Preparation And Tribological Properties Of Manganese And Copper Doped Titanium Nitride Films For Surface Modification Of Growing Rods

The growing rod system is a medical implant,which is most widely used in the therapy of early-onset scoliosis(EOS).However,the abrasion and corrosion during its service process is crucial for the clinical application of growing rod.The films with good wear resistance and corrosion resistance can improve the properties of growing rod system,thereby reducing the related complications,and promoting the clinical application.Titanium nitride(TiN)film is a typical hard ceramic coating,which has the advantages of high hardness,corrosion resistance,and good biocompatibility.It has been used as surface modification material for medical implants widely.The doping of transition metals such as Ag and Cu can improve the adhesion performance between film and substrate,and tribological properties of the film.Mn and Cu are trace elements which are necessary for human health and play an important role in physiological activities.Studies have shown that doping Mn and Cu into TiN films appropriately can improve the biocompatibility of TiN films.In this thesis,Mn and Cu metal doped TiN(TiMnN/TiCuN)films were prepared by a four-target unbalanced magnetron sputtering system(UBMS500).The effect of doping Mn and Cu on the properties of TiN films was studied.Considering the physiological environment of human body,the tribological behavior of TiMnN/TiCuN films in the phosphate buffer solution(PBS)and bovine serum albumin(BSA)solution was studied.The results showed that the relatively loose columnar structure was observed in TiN film,while the columnar structure was refined by the incorporation of Mn,which improved the film densification.The hardness,toughness,adhesion performance and wear resistance of TiN films were improved by the doping of Mn,and the films with2.2 ? 5.6 at.% Mn content exhibited better mechanical properties.When wore in the BSA solution,the interaction between Mn ions and the protein played an important role in the tribological behavior.During friction in the BSA solution,the released Mn ions promoted the production of protein deposits.And the structure of protein molecules in deposits denatured under the shear force of Si C ball during friction.The interaction between Mn ions and the protein promoted the formation of carbonaceous layer on the friction interface,which can act as a solid lubricant and improve the wear resistance of films.The doping of Cu also refined the columnar structure of film,and also hardness,hydrophobicity and adhesion performance of TiN films were improved.The film with4.2 at.% Cu content exhibited the best hardness and hydrophobicity.When wore in the air,Cu in the film diffused to the friction interface to form a lubricating film,which reduced the wear rate of the film.When wore in the PBS,a water film composed of PBS was formed on the wear track.During friction,the phosphate in the water film deposited on the wear track,which can avoid the contact between the films and the Si C ball,reducing the wear rate of films.When wore in the BSA solution,compared with TiN film,TiCuN film has better hydrophobicity,which is related to the aggregation and deposition of protein,and a lubricating layer containing C was formed on the wear track,which can improve the lubrication and reduce the wear rate.Both in the air and BSA solution,the TiCuN film with 4.2 at.% Cu content exhibited most excellent wear resistance.In this thesis,it was proved that when wore in the BSA solution,TiN films were improved by doping of Mn and Cu,and the protein denaturated,forming a carbonaceous layer on the friction interface.The tribological properties of the films in the BSA solution were improved by the lubrication layer effectively.However,the denaturing process of protein in the formation of the lubricating layer remains to be discussed in detail.