Search

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.

The single-phase multi-principal-component CoFeMnTiVZr alloy was obtained by rapid solidification and examined by a combination of electrochemical methods and gas-solid reactions. X-ray diffraction and high-resolution transmission electron microscopy analyses reveal a hexagonal Laves-phase structure (type C14). Cyclic voltammetry and electrochemical impedance spectroscopy investigations in the hydrogen absorption/desorption region give insight into the absorption/desorption kinetics and the change in the desorption charge in terms of the applied potential. The thickness of the hydrogen absorption layer obtained by the electrochemical reaction is estimated by high-resolution transmission electron microscopy. The electrochemical hydrogen storage capacity for a given applied voltage is calculated from a series of chronoamperometry and cyclic voltammetry measurements. The selected alloy exhibits good stability for reversible hydrogen absorption and demonstrates a maximum hydrogen capacity of ∼1.9 wt% at room temperature. The amount of hydrogen absorbed in the gas-solid reaction reaches 1.7 wt% at 298 K and 5 MPa, evidencing a good correlation with the electrochemical results.

Metallic glasses have attractive properties, but since the glassy state is inherently metastable, they are not normally considered for applications at elevated temperatures. Yet, studies have shown that multicomponent and pseudo high-entropy (PHE) compositions can confer useful heat resistance. The formation, thermal stability, and mechanical and chemical properties of multicomponent Fe-(Cr, Mo)- and Zr-based bulk metallic glasses (BMGs) are reviewed to assess their potential as heat-resistant structural materials. The composition Fe43Cr16Mo16C15B10 is castable and fully glassy with rod diameters up to 2.7 mm. Glassy coatings of this material with low porosity, good mechanical properties, and good corrosion resistance can be produced by high-velocity spray coating. The compositions Zr55–65Al7.5–10(TM1,TM2)27.5–35 (TM1 = Fe, Co, Ni, TM2 = Cu, Pd, Ag, Au) yield PHE BMGs, in which a stable cluster-like glassy phase without crystalline precipitates is formed by annealing at temperatures well above the first calorimetric transformation. It is suggested that proliferation of alloy components is an effective method to synthesize metastable metallic materials that retain high strength at elevated temperatures.

Heating-induced crystallization of high-entropy (HE) (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)86‒89B11‒14 amorphous (am) alloys is examined to develop new structural materials with low B contents. The crystallization of 11B alloy occurs in three stages: first nanoscale bcc precipitates form in the amorphous matrix, second nanoscale fcc precipitates form, and the residual amorphous phase disappears in the third stage which yields borides in addition to the bcc and fcc phases. Crystallization of 14B alloy is the same, except that the order of appearance of bcc and fcc is reversed. The bcc and fcc particle diameters are 5–15 nm and remain almost unchanged up to ∼960 K. On annealing, ultrahigh hardness of 1500–1550 (unprecedented for boride-free structures) is attained just before the third crystallization stage. This hardening and the thermal stability of the novel [am + bcc + fcc] structures are remarkable at such low boron content and encouraging for development as ultrahigh-strength alloys. The results are interpreted in terms of the nature and extent of partitioning of elemental components between the bcc/fcc phases and the amorphous matrix, and the size and defect structures of the bcc and fcc precipitates. The magnetic flux density at room temperature increases by precipitation of bcc and decreases by appearance of fcc. Slower quenching of the 11B alloy shows a pseudo-polymorphic crystallization that may be characteristic of multicomponent HE systems.

Shear-induced segregation, by particle size, is known in the flow of colloids and granular media, but is unexpected at the atomic level in the deformation of solid materials, especially at room temperature. In nanoscale wear tests of an Fe-based bulk metallic glass at room temperature, without significant surface heating, we find that intense shear localization under a scanned indenter tip can induce strong segregation of a dilute large-atom solute (Y) to planar regions that then crystallize as a Y-rich solid solution. There is stiffening of the material, and the underlying chemical and structural effects are characterized by transmission electron microscopy. The key influence of the soft Fe–Y interatomic interaction is investigated by ab-initio calculation. The driving force for the induced segregation, and its mechanisms, are considered by comparison with effects in other sheared media.

