Reserch Of Nickel Plating Carbon Nanotubes And CNTs/SiCp/Mg Composites Material

Magnesium materials is a promising new materials, as it has many potential advantages, such as high specific strength, specific stiffness and good performance in machining and so on, but, as many other materials, they still have defects, such as tensile strength and hardness shortage, etc. In order to make up for these shortcomings, this research adopted a nickel plating carbon nanotubes and silicon carbide two-phase enhanced method, preparing magnesium matrix composite materials, then tested their mechanical properties.Quasi-straight carbon nanotubes have been produced by using an improved graphite anode arc plasma method. The raw product were acidified by a kind of mixed acid consisted of strong sulfuric acid and strong nitric acid. The result showed that not only were the carbon nanotubes purified , but also grafted by many functional groups. In later chapters, the paper theoretically discussed this principle in detail. The mechanism of acidification process, and chemical reactions of carbon nanotubes were analyzed compared with graphite. The paper also pointed out that in this process the complete carbon nanotubes without defect can in surface graft functional groups without destructing the carbon nanotubes skeleton of six-member ring.After purification, these carbon nanotubes were sensitized, activated before nickel plating. Then they were coated with Ni-P alloy using an electroless plating method. After that, the layer of Ni-P alloy transformed from its structure of amorphous to nanocrystal by heat treatment. The results of the XRD and SAED showed that now the layer existed three phase, Ni-P compounds Ni3P, nickel nanocrystal of face center cubic structure, nickel nanocrystal of hexagonal close packed structure after heat treatment. Among them, the hexagonal close packed structure of the nickel is on macroscopic unstable. Based on the experimental data, applying thermodynamics principle, the author discussed the problem more profoundly, then pointed out that the real reason of the two-phase coexisting is the nano scale.CNTs and SiCp reinforced magnesium matrix composites were successfully fabricated using slurry methods of stirring liquid. With the increasing content of CNTs, both the microhardness and elastic modulus of the composites increased, while the elongation rate and tensile strength increased firstly, then decreased when after come to the peak. When the volume fraction of SiCp is under 3%, the tensile strength, elastic modulus and microhardness of the composites improved constantly with rising SiC content, but the elongation rate declined.When the volume fraction of CNTs is 1.1%, the CNTs/2vol%SiCp/Mg composite performs best, the elastic modulus, and microhardness of composite improved 51.8%,19.5% and 80% respectively, but the elongation rate reduced comparing with Mg matrix. For these composites, the volume fraction of CNTs could not beyond 1.1%. Otherwise, the elongation of composite and their tensile strength could reduce remarkably and the increase of the microhardness and elastic modulus also become slow due to agglomeration of the CNTs. The addition of SiCp and CNTs could refine the primary grains of composite remarkably.