Study On Hot Deformation Behavior Of Ti-5.5Al-3Nb-2Zr-1Mo Titanium Alloy

Ti-5.5Al-3Nb-2Zr-1Mo titanium alloy is a near-?type titanium alloy.It has the characteristics of medium strength,high plasticity,high toughness,corrosion resistance,and excellent weldability and is an ideal metal material for marine environment.In order to find out a reasonable hot working process for titanium alloys and control the microstructure and properties of titanium alloy components,the research on the hot deformation behavior,microstructure evolution and dynamic phase transformation laws of titanium alloys has important theoretical significance and application value.This article takes Ti-5.5Al-3Nb-2Zr-1Mo titanium alloy as the research object.The thermal deformation behavior at the temperature range of 855??1015?,strain rate range of 0.001s^-1?10s^-1,and the amount of deformation is 30%and 60%.The thermal deformation behavior within the range is studied,and the microstructure evolution and dynamic phase transformation laws are characterized and analyzed by metallography,scanning electron microscopy,and electron backscatter diffraction.The research contents are as follow:1.Titanium alloy undergoes obvious dynamic softening during hot compression,and the flow stress decreases with the increase of deformation temperature and increases with the increase of strain rate.Based on the experimental data of the true stress-strain curves,the constitutive equation of the alloy is constructed,and the thermal deformation activation energy of the titanium alloy in the(?+?)phase region is 644kJ/mol,and the thermal deformation activation energy in the ? phase region is 242kJ/mol.2.Based on the dynamic material model(DMM)and Prasad instability criterion,the processing map within the range of experimental conditions is drawn.The results show that when the strain rate is 0.001^-1?0.1s^-1,the value of the power dissipation factor is higher.Combined with the power dissipation diagram,it can be determined that the ideal processing temperature range of Ti-5.5Al-3Nb-2Zr-1Mo titanium alloy is 860??910?,the strain rate is between 0.001^-1?0.1s^-1.3.The microstructure evolution and dynamic phase transformation of the alloy were studied and analyzed,and the high-temperature ? phase was reconstructed according to the Burgers orientation relationship between the needle-like?phase precipitated by cooling and the original ? matrix.The results show that the main softening mechanism of titanium alloy in the(?+?)phase region is dynamic recrystallization,and a large number of fine recrystallized grains and high-angle grain boundaries have formed at the deformed grain boundaries;in the ? phase region,the softening mechanism is dynamic recovery.After deformation,the coarse ? grains have transformed into slender needle-like ?-phase structure interlaced in the grains after cooling;according to the orientation of the needle-like ? phase,the high-temperature ? phase is reconstructed,and it can be found that the high-temperature ? phase are coarse ? grains.When the cooling starts,the needle-like ? phase is precipitated inside the original ? grains.