Segregation at interfaces in lightweight alloys towards tailored mechanical properties

Methods

To investigate the behavior of solute elements in magnesium alloys, we employ molecular dynamics (MD) simulations along with transition state tools like the nudged elastic band (NEB) method. These techniques will help us explore the potential energy surface, identify local minima, and determine transition paths between them. We utilize classical potentials such as Embedded Atom Method (EAM) and Modified EAM (MEAM), and if necessary, first-principle calculations to accurately model interatomic interactions.

The Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), an open-source code widely used in materials science as well as chemistry and biology, will be our primary simulation tool. LAMMPS solves Newton’s equations of motion using a velocity-Verlet time integration scheme and employs semi-empirical inter-particle interaction potentials. It optimizes particle interactions through neighbor lists and predefined cut-offs while achieving parallelization via message-passing techniques (MPI) and spatial decomposition for effective load balancing.

We do not plan to modify or develop the LAMMPS source code significantly during this project. For data analysis and visualization, we will use OVITO, which is capable of handling large-scale structures efficiently.

Results

Symmetric tilt GBs & Segregation energy map:
We constructed 51 a-axis symmetric tilt grain boundaries (STGBs) with rotation angles from 0° to 90° using Liu_EAM and Kim_MEAM potentials. The excess potential energies of these GBs were calculated, revealing six local minima at specific angles corresponding to coherent boundaries free from intrinsic defects. Other configurations exhibited arrays of dislocations categorized into five sets based on their tilt angles.

Additionally, we generated segregation energy maps by selecting atoms within 3 nm of the GBs and replacing them with solute atoms (yttrium or zinc). These maps illustrate per-site segregation energies and indicate solute preferences at GB sites, providing benchmarks for future continuum models designed to predict solute segregation behaviors.

Dislocation-GB interactions:
To explore the influence of solutes on the mechanical properties of magnesium alloys, we performed molecular dynamics (MD) simulations focusing on dislocation-grain boundary interactions. Our initial investigations centered on the tensile twin boundary in pure magnesium. As shear stress increased, a basal screw dislocation interacted with the twin boundary but was initially hindered by it. At a critical shear stress of 810 MPa, the dislocation successfully slipped through the twin boundary and continued to glide along the prismatic plane as a prismatic screw dislocation.

When introducing a basal dislocation at an atomic layer further away from the boundary (layer 2), it could still pass through; however, the critical shear stress increased to 830 MPa due to additional resistance encountered during its glide from layer one to layer two before slipping through. These findings highlight how solute elements affect mechanical behavior by altering dislocation dynamics at grain boundaries, offering valuable insights for optimizing magnesium alloys’ performance in various applications.

Discussion

The construction of 51 a-axis symmetric tilt grain boundaries (STGBs) revealed six local minima corresponding to coherent boundaries, highlighting their role in enhancing material properties. These constructed structures will be used as the initial setup to study the nanomechanical properties using micropillar compression or nanoindentation tests. The segregation energy maps for yttrium and zinc indicate solute preferences at grain boundaries, serving as benchmarks for future models predicting solute behavior.

Molecular dynamics simulations demonstrated that basal screw dislocations interact significantly with twin boundaries, requiring critical shear stresses to overcome barriers. These preliminary works explore general methods to study dislocation-GB interactions. In our future work, we will expand the investigation to study how dislocations interact with different pristine or solute-decorated GBs to explore the effects of solutes on mechanical properties in magnesium alloys.
Keywords

Additional Project Information

DFG classification: 406-03 Microstructural Mechanical Properties of Materials
Software: LAMMPS
Cluster: CLAIX

Publications

Mahendran.D – Investigation of [11-20] symmetric tilt grain boundary properties in magnesium and its alloys using atomisitc simulations, Master thesis

Freund, Martina ; Xie, Zhuocheng ; Sun, Pei-Ling ; Berners, Lukas ; Spille, Joshua ; Wang, Hexin ; Thomas, Carsten ; Feuerbacher, Michael ; Lipinska-Chwalek, Marta ; Mayer, Joachim ; Korte-Kerzel, Sandra – Influence of chemical composition on the room temperature plasticity of C15 Ca-Al-Mg Laves phases,
https://dx.doi.org/10.1016/j.actamat.2024.120124

Stollenwerk, Tobias ; Huckfeldt, Pia Carlotta ; Ulumuddin, Nisa Zakia Zahra ; Schneider, Malik ; Xie, Zhuocheng ; Korte‐Kerzel, Sandra – Beyond Fundamental Building Blocks: Plasticity in Structurally Complex Crystals,
https://dx.doi.org/10.1002/adma.202414376

Ulumuddin, Nisa ; Korte-Kerzel, Sandra ; Xie, Zhuocheng – First-principles insights into the site occupancy of Ta–Fe–Al C14 Laves phases,
https://dx.doi.org/10.1016/j.commatsci.2025.113856

Ganguly, Anumoy ; Wang, Hexin ; Guénolé, Julien ; Prakash, Aruna ; Korte-Kerzel, Sandra ; Al-Samman, Talal ; Xie, Zhuocheng – Grain boundary segregation spectrum in basal-textured Mg alloys: From solute decoration to structural transition,
https://dx.doi.org/10.1016/j.actamat.2024.120556

Wang, Hexin ; Guénolé, Julien ; Korte-Kerzel, Sandra ; Al-Samman, Talal ; Xie, Zhuocheng – Defects in magnesium and its alloys by atomistic simulation: Assessment of semi-empirical potentials,
https://dx.doi.org/10.1016/j.commatsci.2024.113025