Wear of cryo-treated engineering polymers and composites

Polymers and composites are extensively used in wear situations dominated b y various types of abrasive mechanisms. Incorporation of fillers and fibers , heat treatment and surface engineering by various chemical and physical t echniques have been successfully employed to enhance wear behavior of metal s as well as non-metals. In the case of metals, cryo-treatment is an emergi ng technique for improving wear resistance. However, this tool has not been applied for polymeric materials. Hence, in this paper investigations on th e influence of cryo-treatment on wear performance of a series of thermoplas tic engineering polymers such as Polyimide (PI), Polyetherimide (PEI), Poly tetrafluoroethylene (PTFE), Polycarbonate (PC) and Polyurethane (PU) are pr esented. A series of composites of PI, PEI and its copolymer with increasin g amount of short glass fiber and solid lubricants was also investigated. T he selected materials were cryogenically treated at liquid nitrogen tempera ture for 24 h. Abrasive wear performance was evaluated at ambient temperatu re for a single pass on a pin-on-disc machine using Silicon Carbide (SIC) p aper as a counterface. Comparison of wear rates of treated and untreated sa mples under various loads revealed that this technique has potential to inc rease the wear resistance of some polymers and composites, Fiber loading hi gher than 20%, however, showed deterioration in wear after cryo-treatment. The extent of influence of cryo-treatment on wear resistance depended on th e type of base matrix and the nature and amount of fibre or particulate fil ler. Changes in crystallinity and hardness were studied and correlated with observed wear behavior. Scanning electron microscopy (SEM) was used to inv estigate changes in morphology due to cryo-treatment. (C) 1999 Published by Elsevier Science S.A. All rights reserved.