Crystalline Alloys Research Articles

Comparative study of amorphous and crystalline Zr-based alloys in response to nanosecond pulse laser ablation

Comparative study of amorphous and crystalline Zr-based alloys in response to nanosecond pulse laser ablation

Electrodeposition of Complex High Entropy Oxides via Water Droplet Formation and Conversion to Crystalline Alloy Nanoparticles.

A combination of electrodeposition and thermal reduction methods have been utilized for the synthesis of ligand-free FeNiCo alloy nanoparticles through a high-entropy oxide intermediate. These phases are of great interest to the electrocatalysis community, especially when formed by a sustainable chemistry method. This is successfully achieved by first forming a complex five element amorphous FeNiCoCrMn high-entropy oxide (HEO) phase via electrodeposition from a nanodroplet emulsion solution of the metal salt reactants. The amorphous oxide phase is then thermally treated and reduced at 570-600 °C to form the crystalline FeNiCo alloy with a separate CrMnOx cophase. The FeNiCo alloy is fully characterized by scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental analysis and is identified as a face-centered cubic crystal with the lattice constant a = 3.52 Å. The unoptimized, ligand-free FeNiCo NPs activity toward the oxygen evolution reaction is evaluated in alkaline solution and found to have an ∼185 mV more cathodic onset potential than the Pt metal. Beyond being able to synthesize highly crystalline, ligand-free FeNiCo nanoparticles, the demonstrated and relatively simple two-step process is ideal for the synthesis of tailor-made nanoparticles where the desired composition is not easily achieved with classical solution-based chemistries.

Deformation behavior of a nanoporous metallic glass at room temperature

The mechanical properties and plastic deformation of a Cu55.4Zr35.2Al7.5Y1.9 nanoporous metallic glass (MG) have been studied using depth-sensing nanoindentation combined with electron microscopy characterization. The nanoporous MG exhibits an initial relative density of 50.9% and a bicontinuous structure with 20.84 ± 1.49 nm-diameter interconnecting ligaments. It is brittle in tension, whereas it has significant homogeneous plasticity under compression. It has a hardness of 0.67 ± 0.06 GPa and Young's modulus of 14.72 ± 0.74 GPa from nanoindentation. While under tensile and compression, it has a yield strength of 0.22 to 0.23 GPa and an effective modulus of 10.37 ± 0.99 GPa. The discrepancy between the moduli is caused by irreversible shear transformation zone (STZ) plasticity that takes place well ahead of the yield point. The deformation in the nanoporous MG begins with both elastic and plastic bending in ligaments and transfers to plastic uniaxial deformation in ligaments at a critical strain near 0.03, at which a significant change in stiffness is observed. The yielding stress follows the universal scaling law predicted by the critical-like behavior in glassy systems. The strength to modulus ratio is well maintained in this nanoporous MG and is higher than the porous crystalline alloys. Our experimental study clarifies the fundamental failure mechanism and deformation behavior in nanoporous MGs.

Microstructure and magnetic properties of Sm-Co-based amorphous nanocrystals controlled by B addition

The crystalline Sm-Co alloys show excellent hard magnetic properties, while the amorphous Sm-Co alloys have a poor performance. In this paper, Sm12Co76-xFe4Zr7Cu1Bx (x = 0, 2, 4, 5, 5.2) ribbons were melt-spun at 40 m/s, and the effects of B content on the phase composition, microstructure, and magnetic properties of the ribbons were studied. The results show that the main phase of all ribbons with different B content is Sm(Co, M)7. With an increase in B content, the content of amorphous and fine soft magnetic phases increases. Besides, nano-scale crystalline clusters are embedded in the amorphous matrix, forming different forms of exchange coupling microstructures between the soft and hard magnetic phases. The x = 5 ribbons have the finest grains, the most uniform grain distribution, and the strongest exchange coupling effect. Without heat treatment, their coercivity reaches 19.5 ± 0.9 kOe, and the other magnetic properties are also excellent, Mr = 24.8 ± 1.7 emu/g, M2T = 29.0 ± 1.7 emu/g, and Mr/M2T = 0.858 ± 0.015.

