Single Asperity Plowing of Metallic and Polymeric Surfaces in an Atomic Force Microscope: An Overview of Recent Developments

Previous experimental and theoretical work in plowing phenomena have primarily focused on the effects of many asperities and hence wear phenomena due to a single asperity have not been adequately investigated. In response to this apparaent lack of information around single asperity plowing effects, two of the authors [1] developed an experimental technique wherein the plowing motion of a pyramidal diamond indentor affixed to a stainless steel cantilever is controlled by the piezoelectric transducers of an atomic force microscope and appropriate software macros. Using the mathematical model of Azarkhin and Richmond [2], they were able to estimate the friction stress developed between the substrate and the indentor as well as the material flow stress for selected aluminum alloys. In particular, the measured ridge heights gave an estimate of friction factor for a particular plow track, and the measured normal and plowing forces lead to an estimate of flow strength. The plow track morphologies were found to depend upon material hardness and specific alloying agents in the material, with the softer materials exhibiting oscillatory ridges due to the development of a built-up edge of the indentor, and the harder materials exhibiting detached ridges due to their reduced fracture toughness [3]. The purpose of the present article is to present an overview of recent developments in single asperity plowing of selected metal surfaces in an atomic force microscope. We shall discuss results from dry plowing experiments as well as plowing experiments in the presence of selected boundary additives. Corresponding theoretical modeling developments will also be discussed as well as the roll of indentation size effect in single asperity plowing. We shall also present results of plowing experiments on HMWPE which is used in orthopaedic prostheses. Finally, some discussion about ongoing work will be presented.