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This paper deals with fractional order three-phase-lag (TPL) thermo-elasticity in a micropolar thermoelastic half space medium with voids. The subsequent non-dimensional coupled equations are solved by using the normal mode analysis and eigenvalue approach methods. By doing numerical computations of the physical fields for a substance that resembles a magnesium crystal in the presence of an electromagnetic field, the issue is proven to exist. The effect of the fractional order, the phase lags on the components of temperature, displacement, the stress, and changes in volume fraction field have been depicted graphically. Additionally, a graphic comparison of several types of models employing phase delays and the influence of the magnetic field is displayed. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) and infrared absorption are used to detect Ir4+ ions in β-Ga2O3 crystals. Mg and Fe doped crystals are investigated, and concentrations of Ir4+ ions greater than 1 × 1018 cm−3 are observed. The source of the unintentional deep iridium donors is the crucible used to grow the crystal. In the Mg-doped crystals, the Ir4+ ions provide compensation for the singly ionized Mg acceptors and thus contribute to the difficulties in producing p-type behavior. The Ir4+ ions replace Ga3+ ions at the Ga(2) sites, with the six oxygen neighbors forming a distorted octahedron. A large spin-orbit coupling causes these Ir4+ ions to have a low-spin (5d5, S = 1/2) ground state. The EPR spectrum consists of one broad line with a significant angular dependence. Principal values of the g matrix are 2.662, 1.815, and 0.541 (with principal axes near the crystal a, b, and c directions, respectively). Ionizing radiation at 77 K decreases the Ir4+ EPR signal in Mg-doped crystals and increases the signal in Fe-doped crystals. In addition to the EPR spectrum, the Ir4+ ions have an infrared absorption band representing a d-d transition within the t2g orbitals. At room temperature, this band peaks near 5153 cm−1 (1.94 μm) and has a width of 17 cm−1. The band is highly polarized: its intensity is maximum when the electric field E is parallel to the b direction in the crystal and is nearly zero when E is along the c direction. [ABSTRACT FROM AUTHOR]

To understand inelastic deformation mechanisms for shocked hexagonal-close-packed (hcp) metals, shock compression and release wave profiles, previously unavailable for hcp single crystals, were measured for c-axis magnesium crystals. The results show that the elastic-inelastic loading response is strongly time-dependent. Measured release wave profiles showed distinct peaked features, which are unusual for inelastic deformation during unloading of shocked metals. Numerical simulations show that pyramidal slip provides a reasonably good description of the inelastic loading response. However, {1012} twinning is needed to explain the unloading response. The results and analysis presented here provide insight into the relative roles of dislocation slip and deformation twinning in the response of shocked hcp metals. [ABSTRACT FROM AUTHOR]

Magnesium single crystal samples are compressed at room temperature under quasistatic (∼0.001 s-1) loading in a universal testing machine and dynamic (430, 1000, and 1200 s-1) loading in a split Hopkinson pressure bar system. Stress-strain curves show that (a) the fracture strain slightly increases with the strain rate; and (b) the maximum strength and strain hardening rate increase significantly when the testing changes from quasistatic to dynamic, although they do not vary much when the strain rate for dynamic testing varies in the range of 430-1200 s-1. The operation of the secondary pyramidal slip system is the dominating deformation mechanism, which leads to a fracture surface with an angle of ∼42° with respect to the loading axial direction. A theoretical material model based on Johnson-Cook law is also derived. The model includes the strain hardening and strain rate hardening terms, and provides the stress-strain relations matching with the experimental results. Finite element simulations for the strain rates used in the experiments predict the mechanical responses of the material that agree well with the experimental data. [ABSTRACT FROM AUTHOR]

The influence of the composition on the crystallographic properties of deposited Mg(M)O (with M=Al, Cr, Ti, Y, and Zr) films is studied. For a flexible control of the composition, dual reactive magnetron sputtering was used as deposition technique. Two different approaches to predict the composition are discussed. The first is an experimental way based on the simple relationship between the deposition rate and the target-substrate distance. The second is a route using a Monte Carlo based particle trajectory code. Both methods require a minimal experimental input and enable the user to quickly predict the composition of complex thin films. Good control and flexibility allow us to study the compositional effects on the growth of Mg(M)O films. Pure MgO thin films were grown with a (111) preferential out-of-plane orientation. When adding M to MgO, two trends were noticed. The first trend is a change in the MgO lattice parameters compared to pure MgO. The second tendency is a decrease in the crystallinity of the MgO phase. The experimentally determined crystallographic properties are shown to be in correspondence with the predicted properties from molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

Current-induced spin-torque switching was demonstrated on sub-100 nm magnetic tunnel junction devices fabricated on 200 mm substrates utilizing 180 nm complimentary metal–oxide–semiconductor back-end-of-the-line (BEOL) technology. Low resistance-area (RA) product and high tunneling magnetoresistance (TMR) were achieved by using substrates containing a CoFeB free layer and a thin MgO barrier. To obtain the desired sub-100 nm features, photoresist trimming was applied on patterns created by a 248 nm lithography tool. Furthermore, the magnetic stack was defined using an ion beam etch that stopped on the thin MgO barrier. Field-sweep measurements on elliptical devices that are 80 nm wide and 160 nm long indicated RA∼4 Ω μm2 and TMR∼90%. Upon injecting current into the devices while applying an external offset field of 28 Oe, current-induced switching occurred from parallel (P) to antiparallel (AP) state at +1.3 mA, and from AP to P state at -1.25 mA. BEOL process integration on 200 mm substrates enabled statistical analysis of device properties, such as the observation of two breakdown mechanisms in the devices. [ABSTRACT FROM AUTHOR]

