Abstract
The interplay of interface and bulk dislocation nucleation and glide in determining the motion of twin boundaries, slip-twin interaction, and the mechanical (i.e., stress-strain) behavior of fcc metals is investigated in the current work with the help of molecular dynamics simulations. To this end, simulation cells containing twin boundaries are subject to loading in different directions relative to the twin boundary orientation. In particular, shear loading of the twin boundary results in significantly different behavior than in the other loading cases, and in particular to jerky stress flow. For example, twin boundary shear loading along results in translational normal twin boundary motion, twinning or detwinning, and net hardening. On the other hand, such loading along results in oscillatory normal twin boundary motion and no hardening. As shown here, this difference results from the different effect each type of loading has on lattice stacking order perpendicular to the twin boundary, and so on interface partial dislocation nucleation. In both cases, however, the observed stress fluctuation and “jerky flow” is due to fast partial dislocation nucleation and glide on the twin boundary. This is supported by the determination of the velocity and energy barriers to glide for twin boundary partials. In particular, twin boundary partial edge dislocations are significantly faster than corresponding screws as well as their bulk counterparts. In the last part of the work, the effect of variable twin boundary orientation in relation to the loading direction is investigated. In particular, a change away from pure normal loading to the twin plane toward mixed shear-normal loading results in a transition of dominant deformation mechanism from bulk dislocation nucleation/slip, to twin boundary motion.
Highlights
Among deformation mechanisms in metals, perhaps the most prevalent are dislocation-based or -related ones
Dislocations are modeled at different length and time scales, ranging from continuum scale, mean field descriptions through dislocation density [3] or phase-field [4,5] to mixed atomistic-continuum methods such as atomistic phase-field [6,7] as well as full atomistic models such as molecular dynamics (MD)
To gain additional insight into twin boundary motion resulting from twin boundary dislocation nucleation and glide, the velocity of both interface and bulk partial edge and screw dislocations are determined here
Summary
Among deformation mechanisms in (higher symmetry) metals, perhaps the most prevalent are dislocation-based or -related ones. After discussion of the corresponding simulation set-ups and cases studied, the work turns in Section 3 to a presentation and discussion of simulation results To gain further insight into the case of twin boundary motion via nucleation and glide of twin boundary partial dislocations, the velocity of these and the corresponding energy barriers to glide are determined in Section 3.2 and compared with their bulk counterparts
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