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The phase formation in a rapidly solidified Ag-Y system was evaluated by means of two predictive amorphization criteria: the thermodynamic γ* parameter and the new λ + Δh1/2 criterion. The former considers only the thermodynamic contribution, while the latter combines the effect of an atomic size mismatch between elements and their electronic interaction. The results showed a marginal glass-forming ability (GFA) with the best composition region for glass formation located near the Y-rich eutectic region. The melt-spun ribbon contained an amorphous matrix with a distribution of Y solid solution nanocrystals. Two new metastable phases found in the study were identified. One with an orthorhombic structure was precipitated during crystallization of the highest GFA alloy. The other having a hexagonal structure was formed under rapid solidification of the near-eutectic alloy lying between the Ag51Y14 and Ag2Y phases. The results also showed no improvement in the predictability of the γ* and λ + Δh1/2 amorphization criteria when considering the metastable phases formed during crystallization. [ABSTRACT FROM AUTHOR]

Results of magnetic measurements are presented for a Ho-based bulk metallic glass, which shows similarities and differences with conventional spin glasses (SGs), and significant differences with weak random magnetic anisotropy (RMA) systems. Both ac and dc magnetic measurements indicate a single transition from paramagnetic to speromagnetic or spin glasslike state around 5.6 K. The moderate RMA prevents the formation of long- (or quasilong)-range magnetic order and slows down the spin dynamics in the critical region. Further its isothermal remnant magnetization exhibits a small maximum, instead of a gradual increase with field in SGs. The roles of RMA in the magnetic structure and dynamics of disordered and frustrated systems are discussed by comparisons between the weak RMA system, the moderate or strong RMA system, and conventional SG. [ABSTRACT FROM AUTHOR]

The fracture criterion of metallic glass (MG) is still under debate so far. On the issue of describing the normal stress effect on the tensile fracture behaviors of MGs, there are two fracture criteria: the Mohr-Coulomb (M-C) criterion and the Ellipse criterion. In this study, the normal stress acting on the tensile fracture planes was controlled and varied in a wide range by introducing inclined notches with different inclination angles to a series of Zr-based MG specimens. Based on the experimental results, both the Ellipse criterion and the M-C criterion are compared and analyzed. The experimental results reveal that the Ellipse criterion gives a better prediction than the M-C criterion for the tensile fracture behavior of the investigated Zr-based MG in a wide normal stress range. Moreover, the pressure and normal stress effects were separately considered and some other criteria were further discussed. It is found that under tensile loading, the pressure effect is weak while the normal stress effect is strong. Combined with previously reported results for a variety of MGs, the Ellipse criterion is found to have the capability to describe all the different contributions of the normal stress effect and thus may be suitable as a unified tensile fracture criterion for all MGs with different fracture behaviors. [ABSTRACT FROM AUTHOR]

The glassf-forming ability of (Fe[sub x]Co[sub y]B[sub z]C[sub u])[sub 80]Si[sub 3]Al[sub 5]Ga[sub 2]P[sub 10] with x = 5 - 70, y = 0-63, z = 5-12, and u = 0- 5 amorphous alloys has been analyzed in terms of the width of the supercooled liquid region, the reduced glass transition temperature, and the Vogel-Fulcher-Tammann parameters. Substitution of Fe by Co slightly decreases the glass-forming ability of the studied alloys. The value of the fragility parameter m is discussed in the frame of the general classification scheme of glass-forming liquids. The crystalline phases formed during the first crystallization step are identified. Magnetic moment at low and room temperature, Curie temperature, room temperature magnetostriction, and coercivity decrease with increasing Co content. [ABSTRACT FROM AUTHOR]

Amorphous Fe[sub 74-x]Al[sub 5]P[sub 11]C[sub 6]B[sub 4]Ga[sub x] (x = 0 or 2) powders with a wide supercooled liquid region were prepared by high energy ball milling of rapidly quenched ribbons and subsequently hot pressed in the viscous state to receive bulk glasses. Almost complete coercivity relaxation of the ball milled powders was achieved by annealing. The coercivity H[sub c] of as-milled ribbons drops drastically from more than 2200 Am[sup -1] after 1 h of milling to 14.6 Am[sup -1] after optimum annealing. The coercivity of this powder and that of the as-quenched ribbons (7 Am[sup -1]) differs only by the different contributions of surface irregularities H[sup surf, sub c] to the total coercivity H[sup tot, sub c]. Drastic coercivity relaxation was also achieved by consolidating the as-milled powders. A minimum coercivity H[sub c] of 30 Am[sup -1] was found for the bulk sample after compaction of 1 h ball milled powders. It is of the same order of magnitude as H[sub c] of cast amorphous rods. The milling-induced coercivity increase as well as the coercivity relaxation are discussed in terms of the change of magnetic anisotropy and the creation and elimination of stress and shear bands in the amorphous phase. [ABSTRACT FROM AUTHOR]

