| Crystal defects, such as point defects, dislocations, cracks, phase and grain boundaries, influence many physical properties of solids. Dislocations are responsible for plastic deformation of materials. Because dislocations in semiconductors affect the electronic properties, they play a role in device performance as well. Multiscale modeling techniques for simulating dislocation dynamics and patternings, including microscale, mesoscale, and macroscale approaches, have attracted much attention recently with the advancement of computer hardware as well as software simulation techniques. Through the use of multiscale modeling, different length scales are treated with different methods. For example, local defect structures are treated with atomistic models, and long-rage defect interactions are calculated using a finite element approach. As one of the microscale simulation methods, molecular dynamics (MD) is capable of accessing the core region of defects in crystalline materials. Massive parallel computers have made it possible to carry out billion atom size simulations—a length scale comparable to many experimental techniques, e.g. transition electron microscopy (TEM).; In this context, I present investigations concerning the properties of dislocation dynamics in Aluminum metal and γ-TiAl metal alloy by means of MD simulations with Embedded Atom Method (EAM) potentials describing interatomic interactions.; First, I present work on the morphological instability and pattern formation of a dislocation driven by a nonuniform field. From a simple model I derive a characteristic length scale identified as the minimum unstable wavelength in the problem. This length scale controls the onset of the instability and plays a role in the process of pattern formation. Molecular dynamics (MD) simulations demonstrate the mechanism of the instability and confirm the predictions of the model.; In a second part of my dislocation dynamics investigation, I present a study of jogged screw dislocation motion in γ-TiAl alloy, to show how the presence of jogs reduces dislocation mobility and generates lattice defects due to non-conservative motion. The displacement field of a jogged screw dislocation is obtained by direct integration of the Burgers Equation. This analytic result is then implemented in the MD code SpaSM (Scalable Parallel Short-range Molecular dynamics). Vacancy tubes and interstitial clusters are generated by the non-conservative motion of jogs. The dynamics of defect creation and annihilation processes and the details of the resulting defect structure are discussed. This work provides us the detailed information of the dynamics of a dislocation as well as the correlations among defects. |
