Topological Short-range Order Research Articles

Effect of chemical short-range ordering on thermodynamics, structure, and dynamics of ZrCu-based metallic glass-forming liquids

Chemical-ordering in metallic liquid alloys affects important structural, thermodynamic, and dynamical factors governing the kinetics of the glass formation process and the glass-forming ability. The present study on Zr50Cu50, Zr50Cu45Al5, and Zr50Cu45Ag5 metallic glass-forming liquids reveal that minor addition of Al/Ag in Zr50Cu50 leads to different chemical short-range orders due to the hetero-coordination tendency of Al in Zr50Cu45Al5 and homo-coordination tendency of Ag in Zr50Cu45Ag5. Different chemical short-range ordering causes qualitatively different topological short-range orders in the two ternary alloys. Results of inherent structure energy and excess entropy indicate modification of the potential energy landscape such that the local minima (metabasins) on the landscape of Zr50Cu45Al5 become deeper and less rugged, whereas the metabasins become shallower and more rugged in Zr50Cu45Ag5. Single-particle dynamics investigations clearly demonstrate the effect of difference in the chemical-ordering, topological short-range order, and the potential energy landscape on the atomic diffusion, structural relaxation, and dynamic heterogeneities in the ternary alloys. It signifies that the dynamics of the studied glass-forming alloys is closely linked with the structure and thermodynamics. The study also provides a very useful insight of the correlation between the chemical-ordering and the short-time dynamical features in the studied metallic glass-forming liquids.

A novel criterion for predicting the glass-forming ability in Zr–Cu–Al ternary alloys: A molecular dynamics study

The molecular dynamics simulation is used to investigate the correlation between the atomic scale structure and glass-forming ability (GFA) of the ternary (Zr0.5Cu0.5)100-xAlx (x = 2, 4, 6, 8, 10, 12) bulk metallic glasses. Different techniques, like the Voronoi tessellation, are exploited to quantify this system's topological and chemical short-range ordering. It is found that the potential energy and the virial stress energy density of the icosahedra reveal the geometrical and chemical ordering in this system, respectively. Accordingly, a new GFA prediction criterion is presented, and the criterion's feasibility is demonstrated for various compositions by comparing the predicted and experimental data. It is found that Zr46Cu46Al8, Zr70Cu20Al10, and Zr40Cu10Al50 alloys are the optimal compounds with respect to GFA.

Influence of La on the atomic structure of Al[sbnd]Cu alloy liquid

The influence of La element on the atomic structure of AlCu alloy liquid above the liquidus line was investigated through high-energy x-ray diffraction technology on synchrotron facility and constrained reverse Monte Carlo simulation. The addition of La induced a change in nearest neighbor environments and chemical short-range orders of the atoms, which makes the Cu and La atoms dispersed in the liquid and surrounded by Al atoms. The analysis results of atomic topological short-range order show La element does not promote the icosahedral short-range order in the Al86Cu9 liquid, but increases the number of cluster types and reduces the variance of the cluster fraction, leading to a more disordered structure. These results strongly support that the diversity and distribution of clusters are responsible for the glass-forming ability of alloys, not the specific cluster type. Moreover, La element affects the arrangement of clusters in space, enhancing structural heterogeneity of the liquid and the correlation between clusters with high five-fold symmetry, which can also result in an improvement in glass-forming ability. These findings reveal the role of La element in enhancing glass-forming ability, and have implications for understanding the liquid-glass transition mechanism.

Short-range order of liquid Ti72.3Fe27.7 investigated by a combination of neutron scattering and X-ray diffraction

Abstract In this work we report on investigations into the topological and chemical short-range order of binary Ti72.3Fe27.7 alloy melts. In order to analyse the structure, the melts were investigated by means of neutron scattering and energy dispersive diffraction of synchrotron radiation. The combination of both diffraction techniques allowed the determination of the partial Bhatia Thornton structure factors S NN(Q) and S CC(Q). The experimental results provide evidence of an icosahedral topological short-range order prevailing in the liquid that is accompanied by a pronounced chemical short-range order such that Ti –Fe nearest neighbours are preferentially formed.