Wetting properties and surface energy of four different amorphous alloys compared to the corresponding crystalline alloys

The surface wetting behavior of solid materials was very important in the application of amorphous alloys. However, the surface wetting behavior of amorphous alloys was not yet well understood. In this study, the difference in surface energy (SE) of four different amorphous alloys (Fe48Cr15Mo14C15B6Y2, Cu46Zr42Al7Y5, Zr65Cu17.5Ni10Al7.5, and Zr55Cu30Ni5Al10) and their corresponding crystalline alloys were systematically analyzed. The results show that the SE of amorphous alloys was much lower than their corresponding crystalline alloys. Among four kinds of amorphous alloys, Fe48Cr15Mo14C15B6Y2 amorphous alloy with the lowest SE was selected to prepare the superhydrophobic surfaces with the largest contact angle of 154 ± 2.4° and strong adsorption ability by electrochemical corrosion and chemical modification. Meanwhile, the corrosion resistance of the Fe48Cr15Mo14C15B6Y2 amorphous alloy was greatly improved. This work aimed to enrich the application of amorphous alloys in the field of extreme wettability.

Effect of powder size on strength and corrosion behavior of Mg66Zn30Ca4 bulk metallic glass

Biomedical biodegradable materials have attracted widespread attention since they are naturally decomposed in the body. In particular, Mg-Zn-Ca systems are the most popular degradable metal materials, owing to their good biocompatibility and mechanical properties. Meanwhile, bulk metallic glass (BMG) is known to exhibit a series of advantages over crystalline alloys (including higher strength, hardness, and corrosion resistance), owing to the long-range disorder in atomic arrangement. In this study, Mg66Zn30Ca4 BMG samples with average particle sizes of 22.9, 45.4, and 62.4 µm were prepared via spark plasma sintering (SPS), and the influence of powder particle sizes on mechanical strength, hardness, and corrosion behavior was investigated. The results showed that the strength and hardness decreased with an increase in the particle size. Based on the long-term corrosion test, it can be concluded that a large particle size is beneficial to the corrosion resistance of materials.

Transition from high-entropy to conventional (TiZrNbCu)1−xCox metallic glasses

In this article, we describe the characterization of a newly fabricated amorphous alloy system (TiZrNbCu)1−xCox covering a broad composition range from high-entropy (HEA) to Co-rich alloys (x ≤ 0.43). We investigated thermal stability, atomic and electronic structure, and magnetic and mechanical properties as a function of chemical composition x. One of the important findings is that all studied properties change their dependence on concentration x within the HEA range. In particular, it has been found that the average atomic volume deviates from Vegard’s law for x > 0.2, the concentration for which the average atomic packing fraction suddenly changes. The valence band structure, studied with ultraviolet photoemission spectroscopy, shows a split-band shape with 3d-states of Co approaching the Fermi level on increasing x. Due to the onset of magnetic correlations, magnetic susceptibility rapidly increases for x > 0.25. Very high microhardness increases rapidly with x. The results are compared with those for similar binary and quinary metallic glasses and with those for Cantor type of crystalline alloys.

Key factors of deformation mechanism of Cu-Ag alloy

This work focused on the effect of the structural order and dimensionality on the deformation mechanism of Cu-Ag alloy and the triggering factors of this mechanism. It is revealed that (i) the weakness of the system develops from bulk to nanoscale and crystalline to amorphous systems, (ii) Cu-Ag nanowires are more flexible than their bulk counterparts, (iii) crystalline Cu-Ag alloys are stiffer than amorphous systems. The reason for early yielding and less stiffness of amorphous Cu-Ag nanowire with respect to bulk material is the less fraction of ideal icosahedra. Cu atoms are a key factor to characterize the mechanical response of both amorphous Cu-Ag alloys. While there are two different deformation modes in crystalline systems, the only mode observed in the amorphous alloy is homogeneous deformation. The presence of 〈0,5,2,x〉 (x = 5,6) polyhedral is the reason for the transition of deformation from homogeneous to inhomogeneous in the crystalline Cu-Ag alloys.

Nanoindentation creep behavior of an Fe–Cr–Mo–B–C amorphous coating via atmospheric plasma spraying

Unlike crystalline alloys, disordered amorphous alloys lack long-range order. Even today, the creep mechanisms for amorphous alloys are far from being fully understood. In this work, an Fe–Cr–Mo–B–C (Cr: 25–27 wt%, Mo: 16–18 wt%, B: 2.0–2.2 wt%, and C: 2.0–2.5 wt%) amorphous coating was fabricated on the surface of a 304 stainless steel via atmospheric plasma spraying with a NiAl bonding layer. In this study, the effects of peak load and loading rate on the creep deformation behavior of the Fe-based amorphous coatings were investigated. The results demonstrated that a macroscopic viscous flow behavior was obtained at low peak loads, which led to a larger creep strain rate sensitivity m. At high loading rates, the accumulation of free volume led to an increase in the shear deformation zone and a more uniform plastic rheology. It indicated that at higher loading rates, the amorphous coating had higher m values under steady-state creep.

