Correlating topographic features and mechanisms for macropitting, micropitting, and electrical pitting in bearing steel contacts

Abstract Pitting is a critical damage mode in rolling–sliding contacts that can arise from distinct mechanisms, including rolling contact fatigue and electrically induced discharge. This paper presents insights into the formation and characteristics of macropitting, micropitting, and electrical pitting in rolling–sliding contacts of bearing steels. Experiments were conducted using a TE74 twin-disc tribometer under controlled lubrication and electrical conditions. Under boundary to mixed lubrication, macropitting and micropitting were generated using a base oil and a zinc dithiophosphate-enriched oil, respectively. Electrical pitting was produced by applying a low electrical potential across the lubricated contact under elastohydrodynamic lubrication conditions. The three pitting modes exhibited distinct pit morphologies, crack features, and surface topography evolution. Macropitting was characterised by large, irregular pits formed through aggressive secondary crack propagation, whereas micropitting produced smaller, crescent-shaped pits with limited crack growth. Electrical pitting resulted in near-circular pits without surrounding cracks, indicating a discharge-dominated damage mechanism. Roughness parameters also revealed mechanism-dependent surface modifications, providing a unified topography-based framework for differentiating fatigue-driven and electrically induced pitting.