Simulation Of Microstructure And Mechanical Properties Of Mg Alloy Nano-multilayer Films

Mg-based amorphous alloy has been one of the most attractive research topics in recent years because of its lightweight,high strength,large elastic strain limit,strong glass forming ability and many other excellent properties.However,its mechanics behavior analogous to brittle material has seriously limited its rapid development in the aerospace,electronics,national defense and energy source areas.Hence,how to effectively improve the plasticity of mg-based amorphous alloy is crucial to its wide application.It is generally known that poor ductility and catastrophic failure of mg-based amorphous alloy are caused by the nucleation and rapid propagation of shear bands(SBs).Consequently,hindering rapid propagation of SBs is effective to improve plastic deformation of mg-based amorphous alloy.In order to achieve this goal,on the basis of mg-based amorphous alloy,we propose the idea of constructing two different multilayer samples in this paper.And we investigate relevant factors affecting mechanical behavior of multilayers under tension loading by molecular dynamics simulation method.The main results and conclusions are as follows:(1)The effects of layer thicknesses and aspect ratios on the deformation behavior of MgAl/Mg nanoscale amorphous/crystalline multilayers(NACMs)with equal layer thicknesses of amorphous and crystalline phases are investigated in this paper.The results show that the plastic deformation mode of NACMs changes from cross generalized shear bands dominated deformation to finally single shear band plastic deformation with the increase of layer thickness,and the plastic deformation of NACMs with medium layer thickness is realized through cooperative interactions among crystalline layer,amorphous layer and amorphous/crystalline interfaces(ACIs),which could be treated as a transition progress.The results indicate that the peak stresses of the NACMs are greater than that of monolithic amorphous regardless of layer thickness,which is likely to result from the increase of the strong crystalline phase and the strengthening effect of the ACIs.The results also reveal that the ductility and strength of NACMs could be improved effectively by choosing the appropriate layer thickness.In addition,the deformation behavior of NACMs is also quantificationally disclosed and analyzed in current study.(2)The effects of layer thicknesses and analogous flow defects concentrations(AFDCs)on the mechanical behavior of amorphous/amorphous(A1/A2)nano-multilayers are also investigated in this paper.The results indicate,when layer thickness is small(from 1.8 to 8.5 nm),for any given layer thickness,the plastic deformation of A1/A2 nano-multilayer evolves from a “shear localization” fashion to a “uniform deformation” mode,and eventually to a “shear localization” deformation again with the increase of AFDC.Comparing with the monolithic amorphous,the A1/A2 nano-multilayers with optimum AFDC manifesting uniform deformation achieve a perfect combination of high strength and superior plasticity.What is more,the optimum AFDC could always be found for the sample with arbitrary layer thickness,and shows an upward tendency with increasing layer thickness.When layer thickness is large(13.0 and 25.0 nm),no matter how the AFDC changes,the optimum AFDC disappears for determined layer thickness.In this case,the plastic deformation behavior is arrested in A1 soft layer,resulting in intense shear localization and the reduced plasticity.