Study On Microstructure And Mechanical Properties Of Ti Alloys For Implant

With the increasing aging of the population,more and more elderly people need to replace the diseased teeth,so the demand for dental implants is increasing year by year.Implants would bear the stress effect produced by numerous chewing in the population cavity.In addition,oral cavity special saliva environment,planting experience fatigue phenomenon,serious will break phenomenon,affect the life of implant.At present,the main implant materials used in clinic are pure titanium and Ti-6Al-4V.However,pure titanium has low strength and poor fatigue performance.Ti-6Al-4V contains toxic elements Al?V,its use has been greatly limited.To solve the above problems,two new Ti-Zr alloys,Ti-16Zr and Ti-50Zr(wt.%)alloys and a traditional medical Ti-6Al-7Nb(wt.%)alloy were studied in this paper.The effects of different cold,hot working and heat treatment processes on the microstructure and mechanical properties of the alloy were studied by optical microscope,XRD,SEM,TEM and universal electronic testing machine.The optimum strengthening process of the alloy was determined.The fatigue properties of the strengthened Ti-6Al-7Nb alloy were tested.The fatigue properties of Ti-16Zr and Ti-50Zr alloys were tested for smooth specimens and implants.The experimental results show that after solution treatment at 850? for 1 h(water cooling and air cooling),the mechanical properties of hot-rolled Ti-16Zr alloy such as hardness,strength and ductility did not change significantly;after cold working,the strength and hardness of Ti-16Zr alloy increased significantly,but the plasticity decreased.After annealing,the strength and hardness of cold-worked Ti-16Zr alloy decreased significantly and restored to the level of hot rolling.Cold-worked Ti-16Zr alloy meet the mechanical properties of implants,the strengthening mechanism is solid solution strengthening and dislocation strengthening,and the specific mechanical properties were:Rp0.2=8 13 MPa,Rm=852 MPa,A=14.1%,Z=51.9%,HV=311,?-1?380 MPa.After 700?/1 h solid solution treatment(air cooling),the strength and hardness of hot rolled Ti-50Zr alloy decreased,and the plasticity didn't change basically.The strengthening mechanism of hot rolled Ti-50Zr alloy is solid solution strengthening,fine grain strengthening and dislocation strengthening,and the specific mechanical properties were:Rp0.2=1001 MPa,Rm=1045 MPa,A=12.2%,Z=26.9%,HV=368,?-1?500 MPa.Heat treatment has a great influence on the microstructure and mechanical properties of Ti-6Al-7Nb alloy.With the increase of solution temperature,the hardness of Ti-6Al-7Nb alloy increased significantly.Aging treatment could further improve the hardness,and the hardness of the alloy reached the peak value after 980?/0.5 h water cooling+600?/6 h air cooling.The solution temperature had little effect on the tensile strength of the alloy,but the elongation and the reduction of area decreased with the increase of solution temperature Considering the effect of heat treatment on the tensile and fatigue properties of Ti-6Al-7Nb alloy,the optimum heat treatment process was 930?/0.5 h water cooling+600?/4 h air cooling.The strengthening mechanism of the alloy is fine grain strengthening and secondary phase strengthening,its specific performance was as follows:Rp0.2=920 MPa,Rm=982 MPa,A=16.3%,Z=47.5%,HV=353,?-1?490 MPa.All the indicators have reached the national standard for the processing of surgical implants with titanium and titanium alloys.The fatigue test results of implants show that under three conditions of air,artificial saliva and sandblasting acid etching,the fatigue limits of Ti-16Zr implants were 300 N,300 N and 200 N,respectively.Compared with air condition,the corrosion fatigue of Ti-16Zr implants in artificial saliva resulted in a decrease in fatigue performance.Under the condition of sandblasting acid etching,the increase of surface roughness is easy to cause stress concentration,which leads to the early formation of fatigue crack,which makes the fatigue limit decrease significantly.Under the three conditions of air,artificial saliva and sandblasting acid etching,the fatigue limits of Ti-50Zr implants were 400 N,400 N and 350 N respectively,and the fatigue performance of the implant was similar to that of Ti-16Zr implant.Under the same condition,the fatigue properties of Ti-50Zr implant were superior to Ti-16Zr implant,partly due to the higher strength of Ti-50Zr alloy than that of Ti-16Zr alloy.On the other hand,Ti-50Zr alloy contains more Zr elements,could promote the formation of the surface passivation film,enhance the stability of the passivation film,improve corrosion resistance,which will help improve the corrosion fatigue properties.