In this work, two different approaches were followed to obtain Cu-Al-Ni thin films with shape memory potential. On the one hand, Cu-Ni/Al multilayers were grown by magnetron sputtering at room temperature. To promote diffusion and martensitic/austenitic phase transformation, the multilayers were subjected to subsequent heat treatment at 800 &deg, C and quenched in iced water. On the other hand, Cu, Al, and Ni were co-sputtered onto heated MgO (001) substrates held at 700 &deg, C. Energy-dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy analyses were carried out to study the resulting microstructures. In the former method, with the aim of tuning the thin film&rsquo, s composition, and, consequently, the martensitic transformation temperature, the sputtering time and applied power were adjusted. Accordingly, martensitic Cu-14Al-4Ni (wt.%) and Cu-13Al-5Ni (wt.%) thin films and austenitic Cu-12Al-7Ni (wt.%) thin films were obtained. In the latter, in situ heating during film growth led to austenitic Cu-12Al-7Ni (wt.%) thin films with a (200) textured growth as a result of the epitaxial relationship MgO(001)[100]/Cu-Al-Ni(001)[110]. Resistance versus temperature measurements were carried out to investigate the shape memory behavior of the austenitic Cu-12Al-7Ni (wt.%) thin films produced from the two approaches. While no signs of martensitic transformation were detected in the quenched multilayered thin films, a trend that might be indicative of thermal hysteresis was encountered for the epitaxially grown thin films. In the present work, the differences in the crystallographic structure and the shape memory behavior of the Cu-Al-Ni thin films obtained by the two different preparation approaches are discussed.

Glassy ribbons of Zr65Al7.5Ni10Cu17.5‒xAux (x = 6‒17.5 at%), cold-rolled at liquid-nitrogen temperature, transform into glass and icosahedral quasicrystalline [glass’ + (IQ)] or [glass’ + IQ + dodecagonal quasicrystalline (DoQ) + approximant crystalline (APC)] phases. The rolled ribbons show plasticity, an unprecedented contrast to the extreme brittleness of all alloys containing large size IQ-, DoQ- and APC particles reported to date. After thickness reductions (R) of 50‒70%, the structure is [glass' + IQ] for 6‒15Au and [glass' + IQ + DoQ + APC] phases for 17.5Au. The IQ and DoQ particle diameters are 50‒100 nm and 150‒200 nm, respectively, much larger than the 10‒15 nm for the IQ phase when induced by annealing. On cold-rolling, the Vickers hardness decreases by up to 24% at R = 70%, in contrast to the hardening effect of annealing-induced transformation. Tensile tests on cold-rolled ribbons show evidence for preferential slip at pre-existing shear bands. The rolling-induced quasicrystalline phases have quasiperiodic atomic arrangements that are incompletely developed and do not extend over long range; the high density of internal defects and strains appears to promote plasticity. The success in synthesizing plastic [glass’ + IQ] and [glass’ + DoQ + APC] alloys may provide a new method for ductilization of brittle materials, and is promising for the development of a new type of structural material.

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.

Plasticity improvement in metallic glasses resulting from cycling treatment between room and liquid nitrogen temperature has been reported and attributed to rejuvenation due to a non-uniform thermal expansion coefficient. However, the detailed microscopic effect is still unclear. The present study focuses on the microscopic effect of room-temperature ageing and cryogenic cycling. La70Cu15Al15 and La70Ni15Al15 metallic glasses were subjected to varying ageing times, after which some were also cryogenically cycled. Quasi-static anelastic relaxation measurements were then employed to characterize the time-constant spectra over seven orders of magnitude. The overall anelastic strain decreases with increasing ageing time, but is not noticeably affected by cryogenic cycling. On the other hand, while ageing also causes an increase in characteristic time constants, cycling reverses this effect. The new details shed light on the effect of structural relaxation and rejuvenation on the properties of shear transformation zones.

Structural modification of high-zinc aluminium alloys influences their strength and damping properties. In a series of studies, Al – 27 wt. % Zn alloy (Al-27Zn) has been doped with Cu and Mn, and inoculated with Ti introduced with AlTi-based master alloys. The alloy microstructure and mechanical properties have been studied using light microscopy and measurements of strength, wear resistance and damping capacity. Doping with Cu and Mn significantly increases the strength and wear resistance of the multicomponent Al-27Zn based alloy. Grain refinement leads to significant improvement in ductility, while preserving good tensile strength. Refinement reduces the attenuation coefficient for 1 MHz ultrasound by about 30%, but the refined alloys are still clearly within the range classified as high-damping

© 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.

