The Effect of Redox Reactions during Laser Alloying of Steel with Bismuth Oxide on Tribological Characteristics under Boundary Friction Conditions
摘要
This work investigates the tribological characteristics of the surface of carbon steel alloyed with bismuth oxide with the addition of an oxidizer or a reducing agent, specifically lithium nitrate or highly dispersed graphite powder, respectively. Tribological tests were performed in contact with an aluminum alloy AZh1 under boundary lubrication conditions. It was established that carbon interacts with bismuth oxide during the alloying process under high temperature laser treatment, leading to the formation of metallic bismuth, which negatively affects the performance of the tribological pair under high contact load. Furthermore, a higher carbon content in the powder mixture results in a greater amount of reduced bismuth oxide in the steel surface and a lower load-carrying capacity of the pair at a constant speed of 9.0 m/s. Conversely, the decomposition of lithium nitrate with the release of oxygen during high-intensity laser processing leads to an increased proportion of oxidized bismuth in the alloyed surface. The addition of the oxidizer significantly improves the tribological characteristics of the pair under boundary lubrication friction conditions. A possible mechanism for the occurrence of ultra-low friction and wear coefficients during sliding friction under boundary lubrication for the bismuth–oxide–alloyed steel vs. aluminum alloy friction pair is proposed.