The reflection high energy electron diffraction (RHEED) surface pole figure technique has been applied to an in situ study of the biaxial texture evolution in the anisotropic film of Mg nanoblades. These nanoblades were grown by thermal vapor under the shadowing effect using oblique angle deposition. To compensate for the effects of the anisotropic morphology of the Mg film on the RHEED surface pole figure, a method of intensity normalization has been employed. From the normalized pole figures, we observed a development of [formula] biaxial texture in the film during the growth. When the film grows thicker the texture axes tilt more towards the incident vapor flux. The variation of the azimuthal angle orientation is mainly around the [0001] axis during growth and the azimuthal dispersion angle around the [0001] axis reduces. The change of texture axis tilting angle has been correlated to the change of the nanoblade tilting angle. The azimuthal angle alignment of the nanoblades is argued to be the result of maximizing the vapor flux capture cross section by nanoblades during the growth. [ABSTRACT FROM AUTHOR]

High-resolution studies of polar structures have been performed on the 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (0.9PMN-0.1PT) single crystals by piezoresponse force microscopy. A complex pattern of nanosized polar regions (nanodomains) was observed above the temperature of the structural phase transition. Autocorrelation function technique applied to the analysis of the obtained images revealed clear self-organization of the nanodomains in (110) crystallographic directions and allowed estimating their mean size (∼70 nm at room temperature). Upon heating, the gradual decay of the piezoresponse contrast took place, however, the nanodomains could be still observed at temperatures as high as 385 K. The nature of the observed phenomena is attributed to a peculiar transient state between relaxor and ferroelectric, which developed near the crystal’s surface. [ABSTRACT FROM AUTHOR]

Abstract Spherical MgO nanoparticles were obtained using the method of electric arc spraying of the Mg-C composite electrode, followed by calcination in air. The composition and morphology of nanostructures, formed at spraying, were studied; kinetics of changes in the elemental composition of the carbon-magnesium composite was investigated at annealing in the range of up to 900 °C. It is shown that during arc spraying, core-shell nanoparticles are formed with a carbon core and shell enriched with magnesium nanoparticles, which are oxidized to MgO at contact with the atmosphere. When carbon-magnesium composites are annealed, carbon burns out; the morphology of magnesium oxide nanoparticles is a 250-nm sphere of magnesium crystals of 20–30 nm in size. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Basal 〈a〉 dislocation-{ 1 ¯ 0 1 1 } twin interactions are studied in magnesium. • A stacking fault forms on the pyramidal plane due to the dislocation-TB interactions. • When a dislocation enters the lateral side of the twin, de-twinning occurs. Abstract Basal 〈a〉 dislocation-{ 1 ¯ 0 1 1 } contraction twin interactions are studied in magnesium using molecular dynamics simulations. It is shown that when a basal 〈a〉 dislocation interacts with a ( 1 ¯ 0 1 1) twin boundary, a stacking fault forms along the (1 0 1 ¯ 1) plane because the basal plane of the matrix is nearly parallel to the pyramidal plane of the twin with a deviation of 5.7°. After the second lattice dislocation enters the boundary, the faulted region is erased due to dislocation slip and atomic shuffle. Furthermore, when a basal 〈a〉 dislocation moves toward the lateral side of the twin, de-twinning occurs through a pure-shuffle mechanism. [ABSTRACT FROM AUTHOR]

Abstract Crystallization of diamond in the Mg-Ge-C system has been studied at 7.5 GPa and 1800 °C with the catalyst composition ranging from pure Mg to pure Ge. It is found that with increasing Ge content of the solvent-catalyst, the degree of graphite-to-diamond conversion gradually decreases from 92 to 16%, which is a consequence of the low solubility of carbon in the germanium melt. A decrease in the Mg/Ge ratio leads to a change in the diamond growth form from cube to octahedron and a drastic increase in the number of diamond nucleation centers. The spectral properties of the crystallized diamonds are studied by photoluminescence techniques. The correlations between the Ge content of the Mg-Ge-C system and the luminescence characteristics of the diamond crystals caused by the germanium-vacancy, silicon-vacancy, and nitrogen-vacancy optical centers are established. The results obtained in this study demonstrate that by changing the catalyst composition in the Mg-Ge-C system, it is possible to control the design of the diamond crystals and synthesize isometric, pyramidal, prismatic or needle-like crystals containing Ge-V centers. Graphical abstract Unlabelled Image Highlights • Effect of Mg/Ge ratio on diamond crystallization in the Mg-Ge-C system is established. • Isometric, pyramidal, prismatic and needle-like diamond crystals are synthesized. • Spectral properties of the crystals are determined by Ge-V, Si-V and N-V centers. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of { 10 1 ¯ 2 } twinning in magnesium (Mg) single crystal and its influence on mechanical size effects and strain rate dependent deformation behavior, in-situ microcompression of Mg [ 2 1 ¯ 1 ¯ 0 ] pillars of various sizes from 0.5 μm to 4 μm was carried out in a scanning electron microscope (SEM) and also in a transmission electron microscope (TEM), covering strain rates from 10 −4 to 10 −2 s −1 . The in-situ observations directly showed that the pile-up of prismatic < a > dislocations acts as local stress concentration for the twin nucleation. Preceding the twin nucleation, the lead dislocation from the dislocation pile-up cross-slips to the basal plane and dissociates into partial dislocations, one of which trails a stacking fault (SF) behind. The twin nucleus of a finite size formed at the junction between prismatic < a > dislocations and basal SFs and subsequently propagated rapidly across the pillar. The present in-situ observations reveal that not only the dislocation pile-up but also the dissociation reaction of < a > dislocations play critical roles in the nucleation of { 10 1 ¯ 2 } twins. Furthermore, the { 10 1 ¯ 2 } twinning exhibits a relatively strong size effect in terms of the twin nucleation stress (size exponent n  = 0.7). This pronounced size effect may arise from the fact that the precursor to twin nucleation, namely dislocation pile-up and junction formation, depends more strongly on the crystal size than the ordinary dislocation source operation. Moreover, a noticeable effect of the strain rate is that a higher rate (10 −2 s −1 ) promotes the activation of basal slip within the { 10 1 ¯ 2 } twin. While the twin nucleation occurs more easily at a high strain rate, here the twin growth rate cannot cope with the applied strain rate, so that strain energy accumulation increases with applied strain. When the twin grows to reach the required twin thickness for basal slip, the basal slip promptly activates within the twinned region to release the accumulated strain energy and plastic deformation swiftly catches up with the applied strain rate. [ABSTRACT FROM AUTHOR]

