The Effect Of Passivation On Corrosion Resistance Of Biomedical High Nitrogen Nickel-free Stainless Steel

Compared with traditional austenitic stainless steels,nitrogen(N)alloying gives high nitrogen-free nickel-free stainless steel(HNS)excellent pitting resistance,mechanical properties and biocompatibility,and has great application potential in medical implants.N stabilizes the austenite structure by replacing the nickel(Ni)in HNS,which could effectively avoid the toxic effect of Ni ions releasing on the human body.However,lots of manganese(Mn)was added to HNS to increase the solubility of N,which greatly reduces the general corrosion resistance of stainless steels.And the releasing of metal ions could significantly reduce the biocompatibility.In this case,this paper studies the influence law and mechanism of nitric acid passivation on the general corrosion resistance of HNS.In addition,this paper attempts to develop a simpler and more environmentally friendly passivation treatment,and preliminary study on the effect of passivation on the surface properties of HNS was conducted.This paper has the following main conclusions:(1)The general corrosion resistance of HNS is significantly lower than that of 316L stainless steel and Ti6A14V alloy.The main releasing ions are Fe and Mn ions.After nitric acid passivation,the corrosion rate of HNS could be reduced to 1/20,which is obviously better than the 316L stainless steel after passivation and is equivalent to Ti6A14V alloy.Temperature,concentration and time of nitric acid passivation all have an effect on the general corrosion resistance of HNS.Temperature has the most significant effect on the general corrosion resistance of HNS,while nitric acid concentration has little effect on the general corrosion resistance.With the increase of temperature,the general corrosion resistance of HNS is gradually enhanced,and with the increase of nitric acid concentration,the general corrosion resistance of HNS is only slightly enhanced.After nitric acid passivation,the improvement of the general corrosion resistance of HNS is related to Cr enrichment in the passive film and N enrichment in the form of CrN in the passive film/matrix interface.(2)After water passivation,the ions releasing concentration of HNS is greatly reduced.The temperature and time of water passivation both have a significant effect on the general corrosion resistance of HNS.As the temperature increases,the general corrosion resistance of HNS gradually increases.With the extension of time,the general corrosion resistance of HNS is further improved.Under high temperature and long time of passivation,the general corrosion resistance of HNS could reach the same level as nitric acid passivation,but water passivation requires higher passivation temperature and more passivation time.After water passivation,the improvement of the general corrosion resistance of HNS is related to the thickness increase of passive film and Cr enrichment in the passive film.In addition,N enrichment is not found.Different from nitric acid passivation,water passivation greatly enriches Cr by selective dissolution and reacts with oxygen to form more Cr2O3.Therefore,these improve the general corrosion resistance of HNS.(3)After passivation,the contact angles of the surface of HNS with water and a-bromonene are greatly reduced,and the wetting property is greatly improved.After passivation,the surface tension HNS increases,which is mainly related to the large increase in polar component.The surface of HNS has a positive charge.And after passivation,the amount of excess charge becomes large.The surface of HNS after water passivation has superior wetting properties compared to nitric acid passivation.Therefore,HNS after passivation could obtain more excellent biocompatibility.