Plane Of Mg Research Articles

The effect of solute atom concentration on the generalized planar fault energy and twinnability of basal plane in magnesium alloys

The influence of 39 solute atoms under uniform distribution on the generalized plane fault energy (GPFE) and twinnability of the basal plane in Mg solid solutions at various concentrations has been investigated through first-principles calculations. Firstly, it is revealed that the interaction between solute atoms and the GPFs on basal plane of Mg extends beyond the fault layer to encompass multiple atomic layers. Moreover, it is observed that as the distance from the fault layer increases, the interaction energy is decreased. And the increase in the total interaction energy between the solute atoms and the deformed intrinsic stacking fault (SF) I2 results in a corresponding enhancement of their interaction with other key points of GPF, namely UI2, T2, and UT2, establishing a roughly linear relationship. Finally, based on this interaction, we employ a uniform distribution model to investigate the influence of solute atom concentration on the twinnability of basal plane in Mg solid solution alloys. It is observed that with an increase in solute atom concentration, several conventional elements such as K, S, Sr, Zr, As, as well as most rare earth (RE) elements including Y, Pr, La, Nd, Eu, Gd, Dy, Ce, Tb, Ho, etc., gradually enhanced the twinnability of Mg solid solution alloys. Conversely, certain elements like B, P, Cs, Se, Er, Tl, etc., were found to diminish the twinnability of Mg alloys. This study can provide valuable insights for designing high-strength and toughness Mg alloys.

Unique deformation mechanisms of extruded Mg–Y-Sm-Zn-Zr alloy

In present work, the effect of C texture, with the c axis of grains aligned parallel to extrusion direction (ED), on the deformation modes during tension in extruded Mg–Y-Sm-Zn-Zr alloy was investigated. The results indicated that both the extension twins and pyramidal <c+a> dislocations were activated, whereas basal <a> and prismatic <a> dislocations remained dormant during the early stages of tension. With the increase in tensile strain, the number fraction of extension twins increased continuously and rotated their orientation towards the direction perpendicular to ED. Meanwhile, the prismatic slip was activated in the newly orientated grains exhibiting a deviation angle >60°with respect to ED based on the intragranular misorientation axis (IGMA) analysis. Additionally, Viscoplastic self-consistent (VPSC) simulation confirmed that the activation of pyramidal <c+a>, prismatic <a>, extension twin, coupling with the suppression of basal <a> slip attributed to the highest critical resolved shear stress (CRSS) of basal <a> dislocation. Further analysis by TEM revealed that the precipitation of LPSO and γ′ on the basal plane of Mg, along with the increased volume fraction of extension twin actively obstructed the movement of <a> dislocations, consequently elevating the critical resolved shear stress (CRSS) in basal <a> slip.

First-principles modeling of the anodic and cathodic polarization to predict the corrosion behavior of Mg and its alloys

Theoretical models predicting the corrosion behavior of magnesium (Mg) alloys often require some empirical parameters that are obtained from experiments. Here, we develop a first-principles-based electrochemical model to simulate the anodic and cathodic polarization curves of Mg and its alloys in the aqueous solution. Consistent with experimental observations, our model successfully predicts the anisotropic corrosion resistance of different crystallographic planes in Mg. Moreover, analysis of the anodic dissolution process shows that some alloying elements, such as Cr, Cd, Pt, Au, Hg, Ga, Ge, As, In, and Tl, when present in solid-solution state, could effectively improve the corrosion resistance of Mg matrix. Our model, which does not require any experimental parameters as an input, could be a useful tool for screening better corrosion-resistant Mg alloys.

Synthesis of Fe(III)-doping Morchella-like porous magnesium hydroxide for the enhanced heterogeneous Fenton degradation of amphoteric antibiotics and anionic dyes

A Morchella-like hierarchical porous Fe-doping magnesium hydroxide (Fe(III)-PMH) was synthesized via a one-step hydrothermal process using iron-bearing brucite with the modulation of recyclable L-threonate. The L-threonate facilitated formatting Morchella-like porous structure through controlling specific lattice plane of Mg(OH)2. The as-prepared Fe(III)-PMH features a high specific surface area porous structure and even distribution of steady Fe(III) active sites doped in Mg(OH)2 lattice, contributing to its degradation of amphoteric antibiotics or anionic dyes in the presence of H2O2. The surface alkalinity of Fe(III)-PMH drives the anionic conversion of amphoteric antibiotics or enhances the ionization of anionic dyes. Then these anionic contaminants are rapidly absorbed and oxidized in situ on the positively charged surface of Fe(III)-PMH. For the stable presence of superoxide radicals in Fe(III)-PMH/H2O2 system, a wide range of working pH was obtained (pH 3–11). Moreover, a negligible amount of leached iron ions, and excellent reusability make it durable and promising for industrial applications. This work provides a simple and low-cost preparation of heterogeneous catalysts with good performance, especially for the highly effective enhanced Fenton-like system in the wastewater treatment of amphoteric antibiotics and anionic dyes.