Zr- and Co-based bulk metallic glasses display completely different failure modes under compressive loading. Zr-based metallic glasses always fail in a pure shear mode, whereas Co-based metallic glasses often break into small particles or powder, exhibiting a fragmentation mode. The difference in the failure modes for the two glassy alloys indicates that different mechanisms control the fracture processes, which can be described by a combined effect of surface energy γ, cleavage strength σ0, fragmentation coefficient Fn and fracture mode factor α = τ0/σ0. [ABSTRACT FROM AUTHOR]

We report on the preparation of bulk amorphous Fe67Co9.5Nd3Dy0.5B20 by hot extrusion of melt-spun ribbons. X-ray diffraction studies were performed to check the structure of the as-spun ribbons and the consolidated bulk specimens. Differential scanning calorimetry (DSC) analysis of the amorphous ribbons revealed that crystallization proceeds in two stages. The first crystallization step leads to the formation of soft magnetic α-(FeCo) and (FeCo)3B and the second crystallization step corresponds to the formation of the hard magnetic (NdDy)2(FeCo)14B phase. The hysteresis loop of the as-spun ribbon reveals soft magnetic properties which change to hard magnetic behavior with enhanced remanence after annealing at 973 K for 7 min. X-ray diffraction analysis proves the presence of both soft and hard magnetic phases in the annealed sample. The viscosity of the powder obtained from crushed ribbons was investigated by parallel plate rheometry, showing a distinct viscosity drop in the supercooled liquid region that allows for easy consolidation of the crushed ribbons. The hot extruded sample that was subsequently annealed at 973 K for 7 min exhibits good hard magnetic properties with coercivity H c = 218 kA/m, saturation magnetization J s = 1.36 T, maximum energy product (BH)max = 91.3 kJ/m3 and remanence B r = 1.18 T (after demagnetization field correction), respectively. [ABSTRACT FROM AUTHOR]

In this study, the rate-dependent mechanical behavior of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass was studied using quasi-static and dynamic shear-punch testing at room temperature. The results demonstrate that the shear strength of this alloy is insensitive to the applied strain rate. However, the formation of shear bands and the serrated flow exhibits a significant strain rate effect. The shear banding-induced fracture patterns and the fracture-melting phenomenon were analyzed based on the free volume theory and the energy transfer model. [ABSTRACT FROM AUTHOR]

Nanoindentation tests of Pd40Cu30Ni10P20 bulk metallic glass were performed over a wide range of indentation rates (from 0.04 up to 6.4 mN s-1) under the standard load control mode. New results using the feedback displacement control mode are also presented. The dependence of the pop-in formation on the loading rate is investigated. Variations in hardness and reduced elastic modulus as a function of the indentation rate are observed. A softening effect occurs when increasing the loading rate. This is explained by the differences in plastic deformation achieved at different indentation rates. The displacement control mode was used to avoid the shear localization of the free volume, leading to the almost complete absence of pop-ins along the loading curve. The obtained results suggest that plastic flow in bulk metallic glasses is governed by the rate of creation of free volume, which depends on the strain rate and its localization into shear bands. [ABSTRACT FROM AUTHOR]

The compressive properties and the Vickers hardness of Cu-, Fe-, Mg-, and Zr-based monolithic bulk metallic glasses (BMGs) as well as Ti-based nanostructure-dendrite composites were investigated and compared. The monolithic BMGs exhibit nearly the same yield strength σy and fracture strength σf but poor plasticity. The Vickers hardness Hv of the monolithic BMGs follows the empirical relationship Hv/3 ≈ σy ≈ σf. The Ti-based composites yield at a relatively low stress level (less than 850 MPa) but fail at a very high fracture stress (∼2 GPa) and exhibit a large strain hardening ability. Accordingly, the Vickers hardness Hv of the Ti-based nanostructure-dendrite composites obeys the relationship σy < hv/3 < σf. Based on these results, the relationship between the Vickers hardness and the compressive properties of the investigated materials will be discussed by taking the yield and fracture strength (σy and σf), the strain hardening exponent n, and the elastic and plastic energy stored upon deformation (δE and δp) into account. [ABSTRACT FROM AUTHOR]

The compressive deformation and fracture features of Zr 59 Cu 20 Al 10 Ni 8 Ti 3 bulk metallic glassy samples with aspect ratios in the range of 0.67–2.00 have been investigated. The compressive plastic strain of the glass monotonically increases with decreasing aspect ratio, but the maximum strength almost maintains a constant value of 1.77–1.88&ThickSpace;GPa. All the compressive shear-band angles are equal to&ThickSpace;&nvsim;40° if modified by the rotation of the primary shear bands. [ABSTRACT FROM AUTHOR]

Abstract: The influence of the preparation technique on quasicrystal formation was investigated by comparing the devitrification of Zr58.5Ti8.2Cu14.2Ni11.4Al7.7 metallic glass produced by ball milling of crystalline intermetallic compounds with its corresponding rapidly quenched counterpart produced by melt spinning. Differently from the as-spun ribbon, which is fully amorphous, the as-milled powder displays the presence of a minor amount of a crystalline phase along with the glassy phase. However, the crystallization behavior of both the powder and the ribbon is characterized by the formation of a nanoscale quasicrystalline phase upon partial devitrification, demonstrating that quasicrystal-forming Zr-based alloys can also be produced by solid-state reaction. A possible explanation for the lack of quasicrystal formation reported in other ball-milled Zr-based alloys is proposed, suggesting that the formation of quasicrystals in ball-milled powders may be suppressed by the contamination of the starting material. [Copyright &y& Elsevier]

