First principles calculations of point, line and planar defects in metals

Here we review property predictions for a variety of defects in metal alloys by means of density functional theory. The emphasis of this work is on defects that mediate or influence plastic deformation such as dislocations, solid solutions, and precipitates. The free energy of relevant point and planar defects are estimated from thermodynamic models based on these first principles results. For example, the site selection and density of ternary solutes in ordered intermetallics (e.g. Al₃Sc+X) and the equilibrium profile of interfacial boundaries (IFB) in Al-Al₃Sc are estimated using a lattice gas model appropriate for dilute levels of impurities. For Al-AL₃Sc+Mg alloys impurity segregation of Mg to the Al side of the (100) IFB is predicted, a result recently verified by atom probe tomography. Alternatively, a cluster expansion method is used to study composition profiles and free energies of IFB’s in Ni-Ni₃Al. Finally, we have also developed methods for containing the strain field of isolated dislocations (i.e. line defects) in very small simulation cells. Using this technique we have studied the equilibrium strain field of dislocations in bcc (Mo, Ta, Fe), fcc (Al, Ir), and intermetallic alloys (L10 TiAl). We have evaluated solute dislocation interactions in Mo-X (X=Hf, Ta, Re, Os, Ir and Pt) and these interactions are used to inform a new model of solution hardening and softening at low temperatures. Recently, we have evaluated solute-edge dislocation interactions in Al-Mg alloys and differences between the first principles and continuum estimates of the Cottrell “atmosphere” are presented.

Air Force Research Laboratory, Materials and Manufacturing Directorate Wright-Patterson Air Force Base, Ohio, USA