Wide Supercooled Liquid Region Research Articles

Effect of Chemical Composition on the Thermoplastic Formability and Nanoindentation of Ti-Based Bulk Metallic Glasses.

A series of Ti41Zr25Be34-xNix (x = 4, 6, 8, 10 at.%) and Ti41Zr25Be34-xCux (x = 4, 6, 8 at.%) bulk metallic glasses were investigated to examine the influence of Ni and Cu content on the viscosity, thermoplastic formability, and nanoindentation of Ti-based bulk metallic glasses. The results demonstrate that Ti41Zr25Be30Ni4 and Ti41Zr25Be26Cu8 amorphous alloys have superior thermoplastic formability among the Ti41Zr25Be34-xNix and Ti41Zr25Be34-xCux amorphous alloys due to their low viscosity in the supercooled liquid region and wider supercooled liquid region. The hardness and modulus exhibit obvious variations with increasing Ni and Cu content in Ti-based bulk metallic glasses, which can be attributed to alterations in atomic density. Optimal amounts of Ni and Cu in Ti-based bulk metallic glasses enhance thermoplastic formability and mechanical properties. The influence of Ni and Cu content on the hardness of Ti-based bulk metallic glasses is discussed from the perspective of the mean atomic distance.

Effects and mechanisms of Nb and Fe additions on glass-forming ability and magnetic properties of a Co71.5Gd3.5B25 metallic glass

Aiming to unraveling the effects and mechanisms of Nb and Fe additions on glass-forming ability (GFA) and magnetic properties, especially coercivity (Hc) on Co-based metallic glasses, 2–4 at% Nb and/or 7.15–28.6 at% Fe have been alloyed into a Co71.5Gd3.5B25 alloy by substitution of Co. The results show that alloying either Nb or Fe into the base alloy leads to enhanced stability of supercooled liquid and GFA, and bulk metallic glass (BMG) can be formed for the alloy with 4 at% Nb or 28.6 at% Fe. Combined addition of Nb and Fe further improves the thermal stability and GFA, and lowers viscosity in supercooled liquid state. A (Co0.6Fe0.4)67.5Gd3.5Nb4B25 BMG possess a wide supercooled liquid region (ΔTx) of 85 K, critical sample diameter of 3.0 mm, and minimum viscosity coefficient of 2 × 108 Pa∙s. The enrichment of Fe increases saturation magnetic flux density (Bs), Hc, and saturation magnetostriction coefficient (λs) of the (Co, Fe)-Gd-B-(Nb) metallic glasses; the addition of Nb effectively inhibits the deterioration of magnetic softness caused by Fe while reducing the Bs. The (Co0.6–0.9Fe0.1–0.4)67.5Gd3.5Nb4B25 BMGs possess good soft magnetic properties with the Bs and Hc ranging 0.43–0.69 T and 2.3–5.0 A/m, respectively. Ab initio molecular dynamics simulations indicated that alloying Fe into the Co-based metallic glasses leads to enhanced magnetic anisotropy energy. The increased magnetic anisotropy arising from enlarged λs results in the increased Hc. The combination of high GFA, large ΔTx, low viscosity, and good soft magnetic properties makes the Co-based Co-Fe-Gd-Nb-B BMGs highly promising for applications as micro electromagnetic devices produced through thermoplastic forming.

Geometries and electronic structures of Zr n Cu (n = 2–12) clusters: A joint machine-learning potential density functional theory investigation

Zr-based amorphous alloys have attracted extensive attention because of their large glassy formation ability, wide supercooled liquid region, high elasticity, and unique mechanical strength induced by their icosahedral local structures. To determine the microstructures of Zr–Cu clusters, the stable and metastable geometry of Zr n Cu (n = 2–12) clusters are screened out via the CALYPSO method using machine-learning potentials, and then the electronic structures are investigated using density functional theory. The results show that the Zr n Cu (n ≥ 3) clusters possess three-dimensional geometries, Zr n Cu (n ≥ 9) possess cage-like geometries, and the Zr12Cu cluster has icosahedral geometry. The binding energy per atom gradually gets enlarged with the increase in the size of the clusters, and Zr n Cu (n = 5, 7, 9, 12) have relatively better stability than their neighbors. The magnetic moment of most Zr n Cu clusters is just 1μ B, and the main components of the highest occupied molecular orbitals (HOMOs) in the Zr12Cu cluster come from the Zr-d state. There are hardly any localized two-center bonds, and there are about 20 σ-type delocalized three-center bonds.

