Al纳米线不同晶向力学行为和变形机制的模拟

doi:10.19596/j.cnki.1001-246x.8433

摘要/Abstract

摘要：

采用分子动力学模拟计算方法，考察具有较高层错能的Al纳米线沿不同晶向的力学行为和变形机制。在相同计算条件下与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线进行比较。结果表明：在力学行为方面，Al纳米线的弹性模量呈现明显的结构各向异性，满足E_[111] > E_[110] > E_[100]的关系，这一关系在FCC金属纳米线中普遍成立；Al纳米线的屈服应力随晶向呈现σ_y[100] > σ_y[111] > σ_y[110]的关系，这一关系在具有较低层错能的FCC金属纳米线中不具有普遍性，这与体系中位错形成机制密切相关。根据拉伸变形过程微观结构的演变规律，阐明Al纳米线不同晶向的变形机制，并与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线的变形机制进行比较。结果表明，对于尺度较小的高层错能Al纳米线，Schmid因子和广义层错能均难以准确预测其变形机制。

关键词: Al纳米线, 变形机制, 晶向, 分子动力学模拟

Abstract:

Mechanical behavior and deformation mechanism of Al nanowire along different crystal orientations are investigated with molecular dynamics simulation. They are compared with those of FCC metal nanowires with lower fault energy such as Ni, Cu, Au and Ag under same computational conditions. It is found that the elastic module of Al nanowire along different crystal orientations displays a relationship of E_[111] > E_[110] > E_[100], which is generally true in FCC nanowires. The yield stress of Al nanowire along different crystal orientations displays a relationship of σ_y[100] > σ_y[111] > σ_y[110], which is not generally true in FCC nanowires. Furthermore, deformation mechanism of Al nanowire along crystal orientations is clarified according to the evolution of microstructures. It is compared with that of nanowires of Ni, Cu, Au and Ag. It was found that it is difficult to predict deformation mechanism accurately with Schmid factor and stacking fault energy for Al nanowire with high fault energy in small scales.

Key words: Al nanowire, deformation mechanism, crystal orientations, molecular dynamics simulation

侯兆阳, 牛媛, 肖启鑫, 王真, 邓庆田. Al纳米线不同晶向力学行为和变形机制的模拟[J]. 计算物理, 2022, 39(3): 341-351.

Zhaoyang HOU, Yuan NIU, Qixin XIAO, Zhen WANG, Qingtian DENG. Simulation of Mechanical Behavior and Deformation Mechanism of Al Nanowires Along Different Crystal Orientations[J]. Chinese Journal of Computational Physics, 2022, 39(3): 341-351.

图/表 12

图1 不同晶向Al纳米线的初始构型示意图(a) [100], (b) [110], (c) [111] ((i)、(ii)、(iii)分别为(a)、(b)、(c)的局部放大，绿色和白色的球体分别代表FCC原子和其他类型原子。)

Fig.1 A schematic of initial configuration of Al nanowires with different crystalline orientations (a) [100], (b) [110], (c) [111] ((i), (ii), (iii) are local enlargements of (a), (b), (c), respectively. The green and white spheres represent FCC atoms and other atoms, respectively.)

表1 不同晶向FCC金属的Schmid因子和预测变形机制[10] (全位错滑移、部分位错滑移和孪生化分别用f-slip、p-slip和twin表示。)

Table 1 Schmid factors and predicted deformation mechanisms of FCC metals with different orientations[10](Slip by full dislocation, slip by partial dislocation and twinning are indicated by f-slip, p-slip and twin, respectively.)

Crystal orientation	Leading partial	Trailing partial	Prediction from Schmid factor
[100]	0.24	0.47	f-slip
[110]	0.47	0.24	twin/p-slip
[111]	0.16	0.31	f-slip

表2 FCC金属结构的层错能(γsf、γusf和γutf分别表示稳定层错能、不稳定层错能和孪晶层错能。)

Table 2 Stacking fault energy of FCC metals (γsf, γusf and γutf represent stable stacking fault energy, unstable stacking fault energy and twin stacking fault energy, respectively.)

