Transitions in abrasive wear mechanisms: Effect of the superimposition of interactions

During abrasive wear, the prevailing wear mechanism has been shown to be connected to the movement of the active particles present at the wear interface. Two particle dynamics can occur: (i) rolling, which is evidenced by the presence of indentations on the worn surface, and (ii) sliding, which produces scratching and/or ploughing. The particle dynamics can vary with the imposed tribological conditions. In this work, single abrasive particle interactions are simulated using well-controlled indentation or scratch tests where an indentation represents the contact of a rolling abrasive particle without sliding, which can lead to deformation or cracking, and a groove represents the sliding of an abrasive particle, which can lead to ploughing, wedge formation, cutting or cracking. Two horizontal sliders (0.1 μm resolution) drive the sample while the indenter is controlled by a piezoelectric translator with a resolution of 5 nm. A 3D load cell controls and measures the load. A new parameter was introduced to evaluate wear mechanism transitions, which was called superimposition of interactions. In order to study the effect of superimposition, series of indentations and parallel scratches were created by varying the distance between mono-interactions and the size of the mono-interactions. The mass loss was determined using laser interferometry by measuring the volume of material above and below the initial surface. The results clearly showed transitions in the wear mechanisms when the degree of superimposition was varied for both the indentation and the scratch tests. Sequences of indentations produced on tool steel samples resulted in mass loss when the degree of superimposition of indentations was higher than 50%, whereas sequences of parallel scratches on tool steel samples resulted in mass loss for degrees of superimposition higher than 80%. Scratch tests on copper showed that the wear mechanism changed from ploughing and wedge formation at a low degree of superimposition to microcutting at a high degree of superimposition. Subsurface hardness increased slightly as a function of the superimposition degree, since surface work hardening was intensified for high degrees of superimposition. Also, the superimposition of the scratches reduced the support for subsequent scratches, increasing mass removal for higher degrees of superimposition.