| Compared to the stainless steel and cobalt based alloy,the density and elastic modulus of Ti-6Al-4V alloy was more closer to biological bone,and it has higher strength-to-weight ratio,excellent corrosion resistance and good biocompatibility,so that it is widely used in artificial joints,bone plates and other medical devices.However,the problems such as its poor wear resistance that resulted in periprosthetic osteolysis and implant aseptic loosening;there is not bioactivity on the surface which means it could not induce new bone growth and could not come into being good osseointegration as well;the release of harmful ions such as Al,V and so on,which may cause infections and allergies to happen,still need to be solved.Therefore,in this study,the bioactive coatings of hydroxyapatite(HA)were deposited to improve the biological activity of Ti-6Al-4V alloy by magnetron sputtering,a corrosion and wear-resistant coating TiN was inserted into between HA and Ti-6Al-4V to enhance the wear behavior and hinder the release of metal ions.And the element and phase composition,surface morphology,interface structure,mechanical properties,corrosion resistance,bio-tribological properties and the biodegradability behavior of TiN,HA/TiN coatings were tested,to evaluate the performance of pure TiN and HA/TiN coatings deposited Ti-6Al-4V alloy comprehensively.The experimental results showed that the colour of TiN coatings deposited by reactive magnetron sputtering not only depends on the sputtering power of Ti target,but also related to the partial pressure of N2 closely.The TiN coatings surface with golden colour were uniform and dense without defects,the surface roughness was only 5.8nm,deposition rate was about 8.6μm/h and grew by columnar crystals and without obvious interface between substrate and TiN;the lower inner-stress,bulk worn loss,friction coefficient of TiN coatings were obtained when the ratio of sputtering power to N2 partial pressure was between 13.45 and 13.88.Under the lubricate of calf serum,the wear loss of TiN coating was only 1.3% compared to Ti-6Al-4V,whats more,the lower and more stable friction coefficient was gained.For HA/TiN coatings,the inner-stress was decreasing with the increasing of Ar pressure,and that increased first and then decreased with bias increasing before heat treatment.The amorphous HA was transform to crystal structure and recovered the bioactive group hydroxyl(-OH)by heat treatment.The recrystallization process of HA also made small particle aggregation and the surface roughness of HA/TiN coatings were between 17.8 and 45.2nm,much higher than single TiN coating.The bonding force of single HA was just 7.5N,but that was varied between 16.9N and 40.0N after a transition layer of TiN was deposited between Ti-6Al-4V and HA.The corrosion resistance of HA/TiN coatings were superior to Ti-6Al-4V and single TiN coatings,and the presence of TiN layer could reduce the release of V ions greatly,reduced by 88%.The wear loss of HA/TiN coatings would rise when the sputtering bias decreasing or the pressure of Ar increasing.And the friction coefficient of HA/TiN coatings in the early stage would be stable and the values was positively correlated with the surface roughness;and then,it would reduce and stable at around 0.2 gradually.Due to the presence of the surface oxide layer(Ti O2),Ti-6Al-4V alloy still showed good biocompatibility,but the Ti-6Al-4V with HA/TiN coatings would have better biological activity. |
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