温度对CoCrFeMnNi高熵合金冲击响应和塑性变形机制影响的分子动力学研究

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

高熵合金作为一类新兴合金材料,由于其优异的力学性能,在航空、航天、军事等领域具有广阔的应用前景.本文利用分子动力学方法,探讨了温度对CoCrFeMnNi高熵合金冲击响应和塑性变形机制的影响.研究发现,初始温度的增加使得冲击压力、冲击波传播速度和冲击温升下降.冲击Hugoniot弹性极限随着温度的上升线性下降.随着冲击强度的增加,CoCrFeMnNi高熵合金发生了复杂的塑性变形,包括位错滑移、相变、变形孪晶和冲击诱导非晶化.在较高的初始温度下,CoCrFeMnNi高熵合金内部出现无序团簇,其和由面心立方晶体结构转变而成的体心立方晶体结构以及无序结构是位错成核的重要来源.由于Mn元素具有相对较大的原子体积和势能,所以在Mn元素的周围会出现较大的晶格畸变和局部应力,从而为冲击诱导塑性变形提供较大的贡献.在温度较高时,Fe元素对塑性变形的贡献和Mn元素一样重要.研究结果有助于深刻理解CoCrFeMnNi高熵合金的冲击诱导塑性和相关变形机制,为CoCrFeMnNi高熵合金在不同温度下涉及高应变率冲击过程的应用提供理论支撑.

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.In this paper,we investigate the effects of temperature on the shock response and plastic deformation mechanism of CoCrFeMnNi high-entropy alloys by using molecular dynamics method.The effects of temperature on the atomic volume and the radial distribution function of CoCrFeMnNi high-entropy alloy are studied.Then,the piston method is used to generate shock waves in the sample to study the shock response of CoCrFeMnNi high-entropy alloy.We observe the evolution of atomic-scale defects during the shock compression by the polyhedral template matching method.The results show that the shock pressure,the shock wave propagation velocity,and the rising of shock-induced temperature all decrease with the initial temperature increasing.For example,when piston velocity U_(p)=1.5 km/s,the shock pressure at an initial temperature of 1000 K decreases by 6.7%in comparison with that at 1 K.Moreover,the shock Hugoniot elastic limit decreases linearly with the increase of temperature.The Hugoniot U_(p)-U_(s)curve of CoCrFeMnNi HEA in the plastic stage can be linearly fitted by the formula U_(s)=c_(0)+sU_(p),where c_(0)decreases with temperature increasing.As the shock intensity increases,the CoCrFeMnNi high-entropy alloy undergoes 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(body-centered cubic)structure transformed from FCC(face-centered cubic)and disordered structure are significant dislocation nucleation sources.Compared with other elements,Mn element accounts for the largest proportion(25.4%)in disordered cluster.Owing to the large atomic volume and potential energy,large lattice distortion and local stress occur around the Mn-rich element,which makes a 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 are conducive to understanding the shock-induced plasticity and deformation mechanisms of CoCrFeMnNi high-entropy alloys in depth.