Study On Compression Deformation And Dynamic Shear Instability Behavior Of Pure Ti And Ti-(0.02,0.04)wt.%N Alloys

Titanium alloys have many advantages,such as high specific strength and corrosion resistance.It is widely used in aerospace,weapon industry and other fields,and is a lightweight structural material with great potential.The dynamic mechanical properties and deformation behaviors of titanium alloys have attracted much attention due to the fact that titanium alloys are often subjected to shock waves when serving in such environments.The effects of A1 and V on mechanical properties,deformation mechanisms and plastic instabilities of titanium alloys under dynamic deformation have been reported.In this paper,the interstitial element N is introduced into high purity titanium,and the effects of N content on the quasi-static and dynamic compressive mechanical properties,deformation behaviors and dynamic shear instabilities of titanium alloys are studied.Firstly,the compressive deformation behaviors of pure titanium,Ti-0.02N and Ti-0.04N alloys under quasi-static(1×10-3s-1)and dynamic(3×103s-1)deformation conditions were investigated.The results show that all three alloys have strain hardening and strain rate hardening effects.It was found that twinning is an important deformation mechanism both under quasi-static and dynamic compression conditions by using EBSD technology.Through the calibration of twinning types,it was found that {1012} and {1122} twins occurred during the quasi-static compression deformation,and {1012},{1122} and{1121} twins occurred during the dynamic compression deformation.With the increase of N content,the quasi-static and dynamic strength of the three alloys increased,and the twinning types did not change.However,the statistical results showed that the proportion of twinning grains decreased with the increase of N content,indicating that the twinning behaviors were inhibited with the increase of N content.Subsequently,the calculation model of "Schmid factor" was used,and the critical twin Schmid factors corresponding to different types of twin production of three alloys under quasi-static and dynamic deformation conditions were obtained by using Schmid factor contour plot.It was found that the increase of N content caused the critical twin Schmid factor to increase both under quasi-static and dynamic compression,which may be the reason why the twinning behaviors of the alloys were inhibited with the increase of N content.Finally,the dynamic shear instability behaviors of pure titanium,Ti-0.02N and Ti-0.04N alloys were studied.Shear loading was performed using the dynamic shearing device and the shear stress-time curve was acquired to measure the maximum shear stress during dynamic shearing.The shear strain was measured by the change of the pre-scratch before and after the deformation of the specimen,and the critical instability shear strain was determined by the microstructure observation after shearing.The results showed that the addition of N element in pure titanium significantly increased the maximum shear resistance of the material,but the critical shear instability strain was significantly reduced.Microstructure analysis showed that under the dynamic shear conditions,the adiabatic shear failure occurred in all three alloys,and the proportion of each type of twins around the direct action zone of shear load decreased with the increase of N content.