Investigation of grain size effects and other stacking fault width dependencies using a DFT-informed 3D phase field dislocation dynamics (PFDD) model
Abigail Hunter (Los Alamos National Laboratory), Irene Beyerlein (Los Alamos National Laboratory), Timothy Germann (Los Alamos National Laboratory)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium A
Mon 10:45 - 12:15
CIT 165
As characteristic length scales shrink (< 100nm), alternative deformation mechanisms not seen in bulk and course-grained material counterparts emerge. For example, fcc metals plastically deform through the motion of extended dislocations due to energetic benefits found while shifting through the crystal lattice. In bulk and large-grained materials, these extended dislocations stay close together (~1-10nm) and are often assumed to be a single perfect dislocation. However, when the internal microstructure approaches tens of nanometers, plasticity is primarily mediated through the motion and interaction of partial dislocations, resulting in large stacking fault widths (SFWs) (on the order of the grain size) and can no longer be described as a perfect dislocation. Classically, descriptions of partial dislocations and stacking faults are assumed to depend only on the intrinsic stacking fault energy (SFE). We present a 3D phase field dislocation dynamics (PFDD) model that accounts for partial dislocations by incorporating a dependence on the entire material -surface through direct connection to atomistic methods. We investigate the effect of grain size on SFWs created by partial dislocations that emerge from grain boundaries using the 3D PFDD model. Variations in grain size and the presence of grain boundaries impact the size of SFWs by affecting the internal stress state of the grain. The PFDD model utilizes a parameterized -surface that is directly informed by material -surfaces simulated by either ab initio density functional theory (DFT) or molecular dynamics (MD). This incorporates a dependence on unstable SFEs in addition to the intrinsic SFE and establishes a link between atomic-scale numerical methods and the PFDD model. This enables us to follow the dynamics of several nucleating and interacting dislocations based on appropriate calculation of the SFW and accurately probe the physics that underlies plastic deformation of even the smallest volumes.