Shear localization in ultralow wear of PEEK/UPE composites

Certain polytetrafluoroethylene (PTFE) composites can form a shear localization structure at the sliding interface by developing running and transfer films, thus achieving an ultralow wear rate of similar to 10(- 7) mm/Nm. However, PTFE, as a per- and polyfluoroalkyl substance (PFAS), raises significant biological toxicity concerns in tribological applications. Based on the shear localization hypothesis, we propose replacing PTFE with ultrahigh- molecular-weight polyethylene (UPE) at the tribo-interface and utilizing PEEK/UPE composites as PFAS-free, ultralow-wear candidates. Wear tests demonstrate that PEEK/UPE composites offer superior anti-wear performance compared to traditional ultralow-wear composites under various conditions. Micromechanical measurements reveal enhanced mechanical properties of tribofilms, which resulted in the ultralow-wear shear localization at the PEEK/UPE tribo-interface. Surface analysis suggests that mechanochemically carboxylated UPE and PEEK polymers play a critical role in maintaining stable shear localization. Contact mechanics calculations further indicate that the robustness of the shear localization of PEEK/UPE composites is attributed to the higher van der Waals force of UPE against steel counterface than that of PTFE.