Preparation and Tribological Properties of Ni−Al₂O₃−PTFE Composite Coatings for Rotor Shaft

Aiming at the drawback of short repair intervals of domestic aviation transmission systems, the hard particles Al₂O₃ and lubrication material PTFE were used as particles, employed with the brush plating technology to prepare Ni−Al₂O₃, Ni−PTFE and Ni−Al₂O₃−PTFE composite coatings on the surface of T2 copper sheet, which is a commonly used transition layer metal material on the rotor shaft. Scanning electron microscopy and microhardness instruments were employed to characterize and analyze the microstructure, element content distribution, and hardness of the coatings. The friction and wear tests on the coated samples were conducted with a self-made pin plate friction and wear testing machin to explore the frictional properties and wear mechanism of the coating. The results show that with the increase of Al₂O₃ particle content, the surface microcrystalline unit size of Ni−Al₂O₃−PTFE decreases and the microhardness increases. The maximum microhardness of Ni−Al₂O₃−PTFE (3∶1) is 236 HV, which is about 66% higher than that of Ni−PTFE composite coating. The Ni−Al₂O₃−PTFE composite coating combines the advantages of Al₂O₃ and PTFE, which not only reduces friction, but also has excellent wear resistance. The anti-friction performance of Ni−Al₂O₃−PTFE (1∶1) composite coating is the best, with a friction coefficient reduction of about 52% compared to Ni−PTFE composite coating. The wear resistance of Ni−Al₂O₃−PTFE (3∶1) composite coating is the best, and its wear rate is reduced by about 85% compared to Ni−PTFE composite coating. The wear form of Ni−Al₂O₃−PTFE composite coating is mainly mechanical wear, with slight oxidative wear and adhesive wear. The micro-convex plastic deformation on the surface of composite coating can provide a lubrication film for the friction surface, of which PTFE is a self-lubricating particle, and Al₂O₃ particles play a role in supporting and strengthening the coating, preventing the coating from wear.