Acta Metall Sin  2020, Vol. 56 Issue (5): 795-800    DOI: 10.11900/0412.1961.2019.00305
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Motion Characteristics of <c+a> Edge Dislocation on the Second-Order Pyramidal Plane in Magnesium Simulated by Molecular Dynamics
LI Meilin1, LI Saiyi1,2()
1.School of Materials Science and Engineering, Central South University, Changsha 410083, China
2.Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410012, China
Abstract

Magnesium has a hcp lattice structure, in which insufficient independent slip systems are available to accommodate applied plastic deformation at room temperature. The ductility of Mg is intimately related to the fundamental behaviors of pyramidal <c+a> dislocations, which are the major contributor to c-axis strain. In this study, the motion of <c+a> edge dislocation on the second-order pyramidal plane in Mg under external shear stress of different magnitudes and directions are simulated by molecular dynamics at 300 K, and the motion and structural evolution of dislocations are studied. The results show that the effective shear stress causing dislocation motion is lower than the external applied one and the dislocation velocity increases linearly with increasing applied shear stress. Under the same level of external shear stress, the dislocation velocity in shearing leading to c-axis tension deformation is higher than that for shearing leading to c-axis compression, and in both cases the corresponding viscous drag coefficients are significantly higher than those for basal and prismatic edge dislocations at the same temperature. The tension-compression asymmetry of dislocation motion is essentially related to the effect of applied shear stress on the extended dislocation width.

 ZTFLH: TG146.2
Fund: National Natural Science Foundation of China(51571213);Natural Science Foundation of Hunan Province(2017JJ2312)
Corresponding Authors:  LI Saiyi     E-mail:  saiyi@csu.edu.cn
 Fig.1  Schematic of the model for the motion of an edge dislocationColor online Fig.2  Variations of effective shear stress (τeff) (a) and average effective shear stress ($τˉeff$) (b) with the applied shear stress (τapp) under positive shear (t—time) Fig.3  Displacement (d)-t curves for the dislocation core under different τapp (positive shear) (The arrows indicate the starting points when τeff enters into a relatively stable stage as shown in Fig.2a) Fig.4  Dislocation velocity (v) as a function of $τˉeff$ under positive shear and negative shear Fig.5  Dislocation core structures under τapp=50 MPa (a1, b1), τapp=150 MPa (a2, b2) and τapp=250 MPa (a3, b3) (l—width of extended dislocation, b—modulus of Burgers vector)(a1~a3) positive shear (b1~b3) negative shear Fig.6  Variations of l with τapp under positive shear and negative shear
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