Effect Of Amorphous Phase On The Mechanical Behavior Of Mg Alloys: A Molecular Dynamics Study

Magnesium(Mg)and its alloys are light metal materials with excellent properties,which have good prospects in application.However,Mg alloys are lack of plasticity and formability,owning to the number of dislocations slip systems is limited by the special crystal configuration.Recently,it is confirmed that the dual-phase Mg alloy is characterized by good plasticity,which can be obtained by replacing the grain boundary with the nano amorphous phases.Nevertheless,the influences of amorphous phase on the deformation behavior of crystalline phase and dualphase Mg alloy are not clear.To solve this problem,the dual-phase crystalline/amorphous nanolaminate was set up to investigate the effect of amorphous phase thickness on the plastic deformation behavior.The dual-phase Mg alloy model with pre-existing nano crack was constructed to study the effect of thickness and orientation of amorphous phase(the angle between the tensile direction and the normal direction of crystalline/amorphous interface)on the interaction mechanism between dislocations and amorphous phase.The main results and conclusions are summarized as follows:(1)In the model of dual-phase nanolaminates,the thickness of amorphous phase had great influence on the mechanical behavior of crystalline Mg and the deformation mechanism of nanolaminates.When the tensile loading was applied along [0001] crystalline orientation,as the amorphous phase thickness increased,the deformation behavior of crystalline phase transformed from the slip of dislocations and initiation of new grain to the incomplete basal/prismatic(BP)transformation,and finally to the complete BP transformation.The nucleation stress of BP interface decreased with increasing amorphous phase thickness,and the amorphous phases with large thicknesses facilitated the nucleation of BP interface.At the same time,the deformation mechanism of nanolaminates changed from localized deformation to homogenous deformation.When the tensile loading was applied along [1?010] direction,the deformation mechanism was almost unchanged with increasing thickness of amorphous phase,indicating that the effect of amorphous phase thickness on the plastic deformation of sample depended on the crystalline orientation.(2)In the dual-phase Mg alloy model with pre-existing nano crack,both thickness and orientation of amorphous phase could significantly influence the interaction mechanism between dislocation and amorphous phase.When the amorphous phase orientation was 0°,for the sample with small amorphous phase thickness,the ability to impede the movements of dislocations was weak and dislocations could easily pass through it.The deformation behavior of sample was dominated by the nucleation and sliding of dislocations.When the amorphous phase thickness increased to the critical value of 2.0 nm,the amorphous phase showed larger resistance to dislocation motions.The initiation and growth of new grain played predominant roles in the late plastic deformation process.In addition,as the amorphous phase orientation increased from 0° to 90°,the deformation behavior of dual-phase Mg alloy changed from dislocations activities to interface slip,and then again to the nucleation and gliding of dislocations.The transformation of deformation mechanism was ascribed to the variation of quasi Schmid factors for interface slip under different amorphous phase orientations.