Phase Transformations from Nanocrystalline to Amorphous (Zr70Ni25Al5)100-xWx (x; 0, 2, 10, 20, 35 at. %) and Subsequent Consolidation.

Glasses, which date back to about 2500 BC, originated in Mesopotamia and were later brought to Egypt in approximately 1450 BC. In contrast to the long-range order materials (crystalline materials), the atoms and molecules of glasses, which are noncrystalline materials (short-range order) are not organized in a definite lattice pattern. Metallic glassy materials with amorphous structure, which are rather new members of the advanced materials family, were discovered in 1960. Due to their amorphous structure, metallic glassy alloys, particularly in the supercooled liquid region, behave differently when compared with crystalline alloys. They reveal unique and unusual mechanical, physical, and chemical characteristics that make them desirable materials for many advanced applications. Although metallic glasses can be produced using different techniques, many of these methods cannot be utilized to produce amorphous alloys when the system has high-melting temperature alloys (above 1500 °C) and/or is immiscible. As a result, such constraints may limit the ability to fabricate high-thermal stable metallic glassy families. The purpose of this research is to fabricate metallic glassy (Zr70Ni25Al5)100-xWx (x; 0, 2, 10, 20, and 35 at. %) by cold rolling the constituent powders and then mechanically alloying them in a high-energy ball mill. The as-prepared metallic glassy powders demonstrated high-thermal stability and glass forming ability, as evidenced by a broad supercooled liquid region and a high crystallization temperature. The glassy powders were then consolidated into full-dense bulk metallic glasses using a spark plasma sintering technique. This consolidation method did not result in the crystallization of the materials, as the consolidated buttons retained their short-range order fashion. Additionally, the current work demonstrated the capability of fabricating very large bulk metallic glassy buttons with diameters ranging from 20 to 50 mm. The results indicated that the microhardness of the synthesized metallic glassy alloys increased as the W concentration increased. As far as the authors are aware, this is the first time this metallic glassy system has been reported.

Transition from High-Entropy to Conventional Alloys: Which Are Better?

The study of the transition from high-entropy alloys (HEAs) to conventional alloys (CAs) composed of the same alloying components is apparently important, both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of the corresponding CAs. However, this transition has thus far been studied in only two types of alloy systems: crystalline alloys of iron group metals (such as the Cantor alloy and its derivatives) and both amorphous (a-) and crystalline alloys, TE-TL, of early (TE = Ti, Zr, Nb, Hf) and late (TL = Co, Ni, Cu) transition metals. Here, we briefly overview the main results for the transition from HEAs to CAs in these alloy systems and then present new results for the electronic structure (ES), studied with photoemission spectroscopy and specific heat, atomic structure, thermal, magnetic and mechanical properties of a-TE-TL and Cantor-type alloys. A change in the properties of the alloys studied on crossing from the HEA to the CA concentration range mirrors that in the ES. The compositions of the alloys having the best properties depend on the alloy system and the property selected. This emphasizes the importance of knowing the ES for the design of new compositional complex alloys with the desired properties.

Shape memory effect in metallic glasses

Shape memory effect in metallic glasses

Synthesis and Characterization of FeNi-based Composite Powder from the Mixture of Fe-based Amorphous Powders and Crystalline Ni powders

Fe–Ni alloys have attracted interest as important magnetic alloys without rare-earth (RE) elements, which exhibit a wide variety of magnetic properties depending on the atomic ratios of Fe and Ni. Here, we attempted to synthesize Fe-Ni magnetic materials using a Fe based amorphous alloy precursor that is thermodynamically metastable and has more open atomic packing structure than crystalline alloys. High energy ball milling was applied to promote the formation of various Fe-Ni phases using mixtures of the amorphous precursor powder and 10-50% crystalline Ni powder. The as-milled composite powders as well as the composite powders annealed at 673 K were analyzed by X-ray diffractometer, differential scanning calorimeter, scanning electron microscope, and vibrating sample magnetometer to investigate their magnetic properties in terms of phase transformation behavior of the composite powders.