Abstract: The crystallization behavior of (Zr0.616Ti0.087Nb0.027Cu0.15Ni0.12)100-xAlx melt-spun glassy ribbons with x = 7.5 and 0 has been investigated. The glasses devitrify by the precipitation of an icosahedral quasi-crystalline phase in the first step of the crystallization process, indicating that the absence of Al does not hinder quasicrystal formation in the present alloys. [Copyright &y& Elsevier]

In this work the Al85Ni9Nd4Co2 alloy was used as a starting point for examining the possibility of forming bulk glassy Al-based materials by combining rapid quenching and ball milling techniques. Fine glassy powders were obtained by ball milling melt-spun amorphous ribbons using a severe cryogenic processing regime. The thermal stability data of the powders as obtained by constant-rate heating and isothermal DSC experiments together with viscosity measurements are discussed with respect to feasible consolidation conditions. The powder compaction was done by two methods (uni-axial hot pressing and extrusion) at 513 K for up to 15 min. Only the uni-axial hot pressing led to bulk Al85Ni9Nd4Co2 samples with similar glassy structure and Vickers microhardness values comparable to those of the initial melt-spun ribbons. [ABSTRACT FROM AUTHOR]

Nd60FexCo30-xAl10 (0≤x≤30) alloys were prepared by copper mold casting. The magnetic properties were studied by VSM and SQUID magnetometers. These measurements show the presence of two different magnetic phases with ordering temperatures of 50 K and 496 K for the Fe-containing alloys. A step in the M–H hysteresis loops at temperatures below 50 K supports the presence of the two different magnetic phases. The temperature dependence of the coercivity exhibits a peak at about 50 K above which it follows a law that describes hard magnetic behaviour based on pinning site inhomogeneities interacting with domain walls. [Copyright &y& Elsevier]

The Fe77.5-x-y-zCrxMoyGazP12C5B5.5 bulk glassy alloy was prepared in the shape of rods and ribbons using copper mold casting and melt spinning, respectively. The structure was investigated by X-ray diffraction (XRD) and the thermal stability was checked by differential scanning calorimetry (DSC). It was found that the samples consist of an a single amorphous phase and exhibit a rather wide supercooled liquid region before crystallization. Some characteristic thermal properties of the amorphous samples as a function of the geometrical dimensions are discussed, as well as the dependence of the glass-forming ability on composition. Additionally, some magnetic data like coercivity Hc, saturation polarization Js and Curie temperature Tc are presented. [Copyright &y& Elsevier]

We report about the microstructure and the mechanical properties of slowly cooled Zr–Nb–Cu–Ni–Al alloys with a glassy or a nanocrystalline matrix and ductile bcc precipitates. These alloys exhibit significantly improved mechanical behavior compared to monolithic glass, because the in situ formed composite undergoes work hardening and plastic deformation prior to failure. Changes in composition and cooling rate lead to different volume fractions and dendrite sizes of the bcc phase and, hence, to different values of yield strength, elastic and plastic strain. The glassy or nanocrystalline structure of the matrix influences mainly the elastic strain limit of the composites. This opens the possibility of obtaining tailored mechanical properties and could extend the range of industrial applications of such materials. [Copyright &y& Elsevier]

We report a close correlation between the internal states and plasticity in a bulk metallic glass (BMG) and discover that the optimization of copper-mold casting current can induce large plasticity stably in an otherwise brittle BMG. It is possible to confirm that larger plasticity corresponds to the internal states with more average free volume (FV) as revealed by lower density, higher enthalpy change, and higher Poisson's ratio. The enhanced plastic deformation mechanism is interpreted based on the FV model of BMGs, and our results may have some implications for understanding the role of the FV during plastic deformation of BMGs. [ABSTRACT FROM AUTHOR]

The structural behavior of Cu64.5Zr35.5 bulk metallic glass under compressive stress was investigated by means of in situ high energy x-ray synchrotron diffraction. The topological and chemical short-range order of the glass changes reversible upon loading within the elastic range. The number density of Cu–(Zr,Cu) and Zr–Zr nearest neighbor atomic pairs becomes oriented along the loading direction. The macroscopic stress state is reflected by the medium-range order. The determination of the components of the strain tensor from the shift of the positions of the nearest neighbor distances is not possible due to the structure changes. [ABSTRACT FROM AUTHOR]

This work presents results on the microstructure and mechanical properties of the steel composition Fe84.3Cr4.3Mo4.6V2.2C4.6 subjected to preparation conditions typically used for manufacturing of bulk metallic glasses. Thermodynamical aspects and kinetic limitations on the specific solidification process of phase formation, particularly those, which are strongly dominated by diffusion controlled mechanisms, promote the formation of nonequilibrium phases, such as martensite and complex carbide structures already in the as-cast state. This combination of high strength phases yields material with highly desirable properties, such as an engineering compression strength of more than 4000 MPa surprisingly combined with a fracture strain of about 12%. [ABSTRACT FROM AUTHOR]

Reports on the precipitation of nano-sized quasicrystals by Zr[sub 62-x]Ti[sub x]Cu[sub 20]Ni[sub 8]Al[sub 10] amorphous alloys in the primary transformation step upon annealing. Titanium as a decisive component favoring quasicrystal formation; Ductility of nano-sized quasicrystals; Mechanical properties of quasicrystalline alloys; X-ray diffraction patterns.

