Nanoindentation Studies of Contact Materials Used for Sliding Electrical Contacts

Nanoindentation is used to probe the local mechanical properties of materials such as hardness or elastic modulus. In addition, modern instruments also allow scanning the surface using either the nanoindenter or the sample stage in order to derive the 3D surface topography. The aim of the investigations described in this paper is two-fold: Firstly, hardness and elastic modulus measurements of some selected materials, especially thin hard-gold layers, are described. Secondly, the stage movement of the nanoindenter (G200, MTS) is used to probe the 3D surface structure and the potential of this method to quantify wear is studied. It is shown that the surface structure of materials used for sliding electrical contacts makes precise measurement of hardness and elastic modulus challenging. The reason is that smooth surfaces are not necessarily good electrical contacts. However, a nanohardness experiment normally necessitates a flat geometry at the measurement position. Hence, caution is required when comparing values derived from samples with different surface structures. Surface analysis of a wear track of a sliding electrical contact employing a pancake slip ring design was performed. A comparison with results obtained using confocal microscopy shows that the indenter system can successfully be used for elucidating the surface structure from the micrometer to the millimetre scale.