First-principles calculations of impurity diffusion coefficients in dilute Mg alloys using the 8-frequency model

Grain refining is one of the most important issues in the applications of Mg alloys, which directly determines mechanical properties and deformability. Therefore the understanding of grain refining mechanism during solidification will be benefit to develop new grain refiners. Herein refining role was elucidated by the first principles calculations based on adsorption behavior of a Mg atom on the closest-packed planes of grain refiners (Zr (001), Al2Y(311) and Al4C3(102)). Taking into account different sites, the site with the maximum adsorption energy value generally corresponded to the most possible location. The adsorption energy results show that the possible refining turn follows Al4C3(102)>Zr (001)>Al2Y(311). Meanwhile, the structural optimization confirmed that the Mg atom connected with two C atoms on the top of zig-zag plane of Al4C3(102), three Zr atoms at the hcp position on Zr (001), and two Y atoms and one Al atom at the bottom of zig-zag plane of Al2Y(311). The density of states revealed that the variation of d-orbital electrons of Mg atom became apparent during adsorption process. The values of Mulliken charges were 0.898 e in Al4C3(102), 0.410 e in Zr (001) and 0.245 e in Al2Y(311), respectively. This tendency agrees well with the previous experimental results. It indicates the adsorption energy on the closest-packed planes can be regarded as a prerequisite to select new grain refiners for Mg alloys in future.

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CALCULATIONS OF SELF-DIFFUSION PROCESS AND COEFFICIENT IN ORDERED B2 AlCo

Modern Physics Letters B ◽

10.1142/s0217984913410340 ◽

2013 ◽

Vol 27 (19) ◽

pp. 1341034

Author(s):

ZHI-SHENG NONG ◽

JING-CHUAN ZHU ◽

YONG CAO ◽

XIA-WEI YANG ◽

ZHONG-HONG LAI ◽

...

Keyword(s):

Diffusion Process ◽

First Principles ◽

Diffusion Coefficients ◽

Density Functional ◽

Nearest Neighbor ◽

The Self ◽

First Principles Calculations ◽

Self Diffusion ◽

Diffusion Mechanisms ◽

Semi Empirical

The self-diffusion process in B2 type intermetallic compound AlCo has been investigated by the first-principles calculations within the frame work of density functional theory (DFT). The obtained mono-vacancy formation, migration and activation energies for four self-diffusion mechanisms, the next-nearest-neighbor (NNN) jump, [110] six-jump cycle (6JC), straight [100] 6JC and bent [100] 6JC diffusion show that the NNN jump mechanism of Co vacancy requires the lowest activation energy (Q = 6.835 eV ) in these diffusion mechanisms, which indicates that it is the main way of self-diffusion in AlCo . The electronic structure including the electron density difference on (-1 1 0) plane as well as atomic Mulliken populations were calculated, and the change of bonding behavior during the [110] 6JC process was discussed in detail. Finally, the self-diffusion coefficients of NNN jump and 6JC mechanisms for AlCo were also studied via the first-principles calculations and semi-empirical predictions, which indicates that the self-diffusion coefficients for NNN jump of Co vacancy show the highest value than the others.

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Predicting Diffusion Coefficients from First Principles via Eyring’s Reaction Rate Theory

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.294.1 ◽

2009 ◽

Vol 294 ◽

pp. 1-13 ◽

Cited By ~ 20

Author(s):

Manjeera Mantina ◽

Long Qing Chen ◽

Zi Kui Liu

Keyword(s):

First Principles ◽

Diffusion Coefficients ◽

Reaction Rate ◽

Harmonic Approximation ◽

Impurity Diffusion ◽

Rate Theory ◽

Simplified Approach ◽

Self Diffusion ◽

Reaction Rate Theory ◽

Jump Frequencies

A simplified approach to predicting diffusion coefficients directly from first-principles is proposed. In this approach, the atomic jump frequencies are calculated through the Eyring’s reaction rate theory while the temperature dependence of diffusion coefficients are accounted using phonon theory within the quasi-harmonic approximation. The procedure can be applied to both self-diffusion and impurity diffusion coefficients and different crystal systems. Applications to self-diffusion coefficients in fcc Cu, bcc Mo, hcp Mg and impurity diffusion coefficients of Li in fcc Al, W in bcc Mo and Cd in hcp Mg show agreement with experimental measurements.

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Prediction of Diffusion Coefficients in Liquid and Solids

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.364.182 ◽

2015 ◽

Vol 364 ◽

pp. 182-191 ◽

Cited By ~ 8

Author(s):

William Yi Wang ◽

Bi Cheng Zhou ◽

Jia Jia Han ◽

Hua Zhi Fang ◽

Shun Li Shang ◽

...

Keyword(s):

Molecular Dynamics ◽

First Principles ◽

Diffusion Coefficients ◽

Tracer Diffusion ◽

First Principles Calculations ◽

Dominant Contribution ◽

Creep Properties ◽

Exchange Correlation ◽

Self Diffusion ◽

Tracer Diffusion Coefficients

Our activities in predicting diffusion coefficients in fcc, bcc, and hcp solid solutions using first-principles calculations and in liquid usingabinitiomolecular dynamics are reviewed. These include self-diffusion coefficients [1-4], tracer diffusion coefficients in dilute solutions [5-7], calculation of migration entropy [8], tracer diffusion coefficients in metallic and oxide liquid [9, 10], and effects of vacancy on diffusion of oxygen [11, 12]. The effects of exchange correlation functionals are examined in some cases along with charge transfer between solute and solvent elements. The dominant contribution of diffusion on the effects of Re addition on the creep properties of Ni-base superalloys is discussed [13].

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