Dynamic Shear Behavior Of CoCrNiSi_0.3 Medium Entropy Alloy

The high-entropy alloy is a new class of alloy different from traditional alloy.The design principle of high entropy alloy is to maximize configuration entropy,and each element forms simple solid solution structure according to equal or nearly equal mole ratio.It’s unique design principle lend it excellent comprehensive mechanical properties,such as high strength,large plasticity,high hardness,wear resistance,corrosion resistance,oxidation resistance,excellent resistance to high temperature softening and low temperature embrittlement performance,so it has broad application prospects in aerospace,national defense science and technology and other extreme service environment.At present,most studies on the mechanical behavior of high-entropy alloys are limited to quasi-static loading,but in the actual service processing,the high-entropy alloys are mostly subjected to dynamic loading.Therefore,investigate of the dynamic mechanical properties of high-entropy alloys is urgently needed.Adiabatic shear behavior is a common phenomenon when materials are subjected to impact loading.The appearance of adiabatic shear band means that the material is almost up to fracture or failure.Therefore,adiabatic shear should be avoided in most engineering applications.There are few studies on the adiabatic shear behavior of high-entropy alloys at present.In this paper,we successfully studied the dynamic shear behavior of CoCrNiSi_0.3alloy.The main contents are as follows:（1）The quasi-static and dynamic compression tests of CoCrNiSi_0.3 medium entropy alloy were carried out with strain rates of 10^-4s^-1,,10^-2s^-1,2150s^-1,3350s^-1 and 5150s^-1,respectively.It is found that the mechanical behavior of this alloy is sensitive to strain rate and has a positive strain-rate sensitivity.By analysing deformation microstructure and texture of the deformed sample using electron back scattering diffraction（EBSD）combined with Channel 5 software,it is found that the alloy subjected to high strain rate loading exhibits a higher twin formation ability than quasi-static loading,and more recrystallization grains are produced as well as a stronger work-hardening capacity under dynamic loading conditions.After compression deformation,the deformation texture evolution tends to be E{111}<110>type.（2）The dynamic shear behavior of CoCrNiSi_0.3 hat-shaped specimen was studied using Split Hopkinson Pressure Bar.The"freezing"experiment was carried out to observe the dynamic shear process by considering the influence of different reserved shear band widths.Under dynamic load,the deformation of hat-shaped specimens concentrates on the corner,and a gap appears at the corner with the aggravation of the deformation degree.Under shear,the intra-grain texture evolves in a specific direction.（3）Based on the crystal plasticity finite element,the dynamic shear behavior of the CoCrNiSi_0.3 alloy can be simulated,in which the required parameters for the model are successfully fitted.The data from different deformation stages during dynamic shear are also extracted and the orientation distribution function diagram is thus received by JTEX software.And the volume fraction of typical texture was further calculated.With the increase of shear deformation,the content of E+F texture increases obviously,and the shear loading plays an important role in the evolution of texture.