| The titanium alloy implants inserted into a human body are usually surrounded by blood-rich tissue,and the serm proteins in blood may lead to their corrosion.Tribocorrision failure is especially common in sliding contact of knee and hip-joint implants during body movements.Such an interplay of a mechanical loading between surfaces and corrosive environments results frequently in a synergistic effect.In most cases,wear leads to an increase in the corrosion rate due to the mechanical destruction of the passive films,which also affects the wear behavior.In any corrosive medium,TiN coatings provide excellent corrosion resistance,tribocorrosion resistance and biocompatibility,which makes it has wide application in the medical field.However,there is difficulty in the practical application of TiN thin films because of the contradiction in the combination of hardness,toughness and tribological properties.To solve this problem,we need to establish a new nano-structure system.In this article,a series of gradient TiN films were prepared by reaction magention sputtering on Ti6A14V substrate.By changing the depositing parameters for getting the TiN coatings with different composition,microstructure and properties along the thickness direction to improve its corrosion and wear resistance.Using X-ray diffraction(XRD)to test the crystal structures;The microstructure of TiN coatings are studied by using SEM and TEM.Using microhardness tester,nano mechanics test system and automatic coating adhesion scratch tester studied the film hardness,elatic modulus,bongding strength,respectively;Contact Angle meter and atomic force microscopy was used to study the hydrophobic property and surface roughness;The corrosion properties was tested by electrochemical workstation and the tribocorrision was studied by using the friction and wear tester combined with electrochemical workstation.We have studied constitutive relationships between film microstructure,crystal structure,mechanical performance with the maximum nitrogen flow and depositing time.The main results are as follows:(1)The increase of nitrogen flow rate has a great influence on the microstructure morphology of TiN thin films.With the increase of nitrogen flow,film surface impurities and defects increase,leading to a bigger roughness.Gradient time in each layer of thin film can influence the grain morphology,the TiN monolayer film has obvious columnar crystal formed,and TiN gradient film can effectively inhibit the formation of columnar crystal.(2)The maximum nitrogen flow rate have a great influence on crystal structure of gradient TiN thin film.When the maximum nitrogen gas flow is 14 sccm,the TiN films show the preferred orientation of(200),with the increase of nitrogen flow rate,the preferred orientation become less obvious.And both in the three different nitrogen flow rate,the XRD spectrums show some transition phase that formed by Ti and N with the stoichiometric ratio,such as TiN0.26.(3)The maximum nitrogen flow rate(?N/Ti)have a obvious influence on mechanical properties of gradient TiN thin film,such as microhardness and bonding strength.With the increase of nitrogen flow rate,the microhardness and adhesion are dropped.When the maximum nitrogen flow rate is 14 sccm,and the maximum microhardness is28.4GPa,the membrane adhesion is better also,and the maximum bonding strength is 88N.(4)Through the TEM observation,composition analysis and nanoindentation test,the gradient TiN structure size,the N content and the mechanical properties of the TiN thin film exhibit obviously change from inner to outer layer.(5)Gradient TiN nanometer film can obviously improve the electrochemical corrosion and corrosion wear behavior of the Ti6A14V substrate.In Hank's simulated body fluid,TiN film occurs the adhesive wear only,and the surface roughness and surface wettability have asignificant impact on corrosion and wear properties of the TiN films.The smaller surface roughness and the better hydrophobicity makes the better the performance of the tribocorrosion. |
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