Investigates the glide and climb phenomena of loops and dislocations in magnesium oxide using electron microscope techniques. Definition of glide and climb for a dislocation; Properties of magnesium oxide single crystals.

Different production processes like casting and twin roll casting of Mg-based alloys have a significant influence on the microstructure and texture of the resulting feedstock material for the subsequent rolling process. This leads to improved mechanical properties in the final sheets produced by twin roll casting. In this paper the processing of an Mg-based alloy MX20 (2 wt% Mn and 0.5 wt% Ca) is demonstrated in a modified gravity casting process as well as in the twin roll casting process. The paper will show the different microstructures of the cast and twin roll cast feedstock material. Rolling trials are conducted and the mechanical properties of the sheets are presented and discussed with respect to arising microstructures and textures. The results demonstrate that the different morphology of precipitates in the cast and the twin roll cast feedstock material is used to improve the mechanical properties of the twin roll cast sheets. [ABSTRACT FROM AUTHOR]

The twinning behavior and deformation mechanisms of a pure magnesium (Mg) single crystal were investigated via Erichsen test at room temperature (RT). In order to establish the unique twinning behaviors according to the position of a deformed specimen, microtexture analyses were performed on two cross-sections of a deformed specimen via the electron backscatter diffraction (EBSD) technique. The EBSD results revealed that thin twin bands with different types of twin variants were developed throughout the deformed specimen. The crystal plasticity finite element method (CPFEM), in relation to both the crystallographic slip and deformation twinning, was used to explain the heterogeneous evolution of the twin bands throughout the deformed specimen during the Erichsen test at RT. CPFEM results such as strain components, relative activity of deformation modes, and accumulated volume fraction of twin variants can effectively explain the experimentally observed heterogeneity of twin bands. [ABSTRACT FROM AUTHOR]

The Mg grain boundary diffusion coefficients were measured in forsterite aggregates as a function of pressure (1 atm and 13 GPa), temperature (1100–1300 K), water content (<1–350 wt. ppm bulk water), and oxygen fugacity (10–18–10–0.7 bar) using a multi-anvil apparatus and a gas-mixing furnace. The diffusion profiles were analyzed by secondary ion mass spectrometer, whereas the water contents in the samples were measured by Fourier transform infrared spectrometer. The activation volume, activation enthalpy, water content exponent, and oxygen fugacity exponent for the Mg grain-boundary diffusion coefficients are found to be 3.9 ± 0.7 cm3/mol, 355 ± 25 kJ/mol, 1.0 ± 0.1, and –0.02 ± 0.01, respectively. By comparison with the Mg lattice diffusion data (Fei et al. 2018), the bulk diffusivity of Mg in forsterite is dominated by lattice diffusion if the grain size is larger than ~1 mm under upper mantle conditions, whereas effective grain-boundary and lattice diffusivities are comparable when the grain size is ~1–100 μm. [ABSTRACT FROM AUTHOR]

As for magnesium (Mg) alloys, it has been noted that they are inferior to plastic deformation, but improvement in the mechanical properties by further refinement of grain size has been recently suggested. It means the importance of atomistic view of polycrystalline interface of Mg crystal. In this study, to discuss the deformation mechanism of polycrystalline Mg, atomistic grain boundary (GB) models by using coincidence site lattice (CSL) theory are constructed and are simulated for their relaxed and deformatted structures. First, GB structures in which the axis of rotation is in [1100] direction are relaxed at 10 Kelvin, and the GB energies are evaluated. Then, the deformation mechanism of each GB model under uniaxial tensile loading is observed by using the molecular dynamics (MD) method. The present MD simulations are based on embedded atom method (EAM) potential for Mg crystal. As a result, we were able to observe atomistically a variety of GB structures and to recognize significant difference in deformation mechanism between low-angle GBs and high-angle GBs. A close scrutiny is made on phenomena of dislocation emission processes peculiar to each atomistic local structure in high-angle GBs. [ABSTRACT FROM AUTHOR]