Ordering in liquid and its heredity impact on phase transformation of Mg-Al-Ca alloys

It is a long-sought goal to achieve desired mechanical properties through tailoring phase formation in alloys, especially for complicated multi-phase alloys. In fact, unveiling nucleation of competitive crystalline phases during solidification hinges on the nature of liquid. Here we employ ab initio molecular dynamics simulations (AIMD) to reveal liquid configuration of the Mg-Al-Ca alloys and explore its effect on the transformation of Ca-containing Laves phase from Al2Ca to Mg2Ca with increasing Ca/Al ratio (rCa/Al). There is structural similarity between liquid and crystalline phase in terms of the local arrangement environment, and the connection schemes of polyhedras. The forming signature of Mg2Ca, as hinted by the topological and chemical short-range order originating from liquid, ascends monotonically with increasing rCa/Al. However, Al2Ca crystal-like order increase at first and then decrease at the crossover of rCa/Al = 0.74, corresponding to experimental composition of phase transition from Al2Ca to Mg2Ca. The origin of phase transformation across different compositions lies in the dense packing of atomic configurations and preferential bonding of chemical species in both liquid and solid. The present finding provides a feasible scenario for manipulating phase formation to achieve high performance alloys by tailoring the crystal-like order in liquid.

Radiation Effects in Amorphous Metallic Alloys as Revealed by Mössbauer Spectrometry: Part I. Neutron Irradiation

Iron-based amorphous metallic alloys (AMAs) of several compositions were exposed to neutron irradiation with fluences of up to 1019 n/cm2. These materials exhibit excellent magnetic properties which predetermine them for use in electronic devices operated also in radiation-exposed environments. Response of the studied AMAs to neutron irradiation is followed by Mössbauer spectrometry which probes the local microstructure. Neutron irradiation leads to rearrangement of constituent atoms, their clustering, and formation of stress centers. The observed modifications of topological short-range order result in changes of spectral parameters including average hyperfine magnetic field, ⟨B⟩, standard deviation of the distribution of hyperfine fields, and position of the net magnetic moment. After irradiation, especially differences in ⟨B⟩-values develop in two opposite directions. This apparent controversy can be explained by formation of specific atomic pairs with different exchange interactions, which depend on the composition of the samples. Part II of this paper will be devoted to radiation effects caused in Fe-based AMAs by ion irradiation.

Fine Structure of Zr<sub>80</sub>Pt<sub>20</sub> Amorphous Alloy Determined from Anomalous X-ray Scattering (AXS) Data by Applying Reverse Monte-Carlo (RMC) Simulation Method

The fine structure of a Zr80Pt20 amorphous alloy was evaluated by anomalous X-ray scattering (AXS) coupled with reverse Monte Carlo (RMC) simulation. Featureless short-range ordered structures were preferentially formed by the Zr component, similar to those described by dense random packing (DRP), while the Pt atoms adopted a somewhat different structure. The Pt atoms adopted Zr-rich coordination and an icosahedral local atomic arrangement, in unique chemical short-range ordering (CSRO) as well as topological short-range ordering (TSRO). The present AXS-RMC analysis also suggested that the pre-peak signal at 17 nm−1 in the X-ray diffraction profile was largely attributed to the correlation between the Pt–Pt pair with a separation of approximately 0.4–0.5 nm. The geometrical and chemical features of the common neighbors of the middle-range Pt–Pt pairs indicate the unique CSRO and TSRO, where both chemical and density fluctuations were observed in two distinct regions: a Zr-rich region with high packing density and a Pt-rich region with low packing density.

Engineering of magnetic properties and magnetoimpedance effect in Fe-rich microwires by reversible and irreversible stress-annealing anisotropy

