Preparation Of Biomedical Titanium Alloy By Powder Metallurgy

Titanium alloy materials have become the representative of high-performance metal materials due to their excellent properties,and have been widely used in biomedicine.However,on the one hand,conventional titanium alloys have elements such as nickel,aluminum and V,which are toxic and allergenic.On the other hand,their elasticity modulus is still higher than that of human bones,which can cause stress shielding and cause loose or fracture of the implant after implantation of an orthopedic implant with incompatible elastic modulus.In order to overcome the above problems,a new generation of non-toxic medical titanium alloys with lower modulus and better biocompatibility has been developed in recent years,in which Ti-24Nb-4Zr-8Sn(Ti2448)has a low elasticity modulus of.High and good corrosion resistance have attracted the attention of many scholars.In this paper,Ti2448 alloy with excellent performance was prepared by powder metallurgy near net shape forming technology.The effects of different processing parameter on the microstructure of the alloy were studied.The factors such as density,oxygen content and phase content were analyzed,and the influence of mechanism was summarized.The effect of different processing parameter on the mechanical properties of the alloy was studied.A method for preparing low elastic modulus,high strength and high plasticity Ti2448 alloy was proposed.The deformation mechanism of the alloy was characterized and revealed,which revealed the mechanism that led to its excellent performance.Firstly,the powder metallurgy sintering process was studied.DSC was used to analyze the phase transition,sample density and oxygen content difference during sintering.The phase transition temperature of the α phase to the β phase is determined,which provides a theoretical basis for the subsequent heat treatment process.The green compacts of different densities were obtained under different pressures,and the optimized pressing pressure under the conditions of the samples was 700 MPa.Both sintering and heat treatment are carried out at elevated temperatures,which can result in an increase in the oxygen content of the sample.Secondly,the microstructure of samples prepared by different processing parameteres was analyzed.From the results of microstructure analysis,it is known that the as-sintered alloy consists of the matrix β phase and the needle-like α phase,and the α phase precipitates from the grain boundary of the high-temperature stable β phase to the intragranular diffusion,and as the sintering temperature increases,the distribution of α phase also becomes more uniforms.The hot isostatically treated sample also consisted of a beta phase and an alpha phase,but the alpha phase content increased.The microstructure of the quenched sample is mainly the β phase,because the β phase does not have time to be converted into the α phase because the cooling rate is faster,that is,when quenching.Then,the mechanical properties of samples prepared by different processes were analyzed.From the results of the nanoindentation test,the elastic modulus and hardness of the α phase are higher than that of the β phase.Combined with the microstructure analysis,the mechanical properties of the sintered and hot isostatically treated samples are significantly lower than those of the quenched samples.The presence of a large amount of alpha phase results in embrittlement of the sample,which,although higher in strength,sacrifices the plasticity of the alloy and increases the elasticity modulus.The optimized process parameters under the experimental conditions were obtained: sintering temperature was 1400 ℃,quenching temperature was 980 ℃,the elastic modulus was 57.2 GPa,the strain rate was 19.33%,and the ultimate tensile strength was 725 MPa.Finally,the deformation mechanism of the optimal process parameters was characterized.The surface morphology,the microstructure,the distribution of element and the material equivalent of the samples before and after the tensile test were analyzed by AFM,SEM and TEM.The experimental results show that the martensitic transformation of the S14+Q980 sample during the stretching process is the cause of the excellent mechanical properties of the sample despite its manufacturing process,especially its high plasticity without sacrificing too much strength.