Evolution Of Microstructure Of Medical Metal Microtube In Cyclic Rotating Bending Process

Medical metal microtubes are the raw materials for many medical instruments,such as cardiovascular metal stents,ureteral metal stents and lumbar puncture minimally invasive metal needle tubes.As implants,they need to possess a number of performance requirements including non-toxicity,non-rejection,strength,elasticity,corrosion resistance and wear resistance.In brief,the mechanical properties of metal microtube have a direct impact on the safety of medical implants.Generally,the passive film with coarse grains on the surface of material keeps loose and open,and its mechanical properties are poor.When the alloy is implanted into human body,the blood of human body acts as a flow electrolyte.The alloy matrix is easier to form chemical primary batteries with alloy components and accelerate the decomposition of matrix electrodes in primary batteries,which will greatly reduce the base.Compared with the coarse-grained materials,the passive film of fine-grained materials usually keeps a uniform and compact state,with excellent mechanical properties,low corrosion current and relatively slow decomposition rate of the alloy matrix,then it can have a certain corrosion resistance.Based on the principle of refining microstructure,severe plastic deformation(SPD)can greatly improve the mechanical properties of metal materials.In this paper,the evolution of microstructure of medical TA1 pure titanium micro-tubes with cyclic rotating bending(CRB)was investigated.The contents of this paper are as follows:(1)The design and development of the equipment of the CRB process for metal microtubes are completed according to the structural characteristics of metal microtubes and the technological characteristics of CRB process;(2)In order to investigate the influence of technological parameters on the evolution of microstructure of medical TA1 pure titanium microtubes,CRB experiments were conducted in different deformation conditions,in which the different deformation temperatures,deformation time,rotating speeds and bending angles were employed.(3)In order to study the microstructure of deformed metal microtubes,the optical microscope was adopted to observe the microstructures of specimens.(4)In order to research the stress-strain distribution and deformation behavior of medical TA1 pure titanium microtubes in CRB process,the numerical simulation of CRB process was conducted.The results of experiments and simulations show that the deformation temperature,bending angle,deformation time and rotating speed all have effects on the microstructure of medical TA1 pure titanium microtubes.The deformation temperature and bending angle have significant effects on the average grain size and the reduction rate of the average grain size.The average grain size of deformed specimen is 19.12?m,the reduction rate of grain size is 25.37%when the deformation temperature of 850?,bending angle of 173°,deformation time of 2min and rotating speed of 20rpm were employed,respectively.In addition,the average grain size of deformed specimens decreases with the increase of accumulated equivalent plastic strain.