Two types of double twin-like crystalline reorientations have been observed in the tension of Mg single crystals by molecular dynamics method. One can be approximately described as a typical { 1 0 1 ¯ 1 } - { 1 0 1 ¯ 2 } double twin, while the interface between the primary { 1 0 1 ¯ 1 } twin and the secondary { 1 0 1 ¯ 2 } twin shows a zigzag appearance consisting of co-existing { 1 0 1 ¯ 2 } twin boundary and basal/prismatic interface. The other is formed by a prior reoriented crystal with a rugged boundary, and a following { 1 0 1 ¯ 1 } twin, while the basal/prismatic interface dominates the boundary between the reoriented crystals. These double twin-like crystalline reorientations with misorientation angles of about 66° randomly occur under the tension along or near the [ 1 2 ¯ 1 0 ] -axis. The migration of basal/prismatic interface and twin boundary is sensitive to the relationship of the crystalline orientation and the loading direction, which causes the reoriented crystal annihilating or growing. Moreover, the migration of special rugged grain boundary between the reoriented crystal and the matrix is revealed to be fulfilled by the local atomic rearrangements, which contributes to the growth of double twin-like reoriented crystals. [ABSTRACT FROM AUTHOR]

A phase-field model is developed to study the formation and autocatalytic nucleation of { 10 1 ¯ 2 } twins in polycrystalline Mg. The twins are found to nucleate most favourably in grains with the most negative interaction energy. Within such grains, the energetically most favoured nucleation site is determined by stresses concentrated near the grain boundaries that are related to the elastic anisotropy of the material. Furthermore, in a structure consisting of three lamellar grains with an incoming twin in the central grain, the simulation results show that before autocatalytic nucleation, the incoming twin often has a lenticular shape. The stress field around the tip of the incoming twin plays the major role in the autocatalytic nucleation. After a twin has nucleated in the neighbouring grain, the incoming and the outgoing twins evolve simultaneously, and the shape of the incoming twin gradually changes from lenticular to parallel-sided plate. Under the condition that the crystallographic orientation of the central grain and the applied strain remains unchanged, the driving force for twin nucleation decreases with increasing misorientation (up to 90°) across the grain boundary. It is further derived that the interaction energy values between the pre-existing stress field of the polycrystalline structure and the eigenstrain of the to-be-nucleated twin is mathematically related to the resolved shear stress of twins. [ABSTRACT FROM AUTHOR]

Pure microcrystalline magnesium (µMg) was reinforced with hexagonal boron nitride (hBN) nanoparticles and was fabricated by powder metallurgy process followed by hot extrusion. For comparison pure magnesium powder was consolidated by hot extrusion too. Both materials exhibited a significant fiber texture. Mg-hBN nanocomposites (nc) and pure Mg specimens were deformed between room temperature and 300 °C under tension and compression mode. The yield strength and ultimate tensile and compression strength as well as characteristic stresses were evaluated and reported. The tensile and compressive strengths of Mg-hBN nc are quiet superior in values compared to monolithic counterpart as well as Mg alloys. The compressive yield strength of µMg was recorded as 90 MPa, whereas the Mg-hBN nancomposite shows 125 MPa at 200 °C. The tensile yield strength of µMg was computed as 67 MPa which is quite lower as compared to Mg-hBN nanocomposite’s value which was recorded as 157 MPa at 200 °C. Under tensile stress the true stress-strain curves are flat in nature, whereas the stress-strain curves observed in compression at temperatures up to 100 °C exhibited small local maxima at the onset of deformation followed by a significant work hardening. [ABSTRACT FROM AUTHOR]

Shear behaviors of single crystal magnesium (Mg) in close-packed (0001) basal plane along the [ 1 ¯ 2 1 ¯ 0 ], [ 1 2 ¯ 10 ], [ 10 1 ¯ 0 ] and [ 1 ¯ 010 ] directions were studied using molecular dynamics simulations via EAM potential. The results show that both shear stress-strain curves along the four directions and the motion path of free atoms during shearing behave periodic characteristics. It reveals that the periodic shear displacement is inherently related to the crystallographic orientation in single crystal Mg. Moreover, different temperatures in a range from 10 to 750 K were considered, demonstrating that shear modulus decreases with increasing temperatures. The results agree well with the MTS model. It is manifested that the modulus is independent with the shear direction and the size of the atomic model. This work also demonstrates that the classical description of shear modulus is still effective at the nanoscale. [ABSTRACT FROM AUTHOR]

The martensitic transformation in Ni 50 Mn 34.5 In 15.5 single crystal was studied by electrical resistivity measurements under controlled and constant uniaxial stress. We observed that the kinetics of the transformation under uniaxial stress, defined as the derivative of the volume fraction of martensite (austenite) with respect to time, present two maxima during heating at a constant rate of 3 K/min. An additional energy is required for the complete transformation to happen and there is a distortion in the hysteretic cycle depending on the rate. The interaction between transformed volume and untransformed volume and inter-variant conversion could be responsible for this distortion adding a local internal stress in the material. The transformation during heating is consequently isothermal. However, a new increase of the austenite restoration rate occurs in an avalanche form when additional superheating leads to an increase in the driving force that does not compensate any more the total strain energy. [ABSTRACT FROM AUTHOR]

This study describes results from mechanical tests conducted on magnesium single crystals in comparison with polycrystalline magnesium. It was found by impact testing that the magnesium single crystal is highly ductile due to energy absorption by twinning and slip, while the polycrystalline samples fracture easily upon impact. Compressive testing along two orthogonal directions at low plastic strains was also performed. The microstructure studies by electron backscatter diffraction and XRD pole figure analysis revealed profuse (1012) twinning when compression is done along the growth plane (72 16 88 62). The twinning and interaction between different twin modes resulted in incipient recrystallization at strains as low as 8% at room temperature. Compression along the nearly orthogonal plane (2 2 4 15) was marked by a much lower degree of both twinning and recrystallization. The variation in microstructural response with the orientation of loading allows for a wide range for tailoring mechanical properties of pure magnesium single crystals without any need of alloying. [ABSTRACT FROM AUTHOR]