The first principle research of CaO and MgO particulate heterogeneous nucleation in Mg alloys

Based on first-principles density functional theory, the adhesion, stability and bonding properties of the interfaces between (0001) plane of Mg and (111) plane of oxide (MgO and CaO) were investigated systematically. Meanwhile, the heterogeneous nucleation ability of these oxide particles in Mg melt were elucidated. The results demonstrated that the stability of the O-terminated surface was higher than that of the X-termination of XO(111) surface under high oxidation potential, and the stability of the X-terminated surface gradually increased with decreasing the oxidation potential. The interfacial adhesion work of Mg/XO-O was higher than that of Mg/XO-X in the same stacking order, indicating that the interface stability of Mg/XO-O was higher than Mg/XO-X. In addition, the results of interface local charge function and Bader charge showed that the atomic charges on the Mg(0001) surface would transfer to the oxygen atoms on the o-termination of XO(111) surface to form ionic bond. The ionic bond strength at the Mg/MgO-O interface was higher than ionic bond strength in Mg/CaO-O interface. Therefore, MgO can be used as a more effective nucleation substrate in Mg melt than CaO.

Controllable crystal growth of Mg(OH)2 hexagonal flakes and their surface modification using graft polymerization

Mg(OH)2 crystals with excellent flame retardance in the application of polymer materials are always in demand. Herein, regular and well-dispersed Mg(OH)2 hexagonal flakes were hydrothermally prepared with the existence of polyethylene glycol (PEG) and then modified by surface grafting-polymerization of methyl methacrylate (MMA) monomers. The results showed that the morphology and dispersity of Mg(OH)2 relied on the precise control of the reaction parameters including hydrothermal conditions, the molecular weight and additive amount of PEG. PEG with a molecular weight of 8000 exhibited an enhanced directing role due to its more appropriate length of molecular chains and intensive interaction with the formed Mg(OH)2 crystallites. The molecular chains of PEG-8000 can be preferentially adsorbed onto the (001) and (101) planes of Mg(OH)2 crystallites and sub-micro hexagonal flakes with low-polarity were consequently assembled. The optimal conditions for preparing Mg(OH)2 hexagonal flakes with higher crystallinity and more regular morphology were determined to be hydrothermal treatment at 120 °C for 12 h with 3 wt% PEG-8000. The dimension and decomposition temperature of the end products were 400 ~ 500 nm and 388 °C, respectively. The surface graft-modified Mg(OH)2 hexagonal flakes exhibited high hydrophobicity with a water contact angle of 148°, indicating an excellent compatibility with polymers.

Orientation dependence of elastic properties of Mg binary alloys: A first-principles study

To better understand the role of alloying elements on the deformation behavior of Mg, the orientation dependence of elastic properties of Mg was investigated under the influence of solute atoms using first-principles methods. Rare earth (RE) elements (Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, and Lu) and non-RE elements (Ag, Al, Cd, In, Pb, Sn, Tl, and Zn) were studied at the concentration of 2.78 at.%. The three-dimensional representation shape of Young’s modulus (E) shows that the elasticity of pure Mg is anisotropic, which is hardly eliminated by adding 2.78 at.% solid solutes. RE elements would give rise to the spindle-shaped 3D representation of E through increasing the value of E along [0001] direction, which shows the strengthened bonding between basal planes of Mg. Moreover, all RE elements would enhance the value of shear modulus (G) on basal planes; meanwhile, the majority of RE would reduce the local minimum value of G on non-basal planes. In contrast, non-RE elements would exert little influence on the 3D representation shape of E of pure Mg and the value of G on the basal plane. Besides, Cd, In, Sn and Zn would marginally reduce the local minimum value of G on prismatic and pyramidal Ⅱ planes, whereas Ag, Pb, Al, and Tl enhance it. At last, the electron localization function was utilized to analyze the bond strength between planes. This fundamental information would complement the basic knowledge of alloying Mg.