We present a blunt mechanism to explain the serrated flow behavior and slight "work hardening" at the beginning of yielding during the compression of metallic glass, which is in line with the piling-up of parallel shear bands on the fracture surface with a gradually increasing space from the edge of surface to inside. Meanwhile, two intrinsic parameters, i.e., strength intensity of blunt behavior, , and global work-hardening sensitivity exponent, , are introduced to characterize the blunt effect on the net increase in flow stress or work-hardening behavior of metallic glass. [ABSTRACT FROM AUTHOR]

Al85Ni9Nd4Co2 metallic glass/nanostructured ribbons and powders were used as starting materials for producing bulk amorphous/nanostructured Al-based alloys. Glassy ribbons were obtained by melt spinning at wheel surface velocities ranging from 5 to 37 m/s. The amorphous ribbons exhibited a supercooled liquid region of ∼20 K, a reduced glass transition temperature of ∼0.47 and ? ∼ 0.328. Mechanical alloying of the elemental powder mixture did not lead to amorphization. However, amorphous powders obtained by milling the glassy ribbons for 9 h exhibited a thermal stability similar to the initial ribbons. Isothermal differential scanning calorimetry measurements were used to determine the consolidation parameters of the glassy powders. Consolidation at 513 K by uniaxial hot pressing and hot extrusion indicated that the former method leads to bulk glassy samples, whereas the latter one yields nanostructured a-Al/glassy matrix composites. [ABSTRACT FROM AUTHOR]

We have examined the effect of Ti and cooling rate on the crystallization of Zr[sub 62-x]Ti[sub x]Cu[sub 20]Ni[sub 8]Al[sub 10](0≤x≤10) amorphous alloys. Ti stabilizes an icosahedral phase in Zr[sub 62-x]Ti[sub x]Cu[sub 20]Ni[sub 8]Al[sub 10](0≤x≤10) alloys. Without Ti (x=0), crystallization produces cubic and tetragonal intermetallic phases, and the crystallization temperature shows no dependence on the cooling rate at which the amorphous alloy was produced. The alloys containing Ti (3≤x≤10) precipitate an icosahedral quasicrystalline phase upon annealing, and show a significant reduction of crystallization temperatures with decreasing cooling rates of casting. We propose that the undercooled melts and amorphous alloys have icosahedral short-range order. The degree of short-range order or medium-range order in the amorphous alloys increases with decreasing cooling rate. Crystallization is easier when the precipitating phase resembles the short-range order of the amorphous solid. Therefore, the crystallization temperature is reduced when the precipitates are icosahedral. The dissimilarity between the structures of the precipitates and the short-range order in amorphous Zr[sub 62]Cu[sub 20]Ni[sub 8]Al[sub 10] may be one of the reasons for its very wide supercooled liquid region. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Zr[sub 57]Cu[sub 20]Al[sub 10]Ni[sub 8]Ti[sub 5] alloy solidifies into an amorphous phase upon rapid quenching or casting at low cooling rates. However, the amorphous alloys formed at different cooling rates exhibit different crystallization behavior. The slowly cooled bulk amorphous alloys prepared by copper mold casting reveal a first crystallization peak at 715 K upon heating at 0.33 K/s and crystallize via precipitation of an icosahedral quasicrystalline phase in the first crystallization step. The rapidly quenched ribbons exhibit a first crystallization peak at 720 K and crystallize by simultaneous precipitation of the quasicrystalline phase together with Zr[sub 2]Cu and Zr[sub 2]Ni intermetallic phases in the first stage of crystallization. It is supposed that the undercooled Zr[sub 57]Cu[sub 20]Al[sub 10]Ni[sub 8]Ti[sub 5] melt has a tendency to develop an icosahedral short-range order, which is favored by low cooling rate. As a result, the bulk amorphous alloy has a short-range order close to a quasicrystalline phase. In contrast, the structure of the ribbon is more similar to that of the melt at high temperature and the atoms are oriented more randomly. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Al content on the glass formation and mechanical properties was studied for (Cu50Zr50)100−x Al x (x =0, 4, 5, 7) bulk metallic glasses. The crystallization temperatures of fully amorphous Cu50Zr50, Cu48Zr48Al4, Cu47.5Zr47.5Al5 and Cu46.5Zr46.5Al7 as-cast rods are 724K, 753K, 758K and 782K, respectively. The mechanical properties were investigated under compression at room temperature. As-cast Cu46.5Zr46.5Al7 shows the highest yield strength (1867MPa), whereas Cu47.5Zr47.5Al5 shows the largest fracture strain of 11.2%. The fracture surfaces of the compressed samples were investigated by scanning electron microscopy and their morphology has been correlated with the compressive plasticity. [Copyright &y& Elsevier]

