Study On Preparation Of Tantalum-Titanium Composite And Tantalum Bioactivity

Titanium alloys are the most widely used metal implant materials because of its excellent mechanical properties,good biocompatibility.However,titanium alloys are biologically inert and can release toxic elements in human body.Tantalum,as a new type of hard tissue repair material,has better biocompatibility and corrosion resistance than titanum alloy but is expensive.The preparation of tantalum as a coating on the surface of titanium alloy can not only utilize the excellent properties of tantalum but also reduce the cost of the product,which is an important research field in the field of hard tissue repair materials.This paper first proposed the preparation of a tantalum layer on the surface of titanium alloy by hot rolling.Firstly,the hot rolling process was simulated by Gleeble thermal simulator to study the effects of thermal simulation temperature and annealing on the interface bonding and metallographic of the composites.The results showed that tantalum-titanium composite with metallurgical bonding interface can be obtained by simulating hot rolling at 950℃and 1050℃.The interface forms a certain thickness of atomic diffusion layer,which can coordinate the inconsistent shrinkage deformation of tantalum and titanium alloy during cooling,and avoid the formation of cracks,pores and other defects at the interface after cooling.The microstructures of the titanium alloy layer obtained at 850℃,950℃and 1050℃were in the form of fibrous bimodal structure,β-transformation structure and Widmanstatten structure,respectively,with the phenomenon of work-hardening.After annealed at 850℃for 40 min,duplex microstructures recrystallized and changed into equiaxed grains,and more acicularαphase precipitates in theβ-transformation and Widmanstatten structure.Tantalum layer grains of 850℃,950℃thermal simulation samples appear fibrous.After annealing,a small amount of recrystallization occurred.During thermal simulation of 1050℃compression,dynamic recrystallization occurs on tantalum layer,grain equiaxed.Based on the thermal simulation experiment,a large-scale hot rolling processes were designed and the effects of different hot-rolling processes and post-hot-rolling annealing temperature on the interfacial bonding,metallographic,room temperature tensile and interfacial bonding strength were studied.The results showed that the tantalum-titanium composite plates with metallurgical bonding can be prepared by compressing more than50%of the tantalum and titanium alloy plates at 980℃and 1050℃hot rolling temperature.The minimum shear strength at the interface of the composite board is higher than 180.9MPa;the hot rolling temperature of the composite board should be controlled around the phase transition temperature of the titanium alloy.There are two resaons.Firstly,the high temperature can ensure higher plasticity of the sheet during hot rolling,promote interfacial bite and atomic interaction diffusion,enhance the interface with the intensity.Secondly,the hot rolling temperature near the transformation point can prevent the rapid growth ofβgrains of titanium alloy to form the wei’s tissue or strip basket structure,and affect the ductility of the composite sheet;the annealed ductility of 980℃hot-rolled composite sheet after being annealed at 750℃for 1h increase.The heat treatment temperature of 1050℃hot-rolled composite plate should be controlled below900℃,to prevent the emergence of sheet layered basket organization in titanium alloy tissue,reduce the plasticity.As a metal material,tantalum can not form osseointegration with bone tissue.This paper studies the surface modification of tantalum by two ways.Firstly,the active layer was prepared on the surface of tantalum by alkaline treatment and pre-calcification.The effect of alkali concentration and pre-calcification on the surface morphology and bioactivity of tantalum was studied.The second was to build a bionic micro-porous structure on the surface of tantalum by micro-arc oxidation,The surface of the micro-nano porous material can promote cell adhesion,proliferation,is an ideal implant surface.The effects of electrolyte system,oxidation time and current density on the morphology of the surface coatings were investigated.The results showed that,by alkali treatment,tantalum can be transformed into bioactive material to improve its ability to form HA in SBF.Alkali treatment concentration should be controlled below 1.0M,above 1.0M,the surface active layer prone to shedding.Low concentration alkali can’t react with tantalum to form an active layer.In this group of experiments,the best concentration of alkali treatment is0.7M;Pre-calcification can further increase the bioactivity of tantalum after alkali treatment.Alkali-treated samples can complete the nucleation process of calcium-phosphorus compounds during the pre-calcification process.After immersing in SBF,the nucleated calcium-phosphorus compounds are transformed into HA to shorten the HA nucleation time.Tantalum after 0.7M alkaline treatment and pre-calcification,soaked in SBF for 4 days,the surface can be covered by the HA layer,greatly improving the biological activity of tantalum;Using Na₂SiO₃ as electrolyte,the tantalum oxide ceramic layer of micro-arc oxidation tantalum is more compact,suitable as a corrosion-resistant,wear-resistant coating.When using Ca（CH₃COO）₂ electrolyte,the ceramic coating layer with micron porous structure can be obtained,which is suitable for the ideal surface of metal implanted material.With the increase of current density,the number of micropores increases and the macropore diameter increases.At high current density,calcium ions in the electrolyte can also be doped into the film layer.