Electrochemical hydrogen storage, mechanical and thermal behaviors of novel Mg-based alloy

In this study, Mg65Ni25Y5B5 metallic glass synthesized by using the melt-spinning technique was examined in terms of its electrochemical hydrogen-storage characteristics and mechanical and thermal behaviors. The X-ray diffraction and scanning electron microscopy results indicated that the alloy ribbon has a fully amorphous structure. The thermal behavior of the alloy ribbon was determined using flash differential scanning calorimetry (DSC). According to flash DSC results, the amorphous alloy ribbon exhibited a distinct glass transition temperature (T g) and a wide supercooled liquid region (ΔT x = T x − T g) before crystallization. Accordingly, T g and ΔT x are 195 and 63°C, respectively. The mechanical behavior of the magnesium (Mg)-based alloy at room temperature was determined by means of a Vickers microhardness (HV) tester. The microhardness value of the alloy ribbon was measured as 336.8 HV. The discharge capacity of the Mg65Ni25Y5B5 alloy reached 313 mAh/g. The cycle stability revealed that the alloy ribbon protected at least 76.7% of its initial discharge capacity at the 12th charge–discharge cycle.

Phase constitution and glass formation of U-Pd-Ni-Si alloys

In order to explore U-based alloys having high glass forming ability (GFA), a series of U-Pd-Ni-Si alloys with 60% U were designed on the basis of the eutectic features of U-Ni and U-Pd base systems together with the Si addition. Their ingots and ribbons were prepared by arc-melting and melt-spinning methods and further examined to reveal the phase constitution and amorphization behavior mainly by X-ray diffraction and differential scanning calorimetry. The results show that these alloys can form U6Ni type (NU) and/or α-U type (AU) phases under a quasi-equilibrium or equilibrium condition and amorphous phase, completely for most of them, under a non-equilibrium condition. A possibly Pd-based glassy phase seemed to unexpectedly arise in two Pd-rich alloy ingots, which would be the first observation of glass formation in U-based alloys solidified at low cooling rates. Within all the U-Pd-Ni-Si alloys, the ones with a big Ni/Pd ratio, thus tending to get NU phase, can achieve substantially higher GFA than the others with small Ni/Pd and a tendency to AU phase. Especially, U60Pd7.5Ni25Si7.5 and U60Pd5Ni25Si10 displayed firstly the reduced glass transition temperature Tg/TL of > 0.6 and a wide supercooled liquid region of ~100 K, exhibiting a GFA level superior to the whole reported U-based metallic glasses (MGs) and comparable to some traditional bulk MGs. All the yields reflect that Ni plays stronger roles in both compounding with U and the glass formation than Pd and Si in these alloys, and also offer guidance for creating novel U-based metallic materials including better MGs.

The role of rare earth elements in tailorable thermal and magnetocaloric properties of RE-Co-Al (RE = Gd, Tb, and Dy) metallic glasses

RE55Co17.5Al27.5 (RE = Gd, Tb, and Dy) metallic glass (MG) rods with critical diameters of 8 mm were successfully fabricated by the copper-mold suction casting method. With the replacement of Gd by Tb and Dy, the thermal stability is improved, while the Curie temperature (Tc) decreases, which is attributed to the strong f-d hybridization and weak magnetic exchange interaction between Co and Tb/Dy. The reversed trend of the glass transition temperatures Tg and Tc was further discussed based on around 33 RE-based MGs for the competition between the dominant thermal effect and magnetic exchange interaction. Dy55Co17.5Al27.5 with a relatively strong dynamic behavior and wide supercooled liquid region of 66 K performs a high cooling efficiency in the hydrogen liquefaction temperature range ascribed to its low Tc below 50 K and rapid response to the applied magnetic field due to the large 4f electron number and low G-factor.