In this work, plane strain finite element simulations of cylindrical void growth ahead of a notch tip in Mg single crystals are conducted to understand the effects of lattice orientation and crack tip constraint on the ductile fracture processes. The constitutive response is represented through crystal plasticity theory accounting for both slip and twinning. Three specimens - shallow, deeply cracked single edge notch tension and deeply cracked four point bend specimens, which display increasing levels of elastic biaxiality ratio (or constraint) are considered. Also two lattice orientations, with c-axis along the thickness direction and normal to the flat surfaces of notch (referred to as A and B) are studied. It is found that void growth and coalescence in orientation A (where predominantly prismatic slip occurs) take place directly ahead of the tip and fracture resistance enhances with reduction in constraint. By contrast, orientation B shows void coalescence by inclined shear bands, displays retarded void growth and higher J at crack initiation. The ductile fracture behavior is analyzed by examining slip, porosity and mean stress development in the voided cells ahead of the notch tip. [ABSTRACT FROM AUTHOR]

In the present study, orientation dependent recrystallization mechanism in pure magnesium is discussed in light of the experimental results. Commercially pure magnesium was subjected to cold rolling of 90% reduction in thickness followed by annealing at 200 °C for different soaking times. Nucleation of no newly oriented grains could be observed during annealing. However, the rate of very low angle grain boundary (VLAGB) movement was found to be the rate controlling step for the formation of recrystallized grains. The formation of sub-grains from the parent grain was observed during annealing of the samples irrespective of the orientation of the grains. However, the rate of sub-grain formation was found to be fastest in the grains of orientations > 40° from the normal direction (ND) of the sample. It was further observed that the growth rate of orientations/grains was decreased with increasing their deviation from ND of the sample. A dominant basal texture was observed in the samples and the maximum weakening of basal texture was observed during 300 s of annealing time. [ABSTRACT FROM AUTHOR]

A series of Dy:LiNbO3 crystals with x mol.% Mg ions ( x =0, 4, 5 and 6 mol.%) were grown by the Czochralski method. The effective segregation coefficient of Mg and Dy ions was studied by the inductively coupled plasma-atomic emission spectrometry (ICP-AES). UV-VIS-NIR absorption spectra and Judd-Ofelt theory were used to investigate their spectroscopic properties. J-O intensity parameters (, , and ) and larger spectroscopic quality factor ( X = 2.26) for Mg:(6 mol.%)Dy:LiNbO3 crystals were obtained. [ABSTRACT FROM AUTHOR]

The current manuscript is devoted to scrutinize the effects of fractional parameter, micropolarity and diffusion on the interactions caused by a ramp type mechanical shock in a generalized thermo-viscoelastic solid half-space. The medium is assumed to be unstrained and unstressed initially and has uniform temperature. The problem has been modeled by employing the fractional generalization of the Lord–Shulman theory to carry the investigation. The governing equations in xz -plane are handled with an analytical–numerical technique based on Laplace–Fourier transforms. Expressions for displacement, stresses, temperature and mass concentration in the physical domain are obtained using a numerical inversion technique. The problem is illustrated by computing the numerical values of the field variables for a magnesium crystal like material. Comparisons of the physical quantities are shown in figures to study the effects of fractional parameter, micropolarity, diffusion and ramp parameter. Some particular cases of interest have also been inferred from the present problem. [ABSTRACT FROM AUTHOR]

The dynamic behavior of Magnesium (Mg) single crystals containing nano-sized voids and the mechanisms responsible for failure under different loading conditions are studied by means of Molecular Dynamics (MD) simulations. Our study reveals that the response is highly anisotropic leading to a brittle to ductile transition in the failure modes under different load orientations. This transition is accompanied by different mechanisms of deformation and is associated with the anisotropic Hexagonal Close Packed (HCP) lattice structure of Mg and the associated barrier for dislocation motion. Remarkably, brittle failure is observed when external loads produce a high stress triaxiality while the response is more ductile when the stress triaxiality decreases. The fundamental mechanisms observed in the simulations, therefore, explain the low spall strength of Mg and suggest the possibility of manipulating some mechanisms to increase ductility and spall strength of new lightweight Mg alloys. [ABSTRACT FROM AUTHOR]

Specifically oriented Mg single crystals, aligned for c -axis extension, were deformed in channel-die plane strain compression in order to form { 10 1 ¯ 2 } extension twins. The amount of twinning shear for { 10 1 ¯ 2 } twins was determined directly from the deflection of marker lines to be s = 0.126 , in excellent agreement with the theoretical value. The twinning shear was discussed with respect to the shear-coupled grain boundary migration by analyzing the formal dislocation content of { 10 1 ¯ 2 } twin boundaries. The respective boundary migration – shear coupling factor is proposed to result from a combination of two elementary coupling modes, 〈 10 1 ¯ 0 〉 and [ 0001 ] . [ABSTRACT FROM AUTHOR]

Recent reports of discontinuous yielding in the uniaxial compression of extruded magnesium suggest that twinning is accompanied by a significant stress decrease in the parent grain, leading to corresponding stress concentrations. We performed crystal plasticity finite element simulations using a simple twinning implementation that includes this “softening” effect for tensile twinning. With this method we were able to reproduce the experimentally observed yield point elongation and the Lüders-like propagation of strain and twinning over the sample. Twin variant selection was analysed in detail at various stages of deformation. Although lower rank variants were found to be activated, most of the twinning activity occurred on variants with the highest global Schmid factor. The stress fluctuations arising from the stress relaxation due to twinning did not appear to alter the dominance of the highest Schmid factor variant significantly. However, when twin softening is included, the twinning strain is dominated by a single variant. Despite giving rise to the highest stress fluctuations during yielding, simulations using the twin stress relaxation implementation actually showed less heterogeneity in stress after yielding. The results of our simple model suggest that “twin softening” could be key to the development of discontinuous yielding in extruded magnesium alloys. [ABSTRACT FROM AUTHOR]

