A STUDY ON THE TRIBOLOGICAL BEHAVIOR OF ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE (UHMWPE) COATED WITH A NI-P LAYER

The tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) has been investigated using friction and wear tests at room temperature (similar to 25 degrees C) and also at a low temperature (s imilar to-20 degrees C) in air, vacuum or CO2 saturated vapour for UHM WPE rubbing against itself and also against a steel counterpart. A sti cking phenomenon took place in saturated CO2 vapour at low temperature (similar to-20 degrees C), which was produced by severe adhesion betw een the UHMWPE polymer rubbing pair. The sticking phenomenon was preve nted by a NbP coating deposited on the surface of the UHMWPE by means of high-speed electro-plating, Non-continuous transfer films of UHMWPE on the NI-P surface layer and the steel surface were observed by scan ning electron microscopy (SEM) and transmission electron microscopy (T EM). The studied coating has a solid lubrication character, so that it s sliding friction coefficient mu and relative wear weight loss of the pin w(t) decreased; the wear mechanism changed from adhesive wear to surface fatigue wear. It is concluded that the tribological behaviour of the UHMWPE polymer could be improved with a metallic coating, such as the Ni-P coating used in this study.