Transfer film evolution and its role in promoting ultra-low wear of a PTFE nanocomposite

► Debris generation and transfer film evolution were observed using In situ microscopy. ► Three distinct and interdependent regimes of wear and transfer were observed. ► Run-in films comprised loosely adhered debris of reducing size. ► Transition films comprised oxidized, nanoscale, and strongly adhered PTFE fragments. ► Transition fragments initiated the steady state transfer film by growing and merging.