The Ti-Nb Modified Layers On Ti-6Al-4V Biomedical Titanium Alloys Prepared By Magnetron Sputtering

Titanium alloys have been widely used in aerospace, chemicalengineering, shipbuilding, automobile industry, bioengineering and other fields dueto its excellent combination property. As the main materials of biological substitutematerials, titanium alloys have been preferred for prosthetic valves, jointreplacement, cardiac simulator, urinary reconstruction and so on. The demands forbiomedical titanium alloys have greatly increased with the improvement of people’sliving as well as the larger population and more serious aging problems. Now thebiomedical titanium alloys have become the best choice for people because of theircheapness, safety, health and long life.The biomedical titanium has developed rapidly in recent years and pure Tialloys、Ti-6Al-4V、Ti6-Al7-Nb were used generally. So far, the application of β-typetitanium alloys based on Ti-Mo、Ti-Nb、Ti-Ta and Ti-Zr has become more and moreextensive owing to its lower modulus of elasticity and high strength. Ti-Nb alloyshave become the most potential biomedical titanium alloys due to its lowestmodulus of elasticity, great biocompatibility and shape memory effect, such asTi-Nb-Sn alloy,developed by Japan, possessing an excellent strength of800Mpaand the lowest elastic modulus of43GPa which is very close to that of human bones.However, the development of β titanium alloys were largely restricted because of itscomplex processing and high cost.Comparatively, the amount of lower-costTi-6Al-4V employed in the field of biomedical titanium alloys has been the largestat the present stage. But when Ti-6Al-4V alloys were placed in body fluids, therelease of V and Al ions caused by corrosion and particles caused by wear are bothharmful to people’s health. To some extent, proper surface modification methodscould improve the wear resistance and corrosion resistant property of Ti-6Al-4V. Inthis work, magnetron sputtering technology was applied to depositing Ti-Nb filmson Ti-6Al-4V to improve its wear resistance and corrosion resistant on the premiseof maintaining its good mechanical performance.Sputtering technology plays an important role in the performance of the films, mainly including sputtering power, sputtering pressure, sputtering time, bias,substrate temperature, target distance and so on. The results of the designedorthogonal experiment indicate that sputtering power has the greatest influence oncorrosion resistance, surface roughness, and surface particle sizes. The filmsdeposited with a sputtering power of200W and a sputtering pressure of0.5Pa showmore optimal comprehensiveproperties.Ti-Nb alloys have advantages of low modulus of elasticity, the shapememoryand hyperelastic behavior.1μm Ti-35wt%Nb films were prepared withmodulation rate of3.54:1and different modulation periods (1000nm,333nm,200nm, and125nm). The results show that the samples with modulation periods of200nm possess well-distributed and smaller particles as well as excellent wearresistance and corrosion resistance. However, the problems of interface and stressstill exist on the surface of the films.Ti-35%wtNb samples with modulation periods of200nm were annealed at200℃、400℃、600℃for1h in vacuum, respectively, in order to eliminate theinterfaces, release the stressand strengthen the surface. After annealing the surface ofthe samples was intact and uniform without obvious cracks. Samples annealed at400℃and600℃showed higher hardness, better wear resistance and corrosionresistance. However, samples annealed at200℃resluted in worse property. It couldbe explained that with increasing the annealing temperatures the atoms obtainedenough energy meeting with the diffusion activation energy to get rid of the restrainof neighboring atoms to diffuse through the layers of the film and substrate. And italso promoted the crystallization and grain growthwhich resulted in smaller stress,less interfaceand higher strength surface. Thus, the surface of these samplesbecomemore intactand uniform and showed higher hardness,better wear resistanceand corrosion resistance.In conclusion, it is feasible to improve the surface properties ofTi-6Al-4V by preparing Ti-35Nb layers through the designed orthogonalexperiments. The sputtering power has the greatest effect on the properties ofNb films by magnetron sputtering Ti-6Al-4V surface. The modified layerswith the200nm modulation period of the samples show excellent propertie sdespite of the existence of stress and interfaces. It is effective to enhance the solid solution on the surface and solve the problems of stress and interfacesby annealing at600℃. And the hardness, wear and corrosion resistance ofthe samples have improved greatly as well.