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Multicomponent alloys of Zr50M50, Zr50(M,Ag)50 and Zr50(M,Pd)50 (M = Fe,Co,Ni,Cu) can be melt-spun to obtain amorphous ribbons. The maximum thickness for fully amorphous ribbons varies with composition in the range 34‒53 μm. In contrast, fully amorphous ribbons are not obtainable for binary Zr50Ni50 or ternary Zr50(Ni,Cu)50 alloys. Heating-induced crystallization occurs through: two stages of amorphous [am] →[ am ′ + B2] → [B2 + B33] for Zr50M50; and [am] → [ am ′ + B2] → [B2 + AgZr] for Zr50(M,Ag)50; and a single stage of [am] → [B2] for Zr50(M,Pd)50, while no B2 phase is formed for the binary and ternary Zr50Q50 (Q = Ni or/and Cu) alloys. As-spun amorphous ribbons have good bending plasticity. Remarkably, Zr50M50 ribbons in tension show 0.22‒0.28% plastic elongation and work-hardening (the yield stress is ∼820 MPa, the fracture stress is ∼1200 MPa). When cold-rolled at room temperature to 30% reduction in thickness, Zr50M50 ribbons show 10% increase in hardness, while retaining good bending plasticity. Cold-rolling induces precipitation of spheroidal B2 and irregular B33 particles, while deformation in tension induces B2, B33 and also plate-like monoclinic precipitates. The B2 and B33 particles form by polymorphic transformation, and include a high density of internal defects. This novel deformation-induced precipitation has not been recognized for any Zr50Q50 binary or ternary alloys. The new multicomponent systems are encouraging for future progress as structural amorphous alloys.

A rejuvenated Zr-based bulk metallic glass is tested in tension: it shows strain-hardening and reaches 0.9% plastic strain at failure. The initial rate of increase of flow stress with strain is 73 GPa, much higher than normal for polycrystalline metals and alloys. This hardening rate and its decay with increasing strain are compared with published data on a representative range of conventional and novel alloys. Taking the onset of necking as failure, and using Considère's analysis, we conclude that the metallic glass, however much rejuvenated, is limited to tensile plastic strains of approximately 1%, because of the rapid decay of hardening rate with strain. Rejuvenation of the metallic glass blocks early catastrophic failure in a predominant shear orientation. In comparison with as-cast samples, the fracture surface of the rejuvenated sample is more rugged and the characteristic vein pattern is denser. The effects of rejuvenation on abrasive-wear behavior are also examined.

We show that, using thermo -elastic processing, metallic -glass foils can be shaped, without being embrittled, into linear and annular wave springs. These springs exhibit an undulatory behaviour, unique to metallic -glass foils, in which under compression the number of arcs in the spring increases, increasing the load -bearing capacity and the spring constant. We evaluate the performance limits of the metallic -glass wave springs, and consider how the undulatory behaviour can be exploited. The metallic -glass springs can operate over the same load -ranges as commercially available crystalline wave springs, but have material volumes (and therefore weights) that are one to two orders of magnitude less. Their energy storage per unit material volume is as high as 2600 kJ m – 3 . We suggest that the undulatory behaviour is important in rendering the springs fail -safe in case of overload. We discuss the range of applicability of thermo -elastic processing, the likely working limit of metallic -glass wave springs, and the potential for application of metallic -glass springs in MEMS devices.

