Visualization and simulation of defect structures in the B2 phase of NiAl

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Virginia Tech

A methodology and infrastructure was established for the generation of images of embedded atom atomistic simulation data showing the deformed crystal lattice with one or more superimposed strain invariant fields. These methods were applied to data from simulations of B2 NiAl to study extended dislocation cores and how these cores react to nearby point defects and applied stress.

Such images may be viewed as a series of images forming an animation such that a simulated quantity, such as applied stress, is cast into time. Three movies were made doing this. Invariant fields are seen to expand and/or contract before and as they slip depending upon their initial characteristics.

Two different interatomic potentials were used to study the relationships between dislocation core structure and mobility for a variety of dislocations. Using the visualization techniques noted above, it was clearly seen that in some cases, the dislocation core transforms to a planar structure before the dislocation glides, whereas in some other cases the core retains the non-planar structure at stresses sufficient to sustain glide.

The effects of stoichiometry deviations on the core structure and motion were also studied for two pure edge dislocations. A 2% deviation from stoichiometry affects the shapes of dislocation cores in agreement with the experimental results of high resolution electron microscopy. This deviation was also found to increase Peierls stress.