We performed nanoindentation measurements on as-cast and high-pressure-torsion deformed Pd-based metallic glass samples with spherical indenters of radius 1, 5 and 8 μm. The different serrated behaviors observed during nanoindentation were connected to the microstructural changes evidenced indirectly by differential scanning calorimetry and directly by electron microscopy. On the deformed sample, the discontinuities remained with the 1-μm indenter, decreased in intensity with the 5-μm indenter and disappeared with the 8-μm indenter. The different plastic zone sizes below the indenters can explain this effect since a larger plastic zone offers more possibility for interactions with pre-existing shear bands.

The influence of cryothermal treatment on the mechanical properties of metallic glasses with different compositions was investigated in the present work. It was found that cryothermal cycling can induce rejuvenation as well as relaxation of the metallic glasses. The local apparent Young’s modulus and its spatial distribution width on the surface of the metallic glass increase after cryothermal cycling, while in the bulk the effect depends on the glass composition. It appeared that this increase is temporary and disappears after a period of room temperature aging. This effect is connected with a large distribution of relaxation times in the metallic glasses due to their heterogeneous structure and the formation of complex native oxides on the outer surfaces of the glasses. Our findings reveal that a cryothermal cycling treatment can improve or degrade the plasticity of a metallic glass, and the atomic bond structure appears to be very important for the outcome of the treatment. Cryothermal cycling affects the structure and mechanical properties of metallic glasses in ways that depend on their composition. These metallic alloys, with their disordered atomic structures, have promising characteristics but before widespread applications are possible their behavior needs to be better understood. An international team of researchers led by Sergey Ketov from the Erich Schmid Institute of Materials Science, Leoben, Austria, have now subjected three such glasses with the general formula Zr60Cu20M10Al10 (where M is iron, cobalt or nickel) to temperature cycles between 77 and 320 K. The treatment was found to temporarily increase their surface stiffness, to a greater extent for the iron-based sample. It also affected their bulk plasticity: an increase was noticed for the iron-based glass, “rejuvenating” the material, whereas the cobalt-based glass was degraded and the nickel-based glass remained largely unaffected. Cryothermal cycling can induce rejuvenation as well as relaxation of metallic glasses. The surface apparent Young’s modulus and its spatial distribution width increase after the treatment, while in bulk effect depends on the glass composition. This increase is temporary and disappears after some time of room temperature aging. Effect is connected with a large distribution of relaxation times in metallic glasses due to their heterogeneous structure and the formation of complex native oxide on the glass surface. Cryothermal cycling can improve or degrade the plasticity of metallic glasses and the atomic bond structure determines the outcome of the treatment.

© 2018 Acta Materialia Inc. Melt-spun amorphous ribbons of Al 90 Y 10 (at.%) (90Al) and Al 84 Y 8.5 Ni 4 Co 2 Pd 1 Fe 0.5 (84Al) are cold-rolled at near to liquid-nitrogen temperature or at room temperature, inducing partial crystallization to nanoscale fcc-Al (α-Al). The crystallization is characterized and contrasted with the distinct sequences of reactions on annealing 90Al and 84Al amorphous alloys. Rolling-induced crystallization leads to softening, opposite to the effect of nanocrystallization induced by annealing. The origins of the hardness changes are analyzed. The rolling induces novel polymorphic crystallization to α-Al with extended solid solubility. This transformation, which occurs equally in 84Al and 90Al, despite the much greater thermal stability of the former, allows the ribbons to retain good bending ductility, and delays the onset of embrittlement on subsequent annealing. Partial crystallization induced by cold-rolling is useful in avoiding the formation of compound phases associated with brittleness, and is a promising process for high-solute Al-based amorphous alloys to be further developed as structural materials.