Antofagasta (Chile) is an arid region, and the climate is strongly influenced by the Atacama Desert, with few sources of fresh water. The pressure to use non-conventional water sources has boosted the construction of numerous desalination plants. High concentrations of secondary ions as calcium and magnesium cause problems in reverse osmosis plants and in other industries such as copper mining and cooling system. Biomineralization process based on hydrolysis of urea has been described in a wide variety of bacterial species with diverse applications. The selection of ureolytic halotolerant bacteria from Atacama Salar and their ability to precipitate calcium and magnesium crystals in seawater is described. Besides crystal structure and morphology were determined by electron microscopy analysis and X-ray diffraction. When assessing the mineral precipitate ability, Rhodococcus erythropolis precipitates a ~ 95% soluble calcium and 8% magnesium. The analysis of crystals showed that correspond to ~ 12.69% monohydrocalcite, ~ 30.72% struvite and ~ 56.59% halite. These results demonstrate that the biomineralization by ureolytic bacteria in seawater has great potential for its application as a pretreatment to improve water quality for industrial processes. [ABSTRACT FROM AUTHOR]

1% Ce-doped and non-doped (Gd 8 AE 2 )(SiO 4 ) 6 O 2 ( AE = Mg, Ca, Sr and Ba) (denoted as GMS, GCS, GSrS and GBS, respectively) single crystals were grown by the Floating Zone (FZ) method to evaluate their optical and scintillation properties. The Ce:GCS and Ce:GSrS samples exhibited scintillation and photoluminescence (PL) around 400 nm due to the 5d-4f transitions of Ce 3+ . On the other hand, Ce:GMS and Ce:GBS showed much weaker emissions in the wavelength range of 500–650 nm, in which the origin was associated with the host matrices. The PL decay curves were approximated by a double exponential decay function for all the Ce-doped samples. The decay times ranged around 10–30 and 40–90 ns, and faster components coincided with those of the non-doped samples. The scintillation decay curves of Ce-doped samples, on the other hand, were approximated by single exponential functions with slower decay constants than those of PL decay. These constants were very similar to those of non-doped samples. In the X-ray induced afterglow measurements, Ce:GCS exhibited the lowest afterglow level. The pulse height spectrum of these samples showed a full-energy peak under 241 Am 5.5 MeV α-ray irradiation. Among these samples, Ce:GSrS exhibited the highest light yield which was around 600 ph/5.5 MeV-α. [ABSTRACT FROM AUTHOR]

An investigation was conducted to examine the mechanical behavior and microstructure evolution during deformation of ultrafine-grained pure magnesium at low temperatures within the temperature range of 296–373 K. Discs were processed by high-pressure torsion until saturation in grain refinement. Dynamic hardness testing revealed a gradual increase in strain rate sensitivity up to m ≈ 0.2. High ductility was observed in the ultrafine-grained magnesium including an exceptional elongation of ∼360% in tension at room temperature and stable deformation in micropillar compression. Grain coarsening and an increase in frequency of grain boundaries with misorientations in the range 15°–45° occurred during deformation in tension. The experimental evidence, when combined with an analysis of the deformation behavior, suggests that grain boundary sliding plays a key role in low strain rate deformation of pure magnesium when the grain sizes are at and below ∼5 μm. [ABSTRACT FROM AUTHOR]

We studied unusual growth macrolayers on the {100} faces of diamond crystals grown in Mg-C and Mg 0.9 Ge 0.1 -C systems at 7.0 GPa and in the temperature range of 1800–1900 °C. The layers were shaped as rectangles highly elongated in one of the [110] directions. The layer elongation (length to width ratio) was different, but did not exceed 23. We found that the ends of the macrolayers in most cases were composed of {111} microfacets, and their growth occurred by layers along these microfacets. Using selective etching, we found that the macrolayers were not associated with outcrops of dislocations and any planar defects on the {100} faces. It is supposed that the formation of these highly elongated layers occurs by two-dimensional nucleation that becomes possible at high carbon supersaturation under conditions of kinetically limited diamond growth in Mg-based systems. [ABSTRACT FROM AUTHOR]

A crystal plasticity finite element method (CPFEM) with a stress relaxation effect for twinning in the constitutive description is employed to simulate twin formation, propagation and growth in Mg single crystals subjected to plane-strain compression along the direction perpendicular to the c -axis of its HCP lattice. Tensile twinning dominates the early stage of plastic deformation and numerical results explicitly show the twinning process including twin formation, propagation and growth. After a twin band (or a narrow twin) is formed, a large gradient of effective stress is found across the band front. Also, the resolved shear stress (RSS) on the twin plane along the twin direction is highly non-homogeneous across the band front. It has been demonstrated that softening facilitates the formation of a twin band and work hardening is contributive to the growth of the twin band. In addition, numerical results indicate that softening plays an important role in the propagation of a twin across a grain boundary with a large misorientation. [ABSTRACT FROM AUTHOR]