© 2020 Elsevier B.V. Fcc-Al (α-Al) + amorphous phase mixtures with ultrahigh hardness are formed by a heating-induced reverse transition from the primary precipitates of α-Al and AlxMy in residual amorphous phase for melt-spun Al84Y9Ni4Co1.5Fe0.5TM1 (TM = V, Nb, Cr, Mo, Mn, Fe, Co, Ni or Cu) amorphous alloys. The resulting particle diameter and volume fraction of the α-Al phase are 5–15 nm and 60–70%, and no internal defects are observed. The solute content in the α-Al phase is 8–11% for the TM = V or Cu alloys. In contrast, the reverse transition is not found for the TM = Zr, Ag or Au alloys, presumably because these elements have atomic radii larger than Al and positive heats of mixing with other solute elements hindering the atomic rearrangements to decompose the AlxMy compound. The [α-Al + amorphous] phase mixture is maintained up to about 700 K and exhibits a Vickers hardness of 550–580, much higher than for the corresponding crystalline alloys. The high hardness at elevated temperature is due to the coexistence of perfect crystal α-Al and high solute-content residual amorphous phase. For a cast conical rod of the TM = Cu alloy, the microstructure is fully amorphous up to a diameter of 0.82 mm, and is an [α-Al + amorphous] phase mixture at larger diameters up to 1.2 mm. The formation of the highly stable [α-Al + amorphous] phase mixtures by the heating-induced reverse transition, as well as the bulk formation (in cast rods) of similar phase mixtures for the TM = V, Nb, Cr, Mo, Mn, Fe, Co, Ni or Cu alloys is promising for future structural and coating materials owing to their high hardness and high elevated-temperature strength.

The composition and structural modification of high-aluminum zinc alloys and high-zinc aluminum alloys influence their wear properties and structural stability. The work described has been aimed at improving properties of the sand-cast Al-Zn-based foundry alloys, particularly their ductility and dimensional stability, by melt inoculation and/or change of chemical composition. In a series of studies, high-aluminum Zn-(25-26) wt.% Al-(1-2.5) wt.% Cu and high-zinc Al-(27-30) wt.% Zn-(1.5-2.5) wt.% Cu alloys have been doped with different levels of added Ti and Mn. The alloys’ structure and mechanical properties have been studied using scanning electron microscopy (SEM), light microscopy (LM), dilatometry and pin-on-disk wear measurements. A small addition of Ti introduced with Zn-4Ti master alloy leads to significant grain refinement of the high-aluminum zinc alloys. A small addition of Ti introduced with Al-3Ti-0.15C master alloy leads to significant grain refinement of the high-zinc aluminum alloys. In the ternary alloys, partially replacing Cu with Ti and/or Mn allows dimensional changes to be reduced while preserving good wear properties.

The structural changes and mechanical properties of a Zr 63 Cu 22 Fe 5 Al 10 bulk metallic glass (BMG), and a Zr 63 Cu 27 Al 10 one made for comparison, were studied on annealing below the crystallization temperature. The phase composition of the samples was studied by conventional X-ray diffractometry and high-resolution transmission electron microscopy including the atomic-scale elemental mapping. The samples were mechanically tested in compression. The Zr 63 Cu 22 Fe 5 Al 10 bulk metallic glass shows a high strength and good deformability at room temperature both in the as-cast state and after prolonged structural relaxation below the crystallization temperature. The reasons for such behavior are discussed in the present work.

The lack of plasticity in metallic glasses (MGs) is currently the main drawback limiting their commercialization. Mechanical treatments such as high-pressure torsion (HPT) or cold rolling have successfully improved the plasticity of some MGs. We asked whether we can quantify the change in shear band behavior associated with this enhanced plasticity. To answer this question, we performed numerous nanoindentation measurements on as-cast, annealed and HPT deformed Pt-based BMG samples. We observed different shear band sliding velocities depending on the samples. The amplitude of the velocity peak decreased after HPT deformation and increased after annealing. This study reveals that the decrease in shear band sliding velocity quantifies the degree of rejuvenation in the material after mechanical treatment. The role of the residual stresses on shear band population density is also presented. Thanks to this new approach, it becomes now possible to compare different mechanical treatments, and their ability to rejuvenate a MG.

