Tribological performance and vibration response attenuation of PTFE/PAI composite coatings for automotive balance shaft module gears

This study develops polytetrafluoroethylene (PTFE) modified polyamide-imide (PAI) composite coatings as functional interfacial layers for metal gears in automotive balance shaft modules, aiming to improve tribological performance and reduce gear-induced vibration. PTFE/PAI composite coatings containing 0, 1, 3, and 5 wt% PTFE were prepared by air spraying. Their microstructure, thermal stability, mechanical properties, and scratch adhesion were characterized, while their friction and wear behavior was evaluated under dry sliding and engine-oil-lubricated conditions. The 3 wt% PTFE/PAI coating shows the best overall performance. Compared with the neat PAI coating, it reduces surface roughness Sa by 44.1% and increases the critical scratch load (Lc) by 12.7%. Under dry sliding conditions, its average coefficient of friction (COF) decreases to 0.079, and its wear rate decreases by 71.0%. Under engine-oil lubrication, the average COF further decreases to 0.036, and the wear rate decreases by 73.6%. These improvements are mainly attributed to improved coating uniformity and interfacial stability, reduced interfacial shear resistance, PTFE-derived interfacial transfer during dry sliding conditions, and the synergistic lubricating effect of the oil film. The optimized coating was further applied to the driving gear surface in a balance shaft module gear pair. Vehicle-bench vibration tests show that the coated gear reduces the full-band RMS acceleration by 18.0%–27.1% and the 2000–3500 Hz band RMS acceleration by 26.5%–38.3% under idle, steady-state, and speed-cycling conditions. These findings demonstrate that PTFE/PAI composite coatings can simultaneously improve friction reduction, wear resistance, and vibration attenuation of metal gears.