Evolution of morphology, microstructure and hardness of bodies and debris during sliding wear of carbon steels in a closed tribosystem

Abstract

Debris generated during sliding wear of steels have an important role on tribosystem's behavior. However, the evolution of morphology, microstructure and hardness of debris and solid bodies, and their role on friction and wear is not quite evident, especially for closed tribosystems. Interrupted pin-on-disk wear tests were carried out on low, medium, and high carbon steel tribopairs, while an adaptation of the test apparatus effectively prevented debris ejection from wear track, simulating a closed tribosystem. The experiment was designed according to a repeated measures ANOVA model for multiple dependent variables that includes running-in duration, wear rates, surface hardness and their ratios, and debris size and shape. Plasticity-dominated severe wear took place in all cases, generating two types of metallic debris: flake-type via adhesion and delamination processes and, after sufficient sliding distance, cutting-type due severe shear deformation caused by the abrasive action of hard asperities. Debris were, at least, 20% softer than worn pins and disks, and provided some lubricating effect when adhered, sheared and rolled between sliding surfaces. Low carbon steel wear generated more soft and adherent debris, resulting in prolonged running-in periods. Finally, steel carbon content did not affect wear mechanisms, debris morphology (size and shape), worn surface hardness and wear rates in closed tribosytems, when a debris-flow controlled process prevails.