The La 55 Al 25 Cu 10 Ni 10 –10 vol.% Ti glassy composites have excellent compressive strength and plasticity at room temperature (RT). At cryogenic temperature (77 K), neither the glassy matrix, nor the Ti particles undergo embrittlement, and the composite retains appreciable toughness. Surprisingly, despite significant shear band plasticity at 77 K, failure occurs in a mixed mode manner, with large areas showing quasi-cleavage features that appear to initiate from cracks at the glass-Ti interfaces, which also limit the overall plastic strain. Interface engineering is the key to further alloy development for even better properties.

The structure of Cu 64 Zr 36 metallic glasses is investigated on the scale of nanometers using local shear strain marking in molecular dynamics simulation. Densely packed clusters with sizes ranging from 1.5 to 2.5 nm are unambiguously shown comparable to the size of the reported medium range order, surrounded by loosely packed interconnecting regions with a low density. The clusters are mainly composed of full and defective icosahedra, while no dominant short-ordered motifs are identified in the surroundings. High resolution transmission electron microscopy reproduces the observation of simulations.

As-spun (Fe0.25Co0.25Ni0.25Cr0.125Mn0.125)100–xBx (x = 9–13 at%) alloys are fully amorphous with bending plasticity and good soft-magnetic properties. Manganese addition favors amorphous phase formation at lower B content than in comparable alloys. On heating, the alloys transform: [am] → [am’ + bcc + fcc] → [fcc] at 9–11% B; and [am] → [am’ + bcc + fcc] → [bcc + fcc + borides] → [fcc + borides] at 12–13% B. Novel observations are the formation of metastable bcc + fcc phases, and an endotherm due to the [bcc + fcc] → [fcc] transition. The Vickers hardness of 9–11% B alloys is ∼650 in the as-spun state, shows a maximum of 1010 for [bcc + fcc] state and then decreases to 750 upon transition to [fcc]. As-cast 9–11% B 2-mm-diameter rods, mainly [bcc + fcc], exhibit compressive strength of 1520–1705 MPa and plastic strain >25%. These high-strength alloys, and the as-spun amorphous alloys with soft-magnetic properties, are encouraging for the further development of structural and functional materials.

High-entropy (Fe0.25Co0.25Ni0.25Cr0.125Mo0.0625Nb0.0625)100‒xBx amorphous alloys are formed with low (8–14 at%) boron contents by melt spinning. With increasing boron, the broad halo in X-ray diffraction shifts to indicate a decreasing average spacing of nearest-neighbor atoms. The crystallization onset temperature and the Vickers hardness increase with boron content. The glass transition is observed even for a low-boron (13 at%) alloy. The 8–11 at% B alloys crystallize in stages: [am] → [am’ + bcc] → [am″ + bcc + fcc] → [bcc + fcc + borides]. The bcc precipitates, diameter ∼10 nm enriched in (Fe,Co) and the fcc precipitates, diameter ∼15 nm enriched in (Ni,Fe), are stable on annealing over a wide range (900–1060 K) below the temperature at which borides form. The bcc phase shows no internal defects, while the fcc phase has defects such as twin boundaries. The microhardness (Hv) of the [am″ + bcc + fcc] nanostructure reaches a high maximum of 1460–1560 kgf‧mm−2, before decreasing rapidly when the formation of borides marks the disappearance of the residual amorphous phase. The high thermal stability of the three-phase nanostructure is attributed to the residual amorphous phase enriched in B, Cr, Mo and Nb. These low-boron metastable alloys with novel three-phase nanostructures are attractive as potential amorphous coatings or ultrahard structural alloys with high thermal stability.

Structural and composition modification of high-zinc aluminum alloys refines their microstructural scale from a few millimeters to a few micrometers. In a series of studies, high-aluminum Al–30Zn alloys were doped with (2–20) wt.% Cu, 1 wt% Mn and small (∼100 ppm) Ti addition. The alloys’ microstructure has been studied using SEM/EBSD (scanning electron microscopy/electron backscatter diffraction) and LM (light microscopy) techniques. A small addition of Ti introduced with Al-3 wt.% Ti-0.15 wt% C (TiCAl) master alloy decreases the grain diameter in the high-aluminum zinc alloys from 1500–2000 μm to 100–200 μm. The high-zinc, high-copper alloy (Al–30Zn–20Cu) cast into a steel mold shows microstructure refinement to 2–5 μm. The observed refinement should improve the ductility of the examined alloys while preserving other properties discussed in the paper.

