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.  

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. 

Figure 4A: Nanoindentation depth with respect to load

Figure 4B: Meyer's Hardness from nano indentation with respect to load

Figure 6A: AFM Scratch methodology - wear volume with respect to the number of passes of the AFM tip

Figure 7: AFM Scratch-Topography Interrupted Methodology (total 40 passes) - Trace-retrace averaged coefficient of friction with respects to the number of passes

Figure 8: AFM Scratch-Topography Continuous Methodology (total 40 passes) - Trace-retrace averaged coefficient of friction with respects to the number of passes 

Figure 10: AFM Scratches Continuous Methodology  (total 2000 passes) - Pile up and removed volume with respects to applied normal load

Figure 12: Degree of Wear versus normal applied load 

Figure 13A: AFM Scratch-Topography Continuous Methodology (total 2000 passes) - Trace-retrace averaged coefficient of friction with respects to the number of passes and various applied normal loads 

Figure 13B: Comparison of AFM Scratch-Topography Continuous Methodology (total 2000 passes) maximum and steady state friction  versus applied normal load