TY - JOUR
T1 - Crystal structure, energetics, and phase stability of strengthening precipitates in Mg alloys
T2 - A first-principles study
AU - Wang, Dongshu
AU - Amsler, Maximilian
AU - Hegde, Vinay I.
AU - Saal, James E.
AU - Issa, Ahmed
AU - Zhou, Bi Cheng
AU - Zeng, Xiaoqin
AU - Wolverton, Chris
N1 - Funding Information:
M.A. (structure prediction) acknowledges support from the Novartis Universität Basel Excellence Scholarship for Life Sciences and the Swiss National Science Foundation (Projects No. P300P2-158407 and No. P300P2-174475 ). V.H. (high-throughput database, special quasirandom structure calculations) was supported by the National Science Foundation through grant DMR-1309957 . J.S. (formation energies and convex hull construction) acknowledges support by the U.S. Department of Energy , Office of Science, Basic Energy Sciences , under Grant No. DE-FG02-07ER46433 . B.-C.Z. (Mg-Gd-Zn calculations) acknowledges support from Beijing International Aeronautical Materials Corp. (BIAM) . C.W. (overall conception of project and leadership) was supported by financial assistance from award 70NANB14H012 from U.S. Department of Commerce , National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD) . Computing resources from the following centers are gratefully acknowledged: the Swiss National Supercomputing Center in Lugano (project s700 ), the Extreme Science and Engineering Discovery Environment (XSEDE) (which is supported by National Science Foundation Grant No. OCI-1053575 ), the Bridges system at the Pittsburgh Supercomputing Center (PSC) (which is supported by NSF award No. ACI-1445606 ), the Quest high performance computing facility at Northwestern University, and the National Energy Research Scientific Computing Center (DOE Contract No. DE-AC02-05CH11231 ).
Funding Information:
M.A. (structure prediction) acknowledges support from the Novartis Universität Basel Excellence Scholarship for Life Sciences and the Swiss National Science Foundation (Projects No. P300P2-158407 and No. P300P2-174475). V.H. (high-throughput database, special quasirandom structure calculations) was supported by the National Science Foundation through grant DMR-1309957. J.S. (formation energies and convex hull construction) acknowledges support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Grant No. DE-FG02-07ER46433. B.-C.Z. (Mg-Gd-Zn γ” calculations) acknowledges support from Beijing International Aeronautical Materials Corp. (BIAM). C.W. (overall conception of project and leadership) was supported by financial assistance from award 70NANB14H012 from U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). Computing resources from the following centers are gratefully acknowledged: the Swiss National Supercomputing Center in Lugano (project s700), the Extreme Science and Engineering Discovery Environment (XSEDE) (which is supported by National Science Foundation Grant No. OCI-1053575), the Bridges system at the Pittsburgh Supercomputing Center (PSC) (which is supported by NSF award No.ACI-1445606), the Quest high performance computing facility at Northwestern University, and the National Energy Research Scientific Computing Center (DOE Contract No. DE-AC02-05CH11231).
Publisher Copyright:
© 2018 Acta Materialia Inc.
PY - 2018/10/1
Y1 - 2018/10/1
N2 - Magnesium alloys have attracted increasing interest due to their potential use as light-weight structural materials but their application is limited by their low strength compared to conventional alloys. Age hardening is commonly employed to form strengthening precipitates in such alloys, which impedes the motion of dislocations, and leads to improved strength. However, the exact composition, crystal structure, and energetics of many of these strengthening precipitates are either unknown or not clearly resolved, making the precise engineering and design of such alloys difficult. Toward this end, we use first-principles density functional theory calculations to elucidate the crystal structures and energetics of a very large set of precipitates in magnesium alloys. For cases where the precipitate crystal structure is not known, we comprehensively search over decorations of many prototype structures, including hcp superstructures, and in addition, perform global structural optimization using the Minima Hopping Method to predict suitable crystal structures. For all the strengthening precipitates, we calculate the formation energies, construct the respective zero temperature convex hulls, and analyze their stabilities. We show that the bulk formation energies per solute atom (essentially, the solute chemical potentials) decrease along the observed sequences of precipitation, validating our calculations in Mg-{Nd, Gd, Y, Y-Nd, Nd-Zn, Gd-Zn, Y-Zn, Al, Zn, Sn, Al-Ca, Ca-Zn} alloy systems. In addition, we construct a monolayer model for the Guinier-Preston zones (GP zones) observed in the Mg-Nd-Zn system during early stages of age hardening, and thereby explain the formation of the γ” (Mg5(Nd,Zn)) phase from the GP zones, as observed in experiments.
AB - Magnesium alloys have attracted increasing interest due to their potential use as light-weight structural materials but their application is limited by their low strength compared to conventional alloys. Age hardening is commonly employed to form strengthening precipitates in such alloys, which impedes the motion of dislocations, and leads to improved strength. However, the exact composition, crystal structure, and energetics of many of these strengthening precipitates are either unknown or not clearly resolved, making the precise engineering and design of such alloys difficult. Toward this end, we use first-principles density functional theory calculations to elucidate the crystal structures and energetics of a very large set of precipitates in magnesium alloys. For cases where the precipitate crystal structure is not known, we comprehensively search over decorations of many prototype structures, including hcp superstructures, and in addition, perform global structural optimization using the Minima Hopping Method to predict suitable crystal structures. For all the strengthening precipitates, we calculate the formation energies, construct the respective zero temperature convex hulls, and analyze their stabilities. We show that the bulk formation energies per solute atom (essentially, the solute chemical potentials) decrease along the observed sequences of precipitation, validating our calculations in Mg-{Nd, Gd, Y, Y-Nd, Nd-Zn, Gd-Zn, Y-Zn, Al, Zn, Sn, Al-Ca, Ca-Zn} alloy systems. In addition, we construct a monolayer model for the Guinier-Preston zones (GP zones) observed in the Mg-Nd-Zn system during early stages of age hardening, and thereby explain the formation of the γ” (Mg5(Nd,Zn)) phase from the GP zones, as observed in experiments.
KW - Age hardening
KW - Crystal structure prediction
KW - First-principles DFT
KW - Magnesium alloys
KW - Minima Hopping Method
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U2 - 10.1016/j.actamat.2018.07.041
DO - 10.1016/j.actamat.2018.07.041
M3 - Article
AN - SCOPUS:85050764610
VL - 158
SP - 65
EP - 78
JO - Acta Materialia
JF - Acta Materialia
SN - 1359-6454
ER -