Mechanical Properties and Strengthening Mechanism of Graphene Nanoplatelets Reinforced Magnesium Matrix Composites
ZHOU Xia1,2(),LIU Xiaoxia2
1. State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China 2. Department of Engineering Mechanics, Dalian University of Technology, Dalian 116024, China
Cite this article:
ZHOU Xia,LIU Xiaoxia. Mechanical Properties and Strengthening Mechanism of Graphene Nanoplatelets Reinforced Magnesium Matrix Composites. Acta Metall Sin, 2020, 56(2): 240-248.
To improve the mechanical properties of Mg alloys and broaden their application fields, high performance Mg matrix nanocomposites have received more and more attention nowadays. Therefore, the research on the basic mechanical properties and strengthening mechanism of new Mg matrix composites at nanoscale has important theoretical and practical significance. The mechanical properties of pristine single-layer graphene nanoplatelets (GNPs) and single-side and double-side nickel-coated GNP (Ni-GNP, Ni-GNP-Ni) reinforced Mg composites (GNP/Mg, Ni-GNP/Mg, Ni-GNP-Ni/Mg) are studied under uniaxial tension by molecular dynamics (MD) simulations. Meanwhile, their tensile properties are also compared with those of double-side nickel-coated GNP with vacancy defects (Ni-defected GNP-Ni) and double-side nickel-coated multilayer GNPs (Ni-nGNPs-Ni) reinforced Mg-based composites. The simulated results show that the mechanical properties of Mg matrix composites are improved significantly by the addition of GNPs. Compared with single crystal Mg, the tensile strength and elastic modulus of GNP/Mg nanocomposites at 300 K and 1×109 s-1 are increased by 32.60% and 37.91%, respectively; while the tensile strength and elastic modulus of Ni-GNP-Ni/Mg composites are increased by 46.79% and 54.53%, separately. In addition, there is a larger increase in the elastic modulus and tensile strength but a smaller increase in the fracture strain for Ni-defected GNP-Ni/Mg composites, while there is a larger increase in the tensile strength and fracture strain but a smaller increase in the elastic modulus for Ni-GNP/Mg composites as compared with those of GNP/Mg composites. The elastic modulus, tensile strength and fracture strain of Ni-GNP-Ni/Mg composites decreases with increase in temperature, showing a temperature softening effect, but the variation in the elastic modulus of the composites is insensitive to temperature. With increasing of the layers or volume fractions of GNPs in Ni-nGNPs-Ni, the elastic modulus, tensile strength and fracture strain of the composites are all increased significantly, and the composites show excellent comprehensive mechanical properties. It is concluded that the main strengthening mechanisms for Ni-GNP-Ni/Mg nanocomposites are strong interface bonding, effective load transfer from the Mg matrix to the Ni-GNP-Ni and dislocation strengthening by analysis of the evolution of atomic structure.
Fig.1 Different models of graphene nanoplatelets (GNPs) reinforced Mg matrix composites(a) Ni-GNP-Ni/Mg (b) Ni-3GNPs-Ni/Mg (c) Ni-5GNPs-Ni/Mg
Interatomic interaction
/ eV
R / nm
Mg—C
0.0028
0.35015
Mg—Ni
0.0024
0.2965
GNP—GNP
0.00284
0.34
Table 1 The parameters of L-J potential function[14,15,16]
Fig.2 Schematics of simulation model of GNP with different chiral parameters of armchair (a) and zigzag (b) subjected to uniaxial tensile loading (F—load)
Fig.3 Tensile stress-strain curves of GNP with different chiral parameters (a) and single crystal Mg (b)
Fig.4 Tensile stress-strain curves of different GNP/Mg nanocomposites
Material
Volume fraction / %
Elastic modulus GPa
Peak stress GPa
Fracture stress GPa
Failure strain
GNP
Mg
Single crystal Mg
0.0
100.0
69.70
5.92
5.92
0.094
GNP/Mg
3.2
96.8
96.12
7.85
3.61
0.182
Ni-GNP/Mg
4.0
96.0
102.32
8.40
4.36
0.188
Ni-GNP-Ni/Mg
5.2
94.8
107.71
8.69
5.24
0.176
Ni-defected GNP-Ni/Mg
5.2
94.8
107.05
8.37
4.72
0.126
Table 2 Mechanical properties of GNP/Mg nanocomposites and single crystal Mg
Fig.5 Tensile stress-strain curves of Ni-GNP-Ni/Mg nanocomposites at different temperatures and a constant strain rate of 1×109 s-1
Fig.6 Tensile stress-strain curves of GNPs/Mg nanocomposites with different layers of GNP
Material
Volume fraction / %
Elastic modulus GPa
Peak stress GPa
Fracture stress GPa
Failure strain
GNP
Mg
Ni-GNP-Ni/Mg
5.2
94.8
107.71
8.69
5.24
0.176
Ni-3GNPs-Ni/Mg
11.8
88.2
161.38
13.31
11.86
0.187
Ni-5GNPs-Ni/Mg
18.0
82.0
211.28
17.89
18.95
0.192
Table 3 Mechanical properties of Ni-nGNPs-Ni/Mg nanocomposites with different layers of GNP
Fig.7 Tensile stress-strain curves of Mg matrix (a) and Ni-coated different GNP reinforcements (b) in the GNPs/Mg composites
Fig.8 Molecular dynamics (MD) snapshots of lattice configuration variation of single crystal Mg without (a~c) and with Ni-GNP-Ni (d~f) in the Ni-GNP-Ni/Mg composite during tensile process (ε—tensile strain)(a) ε=0.094 (b) ε=0.095 (c) ε=0.1 (d) ε=0.087 (e) ε=0.088 (f) ε=0.1
Fig.9 MD snapshots of lattice configuration variation of uncoated-Ni GNP (GNP) (a~c) and double side Ni-coated GNP (Ni-GNP-Ni) (d~f) in the GNP/Mg composite during tensile process(a) ε=0.188 (b) ε=0.189 (c) ε=0.19 (d) ε=0.186 (e) ε=0.187 (f) ε=0.188
Fig.10 Dislocation evolutions and distributions of GNP/Mg (a~d) and Ni-GNP-Ni/Mg (e~h) composites(a, e) ε=0.087 (b, f) ε=0.1 (c, g) ε=0.13 (d, h) ε=0.2
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