Multicomponent Fe-Based Bulk Metallic Glasses with Excellent Corrosion and Wear Resistances

In this study, new multicomponent Fe54M5Cr15Mo6Si2B4P10C4 (M = Fe, Co, and Ni, denoted as Fe59, Fe54Co5, and Fe54Ni5, respectively) bulk metallic glasses (BMGs) with excellent corrosion and wear resistances were synthesized using the J-quenching technique and fluxing treatment. The synthesized Fe-based BMGs possessed a large glass-forming ability, and the maximum diameters of the Fe59, Fe54Co5, and Fe54Ni5 glassy alloy rods reached 5.5, 4.5, and 4.0 mm, respectively. The Fe59 BMG had a wide supercooled liquid region of 65 K. Potentiodynamic tests in 3.5 wt.% NaCl solution showed that the corrosion resistances of the synthesized Fe-based BMGs were relatively better than that of the 316L stainless steel. The Fe59 BMG had the highest corrosion resistance, with the lowest self-corrosion current density in the order of 10−8 A·cm−2. Wear tests showed that the synthesized Fe-based BMGs exhibited excellent wear resistances, and the wear rate of the Fe59 BMG was as low as approximately 1.73 × 10−15 m3·N−1·m−1. The rare-earth-element-free Fe-based BMGs, especially the Fe59 BMG, have a low cost, large glass-forming ability, and excellent wear and corrosion resistance, which make them good candidates for wear-and corrosion-resistant coating materials.

Oxidation induced ductility enhancement of Zr based metallic glass ribbons in vicinity of glass transition temperature

Zr-based metallic glasses (MGs) possess a wide supercooled liquid region, which gives a wide processing window for superplastic forming to make microdevices with demanding size accuracy and surface finishing. The existence of oxygen may have an influence on the thermoplastic deformation process. Therefore, the effect of oxidation on the mechanical behavior of the MGs in the vicinity of glass transition temperature is of great significance for practical forming of MG components. In the present study, the effect of oxidation on tensile properties of Zr50Cu40Al10 metallic glass was investigated. The tested samples were characterized by XRD and SEM analysis. For the samples tested in air, the strength decreases 187 MPa, 61 MPa and 59 MPa and the ductility increases 0.31, 0.36, and 0.77 at 420 °C, 430 °C, and 440 °C, respectively, compared with those tested in flowing argon. ZrO2 preferentially formed during the tensile testing at 420 °C, and both ZrO2 and Al2O3 oxides formed at 430 °C. The dilution of Zr elements in the remaining amorphous matrix caused by preferential oxidation on the surface layer attributes to the decrease in strength and enhancement in ductility of the Zr50Cu40Al10 metallic glasses.

Yttrium Enhanced Glass-Forming Ability of Zr-Based Metallic Glasses

Thermodynamic behavior of Zr56-xCo28Al16Yx (0, 2, 7, 10) bulk metallic glass-forming alloys has been studied using an analytical approach where some of the key thermodynamic quantities such as ΔH, ΔS and ΔG has been estimated using a hyperbolic temperature dependence of specific heat difference ΔCp in the supercooled liquid region. The study is focused on understanding the effect of Yttrium-doping on the thermodynamics of the alloys in the supercooled region and on the glass-forming ability of these alloys. The analytical approach has been found to give estimates of ΔG in a wide supercooled liquid region in excellent agreement with the experimental results. Estimated ΔG values are found to be minimum for Y concentration of 7 and 10% which is consistent with the observed high GFA for these compositions. Fundamental elemental properties such as atomic size, electronegativity, the heat of mixing have been found to play an important role in governing the thermodynamics of the alloys in the supercooled liquid region.

Synthesis, thermodynamic analysis and magnetic study of novel ball- milled Co50Fe25Ta5Si5C15 glassy powders with high thermal stability

In this study, novel glassy Co–Fe–Ta–Si–C alloys were prepared by mechanical alloying, (MA) and the influence of annealing treatment and substitution of Fe for Co on glass-forming ability (GFA), thermal stability and magnetic properties were investigated. Quantitative X-ray diffraction (XRD) analysis by the Rietveld method showed that the new Co50Fe25Ta5Si5C15 powders have an enhanced glass formation rate, especially during the early milling stages compared to the Fe-free Co75Ta5Si5C15 alloy. In good agreement with the XRD measurements, the calculated PHSS thermodynamic parameter revealed that the GFA is notably increased for the new powder. Thermal analysis demonstrated a high thermal stability and a rather wide supercooled liquid region (SLR) of 51 K for the Co75Fe25Ta5Si5C15 glassy alloy. The milling process and subsequent annealing treatment remarkably improved the soft magnetic behavior of the Co75Fe25Ta5Si5C15 powder. The results indicated that the Co75Fe25Ta5Si5C15 glass exhibits a slightly higher coercivity (Hc) and a notably larger saturation magnetization (Ms) than the Co75Ta5Si5C15 alloy in the as-milled state. Furthermore, in the relaxed state, the new alloy possesses a markedly lower Hc of 0.96 kA/m and a higher Ms of 108 Am2/kg than Co75Ta5Si5C15 and large number of ssoft magnetic glasy powders prepared before. The influence of milling time and annealing temperature on the evolution of the magnetic properties were discussed in detail.