Herein, by using both hysteresis loops and the Giant magnetoimpedance, GMI, measurements, the magnetic properties of amorphous FeSiBC microwires have been thoroughly analyzed paying attention on the influence of annealing (under stress or without stress) on the GMI effect and magnetic properties of Fe–Si–B–C microwires. We observed that stress annealing allows the induction of transverse magnetic anisotropy and the GMI effect improvement. This stress-annealing induced anisotropy depends on the stress-annealing conditions: annealing time and stress applied during the annealing and can be partially annealed out by subsequent furnace annealing. However, the reversibility of the stress-annealing induced anisotropy depends on the stress-annealing conditions. Particularly, most of the transverse induced magnetic anisotropy obtained by stress-annealing at high stresses values is irreversible. Stress-annealing followed by annealing without stress allows further improvement of the GMI effect in Fe–Si–B–C microwires in a wide frequency range.Coercivity, remanent magnetization, and magnetoimpedance ratio of FeSiBC microwires can be tuned by annealing conditions: annealing time and stress.All studied microwires present GMI hysteresis. The sample with the highest GMI ratio presents the lowest GMI hysteresis.Observed experimental results are discussed considering relaxation of internal stresses, compressive “back-stresses” arising after stress annealing and topological short range ordering.

Topological and chemical short-range order and their correlation with glass form ability of Mg-Zn metallic glasses: A molecular dynamics study

Mg-based metallic glasses are promising materials for biodegradable implants. Understanding atomistic mechanism behind glass formation in these glasses plays a critical role in developing them for future applications. In the present work, we perform a set of molecular dynamics simulations to study structural origin behind glass form ability of Mg-based Mg-Zn metallic glasses at a wide range of compositions. Pair distribution function, Voronoi tessellation and dynamical analysis were adopted to characterize local structures in these glasses. Structural analysis was performed considering both topological and chemical short-range orders. It was found that structure of Mg-Zn metallic glasses could be best described from the perspective of solute-centered clusters. Zn-centered icosahedra, which have the highest symmetry among all local clusters, are preferred in all compositions and its population reaches nearly 28% regardless of the overall chemical composition. The stability of this local cluster depends at high extent to the chemical short-range order around Zn atoms. At favorable composition, that is equivalent to nearly ideal icosahedron geometry, Zn-centered icosahedra would have highest stability and lowest dynamic, which could hinder atoms involved in these clusters from redistribution and/or crystallization. The results offer a good explanation of experimentally observed maximum glass form ability at Mg70Zn30 composition in Mg-Zn system. It could open a door for the engineering of metallic glass alloys compositions for the optimal glass form ability by means of numerical simulations without involving expensive experimental procedures.

Submicrostructure and Characteristics of the Short-Range Atomic Order in an Amorphous Ti–Ni–Ta–Zr-Based Surface Alloy Formed on a TiNi Substrate by the Electron-Beam Method

This study presents the results of studying the microstructure and topological short-range atomic order in an amorphous Ti−Ni−Тa−Zr-based surface alloy formed by the additive method through pulsed electron-beam liquid-phase mixing of the “Ti70Ta30 film (50 nm)/Zr film (100 nm)/TiNi substrate” system. It is shown that an amorphous structure with a thickness of 2 μm is formed in the cross-section of the surface alloy and is characterized by the gradient chemical composition. It is found that the transition sublayer adjacent to the TiNi substrate has a nanocomposite crystalline structure based on the Ti2Ni intermetallic compound. By means of the atomic radial distribution function method, using electron nanobeam diffraction data, a study of the topological short-range atomic order in the amorphous layer is performed. It is shown that the atomic structure in the amorphous surface Ti−Ni−Тa−Zr alloy has a cluster structure which can be described by the superposition of coordination polyhedra interconnected with each other by common faces corresponding to the different crystalline devitrification phases.

Specific Features of the Atomic Structure of Ti50Ni25Cu25 Alloy Rapidly Quenched from Melt

A complex study of the structure of Ti50Ni25Cu25 alloy obtained in the initial amorphous state by rapid quenching (melt spinning) have been performed for the first time. The investigations are carried out by methods of neutron diffraction, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and electron microdiffraction. It is found that the topological and composition short-range atomic order, corresponding to three superstructure types (B2, L21, and L12), is formed within localized nanodomains (up to 1 nm) in amorphous Ti50Ni25Cu25 alloy upon solidification. It is also demonstrated for the first time that the alloy has an amorphous–crystal structure, which contains (along with individual microspherulites that underwent thermoelastic martensitic transformation B2 ↔ B19) nanocrystalline ensembles with the B2, L21, or L12 structure up to 10 nm in size, which are localized in the amorphous matrix.

