Dislocation-Governed Plastic Deformation and Fracture Toughness of Nanotwinned Magnesium

Abstract

In this work, the plastic deformation mechanisms responsible for mechanical properties and fracture toughness in {10true1¯2}<10true1¯true1¯>nanotwinned (NT). magnesium is studied by molecular dynamics (MD) simulation. The influence of twin boundary (TBs) spacing and crack position on deformation behaviors are investigated. The microstructure evolution at the crack tip are not exactly the same for the left edge crack (LEC) and the right edge crack (REC) models according to calculations of the energy release rate for dislocation nucleation at the crack tip. The LEC growth initiates in a ductile pattern and then turns into a brittle cleavage. In the REC model, the atomic decohesion occurs at the crack tip to create a new free surface which directly induces a brittle cleavage. A ductile to brittle transition is observed which mainly depends on the competition between dislocation motion and crack growth. This competition mechanism is found to be correlated with the TB spacing. The critical values are 10 nm and 13.5 nm for this transition in LEC and REC models, respectively. Essentially, the dislocation densities affected by the TB spacing play a crucial role in the ductile to brittle transition.

Plastic Deformation Behavior of Bi-Crystal Magnesium Nanopillars with a {1012} Twin Boundary under Compression: Molecular Dynamics Simulations

“…Free surface boundary conditions were applied in x, y, and z directions in simulations. The embedded-atom-method (EAM) potential developed by Liu et al [ 49 ] was used to describe the atomic interactions in Mg. Liu’s potential has previously been used extensively to study the deformation of Mg [ 18 , 32 , 36 ]. As summarized in [ 50 ], this potential agrees well with the density functional theory and experimental measurements, in terms of lattice constants, stacking-fault energy, dislocation nucleation, and twinning behaviors.…”

“…Moreover, the influence of TB in polycrystalline magnesium has been investigated via experimental methods [ 25 , 26 , 27 , 28 , 29 ], theoretical methods [ 30 , 31 ], and molecular dynamics simulations [ 32 , 33 , 34 , 35 , 36 ]. Experimental studies indicated that internal defect generation and evolution process in nanotwinned Mg can be significantly influenced by TBs [ 28 , 29 ].…”

Effects of Chemical Short-Range Order and Lattice Distortion on Crack-Tip Behavior of Medium-Entropy Alloy by Atomistic Simulations

“…However, a precise characterization of a crack-tip by experimental observation is extremely difficult. As a supplement to existing experimental techniques and theories, molecular dynamics (MD) simulation is a powerful tool for studying plastic deformation and fracture behavior in HEAs/MEAs at an atomic-scale [41][42][43][44]. The chemical inhomogeneity effects and the atomic-and electronic-level mechanism for grain boundary (GB) deformation and fracture in CrCoNi alloys were investigated by performing MD simulation and first-principle calculation [45].…”

Role of misorientation angle in twinning and dislocation slip for nano Mg bicrystals with [2-1-10] symmetric tilt grain boundaries under uniaxial compression and tension

“…In previous studies, the majority of researchers kept their focus on the atomic structure, formation mechanism, or reaction with incoming dislocations of a certain GB. Research on the global deformation behavior of a bicrystal [22,23] or a polycrystal [24][25][26] model is still limited. For the Mg bicrystalline model, Uranagase and Matsumoto [22] simulated uniaxial tensile and compressive deformation with [-1100] STGB.…”

“…Deformation modes of 16 models, including STGBs with misoreintation angle varied from 0 to 180°, are reported and a preliminary explanation is given using Schmid factor analysis. Zhou and Guo [23] studied the dislocation governed plastic deformation and fracture toughness of {10-12} nanotwinned Mg. Different crack propagation behaviors are observed in samples with different crack positions.…”