Using an in situ Kelvin probe to study changes in sliding metal surfaces

The Kelvin probe (KP) technique was applied to detect changes on the wear track during the sliding of two metals. The KP is based on an electric capacitance technique to measure the difference in the electron work function of metals; therefore it can detect structural and chemical changes on the wear track in situ. It is non-destructive and has other characteristics, such as high sensitivity, applicability in air and simple design. It has been suggested that having an in situ measurement system is a key feature for studying wear mechanisms of ductile materials. This research work has demonstrated that this technique is able to provide new information about sliding processes.; Three main findings were made using the KP: Firstly, the KP signal (KPS) exhibited a well defined periodic variation that could not be detected by conventional friction monitoring for copper alloy materials. The mechanism was found to be the formation and removal of at least partially oxidized material, which was confirmed by post-test analyses. Secondly, the KP detected the chemical changes in air, caused by transfer of material from the pin to the disk for the aluminum disk and bronze pin during sliding. This resulted in decay of the KPS measured in air. Thirdly, the KP showed a quick response to the onset of layer removal, detected as sharp spikes for aluminum disks. Other observations on KPS variations together with their interpretations will also be presented and discussed in this dissertation.; One of the big tasks that one needs to keep in mind during the use of the KP is how to retrieve the desired information from the KPS. Since the KPS is affected by anything that alters the electron work function by structural or chemical changes near the surface of the material, it is sometimes hard to interpret the KPS patterns. However, it is helpful if one uses it under well-controlled conditions and interprets the data with the aid of other analytical instruments. The KP is then a powerful and promising technique for investigating wear mechanisms of ductile materials.