Molecular dynamics study of the effect of temperature on the shock response and plastic deformation mechanism of CoCrFeMnNi high-entropy alloys

Abstract

High-entropy alloys have broad application prospects in aviation,aerospace,military and other fields due to their excellent mechanical properties.Temperature is an important external factor affecting the shock response of high-entropy alloys.Molecular dynamics methods are used to investigate the effect of temperature on the shock response and plastic deformation mechanisms of CoCrFeMnNi high-entropy alloys.The effects of temperature on the atomic volume and the radial distribution function of CoCrFeMnNi high-entropy alloys are studied.Then,the piston method is used to generate shock waves in the sample to research the shock response of CoCrFeMnNi high-entropy alloys.The polyhedral template matching method is used to observe the evolution of atomic-scale defects during the shock compression.The results show that the shock pressure,the shock wave propagation velocity,and the shock-induced temperature rise decrease with the increase of the initial temperature.For example,when piston velocity <i>U</i><sub>p</sub>=1.5 km/s,the shock pressure at an initial temperature of 1000 K decreased by 6.7% compared to that at 1 K.Moreover,the shock Hugoniot elastic limit decrease linearly with the increase of temperature.The Hugoniot <i>U</i><sub>p</sub>- <i>U</i><sub>s</sub> curve of CoCrFeMnNi HEA in the plastic stage can be linearly fitted by the formula <i>U</i><sub>s</sub>=<i>c</i><sub>0</sub>+<i>sU</i><sub>p</sub>.<i>c</i><sub>0</sub> decreases with increasing temperature.With increasing shock intensities,CoCrFeMnNi high-entropy alloys undergo complex plastic deformation,including dislocation slip,phase transformation,deformation twinning,and shock-induced amorphization.At relatively high initial temperature,disordered clusters appear inside CoCrFeMnNi HEA,which together with the BCC structure transformed from FCC and disordered structure are significant dislocation nucleation sources.Compared with other elements,Mn element has the largest proportion (25.4%) in disordered clusters.Due to the large atomic volume and potential energy,large lattice distortion and local stress occur around the Mn-rich element,which provides dominant contribution to shock-induced plastic deformation.At high temperatures,the contribution of Fe element to plastic deformation is as important as that of Mn element.The research results contribute to a deep understanding of the shock-induced plasticity and deformation mechanisms of CoCrFeMnNi high-entropy alloys.