Characterization and thermal analysis of new amorphous Co60Fe18Ta8B14 alloy produced by mechanical alloying

An amorphous Co60Fe18Ta8B14 powdered alloy was prepared by mechanical alloying process. The XRD results confirmed that the amorphous phase becomes a dominant phase above 50 h milling. Observation by scanning electron microscope shows a succession of phenomena of severe plastic deformation, cold welding and fracturing of powder particles. This new amorphous alloy exhibits a wide supercooled liquid region of 83 K and its crystallization occurs by three successive exothermic reactions.

Fabrication and characterization of novel soft magnetic [(Fe0.7Co0.3)71.2B24Y4.8]96Nb4/V2O5 bulk metallic glassy/composite cores with excellent magnetic permeability and low core losses

In the present work, fabrication, characterization and magnetic properties of novel soft magnetic composites (SMCs) based on V2O5 insulated [(Fe0.7Co0.3)71.2B24Y4.8]96Nb4 glassy particles are investigated. The uncoated glassy particles, consolidated at an optimized temperature of 893 K, yield bulk metallic glasses (BMGs) exhibiting a high relative density of 99.5%, a wide supercooled liquid region (SLR) of 92 K, a high initial magnetic permeability of 4310, and a notably low coercivity of 35 A/m. The Fe-based glassy particles in the SMCs are uniformly coated by V2O5 insulation, with negligible interfacial reaction or decomposition of the insulation upon hot consolidation. Additionally, the composite samples, particularly with 5 vol% V2O5, display a high thermal stability comparable to monolithic glassy cores. The V2O5 coated glassy particles preserve their excellent thermoplastic formability and densification behavior upon consolidation, resulting in formation of SMCs with a high relative density (98.5–99%). The prepared composites present a low coercivity (79–100 A/m) and a considerably higher initial permeability (425–475) at 1 kHz compared to most other SMCs prepared before. Furthermore, the performed V2O5 insulation enhances the frequency stability of the initial permeability and increases the relaxation frequency from 700 Hz for glassy cores up to 18 kHz for the composites. Magnetic loss separation analysis reveals negligible excess losses of the samples, while larger hysteresis losses are found for the composite cores up to 2 kHz. The composites with 5 vol% V2O5 exhibit about 55% smaller eddy current losses and 47% lower total core losses at 2 kHz than that of glassy cores. The obtained results suggest that the new composite cores are promising soft magnetic materials for medium frequency range electromagnetic applications.

Phase transformation, thermal behavior and magnetic study of new Co80-xTaxSi5C15 (x = 0, 5) glassy/nanocrystalline alloys prepared by mechanical alloying

Abstract In the current work, new Co80-xTaxSi5C15 (x = 0, 5) alloys were prepared by mechanical alloying (MA) and the influence of milling period on their microstructure, thermal behavior, and soft magnetic properties were examined. The quantitative X-ray diffraction (XRD) analysis, revealed that while the fraction of hexagonal-close packed (hcp) Co-based solid-solution continuously declines by milling time, the content of face-centered cubic (fcc) one initially levels up and subsequently decreases. Furthermore, the microalloying with Ta markedly enhances the amorphization rate, as well as the fraction of amorphous phase from 60 wt% for Co80Si5C15 alloy to near 100% for Co75Ta5Si5C15 alloy after 120 h milling. Thermal analysis reflected the absence of supercooled liquid region (SLR) in Co80Si5C15 alloy, while Co75Ta5Si5C15 alloy shows a relatively wide SLR, with an extension of 41 K, demonstrating its high thermal stability. Magnetic measurements showed that the soft magnetic behavior of both alloys notably improves upon a certain stage of milling. It was shown that the new Co75Ta5Si5C15 glassy alloy represents a promising soft magnetic behavior, i.e., a minimum coercivity (Hc) of 1.2 kA/m, which is notably lower than a minimum value obtained for Co80Si5C15 (3.3 kA/m), as well as those reported for most other Co-based amorphous/nanocrystalline alloys prepared by MA.

