Time: 4:30 p.m.
Place: UHW 11/1120
Matous Mrovec, Fraunhofer-Institut für Werkstoffmechanik IWM, Freiburg, Germany
Mobilities of screw and edge (or mixed) dislocations in alpha-iron, like in other bcc metals, are markedly different at low temperatures. While the mobility of edge dislocations remains large and independent of temperature, the mobility of screw dislocations decreases strongly with decreasing temperature. The reason of this distinct behavior has been traced to a non-planar core structure of the 1/2 < 111 > screw dislocation. This extended, non-planar core is primarily responsible for most peculiarities in mechanical behavior of alpha-iron and other bcc metals such as the strong temperature dependence of the ﬂow and yield stresses, the brittle-to-ductile transition, and the non-Schmid behavior.
We performed extensive atomistic simulations of dislocation properties in alpha-Fe using a recently constructed magnetic bond-order potential. This potential is based on the tight binding theory of chemical bond and is therefore able to describe well non-saturated directional bonds originating from the d-electrons as well as magnetic interactions. It is also computationally efficient so that it enables to simulate complex dislocation conﬁgurations under arbitrary stress conditions. We will discuss the behavior of dislocations at the atomic scale and show how the atomistic studies enable to formulate mobility laws that can be implemented in the discrete dislocation dynamics studies of large dislocation ensembles.