Temperature-driven tribological behaviour of PEO-coated AZ31 sliding against MoS₂-coated steel

Plasma electrolytic oxidation (PEO) treatment typically enhances the wear resistance of lightweight alloys but also significantly increases the coefficient of friction (COF). To address this limitation, particularly for PEO treated magnesium alloys, this study explores the use of MoS₂-coated steel counterfaces under lubricated sliding conditions up to 100 °C. The results showed that PEO-coated AZ31 sliding against MoS₂-coated steel exhibited consistently low COF and wear rates across the temperature range of 25 °C to 100 °C. At temperatures above 50 °C, a stable MoS₂-rich tribolayer formed on the PEO surface, effectively reducing friction and wear, particularly as the oil film thinned with increasing temperature. A slight increase in COF was observed between 75 °C and 100 °C, attributed to the formation of MoO₃, which reduced the lubricating effectiveness of the MoS₂ tribolayer. In contrast, uncoated AZ31, lacking a tribolayer, showed significant increases in friction and wear due to surface oxidation and thermally activated plastic deformation. This study demonstrates that pairing PEO-coated AZ31 with MoS₂-coated steel counterfaces is an effective strategy for lowering COF and wear rates at temperatures up to 100 °C, indicating potential for improving the tribological performance of magnesium alloys in high-temperature applications such as the automotive and aerospace industries. • PEO and MoS₂ reduced COF and enhanced AZ31's performance under high-temp lubrication. • PEO-coated AZ31 vs. MoS₂-steel showed low COF and wear from 25 °C to 100 °C. • Above 50 °C, MoS₂ tribolayer on PEO maintained low friction as uncoated AZ31's wear increased. • Between 75 and 100 °C, MoO₃ formation slightly increased COF, reducing MoS₂’s lubrication effectiveness.