| Objective:A new titanium alloy (Ti-12.5Zr-3Nb-2.5Sn) was developed to meet the needs of clinical requirements for medical titanium alloys and improve the properties of existing titanium alloys.The microstructures, mechanical properties of Ti-Zr-Nb-Sn alloys were investigated to optimizes the alloying constituent.The compatibility wear resistance,corrosion resistance and casting characteristic of selected Ti-12.5Zr-3Nb-2.5Sn alloy that has the excellent properties have been studied.Methods:1. Design, optimize and preparation of alloy:Ti, Zr, Nb, Sn were selected as alloy elements. According to DV-Xa cluster method,design of alloy composition as Ti-xZr-yNb-2.5Sn (x=2.5,10,12.5,15, y=0,1,2,3,4,5,10,15,20) The microstructures, mechanical properties of Ti-Zr-Nb-Sn alloys were investigated to optimize the alloying constituent. Ti, Zr, Nb, Sn were selected as alloy elements. According to proportion of Ti-12.5Zr-3Nb-2.5Sn (wt%), the differential thermal analysis curve were investing. In order to optimize mechanical property, the samples were further aged at different conditions in vacuum resistance furnace and cooled in the furnace.2. Evaluation of mechanical properties:The mechanical properties was tested by universal tensile test machine after quenching process at 850℃for 1.5 hours and aging treatment at 850℃for 3 hours; the microstructure and the fracture morphology were scanned and observed; the alloy microstructure was analyzed with X-ray diffraction phase.3. Evaluation of wear resistance properties:A loading wear test was done by MMV-1 Vertical universal friction and wear testing machine. Ti-Zr-Nb-Sn alloy were two-body wear tested in vitro while the Pure Ti was used as control.Wear resistance was analyzed through measuring the volume wear loss, Wear surface morphology was observed with electron microscope, Debris element analysis was carried out.4. Evaluation of corrosion resistance:In simulated oral environment, the electrochemical behavior of Ti-Zr-Nb-Sn alloy for dental restoration was investigated together with that of Ti-6A1-4V and TA2 as control groups. The anodic polarization curve and polarization resistance of these alloys were analyzed and the element release of Ti-12.5Zr-3Nb-2.5Sn and Ti-6A1-4V alloy after immersion in artificial saliva forld,2d,3d,5d,7d,15dwere measured.5. Evaluation of biological performance:The cell toxicity test, toxicity test, oral mucosa stimulate experiment and sensitization experiments was made to study the biological safety of the new titanium alloys and evaluate its biological properties.6. Evaluation of casting performance:Samples were casted by LZ5-centrifugal casting machine, to study casting temperature of the titanium alloy and to test the alloy casting flow rate, evaluation of alloy casting reaction layer and linear shrinkage.Results:1. The Ti-xZr-yNb-2.5Sn alloy, when the Zr content was the 12.5%, Nb content was 3%, compared with other allocated proportion alloy, had the high tensile strength and elongation ratio, the elasticity coefficient. The mechanical property was good.2. The transition point of alloy was between 769.9 and 841.1℃. The organization was quite chaotic and the crystal boundary was not obvious when the aged temperature was 200℃and 350℃. When the aged temperature was 500℃the organization was quite clear and equiaxed grain was sizeable. But grain was very coarse at 700℃.3. Organizational structure and mechanical properties. The tensile strength, yield strength, elongation and elastic modulus hardness of alloy were 652±34.5MPa,of 590±29.8MPa,93.8±7.9GPa,28.3±2.4% respectively. It clearly showed necking phenomenon. Specimen fracture electron microscopy revealed the formation of organizations in the expansion area. In the metallographic structure, it was showed that the distribution of needle-like a in the thick of (3 grains. XRD display alloy was nearly a-Ti.4. As loads increased, the wear loss of Ti-Zr-Nb-Sn alloy increased.Under 20,50 and 100 N loads, the dominant wear form was different. Volume wear loss and rigidity value of Ti-Zr-Nb-Sn alloy, natural enamel were higher than that of TA2(P< 0.05). The main wear mechanism of Ti-Zr-Nb-Sn alloy was abrasive wear, and enamel and TA2 were adhesion and abrasive wear. Debris element analysis demonstrated that the major component of Ti-Zr-Nb-Sn alloy was Ti, Zr, and Sn, but no Nb; while, the major component of pure TA2 was Ti.5. Polarization curve indicated that Ti-6Al-4V alloy had lower breakdown potential (Eb 0.8V) than Ti-12.5Zr-3Nb-2.5Sn alloy did (> 2.5V). Ti-6Al-4V alloy showed higher passivation current density than Ti-12.5Zr-3Nb-2.5Sn alloy did. The polarization resistance volume Ti-12.5Zr-3Nb-2.5Sn alloy was higher than TA2. With the increasing of dipping time in artificial saliva, the ion release of Ti-12.5Zr-3Nb-2.5Sn alloy and Ti-6Al-4V alloy increased to different degrees. Ti-6Al-4V alloy always showed more ion release than Ti-12.5Zr-3Nb-2.5Sn alloy did in the experiment.6. Biology experiment showed that the alloy cytotoxicity reaction level was 0; no acute toxic reactions, irritation to the oral mucosa, or skin sensitization.7. Casting properties. The casting flow rate was 100% when the alloy were casted at 400℃. Linear shrinkage and the surface reaction layer met the demand.Conclusions:1. The optimized composition of alloy was Ti-12.5Zr-3Nb-2.5Sn. Heat treating regime was quenching process at 850℃for 1.5 hours and aging treatment at 850℃for 3 hours.The mechanical properties were surprior to Titanium obviously, after quenching process and aging treatment.2. The increase of loads enlarges the wear loss of Ti-12.5Zr-3Nb-2.5Sn alloy and changes its dominant wear form. The Ti-12.5Zr-3Nb-2.5Sn alloy had good surface wear resistance than pure Ti and were suitable for dental restoration application.3. Ti-12.5Zr-3Nb-2.5Sn alloy, as well as pure Ti, were superior to Ti-6Al-4V in corrosion resistance.4. Biology experiment showed that the alloy had the good Biological compatibility.5. The surface reaction layer and linear shrinkage met the accuracy requirements of dental demands. |
