Dry lubrication of ferritic stainless steel functionalised with crystalline aggregates of hexadecylphosphonic acid

This paper demonstrates the excellent tribological behaviour afforded by a new functionalisation technique based on the combination of chemisorption and physisorption of self-assembled hexadecylphosphonic acid for application in metal forming. Surface functionalisation of an X2TiCrNb18 ferritic stainless steel with this technique led to the growth of aggregates on the surface. Detailed analysis showed that crystalline aggregates were physisorbed on a chemisorbed molecular layer. Ball-on-plate linear reciprocating sliding tests were performed under high maximal contact pressures in the 0.5-1.1 GPa range using a 100Cr6 counterpart. Results revealed exceptional low-friction and low-wear afforded by a tribofilm originating from aggregates shearing. The tribofilm built up very quickly and presented the interesting feature of reducing the friction coefficient as the contact pressure increased.