Ternary Co-W-B bulk metallic glasses with ultrahigh strength

In this work, a family of ternary Co100-x-yWxBy (at.%, x=15~30, y=11~19) bulk metallic glasses (BMGs) with near-recorded ultrahigh strength up to 6 GPa was successfully developed. With extremely high tungsten content, the Co-W-B BMGs show very high glass transition temperature of 850-975 K and high density of 11.13-12.43 g/cm3, which are much higher than most of Co-based BMGs previously reported. Moreover, the glassy alloys exhibit a good glass-forming ability with critical diameter of 2 mm in diameter and a wide supercooled liquid region of over 80 K. Furthermore, these BMGs possess ultrahigh strength of 5.5–6 GPa, high Young's modulus of 243.6-273.1 GPa, high specific strength of ~ 500 Nm/g and obvious plastic strain of 0.5-2.6 %, respectively. The novel ternary Co-based BMGs with outstanding mechanical properties and less components are promising as structural materials and model system for theoretical research.

New para-magnetic (CoFeNi)50(CrMo)50-x(CB)x (x = 20, 25, 30) non-equiatomic high entropy metallic glasses with wide supercooled liquid region and excellent mechanical properties

In this study, high entropy metallic glasses (HEMGs) were developed through a combination of concepts for designing metallic glasses (main element + transition metal + metalloid element) and high-entropy alloys (more than five elements, each element having an atomic concentration between 5 at.% and 35 at.%). The developed metallic glass alloys are composed of Co-Fe-Ni main elements, transition metals (Cr, Mo) and metalloid elements (C, B). Moreover, the present work reports the thermal, mechanical and magnetic properties of (CoFeNi)50(CrMo)50-x(CB)x alloys with x = 20, 25, 30. The developed as-spun HEMGs exhibit typical paramagnetic properties even for a high amount of ferromagnetic elements (Co, Fe, and Ni) and have high elastic modulus (103–160 GPa) and hardness (14–27 GPa), thus possessing mechanical properties similar to well-known Co-based metallic glasses (Co-Cr-Mo-C-B system). In addition, some of the bulk samples prepared with a diameter of 2 mm form bulk metallic glasses with a high compressive strength around 3.5 GPa. The mechanisms determining the stability of the supercooled liquid, as well as the paramagnetic and mechanical properties for the developed non-equiatomic HEMGs, are discussed.

Development of new Mg-Zn-Sr alloys for medical purpose

In surgery, in addition to joint replacement, which requires permanent implantation of the prosthesis into the human body, there are many other clinical cases where fixation or mechanical support are only temporarily needed during the healing process of the injured or pathological tissue. In this case, biodegradable materials are the optimal choice as these materials do their job and degrade in the human body thereafter. Amorphous magnesium-zinc based alloys are nowadays a very promising group of metallic glasses (MGs). Unfortunately, the brittleness of Mg-Zn MGs and poor glass forming ability (GFA) have hindered their further application. We have developed a composition series of completely new (not published) ternary Mg-Zn-Sr alloys with attractive properties in terms of possible future applications (density comparable to human bones, wide supercooled liquid region, low rate of degradability, etc.). These ternary alloys will serve as precursors for design of future highly alloyed systems with tuned mechanical properties and dissociation rate in human body.

Effect of compositional elements and processing routes on structural and thermal response in Fe-based metallic glasses

The effect of varying thickness on structure and thermal properties is investigated in Fe–B–Nb and Fe–B–Si–Nb glassy alloy systems with the addition of different Nb and Co content, respectively. Accordingly, four alloys with the nominal compositions of Fe76-xB18Nb6+x (x = 0, 2) and (Fe1-yCoy)72B12Si12Nb4 (y = 0, 0.5) are processed in the forms of ribbon and rod. All alloys of ribbons represent amorphous structure, while those of rods explain the crystalline structure with the exception of heteromorphous structure for Co added alloy. The Nb addition causes about same glass transition temperature (Tg) but increases crystallization onset (Tx), resulting in a wider supercooled liquid region (ΔTx = Tx-Tg). Moreover, Nb also improves glass forming ability (GFA) with more free volume generation and higher structural relaxation exothermic heat (ΔH0). The Co addition also improves free volume generation and higher ΔH0 for ribbon, but lower amount free volume generation in bulk alloys (rod) than ribbon.

