Simulation Of Deformation Mechanism Of Magnesium - Based Nanocomposites

Magnesium(Mg)and its alloys are regarded as the lightest structural materials due to their low density.In recent decades,they have been widely used in automobile,aerospace and other fields to achieve the requirements of lightweight.However,as a typical example of hexagonal close-packed(hcp)crystal structure,Mg has a relatively limited number of independent slip systems for dislocation motion.Compared with face-centered cubic(fcc)structure metals,Mg has poor plasticity at room temperature,which limits its application range to some extent.Therefore,it is very crucial to find a method to enhance the plasticity of Mg alloy and to design a high performance Mg-based composite material.In this paper,we enhance the plasticity of polycrystalline Mg by introducing amorphous phase into the nano-polycrystal Mg and forming crystal-amorphous Mg-based nanocomposites used molecular dynamics simulation method.The main contents and conclusions are as follows:(1)The influence of amorphous grains on the deformation mechanism of the Mg-based nanocomposites was studied.The results indicate that the introduction of amorphous grain can effectively inhibit the formation of grain boundary cracks,improve the plasticity of the nano-polycrystal Mg due to cooperative movement of atoms in crystalline and amorphous phases.The plastic deformation of crystal-amorphous Mg-based nanocomposites begins in crystalline grains.With the decrease of grain size,the plastic deformation of crystal phase in Mg-based nanocomposites change from the nucleation of dislocations and growth of tensile twins to the grain boundaries glide and grains rotation,and the plastic deformation mode of amorphous phase change from the shear band dominated deformation to the homogeneous plastic deformation.The results also show that the deformation behavior of nanocomposites obviously depends on temperature,and the amorphous grain plays a more and more important role during plastic deformation of Mg-based nanocomposites with the decrease(or increase)of grain size(or temperature).(2)The effect of amorphous structure interface on the mechanical behavior of the Mg-based nanocomposites was explored.The results show that two different deformation mechanisms of the Mg-based nanocomposites occur depending on amorphous thickness(t).There is a critical amorphous thickness(t_c)for each sample to achieve nearly perfect plasticity,regardless of crystalline phase size(d).When t<t_c,amorphous phase can only bear part of plastic deformation of composite material due to the limitation of the thickness of amorphous phase,the plasticity of the Mg-based nanocomposites is provided by amorphous and crystalline phase.However,the plasticity is provided only by amorphous phase,the crystalline phase hardly participates in plastic deformation when t?t_c.The results also indicate that the optimal matching relationship between d and t_c is linear.