stroke on the fretting behaviour of sputtered W–Si coatings under room and vacuum environments. Fretting tests were carried out with AISI 52100 steel hemispherical ended pin against W–Si coated AISI M2 steel. The tangential force and the applied strokes were monitored during the tests in order to build up the fretting loops. The surface morphology of the wear scars was analysed by optical and scanning electron microscopy (SEM) in order to identify the wear modes and the fretting mechanisms. The shape of the fretting loops was used to characterise the fretting regimes. The formation of adherent films is determinant on the fretting behaviour and depends on the test environment. Electron probe microanalysis (EPMA) was used to analyse the composition of the adherent material and the role of oxides on the formation of the transferred layers. The influence of the coating on the fretting characteristics was discussed comparing coated and uncoated specimens.