| The biomedical titanium alloy has a wide application because of its good biocompatibility,corrosion resistance and mechanical properties.And a lot of hard tis sues such as artificial joints,teeth implants and restorative materials are manufactured by titanium alloy.The hot deformation behavior and microstructure evolution of thermal processing about Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy were studied.It has the great theoretical significance and practical value for optimizing hot working process and regulating microstructure of ? titanium alloy.The new medical Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy was prepared respectively by vacuum melting and Powder Metallurgy.The high temperature compression behavior of the vacuum melting alloy were performed with a Multifunction comparison meter.The high temperature compression behavior of the Powder Metallurgy alloy were performed with a Gleeble-1500 D simulator.Then the high temperature alloy deformation constitutive equations were established,and the thermal deformation behavior of the titanium alloy were studied.The processing maps based on dynamic model(DMM)of titanium alloy in different deformation conditions were constructed.To combine the microstructure analysis,the microstructure evolution and deformation mechanism at high temperature of Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy were investigated.The effect was had by powder metallurgical preparation parameters on microstructures and thermal deformation properties of Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy,the main research results are as follows:(1)The flow stress of the vacuum melting and Powder Metallurgy Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy during hot compression decreases with the increase of temperature and strain rate decreasing.They show the typical deformation characteristics of dynamic recrystallization.And the flow stress increases rapidly with strain increasing first,then the stress decreases after the strain more increases until it reaches a steady state.The thermal deformation activation is calculated by linear regression analysis and the constitutive equation of thermal deformation is obtained.(2)Vacuum melting Ti-14Mo-2.1Ta-0.9Nb-7Zr alloying buckling deformation occurred mainly in low temperature and high strain rate region,and areas of instability increases with strain.Its stable thermal processing thermal parameters are: the zone of a deformation temperatures range of 920?~930?and the strain rate range 0.01s-1~0.06s-1,and the other zone of a deformation temperature 990?~1000?and the strain rate range 0.01s-1~0.17s-1.During thermal deformation of powder metallurgy Ti-14Mo-2.1Ta-0.9Nb-7Zr,rheological instability region focuses on high strain rate region.During the deformation at low temperature and high strain rate,power dissipation rate ? is minimum and materials fall into the flow instability area so that surface crack.(3)With the increase of deformation rate,? phase of Powder metallurgy Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy gradually distorted from the original straight and wide,and dynamic recrystallization enhanced.Meanwhile,new nucleation are numerous and very small.With the increase of temperature,dynamic recrystallization increased.Moreover,the recrystal grains and flaky ? phase grew.(4)The flow stress of Ti-14Mo-2.1Ta-0.9Nb-7Zr alloy prepared by different parameters of Powder Metallurgy decreases with holding time and pressure decreasing.Before deformation,alloy porosity was lowered and lath ? phase grew up with holding time and preparation pressure increasing.With holding time increasing the elementa l ? phase and the pore grew up.The organization after deformation became short rod-like and nemaline to form the line along the vertical direction of the compression.The elemental ? was lengthened.The organization became more fine and the elemental ? phase became longer with holding time and pressure decreasing. |
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