Mechanical, thermal, and physical properties of Mg–Ca compounds in the framework of the modified embedded-atom method

Theoretical and Applied Fracture Mechanics

2016

Self Cite

The interaction between segregated alloying elements (Al, Li, Sn, Y, and Ca) and three crack systems is investigated in magnesium simple crystal under mode I loading condition. Using molecular statics in the framework of the (modified) embedded-atoms method, the effect of segregated alloying elements on both the fracture behavior and the intrinsic fracture toughness were identified, and analyzed quantitatively in the framework of the Rice's theory for dislocation emission at a crack tip (Rice, 1992. J. Mech. Phys. Solids 40 239-271). In addition, the variations of the critical stress intensity factor as a function of the misfit strain between the alloying element and magnesium are discussed. The results revealed the existence of a transition from cleavage to dislocation emission at a crack tip. Such transition from cleavage to dislocation emission at the crack tip depends on (i) the orientation of the crack system, and (ii) the nature of the alloying element segregated at the crack tip. Furthermore, when analyzed as a function of the misfit strain between the alloying element and magnesium, our data suggest a direct relation between the fracture toughness and the misfit strain, independently of crack orientation. While alloying element with compressive misfit strain enhances the intrinsic fracture toughness of magnesium single crystal, alloying element with tensile misfit strain worsens the intrinsic fracture toughness of magnesium single crystal.

Section: Mgx Semi-empirical Potentials In the Literaturementioning

confidence: 99%

Section: Mgx Semi-empirical Potentials In the Literaturementioning

confidence: 99%

See 1 more Smart Citation

Effect of segregated alloying element on the intrinsic fracture behavior of Mg

Theoretical and Applied Fracture Mechanics

2016

Self Cite

“…Since computing resource limits the use of first-principle method to system described by a limited number of atoms, atomistic methods in the framework of (semi)-empirical potential are helpful to model the energetic of systems with larger number of atoms. To reveal the effect of solute elements on the mechanical properties of magnesium (Zu and Groh 2016, Somekawa and Mukai 2013, Groh 2014, Bhatia et al 2015, Kim et al 2015a, Miyazawa et al 2015, Reddy and Groh 2016, Yi et al 2016 or to investigate the defect properties and behavior in ordered magnesium alloys (Xiao et al 2013), parameterization of interatomic potentials for binary systems Mg-X (X = Cu, Al, Si, Gd, Y, Sn, Ca, Fe, Li, Ag) were proposed in the EAM and MEAM frameworks (Liu and Adams 1998, Zhou et al 2004, Wu and Hu 2007, Kim et al 2009, 2015b, Mendelev et al 2009, Jelinek et al 2012, Pei et al 2013, Karewar et al 2014,Groh 2015.…”

Section: Interatomic Potentialmentioning

confidence: 99%

Modified embedded-atom potential for B2-MgAg

Modelling Simul. Mater. Sci. Eng.

2016

Self Cite

Interatomic potentials for pure Ag and Mg–Ag alloy have been developed in the framework of the second nearest-neighbors modified embedded-atom method (MEAM). The validity and the transferability of the Ag potential were obtained by calculating physical, mechanical, thermal, and dislocation related properties. Since the {1 1 1}-generalized stacking fault energy curves obtained from first-principle calculations was used to develop the Ag potential, the critical resolved shear stress to move screw dislocations in Ag single crystal is in good agreement with the experimental data. By combining the ability of the potential to predict the surface energies with its accuracy in describing dislocation properties, the potential is thought to be a predictive model for analyzing the fracture properties of Ag. In addition, the performance of the potential was tested under dynamics conditions by predicting the melting temperature, where a good agreement with experimental value was found. The Ag-MEAM potential was then coupled to an existing Mg-MEAM potential to describe the properties of the binary system MgAg. While the heat of formation, the elastic constants, and the (1 1 0) γ-surface of the MgAg compound in the B2 phase were used to parameterize the potential, heat of formation for MgAg alloys with different stoichiometry, thermal properties of the B2-MgAg compound, as well as dislocation related properties in B2-MgAg compound were tested to validate the transferability of the potential. The heat of formation of Mg5Ag2, MgAg, and MgAg3, the elastic constants and the thermal properties of B2-MgAg obtained with the proposed potential align with first-principles and experimental data. In addition, the core structure of both 〈0 0 1〉 and 〈1 1 1〉 dislocations in {1 1 0} are in agreement with theoretical predictions, and the magnitudes of the critical resolved shear stress obtained at 0 K for both slip systems partially validate the slip behavior of B2-MgAg. Furthermore, the interaction between silver solute element and dislocations from the basal plane is correctly captured by the potential.

“…Miyazawa et al showed the effects of segregated Al on twinning mechanisms in Mg [10]. In addition, Reddy and Groh [11] analyzed the effect of segregated Ca on the yield surfaces of NC magnesium using a MgCa-MEAM potential [13].…”

Section: Introductionmentioning

confidence: 99%

Effect of Li on the deformation mechanisms of nanocrystalline hexagonal close packed magnesium

Karewar

Gupta

Computational Materials Science

et al. 2017

Addition of solutes such as lithium enhances ductility of hexagonal-close-packed (hcp) Magnesium (Mg). However, the atomistic underpinning of Li addition on individual deformation mechanisms remain unclear and is the focus of the present work. We compared the deformation mechanisms in nanocrystalline (NC) and single crystal simulation systems of pure Mg and Mg-Li hcp alloys. Five deformation modes are observed in the pure NC Mg with randomly oriented grains-one basal {0001} 1120 , one pyramidal type-I {1011} 1123 , and three twinning slip systems {1012} 1011 , {1013} 3032 , and {1011} 1012. Distributing 10 at.% Li randomly to this NC Mg decreased its compressive yield strength by 14.5%. This also increases the ductility by activating non-basal deformation modes and by reducing the plastic anisotropy. We benchmarked these results by comparing the effect of Li addition on these deformation modes in Mg single crystals. Finally, we present a formability parameter (F p) model based on unstable stacking fault energy, twin fault energy, and nucleation stress for dislocations (τ N S). Quantifying the changes in F p values for the Mg-Li alloys with respect to pure Mg in single crystal simulations explain the decrease in compressive yield strength and change in deformation mechanisms with Li additions. A sensitivity analysis study, comparing our CD-EAM results with a MEAM potential, shows that the effects of Li on the single deformation mechanisms are potential independent. Lastly, while results for Mg-10 at.% Li random alloy are presented here, similar conclusions can be drawn for other compositions of this hcp Mg-Li alloy.