Abstract: Plastic deformation of Zr52.5Ti5Cu17.9Ni14.6Al10 bulk metallic glass is investigated in a wide range of the strain rates, , and temperatures, T. Based on these results, a map of the plastic deformation modes as a function of strain rate and temperature is depicted. The region of the mixed flow contiguous to the inhomogeneous plastic deformation region is identified. In this region, at large values of ε, the glass softens significantly. This effect is interpreted as a result of the cluster fragmentation. [Copyright &y& Elsevier]

Bulk amorphous FeAlGaPCBSi samples in the shape of discs (diameter of 10 mm and thickness of 3 mm) were prepared from melt-spun ribbons by high-energy ball milling and subsequent compaction of the resulting powder in the supercooled liquid region ΔTx. The stability against crystallization as well as the low viscosity in this region allow to prepare bulk specimens by combination of pressing and heating while the amorphous structure of samples is still maintained. Heating of the powder in the ΔTx region allows to reduce the stress induced in the material during ball-milling. This milling-induced stress causes significant differences in coercivity: the relatively low coercivity characteristic for the melt-spun ribbons (5–10 A m-1) increases after 1 h of ball milling to values of about 550–2300 A m-1. Subsequent heating of the ball-milled powders in the supercooled liquid region leads to a decrease of Hc to values between 9.5 and 250 A m-1. The bulk samples prepared by combination of compaction and heating (hot pressing) show a coercivity of about 11.6–127 A m-1. [Copyright &y& Elsevier]

Intermittent or serrated plastic flow is widely observed in the deformation of bulk metallic glasses (BMGs) or other disordered solids at low temperatures. However, the underlying physical process responsible for the phenomena is still poorly understood. Here, we give an interpretation of the serrated flow behavior in BMGs by relating the atomic-scale deformation with the macroscopic shear band behavior. Our theoretical analysis shows that serrated flow in fact arises from an intrinsic dynamic instability of the shear band sliding, which is determined by a critical stiffness parameter in stick-slip dynamics. Based on this, the transition from serrated to nonserrated flow with the strain rate or the temperature is well predicted and the effects of various extrinsic and intrinsic factors on shear band stability can be quantitatively analyzed in BMGs. Our results, which are verified by a series of compression tests on various BMGs, provide key ingredients to fundamentally understand serrated flow and may bridge the gap between the atomic-scale physics and the larger-scale shear band dynamics governing the deformation of BMGs. [ABSTRACT FROM AUTHOR]

Surfaces of bulk glassy Zr59Ti3Cu20Al10Ni8 samples were shot-peened for different times and their corrosion behaviour was tested in 0.01M Na2SO4 + xM NaCl (x =0; 0.01; 0.1) and 6M HCl. Slight improvement of spontaneous passivity but a decrease of pitting resistance are detected with prolonged shot-peening duration. The corrosion damage evolution is governed by the nature of the mechanically generated defects and their surrounding stress fields. [Copyright &y& Elsevier]

Abstract: A 12mm thick Al85Y8Ni5Co2 plate was spray deposited on a 30mm thick copper substrate pre-heated to 383K. The deposit microstructure consists of an amorphous phase, 50–150nm fcc-Al grains, 0.2–0.7μm Al2Y and Al3Y intermetallic phases and some unidentified phases. The hardness of different microstructural features and the compressive strength of the deposit, after extrusion at 723K, were evaluated. The small size overspray particles as well as the deposit show a glass transition phenomenon. The total crystallization energy of the deposit is 121J/g compared to 83.9J/g for the small sized overspray powder, indicating its high metastability. A compressive strength of 925MPa and a deformation strain of 9% were achieved for the deposit after extrusion. The novel microstructural features in the deposit are attributed to the “chilling effect” on highly undercooled or partially solidified large-size droplets during deposition onto the pre-heated substrate, and the rapid heat extraction thereof due to a close contact at the deposit/substrate interface. [Copyright &y& Elsevier]

Abstract: Fe-based bulk metallic glasses (BMGs) have a high application potential because of their unique soft magnetic properties, mechanical behaviour and high corrosion resistance. Also, they can be obtained directly in the final shape suitable for use as magnetic sensors, magnetic valves, magnetic clutches etc. in different devices. Fe-based alloys able to form magnetic BMGs are of the type transition metal–metalloid and often contain 5 or more elements. Usually, the metalloid content is around 20at.%. Recently, a new Fe-based BMG containing only 3 elements and a very high boron content was synthesized. The preparation of this BMG was done by employing the copper mold casting method and using the fluxing technique. This new BMG is ferromagnetic, with a Curie temperature around 550K and a saturation magnetization of 105Am2/kg. Differential scanning calorimetry (DSC) investigations revealed a reduced glass transition temperature of 0.55 and an extension of the supercooled liquid region of about 31K, values which indicate a relatively good thermal stability. Despite of numerous studies about Fe-based BMGs, there is still a lack of data about the crystallization kinetics. Also, the intermediate metastable phases, which form upon crystallization from the amorphous state, as well as the mechanism of their formation, are not fully understood. The present work discusses the kinetics of the phase formation using the Kissinger analysis and Johnson–Mehl–Avrami plots, correlated with the results obtained upon X-ray diffraction (XRD) of samples with different metastable structures. Additionally, the magnetic behaviour of different phase(s) is presented. [Copyright &y& Elsevier]

