Electroless Plating Magnetic Metal Film On The Surface Of NiTi Memory Alloy

The appearance of medical stents is a great innovation, but coming after the patient using it, the finding shows restenosis ratio of stents is fairly high. Now nitinol and stainless steels are the central materials of stents to remedy narrow pipeline of people. These stents don't possess magnetic properties, so which only have the function of physical therapy but not chemical therapy unless covering magnetic film. Now magnetic medical particle has been prepared, the magnetic medicine will be drown beside stents when patients take it if the stents is covered magnetic film, then which can reduce the negative effect and improve the active impaction.Electroless depositing is an excellent kind technology and was used to prepare the magnetic film on the surface of nitinol alloy in this study. The experiment is constituted with two main parts, the first, the confirmation of prescription and procedure, the effect on Ni-Co-W-P magnetic film by The concentration of sodium tungstate especially; the second, the effect on Ni-Co-W-P magnetic film by heat treatment. The results are followed.1) The accretion of sodium tungstate in electroless-deposited bath can enhance deposition rate and magnetic properties notably, which increase firstly but decrease later with the increment of sodium tungstate concentration. The concentration of sodium tungstate impacts on the activation energies notably. The activation energies increase the concentration of sodium tungstate is improved. The effect of concentration of sodium tungstate was emphasized on studying, the results show deposition rate, magnetic properties, image, finish and adhesion is all better when the concentration of sodium tungstate is 0.8g/L.2) The ideal temperature and time were established. With prolonging of deposition time, the thickness and saturation magnetization of coating increase, but coercive field changes irregularly, 60min is regarded as aptdeposition time. Deposition temperature effects on not only deposition rate, but also magnetic properties of film, which are better point when deposition temperature is 60℃ .3) Adhesion of coating is significant property, heat treatment can eliminate internal stress and is favorable to improve adhesion in one hand, in other hand, which can lead to diffusion of metal atom. Solid solution and compound come into being between substrate and coating, then holding on between substrate and coating turns into metallic, which improves adhesion as well.4) Structure and properties as well as the effect of heat-treatment on the structure and properties of electroless-plated Ni-Co-W-P film were studied and checked by SEM, EDS, X ray diffraction (XRD) , micro Roman spectroscopy and Vsm. Results show that Ni-Co-W-P film as plated is crystallization structure. After heat-treatment at 400℃ for 1.5 hours, 500℃ for 1.5 hours, 600℃ for 1.5 hours, Co is oxidized as CO3O4 easily ; Coercive force(Hc) and saturation Magnetization(Ms) of film are increased at first but are decreased later with the improvement of heat-treatment temperature. After heat-treatment at 300℃ for 1.5 hours, image of film becomes more average and dense, so adhesion increases and is better.