Sliding wear of SINTIMID compounds against steel

Abstract

Polyimide (PI) belongs to the group of hightemperature polymers that have an excellent property profile in a wide range of temperature and environmental conditions. Parts made of PI may be used continuously in air at 533 K (260 °C) and for short excursions to as high as 753 K (480 °C). These properties, along with its excellent creep resistance, have made PI a potential candidate for tribological components in engineering applications, especially at high pressures, velocities and environmental temperatures. The possibility of adding internal lubricants to the base PI polymers allows their use as self-lubricated matrices for high-performance polymer composites exposed to friction and wear loadings under extreme environmental conditions [1, 2]. In this letter an investigation of the sliding wear performance of SINTIMID polyimide formulations under dry sliding conditions against hardened, smooth steel is described. The main objectives were first, to examine the wear performance of these new material formulations when tested at room temperature and certain combinations of contact pressure p and sliding velocity v, and secondly, to show how these materials compare with other highperformance thermoplastic composites that were studied in previous investigations with the same wear apparatus. The materials were delivered as 5-15 mm thick plates, by SINTIMID Co., Lenzing, Austria, and consisted of three material formulations. Besides the unfilled base resin (SINTIMID pur), two resin/filler compositions (SINTIMID 15G, with 15 wt% graphite filler and SINTIMID Pl15, a compound with graphite filler and some other modifers) were available, all of which provided a certain range of property combinations. Fig. 1 shows the crosssection of each version. It can be seen that the graphite fillers exist in the form of irregularly shaped discrete particles in SINTIMID 15G, but in the form of fiat, continuous and discontinuous flakes of different thickness in SINTIMID Pl15. The specimens with a geometry of about 3mm x 3 mm x 5 mm were machined from the material plates. This resulted in an apparent contact area of approximately 9 mm 2 in the sliding wear experiments. The sliding wear tests were performed on a block-on-ring apparatus at ambient temperature and the sliding speeds of v = 1.5 and 3 m s -1 . Steel rings (German Standard 100 Cr6, HRC 60) 60 mm in diameter and with an initial surface roughness R a of about 0.06/~m were used as the counterface. Further details of the typical preparation and test procedures with this instrument were described in several previous publications [3-5]. In order to assess the mechanical properties of SINTIMID material versions, the fracture toughness on the basis of standard