Abstract: Yielding in metallic glasses is often described in terms of the Mohr–Coulomb criterion, τ + μσ ≥ τ 0. It suggests that a material yields when a combination of shear (τ) and normal stresses (σ), linked through the friction coefficient (μ), reaches the critical shear stress (τ 0). In this paper, an increase of the friction coefficient for increasing Poisson ratio is foreseen, if the elastic limit observed under uniaxial (tensile or compressive) and shear stresses remain constant. Experimental values of Young and shear moduli and Poisson ratio of metallic glasses have been collected from the literature. Compressive and tensile yield stresses have been also collected and elastic limits have been calculated. The elastic limit observed under compressive stress decreases with increasing Poisson ratio and it appears similar for metallic glasses based on the same metals. The values of the friction coefficient for metallic glasses have been obtained from the fracture angle observed under uniaxial stress (compressive or tensile) and from the ratio between compressive and tensile strength. Experimental data of the friction coefficient appear rather scattered and a clear trend as a function of Poisson ratio cannot be outlined. The increase of toughness of metallic glasses with increasing Poisson ratio has been ascribed to the corresponding reduction of the compressive elastic limit. [Copyright &y& Elsevier]

Abstract: Bulk Zr50Cu50 partially crystallized glassy specimens have been produced by powder metallurgy methods. Zr50Cu50 powder has been prepared by controlled milling of melt spun glassy ribbons and subsequently consolidated by hot pressing into bulk cylindrical samples of 10mm diameter and 10mm length. The consolidated material exhibits interesting mechanical properties, namely, a perfect elastic regime of 1.5%, high strength of about 1350MPa and hardness of 4.80GPa. However, no macroscopic ductility is visible, most likely due to the residual porosity of the consolidated specimens. These results indicate that powder metallurgy methods may become a valid alternative to casting techniques for the production of glassy and partially crystallized Zr-based alloys. [Copyright &y& Elsevier]

Abstract: Due to their exceptionally high yield strength and yield strain as compared to conventional metallic materials, bulk metallic glasses (BMGs) represent a class of promising engineering materials for structural applications. However, inhomogeneous deformation and severe shear localization at ambient temperature often lead to early failure and limit their reliability as structural materials. Heat treatments around the glass transition temperature (T g) generally aggravate the intrinsic brittleness of BMGs. In this paper, we report on the evolution of a nanoscale inhomogeneous microstructure upon low-temperature annealing in a Zr55Cu30Al10Ni5 BMG. This important outcome is explained by the experimentally observed tendency for chemical decomposition between Cu and Zr of the investigated amorphous system and is in accordance with literature data on various Zr–Cu-based amorphous alloys. Finally, these local fluctuations influence the plasticity of BMGs beneficially, in contrast of the generally accepted embrittlement upon annealing. [Copyright &y& Elsevier]

Abstract: The structural behavior of rapidly quenched amorphous Cu x Zr100− x alloys was investigated in a wide composition range between 35 and 70at.% Cu content. High-energy X-ray diffraction patterns, atomic pair correlation functions, mass density and the thermal stability behavior of the alloys all exhibit monotonic changes with composition. Partial pair correlation functions were determined assuming that they remain unchanged in the different amorphous Cu x Zr100− x alloys and only the weight fractions become altered with changes in composition. The experimental results can be well described by a solid solution-like replacement of Cu and Zr atoms in the whole composition range. No indications are observed neither for the existence of a special atomic arrangement at a particular chemical composition nor for the presence of phase separation in the glassy state of the binary Cu–Zr system. [Copyright &y& Elsevier]

Abstract: Two-phase amorphous and two-phase crystalline Ni58.2Nb20.25Y21.25 alloy samples with coexisting Y-rich and Nb-rich phase fractions were produced by melt-spinning and copper mould casting. Their electrochemical reactivity in the as-quenched or mechanically polished state and after HNO3/HF solution treatment was investigated in nitrogen-purged 0.1M NaOH solution (pH=13) by means of potentiodynamic polarisation experiments. In the as-quenched state the two-phase amorphous samples are blocked by a strong passive layer. The main effect of a HNO3/HF treatment is a selective dissolution of Y-rich phases leading to an excavation of Nb-rich phase regions, i.e. amorphous Ni–Nb–(Y) spheres or Nb6Ni7 grains. The enhanced reactivity of etched Ni58.2Nb20.25Y21.25 ribbons is mainly related to the high reactivity of the residual Y-rich matrix phase, while the Nb-rich spheres with smooth and non-defective surface appear quite inactive. In contrast, in the case of the etched crystalline counterpart the Nb6Ni7 grains provide a highly defective and thus, active surface, which can contribute to an enhanced electrochemical reactivity. The high cathodic performance of a commercial Ni foam for the hydrogen evolution reaction is reached for etched two-phase amorphous and crystalline Ni58.2Nb20.25Y21.25 alloys. [Copyright &y& Elsevier]

