A study on the kinetic response of the electron work function to wear

The history prior to the onset of wear is of importance to fundamental understanding of tribological phenomena. In particular, diagnosis of wear under light loads has attracted increasing interest from the nano/micro-device industry. For a micro-device, it is difficult to use traditional wear testers to investigate its wear behavior due to limited dimensions and light wearing stress. It is therefore necessary to develop a technique to characterize wear on small scales or under light loads. Recently, attention has been put on the Kelvin probing technique for potential wear diagnosis. In this study, attempts were made to investigate changes in the electron work function as a function of the wearing load and time. Copper was selected as a sample material and was studied using a scanning Kelvin probe, a tribometer and an atomic force microscope. Based on the experimental study, a phenomenological model was proposed to describe the onset of wear as well as the history prior to the occurrence of measurable wear. The model provides a simple method to reflect the history of wear, especially, to predict the critical time that corresponds to the onset of wear. Experiments were performed to support the proposed phenomenological model.