Microstructure and depositional mechanism of Ni-P coatings with nano-ceria particles by pulse electrodeposition
(1. College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics,
Nanjing 210016, China;
2. College of Mechanical Engineering, Yangzhou University, Yangzhou 225127, China)
Nanjing 210016, China;
2. College of Mechanical Engineering, Yangzhou University, Yangzhou 225127, China)
Abstract: Nano-CeO2 (RE) particles were co-deposited into Ni-P binary composite coatings by applying pulse current (PC) under ultrasonic (U) field. Morphology, chemical content and crystal microstructure were characterized by environmental scanning electron microscopy (E-SEM) with energy dispersive X-ray analysis (EDXA), XRD diffractometry and transmission electron microscopy (TEM). Experimental results show that Ni-P coating reinforced with 15g/L nano-CeO2, in amorphous state and with compact structure, can be improved in the microhardness from HV0.2580 to HV0.2780 by annealing at 600 °C for 2 h. The highest content of codeposited Ce and deposition rate can reach 2.3% and 68 μm/h, respectively. Furthermore, the effect of RE adsorption and pulse overpotential on depositional mechanism was investigated. n-CeO2 particles or Ce4+ ions with strong adsorption capacity acted as the catalytic nucleus to improve densification effectively. During annealing at 600 °C for 2 h, n-CeO2 particles will uniformly adsorb on crystal grain to preferentially pad and heal up gaps of cracking Ni boundaries, promoting dispersion strengthening with refiner-grained structure.
Key words: Ni-P coating; pulse electrodeposition; overpotential; depositional mechanism; CeO2