Asperity level characterisation of abrasive wear using atomic force microscopy

Using an Atomic Force Microscope (AFM) a nanoscale wear characterisation method has been applied to a commercial steel substrate AISI 52100, a common bearing material. Two wear mechanisms were observed by the presented method: atom attrition and elastoplastic ploughing. It is shown that not only friction can be used to classify the difference between these two mechanisms, but also the ‘degree of wear’. Archard’s Law of Adhesion shows good conformity to experimental data at the nanoscale for the elastoplastic ploughing mechanism. However, there is a distinct discontinuity between the two identified mechanisms of wear and their relation to the load and the removed volume. The length scale effect of the material’s hardness property plays an integral role in the relationship between the ‘degree of wear’ and load. The transition between wear mechanisms is hardness dependent, as below a load threshold limited plastic deformation in the form of pile up is exhibited. It is revealed that the presented method can be utilised as a rapid wear characterisation technique, but additional work is necessary to project individual asperity interaction observations to macroscale contacts.  

Methods
The data was collected by a combinated of nanoindentation, and using AFM in contact mode. The AFM was used to scratch a steel substrate AISI52100 with varying applied load and measure the topography of the susbtrate.