We have developed a torsion machine that can apply pure shear stress to small-diameter rod samples. We report preliminary results on Cu-based metallic glass samples held at constant torque in the elastic range. The inelastic angle of twist increases approximately linearly with the logarithm of time, interpreted as anelastic deformation. Reversal of torque reveals an effect analogous to the Bauschinger effect in polycrystalline metals. The relative deformation rate is increased by a factor of 4.5 on first reversal, an effect discussed in terms of the operation of shear transformation zones and related to structural change in the metallic glass.

Nanoindentation tests using a spherical indenter of tip radius 10 µm have been performed on Zr- and Pd-based metallic glasses, focusing on the cumulative distribution of the first yield load. When normalized using the macroscopic yield stress, the distribution of mean pressure at yield is nearly independent of the glass composition. Collecting literature data, there is a clear indentation size effect in metallic glasses: the smaller the indenter tip radius, the larger the indentation pressure at yield. The magnitude of the size effect in metallic glasses is compared with, and found to lie between, the cases of crystalline metals and ceramics.

Samples of Zr62.5Cu22.5Fe5Al10 bulk metallic glass are subjected to uniaxial compression. Comparison of tests in monotonic loading and cyclic loading (repeated loading to the onset of plasticity, then unloading) shows that the compressive plasticity of the glass is drastically reduced under cyclic loading. It is argued that this effect arises from stress reversal accelerating the concentration of shear on a dominant shear band. The link with compression–compression fatigue results, and the consequences for low-cycle fatigue of metallic glasses are considered.

Lack of plasticity is one of the main disadvantages of metallic glasses. One of the solutions to this problem can be composite materials. Diffusion bonding is promising for composite fabrication. In the present work the diffusion process in glassy multilayer films was investigated. A combination of advanced transmission electron microscopy (TEM) methods and precision sputtering techniques allows visualization and study of diffusion in amorphous metallic layers with high resolution. Multilayered films were obtained by radio frequency sputter deposition of Zr-Cu and Zr-Pd. The multilayers were annealed under a high vacuum (10−5 Pa) for 1 and 5 h at 400 °C, that is, well below the crystallization temperatures but very close to the glass-transition temperatures of both types of the glassy layer. The structural evolution in the deposited films was investigated by high-resolution transmission electron microscopy. It was observed that, despite the big differences in the atomic mass and size, Pd and Cu have similar diffusion coefficients. Surprisingly, 1 h of annealing results in formation of metastable copper nanocrystals in the Zr-Cu layers which, however, disappear after 5 h of annealing. This effect may be connected with nanovoid formation under a complex stress state evolving upon annealing, and is related to the exceptionally slow relaxation of the glassy layers sealed with a Ta overlayer. Keywords: Metallic glasses, Multilayered films, Diffusion, HRTEM

The effects of shot peening (SP) on the nanoindentation response of Cu47.5Zr47.5Al5 metallic glass, both in the as-cast state and after thermally induced structural relaxation (i.e., after annealing close to the glass transition), are investigated. As expected, annealing causes an increase of hardness attributable to annihilation of free volume. Conversely, nanoindentation tests, carried out on a transverse section at different distances from the SP surface, reveal that SP induces mechanical softening. Both the hardness and the reduced Young’s modulus progressively decrease as the peened surface is approached. Finite-element simulations of the nanoindentation curves indicate that the cohesive stress and the Mohr–Coulomb friction coefficient also decrease after SP, an observation which is in line with the induced mechanical softening. Differential scanning calorimetry measurements reveal an increase of the relaxation enthalpy, particularly when SP is performed on the previously annealed metallic glass, consistent with deformation-induced creation of free volume.

