| Titanium alloy for dental implants is mainly Alpha-type titanium alloy.α-type titanium alloys have high plasticity,corrosion resistance and biocompatibility,but its strength is generally low and premature failure,and its product radius will compress the gums.Based on theα-type low Zr content Ti-3Zr alloy,a small amount of oxygen(x=0,0.05,0.10,0.15,0.20,0.25,0.30 and 0.40 wt.%)is added to the alloy by vacuum non-console smelting,supplemented by appropriate thermoplastic deformation to strengthen the alloy.Further improve the comprehensive physical and chemical properties of the alloy through the regulation of oxygen content,thermal deformation process and subsequent heat treatment process.The effects of different oxygen content,thermal deformation process and heat treatment process on the phase transition temperature,crystal structure,microstructure,mechanical properties and corrosion resistance of the alloy were discussed respectively by differential scanning calorimetry(DSC),optical microscopy(OM),X-ray diffractometry(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),electron backscattering diffractometry(EBSD),universal test and electrochemical workstation in order to find the oxygen content,the thermal deformation process and the heat treatment process under the optimal performance.With the increase of oxygen content,the phase transition temperature(T_β)of Ti-3Zr-xO alloy increases gradually,and the room temperature phase is a close-packed hexagonal alpha phase.The room temperature microstructure of the alloys is transformed from Widmanstatten structure into basket-waved structure,which then forms duplex structure and finally forms equiaxed structure.The thickness of the layer of Widmanstatten structure and the grain size of the equiaxed structure decrease with increasing oxygen content.The strength of the alloy increases significantly due to the combined effects of solid solution strengthening and fine grain strengthening caused by oxygen,and the plasticity decreases overall.Many nanometer-scale twins appear in the Ti-3Zr-0.25O alloy.The twins can store and accommodate dislocations and thus have a good toughening effect.Therefore,the alloy of the component has good plasticity while ensuring high strength,and has the best comprehensive mechanical properties.When the Ti-3Zr-0.25O alloy is plastically deformed at 800°C to 850°C,sufficient dynamic recrystallization will occur to form uniform and small equiaxed grains.At this time,the alloy has high strength and plasticity and has good corrosion resistance.As the hot rolling temperature increases,the size of the equiaxed grains grows significantly.At 900°C,the sheet structure begins to form in the alloy,and new{10`11}texture appears at 950°C.At 1000°C,the microstructure is completely transformed into sheet-like Widmanstatten structure.The mechanical properties of the alloy decrease with the increase of temperature in this temperature range.The hot rolling deformation of Ti-3Zr-0.25O alloy with different deformation reductions is carried out at 800°C.With the increase of rolling deformation reduction,the microstructure of the alloys is transformed into equiaxed grains of uniform size by equiaxed grains of different sizes and elongated along the direction of deformation.This is mainly caused by sufficient dynamic recrystallization of the alloy at a higher plastic deformation reduction.Under the influence of fine grain strengthening,the strength of the alloy increases gradually,the plasticity increases gradually and decreases at 90%deformation reduction,which is mainly due to the significant decrease in the number of twin boundaries of the alloy at 90%deformation reduction,and the loss of the toughening mechanism of nano-twins,resulting in a decrease in plasticity.The corrosion resistance of the alloy increases with the increase of the deformation reduction,which may be related to the decrease of the impurity concentration per unit grain boundary area due to grain refinement.The hot-rolled Ti-3Zr-0.25O alloy after annealing at 850℃and then cooled in the water is more uniform in stress concentration and uniformity,and the strength is comparable to that of the hot-rolled sample,and the plasticity is significantly improved.The strength and plasticity of the sample after air cooling have decreased.The corrosion resistance of the water-cooled sample after annealing at 850℃is higher than that of the hot-rolled alloy.The air-cooled sample has reduced corrosion resistance due to the precipitation of the needle-likeαphase.Through the above research and discussion,it is preliminarily concluded that the optimal oxygen doping amount of Ti-3Zr alloy with low Zr content is 0.25 wt.%.The alloy at this oxygen content has a good overall mechanical properties at about 800℃for hot rolling deformation reduction of about70%.Water cooling after annealing at 850℃can also significantly improve the plasticity of hot-rolled alloys.This provides a theoretical basis for the use of the alloy of this component on biomedical dental materials. |
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