Stress and temperature dependence of screw dislocation mobility in {alpha}-Fe by molecular dynamics

Journal Article · Tue Nov 01 00:00:00 EDT 2011 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.84.174103· OSTI ID:21596910

Gilbert, M R ^[1]; Queyreau, S; Marian, J ^[2]

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1. EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)
2. Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, California 94551 (United States)

The low-temperature plastic yield of {alpha}-Fe single crystals is known to display a strong temperature dependence and to be controlled by the thermally activated motion of screw dislocations. In this paper, we present molecular dynamics simulations of (1/2)<111>{l_brace}112{r_brace} screw dislocation motion as a function of temperature and stress in order to extract mobility relations that describe the general dynamic behavior of screw dislocations in pure {alpha}-Fe. We find two dynamic regimes in the stress-velocity space governed by different mechanisms of motion. Consistent with experimental evidence, at low stresses and temperatures, the dislocations move by thermally activated nucleation and propagation of kink pairs. Then, at a critical stress, a temperature-dependent transition to a viscous linear regime is observed. Critical output from the simulations, such as threshold stresses and the stress dependence of the kink activation energy, are compared to experimental data and other atomistic works with generally very good agreement. Contrary to some experimental interpretations, we find that glide on {l_brace}112{r_brace} planes is only apparent, as slip always occurs by elementary kink-pair nucleation/propagation events on {l_brace}110{r_brace} planes. Additionally, a dislocation core transformation from compact to dissociated has been identified above room temperature, although its impact on the general mobility is seen to be limited. This and other observations expose the limitations of inferring or presuming dynamic behavior on the basis of only static calculations. We discuss the relevance and applicability of our results and provide a closed-form functional mobility law suitable for mesoscale computational techniques.

• OSTI ID: 21596910
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 84, Issue 17; Other Information: DOI: 10.1103/PhysRevB.84.174103; (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACTIVATION ENERGY
IRON-ALPHA
MOBILITY
MOLECULAR DYNAMICS METHOD
MONOCRYSTALS
NUCLEATION
SCREW DISLOCATIONS
SIMULATION
SLIP
STRESSES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0273-0400 K
TRANSFORMATIONS
CALCULATION METHODS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
CRYSTALS
DISLOCATIONS
ELEMENTS
ENERGY
IRON
LINE DEFECTS
METALS
TEMPERATURE RANGE
TRANSITION ELEMENTS