4 research outputs found
Prediction of thermal cross-slip stress in magnesium alloys from direct first principles data
We develop a first-principles model of thermally-activated cross-slip in
magnesium in the presence of a random solute distribution. Electronic structure
methods provide data for the interaction of solutes with prismatic dislocation
cores and basal dislocation cores. Direct calculations of interaction energies
are possible for solutes---K, Na, and Sc---that lower the Mg prismatic stacking
fault energy to improve formability. To connect to thermally activated
cross-slip, we build a statistical model for the distribution of activation
energies for double kink nucleation, barriers for kink migration, and roughness
of the energy landscape to be overcome by an athermal stress. These
distributions are calculated numerically for a range of concentrations, as well
as alternate approximate analytic expressions for the dilute limit. The
analytic distributions provide a simplified model for the maximum cross-slip
softening for a solute as a function of temperature. The direct interaction
calculations predict lowered forming temperatures for Mg-0.7at.%Sc,
Mg-0.4at.%K, and Mg-0.6at.%Na of approximately 250C.Comment: 26 pages, 7 figure
First-principles data for solid-solution strengthening of magnesium: From geometry and chemistry to properties
Solid-solution strengthening results from solutes impeding the glide of
dislocations. Existing theories of strength rely on solute-dislocation
interactions, but do not consider dislocation core structures, which need an
accurate treatment of chemical bonding. Here, we focus on strengthening of Mg,
the lightest of all structural metals and a promising replacement for heavier
steel and aluminum alloys. Elasticity theory, which is commonly used to predict
the requisite solute-dislocation interaction energetics, is replaced with
quantum-mechanical first-principles calculations to construct a predictive
mesoscale model for solute strengthening of Mg. Results for 29 different
solutes are displayed in a "strengthening design map" as a function of solute
misfits that quantify volumetric strain and slip effects. Our strengthening
model is validated with available experimental data for several solutes,
including Al and Zn, the two most common solutes in Mg. These new results
highlight the ability of quantum-mechanical first-principles calculations to
predict complex material properties such as strength.Comment: 9 pages, 7 figures, 2 table