Ultralow wear in boundary lubrication: A tribological study of Bi-alloyed steel under high normal loads and sliding speeds

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 ultralow wear is achievable in sliding friction with proper hydrodynamic lubrication or at microscale normal loads, it remains a significant challenge to overcome wear under high normal loads, high sliding speeds, and in boundary lubrication or dry sliding friction. This paper introduces an 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. Ultralow wear 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 up to 9 m/s under extreme lack of lubrication. Achieving ultralow coefficient of friction (COF) and ultralow wear depends on eliminating adhesion between sliding surfaces, reducing the mechanical component of friction through diamond burnishing, and ensuring high fatigue endurance. 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 new approach for a wide range of applications.