Study on a Ni-P-nano TiN composite coating for significantly improving the service life of copper alloy synchronizer rings

Ni-P-nano TiN composite coatings were successfully prepared and used on the TL084 copper alloy synchronizer ring by electroless plating. The bench test on copper alloy synchronizer rings with the optimal processing indicates a service life as high as 2 × 10⁵ cycles with sufficient friction coefficient, far exceeding the engineering requirements. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) were employed to characterize morphology, composition, structure and phase transformation behavior of the nano-composite coatings. Variations in hardness and wear resistance induced by the addition of various amounts of nano TiN particles were also investigated and correlated with microstructural characteristics. Compared with conventional pure Ni-P coatings, remarkable increases in hardness and wear resistance were observed in the nano-composite coatings, which can be ascribed to the nano TiN particles uniformly distributed in the Ni-P matrix. The introduction of TiN nanoparticles into the electroless Ni-P coating does not significantly affect the structure before and after the heat treatment, but can enhance the hardness.