Measuring multi-asperity wear with nanoscale precision

Wear of multi-asperity interfaces remains difficult to predict from first principles, in part because improvements are required in our ability to quantify and track wear across the micro-to nanometer scale. In this work, we developed a 6° of freedom topographical difference method based on large atomic force microscopy (AFM) measurements, up to 90 × 90 μm² in size. We detect wear volumes as small as 1.6 × 10⁻¹¹ ± 3.7 × 10⁻¹² mm³ (0.016 μm³), beyond the sensitivity of many existing techniques for the quantification of wear at multi-asperity interfaces. We show that our wear detection technique can be combined with 100 mN normal force ball-on-flat friction experiments to track nanoscale wear across the entire area of apparent contact.