Tensile and Impact Toughness Properties of a Zr-Based Bulk Metallic Glass Fabricated via Laser Powder-Bed Fusion.

In the past few years, laser powder-bed fusion (LPBF) of bulk metallic glasses (BMGs) has gained significant interest because of the high heating and cooling rates inherent to the process, providing the means to bypass the crystallization threshold. In this study, (for the first time) the tensile and Charpy impact toughness properties of a Zr-based BMG fabricated via LPBF were investigated. The presence of defects and lack of fusion (LoF) in the near-surface region of the samples resulted in low properties. Increasing the laser power at the borders mitigated LoF formation in the near-surface region, leading to an almost 27% increase in tensile yield strength and impact toughness. Comparatively, increasing the core laser power did not have a significant influence. It was therefore confirmed that, for BMGs like for crystalline alloys, near-surface LoFs are more detrimental than core LoFs. Although increasing the border and core laser power resulted in a higher crystallized fraction, detrimental to the mechanical properties, reducing the formation of LoF defects (confirmed using micro-computed tomography, Micro-CT) was comparatively more important.

Interface-driven static and dynamic magnetic properties of ultrathin Fe/Ge multilayers

Ferromagnet-semiconductor (FM-SC) alloy phase with room temperature ferromagnetic properties at the interfaces of FM/SC heterostructures are believed to improve the electron spin injection from the FM to the SC for the realization of spintronic devices. Here we report the formation of a crystalline alloy phase (Fe3Ge) at the interfaces on growing ultrathin Fe/Ge multilayers at an elevated substrate temperature of ∼ 523 K as well as on annealing the multilayer at a temperature > 523 K. The alloy phase formation at interfaces is achieved at a much lower temperature than the Fe3Ge phase formation in bulk material (∼973 K), mainly due to rapid interdiffusion of Fe and Ge at the interfaces which is about 4 (∼2) order higher in magnitude than the diffusion of Ge (Fe) in the bulk crystalline phase. We find a large magnetic anisotropy constant (K ∼ 3 × 106 to 7 × 107 erg/cm3) on the formation of the nanocrystalline alloy phase at interfaces. Ultrathin Fe/Ge multilayers were characterized using x-ray scattering, macroscopic magnetization measurement, and polarized neutron reflectivity (PNR). The temperature-induced diffusion process indicates that the alloy phase is structurally stable up to higher temperature. PNR provided a detailed depth profile of the magnetization in the system and suggested that the alloy phase is ferromagnetic at room temperature. We have also studied the dynamic magnetic properties of these systems by employing ferromagnetic resonance measurements.

Lithiation of the crystalline silicon as analyzed using soft X-ray emission spectroscopy and windowless energy dispersive X-ray spectroscopy

There is no clear consensus on the exact compounds that are generated during the room temperature lithiation of Si, which may include amorphous LixSi or a crystalline Li15Si4 alloy. Here, the lithiation behavior of a single-crystal Si(111) anode was studied using scanning electron microscopy (SEM), soft X-ray emission spectroscopy (SEXS), and windowless energy dispersive X-ray spectroscopy (EDS). A Li-Si alloy generated electrochemically via potentiostatic lithiation was found to have a layered structure that contained the 1st layer of crystalline Li15Si4 (c-Li15Si4) alloy pyramids, the 2nd layer of amorphous Li13Si4 (a-Li13Si4) alloy, and the 3rd layer of Li-diffused LixSi alloy. A maximum cathodic current appeared during this process, and both the c-Li15Si4 and Li-diffused LixSi alloys were observed to grow during the initial lithiation and to maintain almost constant thicknesses prior to reaching the maximum current, while the 2nd layer began to grow after the maximum current. Comparing the experimental and theoretical currents showed that the lithiation of crystalline Si is diffusion-controlled. The low Li diffusion coefficients in the bulk LixSi alloy and bulk Si evidently result in a low current density during Si lithiation.

High strength conductive bulk Cu-based alloy/metallic glass composites fabricated by spark plasma sintering

High strength conductive materials are the basic materials in the fields of electronic communication and mechanical manufacturing. In this study, we synthesize high-strength and high-conductivity bulk CuCrZr alloy/CuZrAl metallic glass composites (CA/CMGCs) via spark plasma sintering (SPS) process. The effect of CuZrAl metallic glass (MG) content on the mechanical and electrical properties of the composites is investigated. The CuZrAl MG provides high strength and the CuCrZr alloy contributes significantly to the plasticity and conductivity of the composites. In addition, it is demonstrated that a good bonding state between metallic glass and crystalline alloy contributes primarily to the high strength and high conductivity of the bulk CA/CMGCs. This study provides insights into the untapped potential of high-strength and high-conductivity Cu matrix crystal/amorphous composites.

