Investigation on the self-lubricating properties of boronized CoCrFeNiMn high entropy alloy in corrosive environments

Boronizing treatment has been considered as a promising strategy to enhance the surface hardness, self-lubrication and wear resistance of high entropy alloy (HEA), endowing the advancements of HEA in engineering applications. However, the anti-friction, anti-wear and corrosion resistance properties of the boronized HEA in sulfuric acid and seawater environments remain unclear. Here, the self-lubrication and corrosion resistance of the boronized CoCrFeNiMn HEA in these corrosive media were studied to assess the applicable environments. Firstly, a boronized layer with thickness of approximately 25 μm on the CoCrFeNiMn HEA surface was fabricated using the powder-pack boronizing treatment. Tribological assessments demonstrated exceptional self-lubricating properties of boronized HEA in various liquid conditions, with over 30 % reduced friction coefficients and over 80 % decreased wear rates. XPS analysis confirmed the formation of a boron-containing tribofilm, enhancing self-lubrication and reducing friction and wear in liquid environments. However, electrochemical tests indicated that the corrosion resistance of the boronized HEA was significantly affected by the liquid medium. The impedance value (|Z|) of boronized HEA decreased to 4.6 % of that of the original HEA in 3.5 wt% NaCl solution, revealing poor corrosion resistance. Conversely, an enhancement of corrosion resistance was observed in 0.05 M H₂SO₄ solutions with the increase of the |Z| value by 8 times. Therefore, for applications requiring service safety, boronizing HEAs are more suitable for acidic environments, but not in seawater environments, offering valuable insights for the industrial application of CoCrFeNiMn HEA in reducing friction and wear.