Shear-banding is a ubiquitous plastic-deformation mode in materials. In metallic glasses, shear bands are particularly important as they play the decisive role in controlling plasticity and failure at room temperature. While there have been several reviews on the general mechanical properties of metallic glasses, a pressing need remains for an overview focused exclusively on shear bands, which have received tremendous attention in the past several years. This article attempts to provide a comprehensive and up-to-date review on the rapid progress achieved very recently on this subject. We describe the shear bands from the inside out, and treat key materials-science issues of general interest, including the initiation of shear localization starting from shear transformations, the temperature and velocity reached in the propagating or sliding band, the structural evolution inside the shear-band material, and the parameters that strongly influence shear-banding. Several new discoveries and concepts, such as stick-slip cold shear-banding and strength/plasticity enhancement at sub-micrometer sample sizes, will also be highlighted. The understanding built-up from these accounts will be used to explain the successful control of shear bands achieved so far in the laboratory. The review also identifies a number of key remaining questions to be answered, and presents an outlook for the field.

Chinese Academy of Sciences; NSF of China [11021262, 50921091]; MOST 973 of China [2012CB937500, 2010CB731603]; EPSRC

Metal–matrix composites are widely applied in the aerospace and automotive industries because of their low density and high rigidity. We focus on composites of magnesium-alloy (AZ91) matrix reinforced with SiC particles, with the aim of building a micro–macro model for their solidification. Heat-flow processes are modelled on the macro-scale, with latent heat release during nucleation and grain growth. Calcula- tions are for a fixed cooling rate, consistent with the micromodel for magnesium primary phase solidifi- cation. The population density of grains in the matrix is assumed to depend on the maximum supercooling and on the mass fraction of SiC particles. The present model gives reasonable agreement with measurements.

The mechanism of liquid–liquid phase separation and factors determining the solid-state microstructure of monotectic alloys are discussed. The effect of the cooling rate on the phase-separated morphology is shown in examples of Al–In, Al–Pb, Ni–Nb–Y and Zr–Gd–Co–Al alloys solidified by different techniques. A remarkable improvement of the microstructure for the Al91Pb9 hypermonotectic alloy cast with TiB2 particles, which catalyze the phase separation, is demonstrated.

Differential scanning calorimetry (DSC) is widely used to study the stability of amorphous solids, characterizing the kinetics of crystallization close to the glass-transition temperature T(g). We apply ultrafast DSC to the phase-change material Ge(2)Sb(2)Te(5) (GST) and show that if the range of heating rates is extended to more than 10(4) K s(-1), the analysis can cover a wider temperature range, up to the point where the crystal growth rate approaches its maximum. The growth rates that can be characterized are some four orders of magnitude higher than in conventional DSC, reaching values relevant for the application of GST as a data-storage medium. The kinetic coefficient for crystal growth has a strongly non-Arrhenius temperature dependence, revealing that supercooled liquid GST has a high fragility. Near T(g) there is evidence for decoupling of the crystal-growth kinetics from viscous flow, matching the behaviour for a fragile liquid suggested by studies on oxide and organic systems.

Full evaluation of the elasticity tensor of a bulk metallic glass (Pd40Cu30Ni10P20) shows anisotropy induced by creep under uniaxial compression changing sign with increasing strain. Anisotropy due to anelastic strain is erased by zero stress annealing. At higher strain anisotropy of opposite sign suggests structural alignment by plastic flow. Induced anisotropy is most evident in the Poisson ratio, may relate to other properties, including the strength and toughness of metallic glasses, and may lead to misinterpretation of annealing effects.

