Yield Behavior And High Temperature Deformation Of Medical Ti-Cu Alloy

Titanium and titanium alloys possess high specific strength and good biocompatibility,which are excellent medical implanation materials for joint prosthesis,bone trauma products,spinal orthopaedic internal fixation system,dental implant and denture,etc.The introduction of Cu element in titanium alloy can not only decrease the melting point of alloy,but also improve the wear resistance,biocompatibility and antibacterial property of alloy.Recent years,Ti-Cu alloy arouse the attention of many scholars,and research results show that the content of Cu in Ti alloy has great influence on its mechanical properties,such as the elongation rate,modulus and hardness,etc.At present,most of the research on Ti-Cu alloys is concentrated on its microstructure,antibacterial properties,compression or tensile strength.However,as a substitute for teeth,bones or joints,the medical Ti-Cu alloy is often in a complex environment or subjected to complex stress states,during the process of chewing food or human motion,or in the process of manufacturing.Therefore,it is necessary to study the composition design,wear resistance and mechanical properties of Ti-Cu alloy under various working conditions.Considering the processing and using environment of Ti-Cu alloy,the mechanical response of Ti-Cu alloy under different loading conditions and temperature conditions is analyzed in this paper.The specific research contents and conclusions are as follows:（1）Ti-Cu alloy were prepared by sponge titanium and metal copper.The phase composition and microstructure of Ti-Cu alloy were characterized by XRD and SEM.The influence of loading mode and loading and unloading parameters on hardness and elastic modulus of Ti-Cu alloy were analyzed by nano indentation system.The results show that the Ti-Cu alloy are composed ofα’phase and Ti₂Cu phase.Compared with cyclic loading and constant load,relatively high elastic modulus and hardness of Ti-Cu alloy was obtained by the continuous stiffness method.Loading rate has little effect on the measured value,but unloading rate has great influence on the measurement results.With the increase of unloading rate,elastic modulus decreased,and the hardness increased.The precipitation of Ti₂Cu phase can effectively improve the strength of the material.（2）The dynamic and static mechanical properties of Ti-Cu alloy under uniaxial compression,tensile,and shear test are measured and analyzed.We focuses on the response of Ti-Cu alloy under combined shear-compression.The mechanical behavior,deformation mechanism,and experiments yield surface of Ti-Cu alloy under various stress states were analyzed and the effect of strain rate on yield behavior of Ti-Cu alloy is studied as well.The results show that with the increase of strain rate,the yield loci of Ti-Cu alloy has almost isotropic expansion trend.（3）By comparing the degree of anastomosis between experimental results of Ti-Cu alloy under different loading states and several theoretical yield criterions,it is found that the Cazacu-Barlat criterion,which takes into account the asymmetric effect of tensile and compression,can describe the yield behavior of Ti-Cu alloy well.On this basis,the Cazacu-Barlat criterion is improved,and a rate dependent Cazacu-Barlat yield criterion is proposed,which enriches the application range of rate dependent yield criteria.（4）The compression test of Ti-Cu alloy at high temperature was carried out,and the effect of temperature and strain rate on the mechanical properties of the alloy was analyzed.The results show that when the temperature is constant,the flow stress increases with the increase of strain rate.When the strain rate is constant,the flow stress decreases with the increase of temperature.The high temperature constitutive model of Ti-Cu alloy is also constructed based on the Arrhenius constitutive equation with a hyperbolic sine form.The model can accurately predict the high temperature flow stress and can describe the deformation behavior of Ti-Cu alloy at high temperature.