Mechanisms of material transfer studied in situ in the SEM:

► Galling studies comprising an aluminium tip sliding against DLC and tool steel. ► Transfer free sliding was observed against polished DLC, but not tool steel. ► Passage of scratches caused transfer upon subsequent sliding against polished DLC. ► The transfer process includes primary, secondary and damage activated transfer. ► Activation and healing of work material constitute previously unidentified mechanisms.