High-Mg andesites (HMAs) and related basalts constitute a volumetrically minor, but genetically important occurrence along most convergent plate margins of various ages on Earth. The details of their petrogenesis can contain critical information for resolving essential geodynamic and crustal evolutionary issues. This zircon U–Pb dating and geochemical study documents the late Permian metamorphosed high-Mg basaltic to andesitic suite from Kaiyuan of northern Liaoning, North China. These rocks feature SiO 2 contents ranging from 48.7 to 63.2 wt.%, high Mg # values of 63–75, an enrichment in large-ion lithophile elements (LILE), and depletion in high field strength elements (HFSE). They possess whole-rock initial 87 Sr/ 86 Sr ratios of 0.70417–0.70457, ε Nd (t) values from − 0.4 to 5.0, and ε Hf (t) values from 5.1 to 11, as well as zircon ε Hf (t) values from − 9.4 to 0.4. These features indicate that their petrogenesis most likely involved precursory metasomatism of mantle peridotites by melts from subduction-related sediments, and subsequent partial melting. With a depleted mantle source and possible tectonic link to post-subduction slab break-off, the Kaiyuan suite could present a spatial reference not only for defining the demarcation line between the North China craton (NCC) and the Central Asian Orogenic belt (CAOB) in the region, but also for tracing the final location of the cryptic suturing zone of the Paleo-Asian Ocean. Synthesizing the suite with coeval igneous episodes as well as concomitant metamorphic events along the Solonker–Xra Moron–Changchun zone leads to the characterization of the eventual closure of the Paleo-Asian Ocean within a double-sided subduction system during late Permian–Early Triassic. [ABSTRACT FROM AUTHOR]

The atomistic pathways of deformation twinning can be computed ab initio , and quantified by two variables: strain which describes shape change of a periodic supercell, and shuffling which describes non-affine displacements of the internal degrees of freedom. The minimum energy path involves juxta-position of both. But if one can obtain the same saddle point by continuously increasing the strain and relaxing the internal degrees of freedom by steepest descent, we call the path strain-controlled, and vice versa. Surprisingly, we find the { 10 1 ¯ 2 } 〈 10 1 ¯ 1 ¯ 〉 twinning of Mg is shuffling-controlled at the smallest lengthscale of the irreducible lattice correspondence pattern, that is, the reaction coordinate at the level of 4 atoms is dominated by non-affine displacements, instead of strain. Shuffling-controlled deformation twinning is expected to have different temperature and strain-rate sensitivities from strain-controlled deformation twinning due to relatively weaker strength of long-range elastic interactions, in particular at the twin nucleation stage. As the twin grows large enough, however, elastic interactions and displacive character of the transformation should always turn dominant. [ABSTRACT FROM AUTHOR]

In this work, growth of cylindrical voids corresponding to different stress states in Mg single crystal under plane strain conditions is analyzed using a crystal plasticity based finite element procedure which accounts for twinning through a quasi-slip approximation. Two lattice orientations are considered with the c-axis along the thickness in one orientation and major principal stress direction in the other. Profuse tensile twinning occurs in the second orientation. To understand its influence clearly, this orientation is also analyzed with tensile twinning intentionally suppressed. The results show a pronounced effect of texture hardening triggered by tensile twinning in slowing down void growth. However, once lattice reorientation occurs, multiple slip systems become active causing more rapid void growth. The simulations also predict a transition in void coalescence mechanism from internal ligament necking to shear localization along an inclined band with reduction in biaxiality stress ratio when tensile twinning occurs. [ABSTRACT FROM AUTHOR]

A nanocrystalline metal contains grains that are extremely small, with a high proportion of grain boundary (GB). For understanding of the mechanical properties of nanocrystalline metals, it is indispensable to elucidate the influence of GBs on plastic deformation. In this study, molecular dynamics simulations of uniaxial deformation tests on magnesium bicrystals with [ 1 ¯ 1 0 0 ] symmetric tilt GBs were performed in order to reveal the role of GBs during the plastic deformation of hexagonal close-packed metals. We found that not only the critical resolved shear stress but also the active deformation mode itself is sensitively dependent on both the misorientation angle between the grains and the loading direction. In particular, ease of nucleation of basal dislocations from the GB could be qualitatively explained by the dependence of the GB energy on the misorientation angle, where dislocation nucleation from the GB is regarded as a process by which GBs accommodate changes in misorientation angle caused by elastic deformation due to an applied load. [ABSTRACT FROM AUTHOR]

Nanostructured Mg2Ni intermetallic compounds were synthesized by high-energy ball milling. Effect of milling time on structure and surface morphology of milled powders were studied using x-ray diffraction and scanning electron microscopy. Crystallite size and degree of crystallinity were confirmed by using transmission electron microscopy and selected area electron diffraction analysis. The particle size of 20 h milled electrode material is 230 nm and it reduced to 40 nm when the milling time is increased to 30 h. Further increase in the milling time reduces the particles size drastically and starts agglomerating. In order to understand the effect of milling time on reaction rates, differential thermal analysis was performed. Activation energy of the milled powders was calculated using Kissinger analysis. 30 h milled powder exhibits lower activation energy than others. Cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge studies were done on the prepared electrode materials. 30 h milled electrode material delivers maximum discharge capacity with a superior capacity retention after 20 cycles at 20 mAg−1. [ABSTRACT FROM PUBLISHER]

Mg single crystals of selected ‘hard’ and ‘soft’ orientations were deformed at ambient temperature in channel-die compression. Specimens with a ‘hard’ basal starting orientation displayed a limited ductility and fractured along { 11 2 ̅ 4 } planes. Compression perpendicular to the c -axis of orientations well aligned for { 10 1 ̅ 2 } extension twinning revealed a very contrasting deformation behavior. Specimens compressed along the crystallographic 〈 11 2 ̅ 0 〉 direction exhibited an exceptionally high room temperature ductility, whereas compression along 〈 10 1 ̅ 0 〉 resulted in failure after an initial sigmoidal stress–strain response. In both cases { 10 1 ̅ 2 } extension twins were found to fully consume the matrix at low strains and convert the starting orientations into orientations corresponding to the respective high Schmid factor twin variants. High strains have also been attained for a prismatic starting orientation where the c -axis was constrained. In specimens, favorably oriented for basal slip, anomalous { 10 1 ̅ 2 } extension twins formed, clustered in bands parallel to the constraint direction. These twins produced a strain opposite to the imposed plane strain deformation and provided a pronounced dynamic grain boundary strengthening effect. [ABSTRACT FROM AUTHOR]

