Preparation And Properties Of Ni-based CNT Composite Coatings

As the development of technology, people have increased their demand in the wear resistance of materials. As a new carbon material, carbon nanotubes have excellent mechanical properties and special tubular structure, therefore those wear-resistant and antifriction composite materials which use CNT as a reinforce body have became the hot spot in the present studies. In this paper, CNT was used as strengthen phase and Ni-based CNT composite coatings were prepared by using electroless deposition and electro-deposition, the properties of the composite coatings were also studied.The carbon nanotubes were pretreated by immersing in a 1:1 mixture of H2SO4 and HNO3. The results show that the carbon nanotubes have been purified, shortened and actived after the treatment, and its suspension in water have also been improved. By studying the effect of surfactants on the dispersion stability of CNT and the properties of Ni-based CNT composite coatings, we find that adding appropriate amount of anionic surfactant SDS can significantly improve the dispersion of CNT in the plating bath, and the resulting composite coatings have a more excellent performance.The morphology of Ni-based CNT composite coatings were observed by using SEM. It can be found that the carbon nanotubes are uniformly distributed in the Ni matrix, the surfaces of the coatings are smooth and the composite coatings have good adhesion to the substrate. The structure of the composite coatings before and after heat treatment was analyzed by XRD. It is seen that Ni-P-CNT electroless composite coating presents a crystallization transformation during heat treatment. At the same time, because of the appearance of Ni3P and other crystalline phase, the hardness and wear resistance of the composite coatings are greatly improved. On the contrary, the corrosion resistance of the coatings is decreased. The annealed Ni/CNT composite coatings still presents a crystal structure which indicates that heat treatment have little effect on its performance.By adding carbon nanotubes into the plating bath, we can find that as the increase of CNT concentration in the bath, CNT content in the coatings and the properties of the coatings are also increased. At the same time, the increase of CNT concentration can improve the plating rate, but lead to an increase to the roughness of the composite coatings. As the CNT concentration in the plating bath exceeds a certain level, the agglomerations of carbon nanotubes become more serious, and the performance of the composite coatings tends to be reduced.The tribological properties of several different coatings were studied. The results show that as the co-deposited of carbon nanotubes, the wear rate and friction coefficient of the composite coatings are significantly decreased, and the wear marks are more smooth .All these indicates that carbon nanotubes play a good anti-friction and self-lubrication function in the wear process, and the addition of carbon nanotubes can greatly improved the tribological properties of the composite coatings.