Study On The Cold Rolling Behavior And Related Problems Of New Biomedical Titanium Alloy

As its good biocompatibility,low modulus and moderate strength,titanium alloy has gradually replaced the traditional medical materials such as stainless steel and has been widely used in the replacement of artificial joints and the fixation of broken bones.Compared with pure titanium and alpha + beta titanium alloy,beta titanium alloy has lower modulus,better processing property and richer strengthening ways.Therefore,it has become the mainstream development direction of biomedical titanium alloy.However,the strength of the solid-solution beta titanium alloy is usually low,and the elastic modulus is high.By rolling,it can not only improve its strength,but also reduce the modulus of elasticity further as the martensitic transformation produced in the rolling process,making it more suitable for medical implants.In this paper,the solid-solution Ti-25Nb-10Ta-1Zr-0.2Fe(TNTZF,wt.%)titanium alloy is cold rolled at-30?,with its rolling reduction is 30~80%,and some samples are perform large deformation aging treatment.XRD,OM,SEM,Instron 3369 mechanical testing machine,electrochemical workstation and other means of observation and analysis are used,to invest the phase composition,texture evolution,mechanical properties and corrosion resistance of the TNTZF titanium alloy under different rolling reduction.The deformation mechanism is analyzed and discussed.The short-time aging treatment under 300?700? is performed on the sample with a reduction of 80%,to invest the short-time aging behavior,composition of the precipitated phase,and the mechanical properties of the alloy under large deformation.The main conclusions are as follows:1)Stress induced martensitic transformation occurs during cold rolling of TNTZF titanium alloy.On the whole,the content of martensite increases first and then decreases with the increase of rolling reduction.When the current pressure is 60%,the content of martensite is the largest.With the increase of deformation,the diffraction peak broadened gradually,which is caused by grain refinement and lattice distortion.The rolling reduction has an important influence on the lattice constant of TNTZF titanium alloy during the rolling process under-30 ?.The change of the lattice constant leads to the change of the stability of the beta phase,and then affects the martensitic phase content during the rolling process.As a whole,the lattice constant change curve is of type M with the increase of rolling reduction.When the rolling reduction is 60%,the lattice constant is the smallest,and the martensite content is the largest.Cross-slip is found in the process of cold rolling of TNTZF titanium alloy at-30 ?.When the rolling reduction is 50%,it is faintly invisible.A 45 degree angle slipe-band can be seen obviously when the rolling reduction between 60%and 80%.The main deformation mechanism of TNTZF titanium alloy is martensitic transformation and dislocation slip.2)The texture strength is not high In the process of cold rolling of TNTZF titanium alloy at-30?,and the y texture is main texture all the time,but with the increase of rolling reduction,the main texture is transformed from {111}<110>and {111}<112>Mixed texture to {111 }<112>texture.3)with the increase of rolling reduction,the strength of the alloy increases and the plasticity decreases continuously in the process of cold rolling of TNTZF titanium alloy at-30 ?,When the rolling pressure is 30 to 40%,the alloy has high strength and excellent plasticity,and the modulus of elasticity is also low.The martensitic phase transformation leads to the apparent softening section of the stress-strain curve in the cold rolling process of TNTZF titanium alloy at-30 ? and the length of softening section is directly positive correlation to the martensite increment.The effect of martensite content on tensile strength is not obvious,but the yield strength is greatly affected.4)On the whole,with the increase of rolling reduction,the corrosion resistance of the alloy decreases,but when the rolling reduction is more than 70%,the corrosion resistance increases.5)Large-deformation can accelerate the aging precipitation behavior of TNTZF titanium alloy.The tensile test results and the hardness show that the aging time is shortened,and the aging temperature is reduced compared with the undeformed aging.the tensile strength and the microhardness of the material can be significantly increased,but the plasticity of the material is reduced at the same time.Aging temperature has great influence on the composition and morphology of precipitated phase in large-deformation aging.As the aging temperature from low to high,the precipitated phase presents the following morphology in turn:uniform precipitation without directionality,precipitation in the form of a network along the slip band,fibrous or band-like precipitation.