Experimental Study And Surface Performance Analysis Of Nickel-Titanium Alloy Composite Polishing By Magnetic Field And Electrochemical Polishing

As a good medical implant material,nickel-titanium alloy can be widely used in the human body,including skull plate,vascular stent,spinal orthodontic device,tooth tapping and other human internal and external environment,so good mechanical properties,corrosion resistance,biocompatibility are needed.The surface properties of materials are closely related to the surface quality and state of materials,so improving the surface state is essential.It seems particularly important.However,the electrochemical polishing of nickel-titanium alloys has developed slowly in China due to the current commercial confidentiality and the stringent test parameters,which do not form a systematic process method and theory.In this paper,the magnetic field electrochemical polishing of Ni-Ti alloy is realized by the self-designed magnetic field electrochemical working platform.On the basis of the analysis of the current research situation at home and abroad,a new electrolyte is put forward,with various additives added and magnetic field assisted electrochemical processing.The efficiency and quality of electrochemical polishing are effectively improved,and the electrochemical polishing corresponding to matching is improved.Chemical polishing parameters improve the surface properties of Ni-Ti alloy.The surface roughness,micro-morphology,mechanical properties,corrosion resistance and biocompatibility of Ni-Ti alloy were effectively improved.In this paper,the perchloric acid system and the new electrolyte with various additives were firstly determined,and the factors affecting the polishing process were analyzed by orthogonal test.Finally,the optimum parameters of the surface morphology and roughness of the magnetic field electrochemical polishing of nickel-titanium alloy were obtained under the condition of magnetic field intensity of 0.2T: current density of 0.8A/cm2,polishing time of 30 s,Yin and yang.The electrode spacing is 15 mm,the electrolyte temperature is 15 C,and the optimum surface roughness is 14 nm.The changes of Ra value of surface roughness,surface micro-morphology and surface micro-height profile were compared and analyzed when different electrochemical polishing parameters were changed,and the reasons were summarized.Finally,by comparing and analyzing the conventional electrochemical polishing of nickel-titanium alloy,the magnetic field electrochemical polishing reduces the processing time,improves the processing efficiency and reduces the surface roughness slightly.Next,the surface properties,mechanical properties,corrosion resistance and biocompatibility of nickel-titanium alloys with different surface treatments were analyzed.The surface quality of different treatment methods was compared by testing the surface properties,which showed that the surface roughness was reduced by magnetic field electrochemical polishing compared with mechanical polishing,with a minimum value of 14 nm.The indentation tester made in laboratory,after nanoindentation test,because electrochemical polishing can remove the cold hardening layer and residual stress produced in the process of mechanical grinding and polishing,the change of elastic modulus is poor.According to the energy spectrum analysis of scanning electron microscopy,it is concluded that Ti/Ni is better than mechanical polishing,which effectively reduces the content of Ni element on the surface and improves the biocompatibility.Through the corrosion resistance test of medium immersion method,two kinds of Hank's simulated body fluids are used to accelerate the corrosion of Ti/Ni.The test shows that magnetic field electrochemical polishing improves the surface quality compared with mechanical polishing.The corrosion resistance is enhanced.