Effect Of Microstructure On The Adiabatic Shear Behavior Of TC4 Titanium Alloy

Due to advantages of light weight,high specific strength,excellent resistance to acid and alkali corrosion,and good mechanical properties at high and low temperatures,TC4titanium alloy has been extensively used in the fields of aircraft industry,marine industry,national defense and military industry.In order to understand the deformation behavior in actual application event more accurately,it is necessary to conduct a systematic study of the mechanical behavior under dynamic loading conditions of TC4 titanium.In this paper,four types of equiaxed structure of TC4 titanium alloy with different primary?phase contents and three types of lamellar structure with different lamellar?_sphase thicknesses are obtained through different heat treatment dynamic deformation experiments under different stress states and different strain rates were conducted by Split Hopkinson Pressure Bar device.The microstructure evolution after dynamic deformation,were caracterized by electron backscatter diffraction(EBSD),scanning electron microscopy(SEM),and optical microscope(OM).The influence of the content of the primary?phase on the dynamic mechanical properties and adiabatic shear behavior of the equiaxed TC4 titanium alloy,and the influence of the thickness of the lamellar?_sphase on the dynamic mechanical properties and adiabatic shear behavior of the TC4 titanium alloy with the lamella structure were studied in the present paper.The main research results are as follows:By changing the annealing temperature in the dual-phase zone and the cooling rate after the?single-phase zone in the heat treatment process,four equiaxed structures and three lamella structure TC4 titanium alloys were obtained.With the increasing of annealing temperature,the content of primary?phase in the equiaxed structure gradually decreases;as the cooling rate after the solid solution in?single-phase zone decreases,the thickness of the lamella?_sphase gradually increases.Under dynamic compression loading conditions,the dynamic compressive strength of the equiaxed TC4 titanium alloy increases with the decrease of the primary?phase content,and its plasticity and impact absorption energy decrease gradually.The equiaxed TC4 titanium alloy exhibits obvious strain rate sensitivity,and it increase continuely with the decrease of primary?phase content.With the increase of the lamellar?_sphase thickness,the dynamic compressive strength of the lamellar structure TC4 titanium alloy gradually decreases,and its plasticity and impact absorption energy increase gradually.Lamellar structure TC4 titanium alloy also has obvious strain rate sensitivity,and it decreases gradually with the increase of the thickness of lamellar?_sphase.Under forced shear loading conditions,adiabatic shear bands were observed in the four types of equiaxed and three types of lamellar TC4 titanium alloy samples.Through the analysis of the stress collapse time and the microscopic morphology of the adiabatic shear bands,it was found that with the decrease of primary?phase content,the adiabatic shear sensitivity of the equiaxed TC4 titanium alloy decreases gradually.With the increasing of thickness of the lamellar?_sphase,the adiabatic shear sensitivity of the lamellar TC4titanium alloy shows a trend of decreasing first and then increasing,and the maximum thickness value of lamellar?_sphase appears at 0.94?m.The micro-hardness of adiabatic shear band of equiaxed and lamellar TC4 titanium alloy is obviously higher than that of matrix;The large number of equiaxed grains with low dislocation density in the adiabatic shear band are the result of dynamic recrystallization.