Room-temperature uniaxial compression of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass at 80% of the yield stress leads to homogeneous viscous flow. The flow in this apparently elastic regime reveals large increases in volume associated with local shearing events in the glass. The extent of this dilatation is masked in more usual tests by significant relaxation of the glass structure during and after shear. The dilatation in deformed metallic glasses can no longer be attributed only to free-volume generation at shear bands.

In the version of this Review Article originally published, parentheses were misplaced and the longitudinal and transverse speeds were inverted in two expressions for Poisson's ratio in Box 2; the expressions should have read, respectively, ν = (3B/G - 2)/(6B/G + 2) and ν = [½(Vl/Vt)2 - 1]/[(Vl/Vt)2 - 1].

Triple lines are created when a new phase is nucleated at an interface. Such heterogeneous nucleation is inevitably affected by the tension of the triple lines. Triple lines can also act as sites for nucleation. Experimental examples and analyses of nucleation involving triple lines are reviewed.

Surfaces of bulk glassy Zr59Ti3Cu20Al10Ni8 samples were shot-peened for different times and their corrosion behaviour was tested in 0.01 M Na2SO4 + xM NaCl (x = 0; 0.01; 0.1) and 6 M 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.

Compression testing shows that at low-oxygen levels (240 ppm) the Cu 49 Hf 42 Al 9 glass deforms predominantly by shear and is quite tough. Specimens with higher oxygen levels (1700 ppm) have oxygen-containing dendrites in an amorphous matrix and show no plasticity. Importantly, the dominant fracture mode is not shear but local tensile failure. Although there is a slight reduction in the toughness of the glassy matrix, the severe embrittlement is primarily because of the brittle dendrites that facilitate crack initiation and propagation.

Shot-peening induces surface compressive stresses in bulk metallic glass components, improving their plasticity. Structural changes in the peened surface of fully glassy and partially crystalline Zr55Al10Cu30Ni5 are studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. An earlier study is extended by examining the effect of sample temperature. While fully glassy samples show no phase change under peening, partially crystalline samples show either amorphization or crystallization depending on temperature. Peening can induce very large stored energy in metallic glasses rendering them susceptible to crystallization below room temperature, a result which may be relevant for improving the plasticity of these materials.

Differential scanning calorimetry heating runs on as-cast and shot-peened bulk metallic glass Pd 40 Cu 30 Ni 10 P 20 show a broad temperature range of heat release (relaxation spectrum) with two peaks. The higher-temperature peak is reduced by shot-peening, suggesting uniform deformation and partial relaxation of the glassy structure. Peening of pre-annealed samples shows the stored energy of cold work to be a few per cent of the work done. Peening increases atomic mobility, revealed by a downward temperature shift of the relaxation spectrum.

Fully amorphous and partially crystallized Mg66Ni20Nd14 and partially crystallized Mg60Cu30Y10 alloys were indented and, subsequently, thinned along the cross-section of the indent by means of a focused ion beam (FIB) for transmission electron microscopy (TEM) observation. Depending on the crystallized fraction and the crystal size, the volume deformed under the indenter tip shows different features that can be associated with the different ability of the shear bands to propagate in the two partially devitrified metallic glasses.

An assessment is made of the extent to which the elastic properties of a metallic glass can be predicted from the properties of the constituent elements. The correlations established do permit estimation of the glass properties, and provide guidelines for the selection of compositions to promote plasticity rather than brittleness.

The flux treatment was applied to increase the glass-forming ability of a glassy [(Fe0.5Co0.5)0.75B0.20Si0.05]96Nb4 alloy. The large bulk glassy specimen with diameter of 7.7 mm was prepared by water quenching the melt immersed in the molten flux of B2O3. The diameter of the specimens is approximately 1.5 times as large as the previous result, even though the cooling rate of copper mold casting should be much higher than that of water quenching. The critical cooling rate for a glassy phase is 150 - 170 K/s, which is much slower than 500 K/s without the flux treatment. The flux treatment improves the glass-forming ability by cleaning the molten metal where heterogeneous nucleation is difficult to take place.