Mössbauer study and magnetic properties of Fe–Si–B–Cu amorphous systems with minor substitution of carbon

The effect of minor substitution of carbon on the structure and magnetic properties of Fe–Si–B–Cu-type metallic glasses was investigated. Structural investigations performed at room temperature with Mossbauer spectroscopy and X-ray diffractometry confirmed amorphous nature of the as-quenched ribbons. Average values of hyperfine magnetic fields do not significantly differ with respect to the minor changes in the metalloid contents (up to 1 at.%). No fluctuations were found in the chemical short-range order (SRO). Only structural deviations in topological SRO were revealed that were confirmed also by DSC and mTGA techniques via changes in the crystallization and Curie temperatures caused by compositional modifications. In addition, magnetic measurements show that substitution of C for Fe leads to slightly higher saturation magnetization corresponding to parallel orientation of the external magnetic field with respect to the plane of the ribbon.

Specific Features of the Atomic Structure of the Ti50Ni25Cu25 Alloy Amorphized during Rapid Quenching from a Melt

This paper presents results of the structural study of the Ti50Ni25Cu25 alloy formed under rapid quenching from a melt. The studies were performed using neutron and X-ray diffraction and transmission and scanning electron microscopy. It has been revealed that this alloy has an amorphous nanocrystalline structure, which contains В2, L21, and L12 ensembles of nanocrystals with sizes to several nanometers in an amorphous matrix alongside with microspherolites, which have sustained the thermoelastic В2–В19 martensitic transition. It has also been shown for the first time that topological and compositional short-range atomic order is formed in the amorphous matrix of the Ti50N25Cu25 alloy in the form of localized nanodomains by the same three types of superstructures (В2, L21, L12).

Tailoring of magnetoimpedance effect and magnetic softness of Fe-rich glass-coated microwires by stress- annealing

There is a pressing need for improving of the high-frequency magneto-impedance effect of cost-effective soft magnetic materials for use in high-performance sensing devices. The impact of the stress-annealing on magnetic properties and high frequency impedance of Fe-rich glass-coated microwires was studied. Hysteresis loops of Fe-rich microwires have been considerably affected by stress- annealing. In stress-annealed Fe- rich microwire we obtained drastic decreasing of coercivity and change of character of hysteresis loop from rectangular to linear. By controlling stress-annealing conditions (temperature and time) we achieved drastic increasing (by order of magnitude) of giant magnetoimpedance ratio. Coercivity, remanent magnetization, diagonal and of-diagonal magnetoimpedance effect of Fe-rich microwires can be tuned by stress-annealing conditions: annealing temperature and time. Observed experimental results are discussed considering relaxation of internal stresses, compressive “back-stresses” arising after stress annealing and topological short range ordering.

The characterisation of atomic structure and glass-forming ability of the Zr–Cu–Co metallic glasses studied by molecular dynamics simulations

In the present work, the glass formation process and structural properties of Zr50Cu50-xCox (0 ≤ x ≤ 50) bulk metallic glasses were investigated by a molecular dynamics simulation with the many body tight-binding potentials. The evolution of structure and glass formation process with temperature were discussed using the coordination number, the radial distribution functions, the volume–temperature curve, icosahedral short-range order, glass transition temperature, Voronoi analysis, Honeycutt–Andersen pair analysis technique and the distribution of bond–angles. Results indicate that adding Co causes similar responses on the nature of the Zr50Cu50-xCox (0 ≤ x ≤ 50) alloys except for higher glass transition temperature and ideal icosahedral type ordered local atomic environment. Also, the differences of the atomic radii play the key role in influencing the atomic structure of these alloys. Both Cu and Co atoms play a significant role in deciding the chemical and topological short-range orders of the Zr50Cu50-xCox ternary liquids and amorphous alloys. The glass-forming ability of these alloys is supported by the experimental observations reported in the literature up to now.

Mössbauer spectrometry analysis of Fe78Si9B13 metallic glass prepared with different quenching wheel speed

Impact of the wheel speed upon microstructure and hyperfine interactions of amorphous Fe78Si9B13 ribbons was studied. Mossbauer spectrometry, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and magnetic measurements were applied. Though minor effects of wheel speed upon macroscopic magnetic properties was found, notable changes in repositioning of magnetic moments of the resonant atoms caused by modifications in the topological short-range order (SRO) were unveiled. No deviations were observed in the chemical SRO. The observed effects were enhanced after annealing at moderate temperatures.