Static and Dynamic Thermal Properties of a Pd40Ni40Si20 Glassy Alloy

The thermal properties of a Pd40Ni40Si20 glassy alloy with the largest supercooled liquid region among the glassy alloys containing Si as a metalloid element are studied using static and dynamic measurement methods. The relatively wide supercooled liquid region of 45 K, defined by the temperature interval between the glass transition temperature (Tg) and the onset temperature of crystallization (Tx), and the viscosity of the supercooled liquid, varying from 2.7 × 1010 to 3.2 × 1011 Pa·s, make this glass suitable for the introduction of controlled pores by a viscous flow in the temperature range Tg~Tx. The obtained activation energy for crystallization, 272 ± 19 kJ/mol, is slightly higher than that of Tg (228 ± 11 kJ/mol), indicating the dominant contribution of the atomic transport barrier in the overall energy barrier for crystallization.

Glass forming ability and a novel method for evaluating the thermoplastic formability of ZrxTi65-xBe27.5Cu7.5 alloys

Zr-Ti-based bulk metallic glass (BMG), in particular Be-Cu-bearing BMG (Vitreloy), displays an outstanding combination of characteristics, i.e. while showing good glass forming ability (GFA) it exhibits low glass transition temperature (Tg) and a relatively wide supercooled liquid region (SCLR, ΔT), facilitating their thermoplastic formability, which is critical for BMG applications. In the present work, the effect of composition on the GFA and thermoplastic formability in ZrxTi65-xBe27.5Cu7.5 BMG alloys are investigated in the range x = 20, 25, 30, 35, 40, 45, 50 at%. Results show that GFA is optimal in the composition range from 30 to 45 Zr at%. In addition, the optimal composition range for thermoplastic formability is consistent with that for GFA. Furthermore, 3-mm diameter BMG rods with the aspect ratio 2:1 are compressed in the SCLR at temperatures T = 643 K and T = Tg + ΔT/2, by applying a constant load of 8 kN, and the thermoplastic formability is evaluated measuring the final diameters d1 and dg-ΔT, respectively. The larger measured dg-ΔT values in the optimal composition range indicates that the ideal temperature for the thermoplastic formability is given by T = Tg + ΔT/2.

Enhancement of superelastic property in Ti–Zr–Ni–Cu alloy by using glass alloy precursor with high glass forming ability

The glass forming ability (GFA), crystallization behavior and subsequent superelastic property after crystallization in Ti50-xZrxNi35Cu15 (x = 5, 10, 15, 20 at%) alloys have been investigated with an aim to develop glassy alloy precursor for shape memory alloy having both high glass forming ability and superior superelastic property. The addition of Zr is effective in improving the GFA exhibiting a critical thickness larger than 100 μm by increasing both liquid stability and resistance to crystallization. The glassy Ti50-xZrxNi35Cu15 alloys are polymorphically crystallized into B2 structure. With increasing Zr content, the grain size after crystallization decreases significantly by accelerated nucleation process. Thus, the stability of austenite increases, resulting in the decrease of Ms. The critical stress for slip deformation gradually increases with alloying Zr up to 15 at%, improving the superelastic recovery. The Ti35Zr15Ni35Cu15 alloy exhibits the highest remnant depth ratio value of 7.2%. By contrast, the superelasticity is significantly deteriorated in the Ti30Zr20Ni35Cu15 nanocrystalline alloy due to the difficulty in stress-induced martensitic transformation which is caused by extremely small grain size and irregular morphology of grain boundary. Considering both glass forming ability and superelastic property, the Ti35Zr15Ni35Cu15 alloy is confirmed to be the most suitable alloy satisfying wide supercooled liquid region (∼40 K), large maximum thickness for amorphous alloy formation (∼100 μm) and excellent superelasticity after crystallization.