Sliding wear behaviour of fibre-reinforced PTFE composites against coated and uncoated steel

The tribological response of PTFE-based composites for mechanical seals can be significantly affected by the nature of the counterface. In this work, glass fibre (GF) and carbon fibre (CF) reinforced PTFE-matrix composites were slid, in a pin-on-disc configuration, against AISI 304 stainless steel, either uncoated or coated with plasma sprayed Cr2O3. When mated with uncoated steel, GF-PTFE composites tended to wear down more, but also produced a thicker and more continuous tribofilm than did CF-PTFE ones. The pulverized glass debris adsorbed humidity and formed a cohesive skeleton to keep the PTFE debris in place, thus resulting in comparatively lower friction coefficients of approximate to 0.20-0.27. On the other hand, the polished Cr2O3 surface, with smooth plateaus and numerous valleys of various sizes, facilitated the retention of transfer material. Therefore, it produced less friction than uncoated steel, both against GF-PTFE and CF-PTFE, although the CF-PTFE pin showed a limited capacity to develop a tribofilm. CF-PTFE, however, suffered more severe wear than did GF-PTFE against Cr2O3, because the carbon fibres fractured more frequently. The bulk temperature of the composites never increased by more than 12 degrees C during the tests, and the rise in temperature depended more on the friction coefficient than on the thermal conductivity and diffusivity of the mated surfaces.

Automated summary

The tribological response of PTFE-based composites for mechanical seals can be significantly affected by the nature of the counterface. Glass fiber (GF) reinforced PTFE composites tend to wear down more against uncoated steel, but produce thicker and more continuous tribofilms compared to carbon fiber (CF) reinforced PTFE composites. The presence of glass debris helps reduce friction coefficients, while the presence of polished Cr2O3 coating on steel surfaces reduces friction by facilitating the retention of transfer material.