Influence Of Initial Microstructure On Microstructural Evolution And Mechanical Behavior During Hot Deformation Of TC4 Alloy

TC4 alloy has been widely used in manufacturing aerospace structural components due to its characteristics of high specific strength,corrosion resistance and thermostability.During the thermal deformation,the deformation temperature,strain rate and reduction play important roles in the thermal deformation and microstructural evolution of TC4 alloy.Furthermore,the initial microstructure has an important influence on it.Therefore,study on the influence of initial microstructure on mechanical behavior and microstructural evolution is attractived,which could supply theoretical basis for building the thermal processing technology and improving the product quality of TC4 alloy.In the present study,the thermo-compressive behavior for TC4 alloy consisted of initial 30%and 100%volume fraction of lamellar structure have been studied,respectively.Based on the flow stress-strain curves,the thermal deformation behavior of two kinds of lamellar structures TC4 alloy under the changing thermal deformation conditions was investigated systematically.In addition,the microstructural evolution of these two kinds of alloys during thermal compression deformation was studied using optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The main conclusions obtained in the present study are as follows:(1)During thermal compression deformation,as the volume fraction of lamellar structure increased,the peak stress of TC4 alloy increased,but its corresponding strain decreased,indicating there existed the larger the volume fraction of lamellar structure in TC4 alloy,the stronger the capacity of deformation energy storage.(2)With the increasing deformation temperature,the flow stress reduced,but the flow stress increased as the strain rate increased,demonstrating that it is a positive strain rate sensitivity for TC4 alloy.(3)Based on the study on the microstructural evolution,it is easier that the dynamic recovery and the dynamic recrystallization occurred with the increasing deformation temperature.At low temperatures,it is the main deformation mechanism that the lamellar structure broken up along with dynamic recovery.Subsequently,with the increase of deformation temperature the fragmented lamellar structure tended to be equiaxed,led that it is easy to nucleate for dynamic recrystallization,resulting in an increased degree of dynamic recrystallization ultimately.(4)The degree of recrystallization decreased with the increasing strain rate.However,it increased as the reduction increased in fully lamellar structure TC4 alloy.