Anisotropy Of Adiabatic Shear Behavior Of TC4 Titanium Alloy

Due to the comprehensive mechanical properties,titanium and its alloys have been widely used in aviation,aerospace and other industries.However,in some occasion,titanium alloys structure components need to bear high impact loading in some specific environments.Therefore,it is important to study the deformation behavior of titanium alloys under high strain rates condition,which can provide reference for the application and performance optimization of titanium alloy and provide theoretical support for the application of complex working environment.In this paper,high-speed impact loading tests of extruded TC4 titanium alloy were carried out by split Hopkinson pressure bar(SHPB)in extrusion direction(ED)and extrusion radial direction(ERD),and at room temperature and 100 ?,200 ?,300 ? and 400 ?.The true stress-strain curves of cylindrical specimen and the time voltage curves of hat-shaped specimen were obtained under different strain rates.The dynamic mechanical properties of TC4 alloy were studied quantitatively as well.Scanning electron microscope(SEM),optical microscope(OM)and electron backscatter diffraction(EBSD)were used to observe the microstructure of the samples before and after the experiment,in order to study the anisotropy of TC4 titanium alloy under high speed impact loading,and explore the effects of loading directions and strain rates on the mechanical properties and failure modes of TC4 titanium alloy.The results show that the cylindrical specimens of extruded TC4 titanium alloy have the feature of continuous deformation yield under high strain rates compression.The microstructure shows that with the increase of strain rate,the white ? phase in the structure will be elongated along the loading direction.At the same time,with the increase of strain rate,the maximum compressive stress increases gradually,and there is a positive strain rate strengthening effect.At room temperature,slip is the dominant deformation mode of TC4 alloy.At high temperature,slip is still the main deformation mode due to the decrease of critical resolved shear stress.For titanium alloy hat-shaped specimen,the adiabatic shear sensitivity of ED direction is higher than that of ERD direction,and micro cavities will form in the adiabatic shear band,and and they merge along the shear direction to form macro cracks.The difference of adiabatic shear sensitivity in ED and ERD directions is mainly due to the different grain size in shear band.With the increase of strain rate,the width of adiabatic shear band will be decreased.However,with the increase of deformation temperature,the width of adiabatic shear band will be increased,and the anisotropy of adiabatic share behavior in ED and ERD will be gradually weakened.When the deformation temperature is above 300 ?,the deformation behavior is basically the same,and the difference between strain hardening rate and microstructure in the two directions becomes small,implying that the deformation anisotropy of TC4 titanium alloy under high strain rates at high temperature was decreased.