Tribo-mechanical interpretation for advanced thermoplastics and the effects of wear-induced crystallization

Despite the available knowledge in tribology of thermoplastic polymers the relation between the dominating wear mechanisms and the influencing material factors are still questionable. The present research aims to relate the tribological properties of thermoplastics to their mechanical behaviour and morphological features. Wearinduced further crystallisation of semi-crystalline polymers has been analysed in relation to measured wear and friction/bulk temperature. In this paper nine different polymers (polyamide-imide - PAI, polyether-imide - PEI, polycarbonate - PC, polyphenylsulfone - PPSU, polyethylene terephthalate - PET, ultra-high molecular weight polyethylene - UHMWPE, polyvinylidene fluoride - PVDF, polyphenylene sulfide - PPS, polyamide 6 - PAC) were compared. All specimens were tested with a large scale linear reciprocating flat-on-flat tribo-tester in dry contact condition against 100Cr6 steel counterface. A contact pressure of 4 MPa and 50 mm/s sliding speed were chosen for all the experiments. Wear testing resulted an increase in crystallinity for the semi-crystalline grades. Amongst them, PET and PPS showed a high relative increase in crystallinity. In case of these two materials, the frictional heating was sufficiently high to modify the morphology of the contact surface but still it was below the melting range. Results of instrumented indentation tests also confirm the significant crystallinity increase by showing higher hardness/spring stiffness after wear testing