Dual-phase amorphous-nanocrystalline nanoporous sites activated in Mo inserted CuTi metallic glass as efficient electrocatalysts for hydrogen evolution reaction

The production of noble metal-free, high-performance, earth-abundant hydrogen evolution reaction (HER) electrocatalysts is a challenging search but indispensably a vital issue for green energy conversion and production. Herein, we report a nanoporous self-supported CuTiMo site nanostructured from Cu60Ti37Mo3 metallic glass as a highly efficient electrocatalyst for HER. The development of nanoporous structure from metallic glassy alloy rather than the conventional crystalline alloy is carried out, and a comprehensive plausible working mechanism of nanoporous structure development is outlined. The novelty of the present research is the nanostructuring of metallic glasses to form crystalline and amorphous dual sites. The dual phased nanoporous electrocatalyst exhibits high catalytic activity comparable to standard Pt-catalyst at higher current densities (>60 mA cm−2). The electrocatalyst is stable even at high current densities (>100 mA cm−2) and needs much lesser overpotential than that of standard Pt/C catalyst for HER reaction at high current densities. The dealloying of defect-free metallic glasses leads to the formation of a large number of catalytic active sites, and the introduction of Mo into the CuTi matrix leads to accelerated H2 adsorption/desorption kinetics. The dealloyed metallic glass requires an overpotential of 220 mV vs. RHE to attain a current density of 100 mA cm−2 in an alkaline HER reaction. Based on the advantages of nanoporous structure development from highly metastable metallic glasses, the high active surface area of nanoporous structure on a high conductive substrate, the exceptional stability for long term and at high current densities, the proposed nanoporous metallic glass composite electrode is of significance for a diversity of applications for green energy production.

Pressure-induced two magnetic collapses in the ferromagnetic L12-Fe3Pd alloy and related elasticity and lattice dynamics anomalies

Pressure effect on the magnetic, mechanical and lattice dynamical properties of the ferromagnetic L12-Fe3Pd crystalline alloy was investigated by first-principles calculations. The calculated properties under ambient pressure are in good agreement with available theoretical results. A two-step pressure-induced collapse of magnetic moment was observed, accompanied by the collapse of the volume. The first one is at about 34.2 GPa, and the other is at about 67 GPa. While the magnetic moment disappears around 84 GPa. Thelattice dynamics calculations under high pressure revealed that the dynamically stable and unstable cases appear alternately. The system is dynamically unstable at low pressures due to the spontaneous magnetization of the system, and then the system is dynamically stable in the pressure range of 33.5 to 66.9 GPa, and this pressure range is between the first collapse pressure and second collapse pressure. The system becomes dynamically unstable again at pressure ranging from 67 to 83.7GPa, and afterwards becomes stable. Elastic constants and their dependence on pressure and related mechanical properties were investigated. Stability criteria show that ferromagnetic L12-Fe3Pd crystalline alloy is mechanically stable over the entire studied pressure range. The bulk modulus exhibits pronounced softening with pressure, and present minimum values at magnetic collapse pressures. The mechanism of elastic softening was analyzed with the magnetoelastic force. From Pugh’s ratio and Poisson’s ratio, the system exhibits brittleness at the vicinity of magnetic collapse pressures. The linear thermal expansion coefficient was calculated based on the quasi-harmonic approximation. The results reveal that the alloy does notexhibit thermal Invar behavior under zero pressure and high pressure. Finally, a high-anisotropy tetragonal structurewith space group symmetry P4/mbm was obtained by soft-mode phase transition theory, and this structure is dynamically and mechanically stable at zero pressure. Theoretical prediction suggested that the P4/mbm structure is energetically favorable than the previously reported structures at the pressure below 32 GPa and also showed that above 32 GPa the hexagonal D019 structure becomes the energetically most stable structure.

Improvement in power inductor performance at 3 MHz by mixing carbonyl iron powder with Fe–Si–Cr crystalline alloy

Improvement in power inductor performance at 3 MHz by mixing carbonyl iron powder with Fe–Si–Cr crystalline alloy