The Research On Electrochemical Polishing Of 316L Stain Steel Stent

This paper, based on the current status of electrochemical polishing technology as well as its application on surface finishing of biomedical implants, focuses on DC-electrochemical polishing of 316L stainless steel, which is widely used for fabricating cardiovascular stent and some other medical implants. Orthogonal experiment method was chose to study the factors influencing the quality of polishing. Further experiments were performed to analyze the composition of the electrolyte, operating temperature, time and voltage respectively. Electrochemical polarization test was executed in Hank's solution to compare corrosion resistance of electrochemical polished sample and of the mechanic polished samples. And micro-hardness test was carried out to evaluate the mechanical properties of the polished samples.The results of the orthogonal experiments show that among four factors investigated the most important factor is the composition of electrolyte. Then the cell voltage, temperature of electrolyte, and the time of process. And the composition of electrolyte and the cell voltage proved to be distinguished influence on the surface quality but others factors are less important. The optimized result was obtained by means of variance analysis.Each single factor above was investigated respectively on the effect to the quality of the electrochemical polishing. Attempts have been taken to discuss the mechanism of the process. The optimized parameters such as the range of the cell voltage, temperature of electrolyte, and the time of process are obtained. Additives of the polishing solution are also determined.The optimal process parameters are concluded as below: The electrolyte consist of H₃PO₄ 2/3 and H₂PO₄1/3. the temperature is 80℃. the voltage is 18V and the processing time is 2 min. and containing of small amount of the mixture of additives is also necessary.Polarization test in Hank's solution shows that the electrochemical polished 316L sample possesses higher corrosion resistance than that of mechanical polished samples. Enhancement of anticorrosion performance of the electrochemical polished sample is attributed to formation of an oxide thin layer on the surface as well as the absence of the work-hard layer which exists on the surface of mechanical polished samples.The micro hardness of electrochemical polished sample is a little lower than that of mechanical polished one due to existence of a thin layer of oxide on later sample surface.Finally 316L stainless steel stent was polished by pulsed-electrochemical polishing. The best result is obtained when duty cycle is 1/4 and rate of on/off time is 1/4. The stent with high surface quality is obtained by the optimized process of electrochemical polishing.