Uniaxial compression is used to apply cyclic loading within the elastic range to samples of Zr 61 Cu 27 Fe 2 Al 10 bulk metallic glass (BMG). The results are twofold. On one hand the microhardness measured on the end-faces of the samples shows an increase of ∼8% together with a slight gradual increase in the Young's modulus after the 2nd cycle. This appears similar to hardening induced by elastic cycling in nanoindentation. The microhardness measured in the centre of the sample or on the side faces of the BMG samples show little or no change as a result of cyclic loading. These results suggest that the apparent hardening of the end-faces is a surface effect attributed, not to relaxation, but to a build-up of anelastic strain, associated with local anisotropy and stresses arising from uneven loading of the samples. This is confirmed by the decay of the apparent hardening after a several days of natural ageing at room temperature. On the other hand an effect similar to structure rejuvenation takes place in the central part of the samples leading to higher specific heat capacity of the cycled samples, larger crystallization and relaxation enthalpies.

Metallic glasses with pronounced high-frequency \ensuremath{\beta} relaxation in their dynamic-mechanical response have been observed to exhibit large plasticity. Due to their disordered atomic structure, it is challenging to identify the microscopic mechanisms of their relaxation behavior. Quasistatic anelastic relaxation measurements have been performed over 10 orders of magnitude of time on $\mathrm{L}{\mathrm{a}}_{55}\mathrm{N}{\mathrm{i}}_{20}\mathrm{A}{\mathrm{l}}_{25}$ metallic glass, which exhibits a strong \ensuremath{\beta} relaxation. The corresponding time-constant spectra were computed from the data---they contain a series of peaks corresponding to an atomically quantized hierarchy of shear transformation zones (STZs), where both the \ensuremath{\alpha} and \ensuremath{\beta} relaxations are consistent with the STZ model. Two different regimes of activation-volume increment between the peaks are observed, suggesting the involvement of different elements in STZs corresponding to \ensuremath{\alpha} vs \ensuremath{\beta} relaxations. Room-temperature structural relaxation significantly affects the former but not the latter.

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.

Strain-hardening (the increase of flow stress with plastic strain) is the most important phenomenon in the mechanical behaviour of engineering alloys because it ensures that flow is delocalized, enhances tensile ductility and inhibits catastrophic mechanical failure. Metallic glasses (MGs) lack the crystallinity of conventional engineering alloys, and some of their properties—such as higher yield stress and elastic strain limit —are greatly improved relative to their crystalline counterparts. MGs can have high fracture toughness and have the highest known ‘damage tolerance’ (defined as the product of yield stress and fracture toughness) among all structural materials. However, the promise of MGs for structural applications is largely thwarted by the fact that they show strain-softening, instead of strain-hardening; this leads to extreme localization of plastic flow in shear bands, and is associated with early catastrophic failure in tension. Although rejuvenation of an MG (raising its energy to values that are typical of glass formation at a higher cooling rate) lowers its yield stress, which might enable strain-hardening, it is unclear whether sufficient rejuvenation can be achieved in bulk samples while retaining their glassy structure. Here we show that plastic deformation under triaxial compression at room temperature can rejuvenate bulk MG samples sufficiently to enable strain-hardening through a mechanism that has not been previously observed in the metallic state. This transformed behaviour suppresses shear-banding in bulk samples in normal uniaxial (tensile or compressive) tests, prevents catastrophic failure and leads to higher ultimate flow stress. Furthermore, the rejuvenated MGs are stable at room temperature and show exceptionally efficient strain-hardening, greatly increasing their potential use in structural applications.

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.

A novel method for measurement of atomic interdiffusivity is applied to amorphous Cu-Zr close to its glass-transition temperature Tg. Sputter-deposited multilayers are examined in cross-section by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Mapping the evolution of composition profiles gives the interdiffusivity, which is orders of magnitude higher than if coupled to the viscosity expected near Tg. Kirkendall drift of interlayer interfaces in both amorphous and supercooled liquid states (i.e. below and above Tg), and associated voiding in the liquid, show that the diffusivity of copper greatly exceeds that of zirconium. Amorphous Cu-Zr is known to show maxima in atomic packing density at sharply defined compositions. The comparison of the two compositions in the present work provides the first direct evidence that denser packing is associated with lower atomic interdiffusivity. The lower interdiffusivity is governed by a lower diffusivity of copper, and reflects a lessened degree of decoupling of the copper (fast) and zirconium (slow) diffusivities in an efficiently packed glass. The new insights help to understand issues ranging from glass-forming ability to the controlled generation of nanovoided structures.

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.

