Research On Deformation Behavior Of Biomedical Ti-12Mo-3Nb Alloy

With the development of economy and the improvement of people's requirements for quality of life,more and more people have needs for limb correction and organ replacement.Biomedical metal materials are best used to replace damaged hard tissue.The main biomedical metal materials are medical stainless steel,cobaltbased alloys,titanium and its alloys.There are cytotoxic side effects,severe allergenicity,and other biological effects in medical stainless steel,cobalt-based alloys and traditional titanium alloys.In addition,their higher elastic modulus will bring about “stress shielding” phenomenon.However,? titanium alloy has low elastic modulus and good biocompatibility,and has become a hot topic in the research of biomedical titanium alloy.Therefore,the work focus on the hot deformation behavior of ?-type Ti-12Mo-3Nb alloy,the microstructure and mechanical properties and deformation behavior of its plate.The hot compression test results show that the flow stress is greatly affected by the deformation parameters.It decreases with the increase of the deformation temperature and the decrease of the strain rate.The analysis results of processing maps show that as the strain increases,the stable region becomes narrower.The power dissipation efficiency increases with the increase of deformation temperature,the decrease of strain rate and the increase of strain.The optimal hot working conditions is 900°C/0.01s-1.The microstructure evolution of dynamic recrystallization(DRX)can be predicted using the modified Avrami formula model.The analysis of the dynamic recrystallization kinetic curve shows that: DRX does not occur until the strain reaches the critical strain.When DRX is initiated,volume fraction of DRX grains increases with increasing strain.Under a specific strain,the volume fraction of DRX grains decreases as the strain rate increases and the deformation temperature decreases.Before the end of dynamic recrystallization,the fine DRX grains increase as the strain rate decreases and the deformation temperature increases.When the progress of DRX is completed,the increase of the deformation temperature and the decrease of the deformation rate lead to coarsened DRX grains.Flow localization is the cause of flow instability during hot-working process.The grain boundary slip occurs during hot deformation,and the deformation mechanism is dynamic recovery and discontinuous dynamic recrystallization.According to the results of hot deformation,the optimal deformation temperature and strain rate are determined,and then multi-step hot deformation is carried out.The experimental results show that as the number of deformation steps increase,the degree of DRX increases.According to the experimental results of multistep hot deformation,the rolling pass of the plate is determined.Furthermore,the final rolling process parameters are determined.Finally,observe the microstructure of the plate,test the mechanical properties and analyze the deformation behavior.The experimental results show that the microstructure of the original sheet of present alloy with 74.7% deformation and the solution treatment is a single ? phase,the microstructure is a single equiaxed grain,and the texture exists in the original alloy sheet.The microhardness test shows that the hardness value of the original sheet of 74.7% deformation is higher than the hardness value after solution treatment.The tensile property test shows that the plasticity of the present alloy sheet after 74.7% deformation after solution treatment is greatly improved.There are some cleavage steps,river patterns,a small number of dimples and tearing edges on the fracture of original plate.The tensile fracture is a quasi-cleavage fracture.After the solution treatment,the alloy fractures consist of dimples.The fracture after the heat treatment is a micro-hole aggregation-type ductile fracture.The microstructure of the 56.5% deformation plate after solution treatment is a single ? equiaxed crystal,and the phase structure is a single ? phase.In the process of compression deformation,when the amount of deformation is small,the present alloy deforms in a slipping manner without twins.As the amount of deformation increases,twins and ?'' martensite begin to appear.Finally,the deformation is carried out by means of slip,stress-induced ?'' martensite transformation and twinning.In the process of bending deformation,when the deflection is relatively small,present alloy only slips during the deformation process.As the deflection increases,the deformation mode is mainly slip,accompanied by the occurrence of twins.