Enhanced Tribological Performance and Self-Locking Torque Stability in Ultrasonic Motors Via PEEK/PTFE–AlCrN Dual Coatings

Abstract To enhance the tribological performance and self-locking torque stability of the friction drive interface in traveling-wave ultrasonic motors, this study proposes a dual-surface enhancement strategy applied to both the rotor and stator. The rotor was coated with a 30 wt% polyetheretherketone/polytetrafluoroethylene (PEEK/PTFE) composite, while an AlCrN coating was deposited on the stator via physical vapor deposition. The tribological properties and motor output performance of various friction pairs were systematically evaluated using a custom-built tribometer and motor testing system. Results demonstrate that the PEEK/PTFE composite paired with AlCrN achieved an ultralow wear-rate of 9.97 × 10−7 mm3/Nm, superior to that obtained when paired with phosphor bronze (1.85 × 10−6 mm3/Nm). Moreover, the PEEK/PTFE–AlCrN combination exhibited the smallest fluctuation in self-locking torque, with a coefficient of variation (CV) of only 3.8%, considerably better than that of the uncoated phosphor bronze stator (CV = 14.3%). This study confirms that the synergistic application of PEEK/PTFE composites and AlCrN coatings effectively improves both wear resistance and torque stability at the ultrasonic motor drive interface, facilitated by the protective stator coating and the formation of a transfer film, thereby offering a novel material-matching solution for reliable motor design in precision driving applications.