In liquids of high glass-forming ability, in which crystal growth rates are low, the rates can be measured over the full range of supercooling from the liquidus temperature down to the glass transition. For systems of low glass-forming ability, growth rates are readily measured at small supercooling and at very large supercooling around the glass-transition temperature, but it is difficult to acquire data over the full range of intermediate supercooling, especially at the maximum in growth rate. Data at intermediate supercoolings are however of considerable interest for understanding glass formation in such systems as pure metals and chalcogenides for phase-change data storage. We will review the methods emerging for making such measurements, and will note that the fragility of the liquid (including possible crossover from ‘fragile’ to ‘strong’ liquid behaviour on cooling) is an important part of understanding fast crystal growth. We also note that there are deficiencies in existing theories of fast crystal growth.

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.

A Co–Cr–Mo alloy with predominantly martensitic structure was prepared by selective laser melting (SLM), where the amount of martensite formed in the SLM specimens is much larger than in the cast samples which can be ascribed to the high density of internal defects such as dislocations and SFs. We observe a hierarchical microstructure spanning over different length scales, consisting of remelted zones and track core regions at the macro-scale, regions with elongated columnar grains and equiaxed grains at the micro-scale, martensitic laths at the submicron-scale, and a high density of dislocations and stacking faults at the nano- and atomic scale. The hierarchical microstructure leads to the outstanding tensile properties of the as-prepared SLM and SLM annealed samples (with yield strength, ultimate tensile strength and fracture strain of ~ 735 MPa, ~ 1211 MPa and ~ 12.8%, and ~ 893 MPa, ~ 1214 MPa and ~ 13.8%, respectively). The mechanisms determining the strength and ductility are discussed in terms of the hierarchical microstructure and internal defects. The cellular structure with a high density of dislocations along their boundaries and the martensitic structure are the reasons for strengthening, while the hierarchical microstructure helps to obtain appropriate ductility. Furthermore, martensitic transformation induced plastic bending of the residual FCC plates was confirmed, which is helpful to maintain the different plastic strain between the heterogeneous structure. The development of the martensitic structure in this Co–Cr–Mo alloy by SLM and its characteristic hierarchical microstructure are promising features for material design and application of high-strength materials with improved strength‒ductility tradeoff.

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.

Heating-induced crystallization of high-entropy (HE) (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)86‒89B11-14 amorphous (am) alloys is examined to develop new structural materials with low B contents. The crystallization of 11B alloy occurs in three stages: first nanoscale bcc precipitates form in the amorphous matrix, second nanoscale fcc precipitates form, and the residual amorphous phase disappears in the third stage which yields borides in addition to the bcc and fcc phases. Crystallization of 14B alloy is the same, except that the order of appearance of bcc and fcc is reversed. The bcc and fcc particle diameters are 5-15 nm and remain almost unchanged up to ~960 K. On annealing, ultrahigh hardness of 1500-1550 (unprecedented for boride-free structures) is attained just before the third crystallization stage. This hardening and the thermal stability of the novel [am + bcc + fcc] structures are remarkable at such low boron content, and encouraging for development as ultrahigh-strength alloys. The results are interpreted in terms of the nature and extent of partitioning of elemental components between the bcc/fcc phases and the amorphous matrix, and the size and defect structures of the bcc and fcc precipitates. The magnetic flux density at RT increases by precipitation of bcc and decreases by appearance of fcc. Slower quenching of the 11B alloy shows a pseudo-polymorphic crystallization that may be characteristic of multicomponent HE systems.

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.

Numerical simulation of DSC traces is used to study the validity and limitations of the Kissinger method for determining the temperature dependence of the crystal-growth rate on continuous heating of glasses from the glass transition to the melting temperature. A particular interest is to use the wide range of heating rates accessible with ultra-fast DSC to study systems such as the chalcogenide Ge 2 Sb 2 Te 5 for which fast crystallization is of practical interest in phase-change memory. Kissinger plots are found to show three regimes: (i) at low heating rates the plot is straight, (ii) at medium heating rates the plot is curved as expected from the liquid fragility, and (iii) at the highest heating rates the crystallization rate is thermodynamically limited, and the plot has curvature of the opposite sign. The relative importance of these regimes is identified for different glass-forming systems, considered in terms of the liquid fragility and the reduced glass-transition temperature. The extraction of quantitative information on fundamental crystallization kinetics from Kissinger plots is discussed.

