Research On Hot Deformation Behavior And Microstructure Evolution Of Ti-4Al-2.5V-1.5Fe Titanium Alloy

Ti-4Al-2.5V-1.5Fe alloy is a low-costα+βdual-phase medium-high strength titanium alloy developed on the basis of Ti-6Al-4V alloy.The mechanical properties of this alloy are similar to those of Ti-6Al-4V alloy.Because of using cheap Fe element to replace some expensive V element,the material cost is reduced,and the grain size can be refined and the alloy strength can be improved.Ti-4Al-2.5V-1.5Fe alloy has good ductility,superplasticity and high strength.It can not only be hot processed but also cold processed.It can be processed into various forms of products such as plates,strips,pipes and so on.It has a broad application prospect.However,there is little research on the relationship between the deformation mechanism,softening mechanism,microstructure evolution and different deformation conditions in the process of hot deformation,and there is no basis for formulating and optimizing the hot working process of the alloy.So it is difficult to provide theoretical guidance for the industrial preparation and processing of the alloy.Based on the above reasons,this article uses the Ti-4Al-2.5V-1.5Fe alloy after two vacuum consumable arc furnace melting and blank forging to conduct Gleeble single-pass and multi-pass cooling and compression experiments to simulate the process of tube extrusion and multi-pass hot rolling of plates.The thermal deformation behavior and microstructure evolution of the alloy under different deformation temperature,strain rate and total deformation amount were studied.The following conclusions are obtained:After single pass thermal compression of Ti-4Al-2.5V-1.5Fe alloy at 800～1000℃and strain rate 0.01～1s^-1,the stress gradually decreased with the increase of deformation temperature and the decrease of strain rate.The thermal activation energy of the alloy is Q=513.1241KJ/mol,and the constitutive equation is.?=2.0557×10²¹[sinh（0.0142σ）]^4.3331exp（-513124/RT）.The deformation instability zone is predicted to be low temperature and high strain rate region by hot working diagram..After single pass hot compression,under the condition of low temperature and high strain rate,the structure of the alloy is mainly elongated lamellar grains,the grains show a dynamic deformation streamline in a certain direction;with the increase of deformation temperature and the decrease of strain rate,the deformed grains gradually spheroidize and turn into equiaxed grains,the grain size increases and the distribution is more uniform.Moreover,fine recrystallized grains began to form in the microstructure.According to the analysis results of the deformation behavior and microstructure evolution of Ti-4Al-2.5V-1.5Fe alloy under single pass hot compression,the results show that the microstructure and properties of the alloy are optimized,the equiaxed grains are increased,the grains are fine and evenly distributed under the parameters of 900～950℃and the strain rate is0.01～0.1s^-1.At this time,the deformation resistance of the alloy is reduced,which is conducive to plastic processing.Therefore,the suitable extrusion process parameters of the alloy tube are determined as temperature 900～950℃,strain rate 0.01～0.1s^-1.After multiple cooling thermal compression of Ti-4Al-2.5V-1.5Fe alloy under the condition of 800～1000℃and strain rate 0.01～1s^-1,the flow stress gradually decreases as the deformation temperature increases and the strain rate decreases However,as the number of compression channels increases,the peak stress of the alloy gradually increases.The results show that the softening rate increases with the increase of deformation temperature and the decrease of strain rate,but decreases with the increase of compression number.After multi-pass temperature reduction and thermal compression,the spheroidized structure gradually changes into equiaxed with the increase of deformation temperature and the decrease of strain rate.The grain size increases and the distribution is more uniform,and the proportion of dynamic recrystallized grains increases.At the same time,the small angle grain boundary began to change into the large angle grain boundary,and the texture strength and direction changed.According to the analysis results of the deformation behavior and microstructure evolution of Ti-4Al-2.5V-1.5Fe alloy in multi-stage cooling hot compression,the deformation resistance of the alloy is reduced when it is compressed at high temperature and low strain rate,and the dynamic recrystallization in the structure causes the softening phenomenon of the alloy,and the structure is optimized.Finally,the suitable hot rolling process parameters range of the alloy plate is 950～1000℃,and the strain rate is 0.01～0.1s^-1。By analyzing the thermal deformation behavior and microstructure evolution in the process of multi-pass compression,the deformation resistance of the alloy with high temperature and low strain rate was reduced,and the alloy is softened due to dynamic recrystallization in the microstructure.Finally,the appropriate hot rolling process parameters of the alloy plate are optimized at 950～1000℃,and the strain rate is 0.01s^-1.In conclusion,by studying the thermal deformation behavior and microstructure evolution of Ti-4Al-2.5V-1.5Fe alloy in the process of single pass and multi pass cooling and hot compression,the relationship between work hardening,stress-strain relationship,softening mechanism,microstructure evolution and deformation bars in the process of hot deformation is revealed.Combined with the relevant research work and production practice,the hot working process parameters of the alloy are formulated and optimized,which can provide theoretical basis and technical guidance for the industrial preparation and processing of Ti-4Al-2.5V-1.5Fe alloy extruded pipse and hot rolled plates.