Abstract: A nano-scale icosahedral phase forms as first crystallization product upon devitrification of multicomponent amorphous (Ti33Zr33Hf33)50(Ni50Cu50)40Al10, (Ti33Zr33Hf33)60(Ni50Cu50)30Al10 and (Ti33Zr33Hf33)65(Ni50Cu50)27.5Al7.5 alloys (numbers indicate at.%). The onset temperatures and the values of the activation energy for the devitrification of the nano-scale icosahedral phase decrease with increasing (Ti33Zr33Hf33) content in these alloys. This indicates that the structural similarity between the amorphous and the icosahedral phases increases with increasing (Ti33Zr33Hf33) content. Furthermore, the devitrified nano-scale icosahedral quasicrystals form in a wide compositional range regardless of the (Ti33Zr33Hf33) content suggesting that the icosahedral phase in these novel multicomponent alloys, developed by equiatomic substitution may have an extensive solid solubility. After further heat treatment the devitrified nano-scale icosahedral phase fully decomposes into MgZn2-type crystals reflecting its metastability. [Copyright &y& Elsevier]

Abstract: Phase formation in the Cu47Ti33Zr11Ni8Si1 alloy synthesized by various solidification techniques has been studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) paying, in particular, attention to the TEM sample preparation. While a reduced cooling rate results in a duplex microstructure, consisting of nanocrystals in an amorphous matrix, glass formation is achieved upon employing a faster quenching rate. The difference in composition and quench temperature influence the phase transition upon heating. The essential differences observed in TEM, notwithstanding the ion-milling effects and the different pre-alloy ingots used for metallic glass synthesis, can be linked to differences in the nucleation and growth mechanism which, in turn, is influenced by the chemical short range order (CSRO) obtained upon quenching. [Copyright &y& Elsevier]

Abstract: Ni60Nb40 metallic glass powders were prepared by mechanical alloying and subsequently combined with Al to form an Al–30wt.% Ni60Nb40 metal matrix composite (MMC). The crystallization of the Ni60Nb40 metallic glass reinforcements and their reaction with the Al matrix during preparation of the MMC were investigated in a differential scanning calorimeter (DSC) upon isothermal annealing. The comparison of the DSC curves of the Ni60Nb40 metallic glass and of the Al–30wt.% Ni60Nb40 composite shows that the amorphous Ni60Nb40 particles have a very strong resistance against reaction with Al but reaction occurs after crystallization of the metallic glass. The analysis of the isothermal annealing DSC curves gives an activation energy of crystallization of the Ni60Nb40 metallic glass of 724kJ/mol. The interfacial reaction between Al and the Ni60Nb40 reinforcements is mainly controlled by diffusion. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicate that during the interfacial reaction, Ni diffuses from the Ni60Nb40 particles to react with Al and form Al3Ni. At the same time, Al diffuses into the reinforcement particles to react with remaining Nb and form Al3Nb. [Copyright &y& Elsevier]

The deformation behavior of rapidly solidified two-phase amorphous Ni–Nb–Y alloy has been investigated by nanoindentation and high-resolution scanning electron microscopy and correlated with the mechanical properties of the two individual phases composing the system (Ni–Y and Ni–Nb). While the elastic deformation of the two-phase alloy obeys the rule of mixtures for a composite, the plastic deformation is governed by the softer matrix but enhanced, in part, by the deflection of shear bands by the globular harder phase. [Copyright &y& Elsevier]

Abstract: The microstructures of Cu47Ti33Zr11Ni8Si1 ribbons and rods synthesized by melt spinning and copper mold casting have been investigated using transmission electron microscopy (TEM) as well as high-resolution TEM (HRTEM). Though a fully amorphous microstructure is observed for the as-spun ribbons, a fine nanocrystalline microstructure is observed for the rods suggesting that the bulk glass-forming ability of this alloy has been previously overestimated. This report attempts to address the reasons for the lack of a fully glassy phase in the rapidly solidified Cu47Ti33Zr11Ni8Si1 alloy. [Copyright &y& Elsevier]

Abstract: The dependence of the microscopic and macroscopic mechanical response of a Cu-based bulk metallic glass (BMG) on the degree of thermal relaxation and different crystalline volume fractions has been studied. The samples were characterised by constant-rate heating differential scanning calorimetry (DSC), macroscopic compression and nanoindentation tests. Macroscopic compression tests revealed that the fracture strength and Young''s modulus increase with increasing annealing time, and therefore, with increasing crystalline volume fraction. However, embrittlement of the material is also found for longer annealing treatments. A perfect solute mixture model of defect-free nanoparticles embedded in an amorphous matrix was used to account for the strengthening effect. Nanomechanical tests have contributed to the understanding of the mechanical behaviour of the heat-treated BMG states under investigation. [Copyright &y& Elsevier]

Abstract: The deformation behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass was studied by in situ scanning electron microscopy (SEM) quasi-static uniaxial compression tests at room temperature. Multiple shear bands were observed with a large plasticity. Microscopic examination demonstrates that slipping, branching and intersecting of multiple shear bands are the main mechanisms for enhancing the plasticity of this metallic glass. Additionally, nano/micro-scale voids and cracks at the intersecting sites of shear bands and preferential etching of shear bands were observed as well. These observations demonstrated that the formation of shear bands in bulk metallic glasses is resulted mainly from local free volume coalescence. [Copyright &y& Elsevier]

