Ultralow Wear Behavior of Iron–Cobalt-Filled PTFE Composites

For the first time, we demonstrate that PTFE filled with iron–cobalt (FeCo) microparticles is an ultralow wear, magnetic, multifunctional tribological material. PTFE filled with 5 wt% of equiatomic, pre-alloyed FeCo powder resulted in steady-state wear rates of 2.8 × 10^–7 mm³/Nm, approaching that of PTFE-filled alumina. Comparable wear rates were not observed for PTFE filled separately with elemental iron (Fe) or cobalt (Co) microparticles. PTFE filled with either Fe or Co microparticles exhibited only incremental improvements in steady-state wear behavior when compared to unfilled PTFE (1 order of magnitude or less improvement). Particle size analysis and morphology indicate that the Fe and Co microparticles are strongly fused agglomerates (5–20 µm) made of smaller primary particles or features, while the FeCo microparticles are large (~ 40 µm), spherical, dense particles. IR spectroscopy shows that PTFE-FeCo composites form more tribochemical species than elemental Fe- or Co-filled composites, leading to the observed improvements in wear rate. The FeCo particles are surprisingly large as a filler for ultralow wear PTFE. From these results, we conclude that the fully dense, metallic, microscale, and intrinsically brittle FeCo particles may be friable and break down during sliding to reinforce and promote stable tribofilms, akin to the previously reported alumina particles in ultralow wear PTFE-alumina composites.