Basal dislocation/precipitate interactions in Mg–Al alloys: an atomistic investigation

The interaction between edge basal dislocations and β-Mg17Al12 precipitates was studied using atomistic simulations. A strategy was developed to insert a lozenge-shaped Mg17Al12 precipitate with Burgers orientation relationship within the Mg matrix in an atomistic model ensuring that the matrix/precipitate interfaces were close to minimum energy configurations. It was found that the dislocation bypassed the precipitate by the formation of an Orowan loop that entered the precipitate. Within the precipitate, the dislocation was not able to progress further until more dislocations overcome the precipitate and push the initial loop to shear the precipitate along the (110) plane, parallel to the basal plane of Mg. This process was eventually repeated as more dislocations overcome the precipitate and this mechanism of dislocation/precipitate interaction was in agreement with experimental observations. Moreover, the initial resolved shear stress to bypass the precipitate was in agreement with the predictions of the Bacon–Kocks–Scattergood model.

Atomic structure of γ″ phase in Mg–Gd–Y–Ag alloy induced by Ag addition

ABSTRACTMg–Gd based alloys are typical high strength magnesium alloys owing to their outstanding age hardening behavior. The mechanical strength of aged Mg–Gd alloys is enhanced by high density prismatic-shaped precipitates in Mg matrix. Moreover, the addition of Ag has been found to enhance the strength of Mg–Gd based alloys further by forming a plate-shaped precipitate, named as γ″, on basal planes of Mg. However, the structure of this precipitate is not well understood due to the complex alloying system. In this work, the atomic structure of γ″ phase is investigated using atomic-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Based on the accurate atomic structure from three independent directions, e.g. in [0001]Mg, [110]Mg and [010]Mg zone axes, the unit cell of γ″ is well established. The γ″ phase has a hexagonal structure, and its lattice parameters are a = 0.55 nm and c = 0.42 nm. The orientation relationship between γ″ phase and Mg matrix is (0001)γ″//(0001)Mg and <110>γ″//<010>Mg.

The plausibility of dislocation slip on {-12-11} planes in Mg

Here, the slip behavior of <c + a> screw dislocations on first-order and second-order pyramidal planes in Mg are systematically investigated. Slip or/and cross-slip on six low Miller-Bravais-index planes, including two new {-12-11} planes that have hitherto not been considered possible, are all observed. This new slip system has a low Peierls stress and generalized stacking fault energy, suggesting that it might be an easy mode. The active cross-slip and new slip system provide new insight into the plasticity mechanisms of Mg.

Atomistic modeling of Mg/Nb interfaces: shear strength and interaction with lattice glide dislocations

Using a newly developed embedded-atom-method potential for Mg–Nb, the semi-coherent Mg/Nb interface with the Kurdjumov–Sachs orientation relationship is studied. Atomistic simulations have been carried out to understand the shear strength of the interface, as well as the interaction between lattice glide dislocations and the interface. The interface shear mechanisms are dependent on the shear loading directions, through either interface sliding between Mg and Nb atomic layers or nucleation and gliding of Shockley partial dislocations in between the first two atomic planes in Mg at the interface. The shear strength for the Mg/Nb interface is found to be generally high, in the range of 0.9–1.3 GPa depending on the shear direction. As a consequence, the extents of dislocation core spread into the interface are considerably small, especially when compared to the case of other “weak” interfaces such as the Cu/Nb interface.

Kinetic Control of Hexagonal Mg(OH)2 Nanoflakes for Catalytic Application of Preferential CO Oxidation

Controlling the growth of nanocrystals is one of the most challenged issues in current catalytic field, which helps to further understand the size and morphology related behaviors for catalytic applications. In this work, we investigated the plane growth kinetics of Mg(OH)2 for catalytic application in preferential CO oxidation. Nanoflakes were synthesized through hydrothermal method. The morphology and structure of nanoflakes were characterized by TEM, SEM, and XRD. By varying the reaction temperature and time, Mg(OH)2 nanoflakes underwent an anisotropic growth. Benefited from the Ostwald ripening process, the thickness of nanoflake corresponding to the (110) plane of Mg(OH)2 was tuned from 7.6 nm to 24.0 nm, while the diameter of (001) plane increased from 18.2 nm to 30.2 nm. The grain growth kinetics for the thickness was well described in terms of an equation, D5 = 7.65 + 6.9 × 108exp(−28.14/RT). After depositing Pt nanoparticles onto these Mg(OH)2 nanoflakes, an excellent catalytic performance was achieved for preferential CO oxidation in H2‐rich streams with a wide temperature window from 140 °C to 240 °C for complete CO conversion due to the interaction between Pt and hydroxyl groups. The findings reported here would be helpful in discovering novel catalysts for application of proton exchange membrane fuel cells.