High-strength in situ composites with enhanced ductility were prepared by various casting methods from Zr–Nb–Cu–Ni–Al alloys related to bulk metallic glass compositions. The composites exhibit a bimodal size distribution consisting of bcc β-Zr dendrites stabilized by the addition of Nb and a nanocrystalline/amorphous matrix. The dendrite and matrix crystallite size and the morphology depend sensitively on casting conditions. The cooling rates estimated from the secondary dendrite arm spacing of the Zr73.5Nb9Cu7Ni1Al9.5 alloy vary between ε≈2.6×103 K/s to 4.0×101 K/s. The effect of processing parameters on the mechanical properties is less significant for the Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 alloy while highly pronounced for the Zr73.5Nb9Cu7Ni1Al9.5 alloy, where optimum properties like fracture stress of 1754 MPa and 17.5% strain to failure were achieved for cast rods 10 mm in diameter. The deformation of the composite proceeds partly through dislocation movement in dendrites and a shear banding mechanism in the nanostructured matrix. [Copyright &y& Elsevier]

Mechanical deformation and thermal expansion behavior of Nd60Fe20Co10Al10 bulk metallic glass (BMG) were studied. A stress overshoot followed by a viscous flow approaching a steady state can be seen in the stress–strain curves within a wide temperature range. Moreover, the flow behavior of the BMG is strongly dependent on the strain rate. The dilatometric measurements of the alloys during continuous heating suggest that the glass transition begins above 470 K, which is accompanied by several weak crystallization processes. The rather unique thermal stability of the Nd–Fe based BMGs is responsible for the difference in homogeneous deformation behavior between the present BMG and other BMGs. [Copyright &y& Elsevier]

The thermal behaviour of Zr-based bulk metallic glasses has been investigated in situ through the glass transition by means of differential scanning calorimetry, high temperature X-ray synchrotron diffraction, electrical resistivity, and dilatometry. The temperature dependence of the X-ray structure factor can be well described by the Debye theory. The Debye temperature of the glassy and the supercooled liquid state of Zr52Ti5Cu18Ni15Al10 is θ=412 and θ=162 K, respectively. The temperature coefficient of the electrical resistivity and the thermal expansion coefficient change also at the calorimetric glass transition temperature. The results point to a significant changes in the dynamics of molecular motion at Tg. [Copyright &y& Elsevier]

The thermal stability and the crystallization process of multicomponent ferromagnetic Fe77C5B4(AlGa)3(PSi)11 metallic glass have been studied by differential thermal analysis (DTA) and differential scanning calorimetry (DSC). From the temperatures values of the main transformations, the glass-forming ability (GFA) and the thermal stability were calculated. The apparent activation energy and the frequency factor were evaluated by the Kissinger method, and an Arrhenius law estimates the constant rate of the crystallization process. Moreover, the as-quenched ribbons were magnetically characterized using thermomagneticgravimetry, vibrating sample magnetometry and Mössbauer spectroscopy. [Copyright &y& Elsevier]

We present the application of a novel electrochemical method to overcome the negative effects associated with oxygen contamination in Zr-based glass-forming alloys. The general principle is to remove oxygen from the material by direct electrochemical reduction in a molten salt electrolyte. An oxygen-containing cathode is submerged in molten CaCl2 or a eutectic mixture with other salts. When a current is applied, oxygen is ionised at the cathode, dissolved in the molten salt and discharged as a gas at the anode. We investigate thermodynamic and kinetic limitations to the reduction in oxygen content and the resulting improvement in glass-forming ability that can be achieved when this method is applied to glass-forming alloys. [Copyright &y& Elsevier]

Amorphous and multiphase crystalline Mg65Y10Cu15Ag10 samples were subjected to potentiodynamic polarisation in electrolytes with pH=5–8.4 and 13. Potentiostatic current transients were recorded for studying anodic passive layers growth mechanisms. Surface states were characterised by Auger electron spectroscopy (AES) depth profiling and atomic force microscopy (AFM). The corrosion behaviour of the quaternary alloy samples containing silver is markedly different compared to that of the earlier studied Mg65Y10Cu25 alloy. The free corrosion potential is more noble and corrosion current densities are lower. Stable anodic passivation was observed in electrolytes with pH≥6, whereas in acidic media dissolution sets in. In neutral to weakly alkaline electrolytes, a mainly high field driven layer growth occurs which was similarly observed for the ternary alloy. In strongly alkaline electrolyte, the growth mechanism tended to shift from diffusion control (ternary alloy) to a more high field driven growth pattern due to the presence of silver in the alloy. Passive layers formed in weakly alkaline electrolyte under participation of all alloying elements, especially copper, are thick and porous. Magnesium and yttrium oxide/hydroxides are the main constituents of the thinner passive layer formed in the highly alkaline electrolyte, but also traces of silver oxides were detected. Also, for this quaternary alloy composition, the multiphase crystalline material exhibits a poorer stability and passivation ability than the single amorphous phase. [Copyright &y& Elsevier]