Friction and wear studies of an internally lubricated polyetherimide composite

Polyetherimide (PEI) is one of the latest generic high-performance engineering thermoplastics. PEI (developed by General Electric (USA) under the trade name ULTEM) is an amber and amorphous polymer with a heat distortion temperature between those of polyarylate resin and thermally stable crystalline polymers such as polyether-ether ketone (PEEK) and polyamideimide (PAI). It has excellent thermal, mechanical and electrical properties along with easy processability. In the work reported here, a wear-resistant formulated composite supplied by GEC (ULTEM 4001) was selected for tribological investigations on a pin on disc machine under unlubricated conditions, against mild steel. Analysis of the composite revealed that this grade contained PTFE (13–15%), which is the most promising polymeric lubricant. A very low and stable frictional coefficient was observed against moderately finished surfaces. However, its specific wear resistance (⋍10−14 m3/Nm) was comparatively lower than that of fibre-reinforced thermoplastics. The wear mechanism was found to be significantly dominated by the presence of PTFE. The friction coefficient was in the range of 0.2 and reduced to a still lower value (0.1) as the apparent contactpressure increased. Scanning electron microscopy was used to investigate the underlying wear mechanism. Film transfer of PTFE was observed to be the principal factor responsible for reduced friction.