It has recently been reported that some Cu-based metallic glasses containing a dispersion of embedded nanocrystals can sustain more than 50% room temperature compressive plastic strains. By carefully observing shear bands containing 3–8 nm crystallite particle dispersions using in situ deformation in tension in a transmission electron microscope, we have found and report here direct evidence of systematic shear delocalisation in the form of shear band thickening and zigzagging as well as crack blunting and zigzagging. Since it is well established that both temperature and free volume rise in active shear bands, it is found that the matter in shear bands containing such small nanoparticle dispersions deforms like a semi-solid slurry. The glassy matrix behaves liquid-like and the nanoparticles constitute a growing solid fraction. Shear delocalisation and crack blunting occur through sharp viscosity increase occurring as the crystallite (solid) fraction grows in the shear band slurry leading to the shear being displaced to neighbouring regions with lower crystalline volume fraction.

Under ambient conditions, plastic flow in metallic glasses is sharply localized into shear bands. The heat content of, and consequent temperature rise at, shear bands in three bulk metallic glasses are compared using a recently reported fusible coating method. The minimum shear offsets necessary to detect local heating are determined. It is shown that the dependence of heat content on offset is consistent with frictional heating in the band. The effective stress on the band undergoing shear is 50–70% of the macroscopic shear stress, a ratio compared with simulations of shear-band initiation and operation. It is also noted that frictional heating can occur not only at shear bands, but also at mixed-mode cracks.

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.

This paper reviews our recent results on the developments and applications of the following four kinds of advanced materials having unique elastic properties in the absence of poisonous and allergic elements, i.e. (1) nanocrystalline Ti-based alloys with low Young's modulus, high tensile strength and high corrosion resistance, (2) new super-elastic Ti-based alloys with a large elastic strain up to 4% and high tensile strength, (3) new Pd-based bulk glassy alloy with a very low critical cooling rate of about 1 K/s, and (4) porous glassy Pd-based alloys with low Young's modulus, large plastic strain and high absorption energy up to failure. These promising properties caused by unique alloy designs and material morphology indicate the possibility that the newly developed advanced alloys are used in various engineering fields including biomedical materials.

The poisoning of grain refinement in aluminium alloys owing to the presence of silicon is investigated using CALPHAD based thermodynamic modelling software. The existence of primary phases other than α-aluminium, namely TiSi2 and TiSi, which are stable at typical melt holding temperatures, is consistent with microstructural observations of other researchers. The compositional and temperature range of these phases are calculated. The software is also used to determine the effect of silicon and titanium additions on the growth rates of α-aluminium grains via the growth restriction parameter Q. These results are used to explain poisoning in silicon containing foundry alloys via a thorough review and discussion of the relevant literature.

A novel electrochemical method is presented for removing oxygen from glass-forming liquids in a molten-salt electrolyte. The effect of the electrolysis time on the glass-forming ability of Zr 55 Cu 30 Al 10 Ni 5 and Cu 47 Ti 34 Zr 11 Ni 8 was evaluated. Differential scanning calorimetry traces clearly show a stabilization of the amorphous phase as the electrolysis is performed for longer times, consistent with the hypothesis that the removal of oxygen from the melt improves its glass-forming ability.

By carefully observing shear bands generated by tensile deformation in a transmission electron microscope, we report evidence of shear delocalization in a Cu-based glass containing nanoparticle dispersions. Nanocrystals grow in shear bands, delocalize the shear and deviate and blunt cracks. The results are consistent with matter in operating shear bands behaving like a semi-solid slurry.

The potential of metallic glasses as structural materials is assessed. A wide-ranging comparison with conventional engineering materials shows metallic glasses to be restricted to niche applications, but with outstanding properties awaiting wider application, for example in micro electro-mechanical systems devices.

