Creation and evolution of roughness on silica under unlubricated wear

TL;DR

This study investigates how surface roughness on silica develops and evolves during unlubricated wear, revealing a common steady state and linking roughness to friction behavior.

Contribution

It provides a detailed mechanism of roughness formation on silica and demonstrates the predictable evolution toward a steady state under wear conditions.

Findings

Surface roughness evolves toward a steady state regardless of initial conditions.

Roughness formation involves creation of spherical wear particles and their accumulation.

Friction coefficient correlates with surface roughness and its evolution.

Abstract

Friction and wear are important phenomena occurring in all devices with moving parts. While their origin and the way they evolve over time are not fully understood, they are both intimately linked to surface roughness. Guided by pin-on-disc experiments, we present the steps giving rise to the formation of surface roughness on silica, first by the creation of roughly spherical wear particles whose size is related to a critical length scale governing the transition between ductile and brittle behavior, then by the accumulation of these small particles into a larger third body layer, or gouge. We show that, for the explored range of loading conditions, the surface roughness evolves toward a common steady state under unlubricated wear regardless of the initial surface roughness, hinting toward the possible predictability of roughness evolution in wearing components. The friction coefficient is shown to be related to the surface roughness and its time evolution is discussed as well.