First-principles modeling of anisotropic anodic dissolution of metals and alloys in corrosive environments

There have been extensive experimental observations of the anisotropic corrosion behavior of metals and alloys, and their mechanisms were assumed to be correlated with the so-called surface energy or the work function. However, to date, a specified mechanism or theory to interpret anisotropic corrosion behavior remains unclear. Here, we determine the anisotropic anodic dissolution of metals and alloys in corrosive environments by developing a formula to specify the relationship between the electrode potential (U) and the current density (I) by considering the basic parameters of our defined surface energy density (Esurf/ρ) and the work function (Φ). Therefore, we build an ab initio model to evaluate the anisotropic anodic dissolution behavior of metals and alloys using the inputs obtained within density functional theory. This theory is further validated in the case of variations in the crystallographic planes of Mg. Moreover, some selected alloying additions such as Ga, Cd, Hg, In, As, and Cr are theoretically elucidated to effectively reduce the anodic dissolution rates of the Mg matrix to some extent, in close agreement with available experimental observations. This model is capable of predicting the anisotropic anodic dissolution behavior, providing a promising perspective for designing better corrosion-resistant alloys.

Anisotropic Mg Electrodeposition and Alloying with Ag-based Anodes from Non-Coordinating Mixed-Metal Borohydride Electrolytes for Mg Hybrid Batteries

A highly anisotropic electrodeposition was observed using the hybrid battery electrolyte Mg(BH4)2 with LiBH4 in diglyme. At low overpotentials high aspect ratio platelet morphologies are observed with a strong fiber texture composed of a {10-10} and a {11-20} component, the first evidence of behavior of this kind in magnesium battery electrolytes. At high overpotentials the deposit aspect ratio is indistinguishable but the texture is shown to be primarily composed of a {11-20} fiber texture. The kinetic parameters relative to the relevant crystallographic faces are extracted from electron microscopy images and compared with the observed bulk rate extracted from the electrochemical data. The use of polycrystalline Ag foil substrates with little preferred orientation at the surface allowed highly polycrystalline nucleation at lower overpotentials than that of platinum, likely due to Ag alloying with Mg. Characterization using focused ion beam (FIB) cross-sections with Auger Electron Spectroscopy (AES) elemental analysis confirm that the deposits are primarily Mg although Mg‐Ag alloys of various compositions were observed. It is proposed that the orientation at slow rates of growth is due to the underlying kinetics of adatom diffusion on Mg and that higher rates diminish the phenomenon due to decreased time for adatom diffusion and instead are governed by the rates of adatom formation or more specifically the adatom vacancy formation on the different low-index planes of Mg.

Role of yttrium in activation of 〈c + a〉 slip in magnesium: An atomistic approach

The effect of Y addition on the slip behavior of an edge dislocation on basal, prismatic and second-order pyramidal slip planes of Mg has been investigated using a molecular dynamics simulation. It is found that Y increases the critical resolved shear stress of basal slip more than that of non-basal slip and eventually reduces the difference in the CRSS between different slip systems, which is proposed as the reason for the experimentally reported activation of 〈c+a〉 slip in Mg–Y alloys.

The elasticity anisotropy in the basal atomic planes of Mg(OH)2 and Ca(OH)2 associated with auxetic elastic properties of the hydrogen sub-lattice

Within the framework of the Hook’s generalized law and using the experimental data for characteristic crystallographic parameters and stiffness constants available from literature, the individual elastic properties of constituent octahedral layers and interlayers of the (0001) atomic planes in the Mg(OH)2 and Ca(OH)2 crystal lattices are theoretically quantified from intermolecular interaction energy. It is shown that, under uniaxial type of deformation applied along the (0001) basal planes, in the “load-deformation response” the octahedral layers and interlayers exhibit the positive and negative Poisson’s ratio, respectively. Manifestation of such a type strong elastic anisotropy in the basal atomic planes and auxetic elastic behavior of the hydrogen sub-lattice (interlayers) upon applied uniaxial load result from a large difference in the strength of bonding within octahedral layers and interlayers. The intermolecular binding energy is contributed both by “hydroxyl–hydroxyl” and “metal atom–hydroxyl” dispersion interactions, whereas the Young’s modulus in the direction parallel to a (0001) plane is practically contributed only by the former interaction. For this Young’s modulus, an approximate analytical expression is derived, which is convenient for a physical analysis and presumably is also applicable to other metal hydroxides with brucite structure. The proposed theoretical model may be extended to hydrostatic type loading of metal hydroxides for analysis of the hydrogen associated bonding under high-pressure conditions. The approach applied in this study to estimate the dispersive energy may be useful in the evaluation of the physisorption energy for system “H2–metal hydroxide” in terms of the potential application of metal hydroxides as hydrogen storage materials.