The effects of amorphous boundary (AB) spacing on the deformation behavior of crystalline/amorphous (C/A) Mg/Mg Al nanocomposites under tensile load are investigated using molecular dynamics method. The results show that the plasticity of nano-polycrystal Mg can be enhanced with the introduction of C/A interfaces. For samples 5.2 nm in AB spacing and larger, the superior tensile ductility and nearly perfect plastic flow behavior occur during plastic deformation. The studies indicate that the cooperative interactions between crystalline and amorphous are the main reason for excellent ductility enhancements in C/A Mg/Mg Al nanocomposites. [ABSTRACT FROM AUTHOR]

Plasticity in magnesium crystals oriented for c -axis compression has been usually attributed to 〈 c + a 〉 dislo c ation slip on second-order pyramidal {11 2 ¯ 2} planes. Through molecular dynamics simulations, we investigated the formation and slip characteristics of 〈 c + a 〉 dislocations on second-order pyramidal planes. It is shown that the critical c -axis compressive stress for these dislocations is almost seven times that for 〈 c + a 〉 dislocations on first-order pyramidal {10 1 ¯ 1} planes. In particular, it is concluded that first-order pyramidal near-screw 〈 c + a 〉 dislocations play a predominant role during the c -axis compression of magnesium crystals. Careful reexaminations of published experimental observations show good agreements with the current predictions. [ABSTRACT FROM AUTHOR]

A detailed analysis of the loading mode dependence of the deformation mechanisms in randomly textured cast magnesium is presented. An elasto-plastic self-consistent model (EPSC) is used to model the dislocation slip and twinning activity, respectively. The results are quantitatively compared with experimental data obtained by in-situ neutron diffraction (ND) and acoustic emission (AE). Both EPSC calculations and ND line profile analysis show an increased activity of prismatic slip with increasing strain and a loading mode dependence of the activation of the second-order pyramidal slip. The AE measurements and the modeling indicate a difference in the number of nucleated twin variants and the twinned volume in tension and compression. [ABSTRACT FROM AUTHOR]

A planar optical waveguide in MgAlO crystal sample was fabricated using 6.0 MeV oxygen ion implantation at a fluence of 1.5 × 10 ions/cm at room temperature. The optical modes were measured at a wavelength of 633 nm using a model 2010 prism coupler. The near-field intensity files in the visible band were measured and simulated with end-face coupling and FD-BPM methods, respectively. The absorption spectra show that the implantation process has almost no effect on the visible and near-infrared band absorption. [ABSTRACT FROM AUTHOR]

Pyramidal slip mechanism plays an important role inc-axis micro-compression of hexagonal closed-packed metals. In this article, the detailed slip paths, respectively, onandplanes in magnesium single crystal are given by molecular dynamics. The pyramidal slip onplane is suggested to consist of an edge-type partial dislocation and opposite basal movements on neighbouring basal planes, while theslip dissociation is achieved by two partial dislocations with a strip of stacking fault. Results imply that the slip onplane is more likely to nucleate with a relatively easy dissociation type comparing to the one onplane. No twinning is found underc-axis compression by examining the stepwise movement of atoms involved, fully supporting the recent experimental observations of micro-compression and the theoretical analysis on twinning formation proposed by our previous work. [ABSTRACT FROM PUBLISHER]

Using electron backscatter diffraction, the microstructural features of tension–compression–tension (T–C–T) tertiary twins are studied in coarse-grained pure polycrystalline magnesium subjected to monotonic compression along the extrusion direction in ambient air. T–C–T tertiary twins are developed due to the formation of a compression–tension double twin inside a primary tension twin. All the observed T–C–T twin variants are of TiCjTjtype. TiCi+1Ti+1(or TiCi−1Ti−1) variants are observed more frequently than TiCi+2Ti+2(or TiCi−2Ti−2) variants. The number of tertiary twin lamellae increases with the applied compressive strain. [ABSTRACT FROM AUTHOR]

The internal friction of magnesium single crystals, bicrystals and polycrystals has been studied between room temperature and 450°C. There is no internal friction peak in the single crystals, but a prominent relaxation peak appears at around 160°C in polycrystals. The activation energy of the peak is 1.0 eV, which is consistent with the grain boundary self-diffusion energy of Mg. Therefore, the peak in polycrystals can be attributed to grain boundary relaxation. For the three studied bicrystals, the grain boundary peak temperatures and activation energies are higher than that of polycrystals, while the peak heights are much lower. The difference between the internal friction peaks in bicrystals and polycrystals is possibly caused by the difference in the concentrations of segregated impurities in grain boundaries. [ABSTRACT FROM AUTHOR]

A new constitutive model to describe twin nucleation, propagation and growth for magnesium crystals is developed and implemented in the recently developed Elastic Viscoplastic Self-Consistent polycrystal model. The new model explicitly takes into account the stress relaxation associated with twin nucleation. It is demonstrated that the new twinning model is able to capture key macroscopic features associated with twin nucleation, propagation and growth observed experimentally. [ABSTRACT FROM AUTHOR]