At ambient temperature the plastic flow shown by metallic glasses is localized into shear bands1,2. This localization and the liquid-like features seen on fracture surfaces are consistent with shear softening in the bands. The extent to which this softening is a result of local heating has remained controversial, with estimates of the local temperature rise ranging from less than 0.1 kelvin to a few thousand kelvin3,4,5,6,7,8,9,10,11. Here we present a new experimental method based on a fusible coating, which shows that the temperature rise, over a few nanoseconds, can be as high as a few thousand kelvin; nevertheless, the temperature rise does not seem to control the shear-band thickness. It is important to understand the mechanisms of shear banding and associated softening because these are the principal factors limiting structural applications of bulk metallic glasses, which have some attractive mechanical properties such as high yield strength12,13.

Techniques for making metal cellular structures have been successfully developed to commercialize aluminium and nickel foam. Work to extend these methods to create steel and titanium foams is well advanced. The question arises: in which applications might they find success? Here we apply a general methodology for exploring potential applications to answer this question.

Interest in finding binary alloys that can form bulk metallic glasses has stimulated recent work on the Cu–Zr system, which is known to show glass formation over a wide composition range. This work focuses on copper mold casting of Cu50Zr50 (at.%), and it is shown that fully amorphous rods up to 2-mm diameter can be obtained. The primary intermetallic phase competing with glass formation on cooling is identified, and the glass-forming ability is interpreted in terms of a metastable eutectic involving this phase. Minor additions of aluminum increase the glass-forming ability: with addition of 4 at.% Al to Cu50Zr50, rods of at least 5-mm diameter can be cast fully amorphous. The improvement of glass-forming ability is related to suppression of the primary intermetallic phase.

In wrought aluminium alloys, the fragmentation of coarse, iron bearing intermetallic particles by hot rolling is an important development in industrial processing. Here a model 3000 series alloy is used to show that fragmentation can occur prior to hot rolling, during the homogenisation heat treatment. Some fragmented particles display a curved morphology of break-up that results from matrix wetting of two phase (or 'duplex') interfaces in Al6(Fe,Mn) particles partially transformed to an α-Al–(Fe,Mn)–Si phase. In contrast, samples rapidly heated to temperature in a fluidised bath show an angular break-up indicative of tensile stresses induced by thermal expansion mismatch between the intermetallic particles and aluminium matrix. Although this break-up should not be industrially significant, the transformation induced break-up by wetting may be. More generally, internal boundaries resulting from the transformation to α-Al–(Fe,Mn)–Si phase may be mechanically weak fracture initiation points during h...

The crystallisation and mechanical properties of the light alloy, Mg60Cu30Y10 bulk metallic glass (BMG) have been investigated by differential scanning calorimetry and instrumented indentation. Generally, the low-temperature plasticity of BMGs can be improved by partial devitrification to give an ultra-fine crystal structure in the amorphous matrix. From the indentation tests, increases in hardness and elastic modulus were observed after both the first and second stages of crystallisation. Plastic instabilities have been observed in the instrumented-indentation loading curves, even for samples with a significant crystallised fraction.

Bulk metallic glasses (BMGs) are not cheap materials, and they are unlikely to become so for some time. Finding applications for them relies on identifying products in which the BMGs can offer sufficiently high improvements in performance to justify the cost. The research applies the notions of material-property space and performance indices and explores three strategies for systematically finding potential applications for a “new” material. Different approaches to compare the “new” material with conventional materials identify the potential victims for substitution, in which established current applications suggest promising applications for the “new” material. The output is a ranked list of technically viable applications. They are then subjected to a market analysis. Finally, an analysis is made of current and future applications of bulk metallic glasses.

Nanoindentation loading curves on metallic glasses can show sharp, constant-load steps. The relationship of these steps to shear-band initiation is explored for a wide range of metallic glasses, from thin films to bulk. On a given loading curve, there is a well defined strain for initiation of shear bands. The steps may be blurred by instrumental effects or partial devitrification. The nanoindentation results do not suggest a transition in deformation mode as a function of strain rate.