Effect of manganese on the creep behavior of magnesium and the role of α-Mn precipitation during creep

Mg–Mn binary alloys (Mn < 2 wt%) exhibit superior creep resistance over pure Mg, even though the only stable precipitate (α-Mn) has no significant effect on the room-temperature (RT) mechanical properties of Mg. To determine the strengthening and deformation mechanisms of Mg–Mn alloys under creep conditions, the activation energies of creep deformation (Qc) were calculated from compression creep curves (σ: 15 MPa, 100–225 °C) and microstructure analysis was conducted on as-cast (AC), heat treated (HT) and creep tested (CT) samples via transmission electron microscopy (TEM). Creep tests (150 h) indicated that Mn enhances the creep resistance of Mg over a wide temperature range (100–225 °C). The creep enhancement in Mg–Mn alloy was attributed to the dynamic precipitation of α-Mn on the (0 0 0 1) planes of Mg during creep, which hinders dislocation motion. The HT samples exhibited growth of thin α-Mn rods elongated mainly parallel but also perpendicular to basal planes of Mg matrix. Two different orientation relationships were found between α-Mn rods and α-Mg matrix. Activation energy (Qc) calculations for pure Mg indicated pipe diffusion for the low temperature range (100–150 °C) and cross-slip for the high temperature range (150–225 °C). The Mg–1.5Mn alloy showed dislocation climb and cross-slip for the low temperature (100–175 °C) and the high temperature range (175–225 °C), respectively.

In situ transmission electron microscopy observation of the decomposition of MgH 2 nanofiber

In this paper, we presented an investigation of the phase transformation of MgH 2 to Mg, in which a sample of a single-crystal MgH 2 nanofiber was prepared by hydriding chemical vapor deposition (HCVD) and observed by in situ (high-resolution) transmission electron microscopy (TEM). The results indicated that the orientation relationship between MgH 2 and Mg during the phase change was: one of the zone axis of MgH 2 <110> parallel to Mg [0001] zone axis, or one of the plane {110} of MgH 2 parallel to the basal plane of Mg (0001). On the basis of the obtained results, we proposed a structural model for the phase change of MgH 2 to Mg.

Basal and prism dislocation cores in magnesium: comparison of first-principles and embedded-atom-potential methods predictions

The core structures of screw and edge dislocations on the basal and prism planes in Mg, and the associated gamma surfaces, were studied using an ab initio method and the embedded-atom-method interatomic potentials developed by Sun et al and Liu et al. The ab initio calculations predict that the basal plane dislocations dissociate into partials split by 16.7 Å (edge) and 6.3 Å (screw), as compared with 14.3 Å and 12.7 Å (Sun and Liu edge), and 6.3 Å and 1.4 Å (Sun and Liu screw), with the Liu screw dislocation being metastable. In the prism plane, the screw and edge cores are compact and the edge core structures are all similar, while ab initio does not predict a stable prismatic screw in stress-free conditions. These results are qualitatively understood through an examination of the gamma surfaces for interplanar sliding on the basal and prism planes. The Peierls stresses at T = 0 K for basal slip are a few megapascals for the Sun potential, in agreement with experiments, but are ten times larger for the Liu potential. The Peierls stresses for prism slip are 10–40 MPa for both potentials. Overall, the dislocation core structures from ab initio are well represented by the Sun potential in all cases while the Liu potential shows some notable differences. These results suggest that the Sun potential is preferable for studying other dislocations in Mg, particularly the ⟨c + a⟩ dislocations, for which the core structures are much larger and not accessible by ab initio methods.

Atomistic simulation of the self‐diffusion in Mg (001) surface

AbstractBoth the formation energies and the intra‐ and inter‐layer diffuse activation energies of a vacancy in the first six lattice planes of Mg (001) surface have been calculated by combining the modified analytical embedded‐atom method (MAEAM) with molecular dynamics (MD). The results show that the effect of the surface on the formation and migration of the vacancy is only down to the third‐layer. It is easer for a single vacancy to form and to migrate in the first layer. Furthermore, the vacancy in the second layer is favorable to migrate to the first layer. This is in agreement with the experimental results that the first layer has the highest concentration of the vacancy. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)