Cu/Ti纳米层状复合体塑性变形机制的分子动力学模拟研究

Exploring Plastic Deformation Mechanism of Multilayered Cu/Ti Composites by Using Molecular Dynamics Modeling

利用分子动力学方法对具有特征晶体取向的Cu/Ti层状复合体在单轴拉伸和平面应变压缩2种变形过程中的微观力学行为进行了研究。模拟结果显示,拉伸载荷作用下,位错优先在Cu/Ti异质界面处形核并沿着{111}晶面向Cu层内部运动,变形机制为层内约束滑移。随着位错的增殖,位错之间发生交互作用并在Cu层内形成插入型层错和形变孪晶。而在此形变过程中Ti层内未发现塑性变形系统的启动。随着载荷继续增大,Cu/Ti界面处的应力集中导致复合体发生断裂。在平面应变压缩变形的模拟中,发现Cu/Ti界面处的应力集中促使Ti层中形成剪切带,剪切带内部及其近邻区域仅存在少量位错。随着外加应变增大,多种变形机制的共同作用引起晶粒旋转,同时复合体内的原子无序度增加。此外,不同初始取向和不同应变速率下的Cu/Ti复合体的微观塑性变形机制和力学性能存在显著差异。研究结果揭示了包含有密排六方金属层状复合材料的微观形变机制。

Multilayered metallic composites have attracted great interest because of their excellent characteristics.In recent years,the mechanical behavior of Cu/Ti composites is described in terms of macroscopic or mesoscopic scales,but the micromechanism regarding dislocation slip,twinning and shear banding at heterogeneous interfaces remains unclear.In this work,the molecular dynamics method is used to study the uniaxial tensile and plane strain compression deformation of the Cu/Ti multilayered composites with characteristic initial crystal orientations.The simulation results show that under the tensile load,dislocations are preferentially nucleated at the heterogeneous interface between Cu and Ti,and then slip along {111} plane within the Cu layers.The corresponding mechanism is confined layer slip.With the multiplication of dislocations,dislocations interact with each other,and intrinsic stacking faults and deformation twins are formed in Cu layers.However,no dislocation slip or twinning is activated within the Ti layers at this stage of deformation.As the load increases,the stress concentration at the Cu/Ti interface leads to the fracture of the composites.For the composites under plane strain compression,the stress concentration at the Cu/Ti interface triggers the formation of shear bands in the Ti layer,and there are only very limited dislocations within the shear bands and their adjacent area.With the increase of applied strain,the common action of various deformation mechanisms causes the grains to rotate,and the disorder degree of complex atoms increases.In addition,the micro-plastic deformation mechanism and mechanical properties of Cu/Ti complex with different initial orientations and strain rates are significantly different.The results reveal the microscopic deformation mechanism of the laminated composites containing hcp metals.