Metal	γ_sf(mJ·m^-2)		γ_usf(mJ·m^-2)	γ_utf(mJ·m^-2)	γ_usf(γ_utf - γ_sf)	(γ_usf- γ_sf)(γ_utf-γ_sf)
Metal	Computation	Experiment	γ_usf(mJ·m^-2)	γ_utf(mJ·m^-2)	γ_usf(γ_utf - γ_sf)	(γ_usf- γ_sf)(γ_utf-γ_sf)
Al	144.68	120~144^[17]	150.67	170.03	5.94	0.24
Ni	124.62	125^[15]	363.26	426.85	1.20	0.79
Cu	45.39	45^[15]	182.33	201.26	1.17	0.88
Au	32.37	32^[15]	102.37	120.04	1.16	0.80
Ag	16.13	16^[17]	90.24	101.20	1.06	0.87

图2 基于广义层错能的双参数法预测的FCC金属在不同晶向的变形机制(蓝色区域(p-slip)：τ1 < τ2且τ1 < 1；粉色区域(f-slip)：τ1 > τ2且τ2 < 1；白色区域(twin)：τ1 > 1且τ2 > 1。)

Fig.2 Deformation mechanisms of FCC metals with different crystal orientations predicted with generalized stacking fault energy and Schmid factor (Blue area (p-slip): τ1 < τ2 and τ1 < 1; Pink area(f-slip): τ1 > τ2 and τ2 < 1; White area (twin): τ1 > 1 and τ2 > 1.)

图3 不同晶向Al纳米线拉伸过程的应力-应变曲线

Fig.3 Stress-strain curves of Al nanowire with different crystal orientations during tensile processes

图4 不同晶向Al、Ni、Cu、Au和Ag纳米线在拉伸载荷下的力学特性(a) 弹性模量(E)，(b) 屈服应力(σy)，(c) 断裂应变(εf)

Fig.4 Mechanical properties of Al, Ni, Cu, Au and Ag nanowires under tension loading (a) elastic modulus (E), (b) yield stress (σy), (c) fracture strain (εf)

图5 [100]晶向Al纳米线拉伸过程微观变形机制(a) 应力-应变曲线，(1)~(4)为特征应变点；(b) 拉伸时微观结构演变过程；(绿色球体代表FCC原子，红色球体代表HCP原子，白色球体代表其他原子。) (c) 体系剪切应变分布；(d) 体系内位错分布(蓝色线条代表全位错，绿色线条代表Shockley部分位错。)

Fig.5 Deformation process of Al nanowire with [100] crystal orientation under tensile loading (a) Stress-strain curve; Points (1)~(4) are characteristic strain points; (b) Microstructure evolution of Al nanowire under tensile loading; (Green spheres are FCC atoms. Red spheres are HCP atoms. White spheres are other atoms.) (c) Distribution of shear strain in the system; (d) Dislocation distribution in the system (The blue lines represent full dislocations. The green lines represent Shockley partial dislocations.)

图6 [100]晶向Ni, Cu, Au和Ag纳米线在较低屈服点的微观结构

Fig.6 Microstructures of Ni, Cu, Au and Ag nanowires with [100] crystal orientation at lower yield points

图7 [110]晶向Al纳米线拉伸过程微观变形机制(a) 应力-应变曲线，(1)~(5)为5个特征应变点；(b) 拉伸时微观结构演变过程；(绿色球体代表FCC原子，红色球体代表HCP原子，白色球体代表其他原子。) (c)应变为ε=0和ε=0.475时纳米线的纵向截面和局域放大图

Fig.7 Deformation process of Al nanowire with [110] crystal orientation under tensile loading (a) Stress-strain curve; Points (1)~(5) are characteristic strains points; (b) Microstructure evolution under tensile loading; (Green spheres are FCC atoms. Red spheres are HCP atoms. White spheres are other atoms.) (c) Longitudinal cross sections of nanowire at ε=0 and ε=0.475, together with enlarged view of local configurations

图8 [110]晶向Ni、Cu、Au和Ag纳米线颈缩后的微观结构

Fig.8 Microstructures of Ni, Cu, Au and Ag nanowires with [110] crystal orientation after necking

图9 [111]晶向Al纳米线拉伸过程微观变形机制(a) 应力-应变曲线，(1)~(4)为4个特征应变点；(b) 拉伸时微观结构演变过程；(绿色球体代表FCC原子，红色球体代表HCP原子，白色球体代表其他原子。)(c)体系在特征应变点(4)附近(ε=0.160)处的剪切应变分布

Fig.9 Deformation process of Al nanowire with [111] crystal orientation under tensile loading (a) Stress-strain curve; Points (1)~(4) are characteristic strains points; (b) Microstructure evolution under tensile loading; (Green spheres are FCC atoms. Red spheres are HCP atoms. White spheres are other atoms.) (c) Shear strain distribution of the system at a strain of ε=0.160

图10 [111] Ni、Cu、Au和Ag纳米线颈缩后的微观结构

Fig.10 Microstructures of Ni, Cu, Au and Ag nanowires with [111] crystal orientation after necking

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