The physical origin of observed repulsive forces between general dislocations and twin boundaries in FCC metals: An atom-continuum coupling study

doi:10.1016/j.jmst.2021.08.058

Abstract

Abstract:

The combination of ultrahigh strength and excellent ductility of nanotwinned materials is rooted in the interaction between dislocations and twin boundaries (TBs). Quantifying the interaction between TBs and dislocations not only offers fresh perspectives of designing materials with high strength and ductility, but also becomes the cornerstone of multiscale modeling of materials with TBs. In this work, an atom-continuum coupling model was adopted to quantitatively investigate the interaction between dislocations and TBs. The simulation shows that the dislocation-TB interaction is much weaker than the interaction between dislocations at the same distance. Simulation of the early stage of dislocation pileups further verifies that the experimentally observed repulsive forces are essentially from the dislocations or kink-like steps on TBs. The interaction between TBs and dislocations with different Burgers vectors was demonstrated referring to the elastic theory of dislocations. With the intrinsic interaction between dislocations and TBs being clarified, this work will promote further development of the multiscale simulation methods, such as discrete dislocation dynamics or phase-field method, of materials with TBs by providing a quantitative description of the interactions between TBs and dislocations.

Key words: Twin boundary, Intrinsic interaction, Repulsive force, Dislocation pileup, Atomistic simulation, Anisotropic elasticity

Jiayong Zhang, Hongwu Zhang, Qian Li, Lizi Cheng, Hongfei Ye, Yonggang Zheng, Jian Lu. The physical origin of observed repulsive forces between general dislocations and twin boundaries in FCC metals: An atom-continuum coupling study[J]. J. Mater. Sci. Technol., 2022, 109: 221-227.

Figures/Tables 6

Fig. 1. Elastic interaction between a single non-screw dislocation and a single TB. Schematic representation of the coupling model is shown in the inset. Atoms in the inner and bridge region are color-coded according to the stress ${{\sigma }_{xz}}$ caused by a non-screw dislocation. The energy variation of the system as the dislocation–TB distance changes for (a) copper and (b) nickel. The lines with black square marks represent the results of region A calculated with the atomistic simulation, while others show the total energy and the variable n is the ratio of the thicknesses of continuum region C to the size of region A.

Table 1. Elastic constants calibrated with the EAM potentials.

Materials	Elastic constant (GPa)
Materials	C₁₁	C₁₂	C₄₄
Copper	169.89214	122.59543	76.20569
Nickel	247.84734	147.82042	124.8346

Fig. 2. Elastic interaction between two non-screw dislocations with the same Burgers vector. Schematic representation of the coupling model is shown in the inset. Atoms in the inner and bridge region are color-coded according to the stress ${{\sigma }_{xz}}$ caused by a non-screw dislocation. The energy variation of the system as the distance between dislocations changes: (a) copper and (b) nickel. The lines with black square marks represent the results of the inner region calculated with the atomistic simulation, while others show the total energy and the variable n is the ratio of the thicknesses of region C to the size of region A.

Fig. 3. Comparison between the elastic interaction of two non-screw dislocations and the interaction of one dislocation and one TB for (a) copper and (b) nickel. The curves for dislocation-dislocation interaction are manually offset upwards by 0.1 concerning the curve for dislocation-TB interaction. The local atomistic configuration of dislocations and TBs in different coupling models are shown in the insets of (a).

Fig. 4. (a) Stress-dependent distance between a blocked heading dislocation and the following dislocation with/without the presence of TBs. (b) Schematic representation of the model used in the simulation. The symbol f represents the Peach-Koehler force due to the applied shear stress. (c,d) Configurations of dislocations pileup caused by (c) a TB or (d) an immobile dislocation. Atoms are color-coded by the atomistic shear stress σyz.

Fig. 5. (a) Schematic diagram of the dislocation line, its Burgers vector and slipping plane. The xoz plane is assumed to be a TB. (b) Variation of factor $\bar{E}$ as the Burgers vector changes its direction. Values of $\bar{E}$ are in the units of 10-3 eV/Å.

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