Microstructure and magnetic properties of amorphous Fe51Co12Si16B8Mo5P8 alloy

Abstract Microstructure and thermomagnetic characteristics of the amorphous Fe51Co12Si16B8Mo5P8 alloy in the as-quenched state and after 1 h of annealing at 573 K and 773 K are studied. The structural investigations performed by Mössbauer spectroscopy and X-ray diffractometry confirmed the amorphous structure of the analysed materials. An increase in the annealing temperature up to 773 K does not lead to crystallization of the amorphous alloy. Only structural rearrangement that causes changes in the topological short-range order and annealing out of free volume is observed. This behaviour was confirmed by modifications of the shapes of hyperfine field distributions derived from the corresponding Mössbauer spectra of the investigated alloys. The Curie temperatures of the as-quenched and annealed Fe51Co12Si16B8Mo5P8 alloy at 573 and 773 K are 400, 405 and 421 K, respectively.

Medium Range Ordering realized in Zr80Pt20Amorphous Alloy

The short- and medium-range ordering structure in Zr80Pt20 amorphous alloy has been investigated by anomalous X-ray scattering coupled with reverse Monte-Carlo simulation. Pt prefers to construct a Zr-rich icosahedral complex with unique chemical and topological short-range ordering. The present analysis also revealed the medium-range ordering of Pt-Pt pairs corresponding to the pre-peak signal at 17 nm−1 in the diffraction profile. The chemical and topological features around Pt and bonding structure correspond well with those of Mn in the approximant phase of α-AlMnSi.

Constant real-space fractal dimensionality and structure evolution in Ti62Cu38 metallic glass under high pressure

The structure of binary $\mathrm{T}{\mathrm{i}}_{62}\mathrm{C}{\mathrm{u}}_{38}$ metallic glass is investigated under pressures up to 33.8 GPa using the pair distribution function analysis based on high-energy x-ray scattering and reverse Monte Carlo (RMC) simulations. At a global scale, its relative volume shows a continuously smooth curve as a function of pressure. The isothermal bulk modulus of $\mathrm{T}{\mathrm{i}}_{62}\mathrm{C}{\mathrm{u}}_{38}$ metallic glass is estimated as ${B}_{0}=132(3)\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ with ${B}_{0}^{\ensuremath{'}}=5.8(0.4)$. At a local scale, the atomic packing structure under compression conditions, which is extracted from RMC simulations, shows that the topological short-range order is dominated by the deformed icosahedron polyhedra and basically maintains stable. From the relationship between the relative volume and changing ratio of the atomic separation distances, the real-space fractal dimensionality of this metallic glass is determined as about 2.5 for all of the first four peaks. This experimental result reveals the consistent nature of the fractal feature on the degree of self-similarity in this sample within the entire experimental pressure range.

High temperature behavior of functional TiAlBSiN nanocomposite coatings

Abstract This article reports on the thorough characterization of structural-phase transformation in amorphous TiAlBSiN coating after high temperature annealing at 900 °C in ambient air. The influence of annealing on the tribo-mechanical behavior of the coating at nano and micro scale was also examined. The research included multiple experimental techniques, i.e. AFM, SEM, TEM, HR-TEM, EDS, XPS and Raman spectroscopy. Experiments showed that the amorphous phase of the TiAlBSiN coating undergoes a structural transformation, evidenced in the changes of parameters such as topological and chemical short-range order after the post-deposition annealing at 900 °C in air. The observed structural transformation, leads to a phase separation with the formation of a three dimensional nc-TiAl 3 /a-SiBN(O) nanocomposite structure. The relative increase of hardness, reduced elastic modulus, H/Er ratio and H 2 /E 3 r ratio after high temperature treatment of TiAlBSiN coatings is also reported. The complex interdependency between chemistry, morphology and relative composition of the amorphous TiAlBSiN coating phase, during the high temperature treatment, with the respective change of the tribo-mechanical characteristics, are evidence of the improvement of the coating properties in response to the environmental conditions and high temperature. This work contributes particularly to the development and understanding of flexible nanocomposite protective coatings and their changes at high temperature of operation.