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
Cite this article:
LI Meilin, LI Saiyi. Motion Characteristics of <c+a> Edge Dislocation on the Second-Order Pyramidal Plane in Magnesium Simulated by Molecular Dynamics. Acta Metall Sin, 2020, 56(5): 795-800.
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.
Fig.1 Schematic of the model for the motion of an edge dislocation Color online
Fig.2 Variations of effective shear stress (τeff) (a) and average effective shear stress () (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 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
Chen Z H. Wrought Magnesium Alloy [M]. Beijing: Chemical Industry Press, 2005: 48
陈振华. 变形镁合金 [M]. 北京: 化学工业出版社, 2005: 48
3
Liu B Y, Liu F, Yang N, et al. Large plasticity in magnesium mediated by pyramidal dislocations [J]. Science, 2019, 365: 73
doi: 10.1126/science.aaw2843
pmid: 31273119
4
Bertin N, Tomé C N, Beyerlein I J, et al. On the strength of dislocation interactions and their effect on latent hardening in pure magnesium [J]. Int. J. Plast., 2014, 62: 72
5
Jiang J J, Miao L, Liang P, et al. Computational Material Science—Design Practice Method [M]. Shanghai: Higher Education Press, 2010: 162
Bacon D J, Osetsky Y N, Rodney D. Chapter 88 dislocation-obstacle interactions at the atomic level [J]. Dislocations Solids, 2009, 15: 1
7
Groh S, Marin E B, Horstemeyer M F, et al. Dislocation motion in magnesium: A study by molecular statics and molecular dynamics [J]. Modell. Simul. Mater. Sci. Eng., 2009, 17: 075009
8
Fan H D, El-Awady J A. Towards resolving the anonymity of pyramidal slip in magnesium [J]. Mater. Sci. Eng., 2015, A644: 318
9
Fan H D, Wang Q Y, Tian X B, et al. Temperature effects on the mobility of pyramidal <c+a> dislocations in magnesium [J]. Scr. Mater., 2017, 127: 68
10
Obara T, Yoshinga H, Morozumi S.{11$\bar{2}$2}<$\bar{1}$$\bar{1}$23> slip system in magnesium [J]. Acta Metall., 1973, 21: 845
11
Meyers M A, translated by Zhang Q M, Liu Y, Huang F L, et al. Dynamic Behavior of Materials [M]. Beijing: National Defense Industry Press, 2006: 230
Mordehai D, Ashkenazy Y, Kelson I, et al. Dynamic properties of screw dislocations in Cu: A molecular dynamics study [J]. Phys. Rev., 2003, 67B: 024112
13
Olmsted D L, Hector L GCurtinJr, , et al. Atomistic simulations of dislocation mobility in Al, Ni and Al/Mg alloys [J]. Modell. Simul. Mater. Sci. Eng., 2005, 13: 371
14
Plimpton S. Fast parallel algorithms for short-range molecular dynamics [J]. J. Comput. Phys., 1995, 117: 1
15
Osetsky Y N, Bacon D J. An atomic-level model for studying the dynamics of edge dislocations in metals [J]. Modell. Simul. Mater. Sci. Eng., 2003, 11: 427
16
Kim K H, Jeon J B, Lee B J. Modified embedded-atom method interatomic potentials for Mg-X (X=Y, Sn, Ca) binary systems [J]. Calphad, 2015, 48: 27
17
Berendsen H J C, Postma J P M, van Gunsteren W F, et al. Molecular dynamics with coupling to an external bath [J]. J. Chem. Phys., 1984, 81: 3684
doi: 10.1063/1.448118
18
Fan H D, El-Awady J A, Wang Q Y. Towards further understanding of stacking fault tetrahedron absorption and defect-free channels—A molecular dynamics study [J]. J. Nucl. Mater., 2015, 458: 176
doi: 10.1016/j.jnucmat.2014.12.082
19
Cho J, Molinari J F, Anciaux G. Mobility law of dislocations with several character angles and temperatures in FCC aluminum [J]. Int. J. Plast., 2017, 90: 66
20
Thompson A P, Plimpton S J, Mattson W. General formulation of pressure and stress tensor for arbitrary many-body interaction potentials under periodic boundary conditions [J]. J. Chem. Phys., 2009, 131: 154107
doi: 10.1063/1.3245303
pmid: 20568847
21
Regazzoni G, Kocks U F, Follansbee P S. Dislocation kinetics at high strain rates [J]. Acta Metall., 1987, 35: 2865
22
Stukowski A. Visualization and analysis of atomistic simulation data with ovito-the open visualization tool [J]. Modelling Simul. Mater. Sci. Eng., 2010, 18: 015012
doi: 10.1093/nar/gky381
pmid: 29800260
23
Larsen P M, Schmidt S, Schiøtz J. Robust structural identification via polyhedral template matching [J]. Modell. Simul. Mater. Sci. Eng., 2016, 24: 055007
24
Hirth J P, Lothe J. Theory of Dislocations [M]. 2nd Ed., New York: John-Wiley, 1982: 73
25
Nabarro F R N. Dislocations in a simple cubic lattice [J]. Proc. Phys. Soc., 1947, 59: 256
doi: 10.1088/0959-5309/59/2/309
26
Kumar A, Morrow B M, McCabe R J, et al. An atomic-scale modeling and experimental study of <c+a> dislocations in Mg [J]. Mater. Sci. Eng., 2017, A695: 270
