Investigating Wearless Performance of Bismuth-Alloyed Steel Sliding Against Different Materials in Boundary Lubrication

Abstract

Wearless sliding friction in the lack of lubrication remains one of the primary goals of scientific research, as wear greatly reduces the life of mechanical components. While wearless friction is achievable in sliding friction with proper hydrodynamic lubrication or at microscale normal loads, it remains a significant challenge to overcome wear at high normal loads, high sliding speeds, and in the boundary lubrication. This paper introduces a novel approach to significantly mitigate wear in plain bearings operating under boundary lubrication at high normal forces and sliding speeds. The plain bearings were constructed from steel shafts tested against different materials. The surfaces of the steel shafts were alloyed with bismuth oxide using a novel high-energy short-pulse laser treatment. In order to incorporate the bismuth oxide into the surface layers of the steel, MnO2 was utilized as a carrier. Achieving an ultralow coefficient of friction is essential but is not a sufficient condition to ensure wearless performance. Wearless friction was observed for the Bi-alloyed steel disk sliding against aluminum countersurface at normal loads up to 250 N (~5 MPa) and a sliding speed of 9 m/s under extreme lack of lubrication. The results of tribological tests demonstrate an exception to the Frenkel-Kontorova-Tomlinson model for wearless friction. The test results for Bi-alloyed steel–aluminum pair offer a groundbreaking and promising approach for a wide range of applications.

Keywords: wearless friction, boundary lubrication, plain bearings, ultralow coefficient of friction, bismuth oxide, laser alloying