Phase-change chalcogenides, specifically those containing tellurium, have amorphous/glassy phases that can undergo fast crystallization. The crystallization time is short

The foundry engineering still needs new cast materials of improved properties. These can be achieved by elaborating completely new alloys and metal matrix composites or by elaborating the alloys/composites basing on the already very well-known matrixes. The good example of the latter solution are high-aluminium zinc (H-Al Zn) and high-zinc aluminium cast alloys (H-Zn Al). Both of these groups show good damping and strength properties but rather low ductility and insufficient structural (and dimensional) stability, caused by long term transformation of the Cu-containing bearing phases. The performed works were devoted, among others, to building composites of improved structural stability reinforced with ternary (Al, Zn)-Ti aluminides. The in-situ reinforcement was built by needle-shape ternary aluminides based on the DO22 TiAl3 binary phase introduced with AlTi-based master alloys or by compacted semi-globular ones based on the L12 Zn3Ti particles introduced with a ZnTi-based master alloy. The mentioned particles substitute partly or totally for Cu-based bearing phase and the influence of this substitution on the structural stability and tribological properties is also discussed in the paper.

Due to their inherent metastability, metallic glasses crystallize upon thermal activation, which involves nucleation and growth. It is debatable, however, whether steady-state kinetics of crystal nucleation and growth apply when glasses are heated quickly. We partially devitrified a CuZr-based bulk metallic glass at heating rates in the range of 0.08–180 K s −1 . Immediate quenching after heating preserves the partially transformed microstructure and allows direct observation of crystallite sizes and numbers. The crystallization reaction changes from eutectic to polymorphic at high heating rates and uniformly dispersed metastable shape-memory crystals precipitate in the glass. A beneficial side effect of this microstructure is a strongly enhanced room-temperature deformability. The analysis of crystal populations suggests that the nucleation rate on fast heating is effectively lower than in the steady state. At the later stage of crystallization by flash-annealing, the glass sample is traversed by a thermal front that migrates almost ten times faster than the crystal-liquid interface in levitation experiments. This phenomenon is related to the high population of crystals already present. Flash-annealing, thus, not only permits tailoring of BMG composites to overcome the intrinsic brittleness of monolithic BMGs, but also permits study of the fundamental crystallization processes in highly undercooled melts.

Thermal stability and crystallization of three multicomponent glassy alloys, Al86Y7Ni5Co1Fe0.5Pd0.5, Al85Y8Ni5Co1Fe0.5Pd0.5 and Al84Y9Ni4Co1.5Fe0.5Pd1, were examined to assess the ability to form the mixture of amorphous (am) and fcc-aluminum (α-Al) phases. On heating, the glass transition into the supercooled liquid is shown by the 85Al and 84Al glasses. The crystallization sequences are [am] → [am + α-Al] → [α-Al + compounds] for the 86Al and 85Al alloys, and [am] → [am + α-Al + cubic AlxMy (M = Y, Ni, Co, Fe, Pd)] → [am + α-Al] → [α-Al + Al3Y + Al9(Co, Ni)2 + unknown phase] for the 84Al alloy. The glass transition appears even for the 85Al alloy where the primary phase is α-Al. The heating-induced reversion from [am + α-Al + multicomponent AlxMy] to [am + α-Al] for the 84Al alloy is abnormal, not previously observed in crystallization of glassy alloys, and seems to originate from instability of the metastable AlxMy compound, in which significant inhomogeneous strain is caused by the mixture of solute elements. This novel reversion phenomenon is encouraging for obtaining the [am + α-Al] mixture over a wide range of high temperature effective for the formation of Al-based high-strength nanostructured bulk alloys by warm working.

The temperature-dependent viscosity η(T) is measured for the equilibrium liquid of the chalcogenide Ag-In-Sb-Te (AIST), the first time this has been reported for a material of actual interest for phase-change memory. The measurements, in the range 829-1254 K, are made using an oscillating-crucible viscometer, and show a liquid with high fragility and low viscosity, similar to liquid pure metals. Combining the high-temperature viscosity measurements with values inferred from crystal growth rates in the supercooled liquid allows the form of η(T) to be estimated over the entire temperature range from above the melting point down to the glass transition. It is then clear that η(T) for liquid AIST cannot be described with a single fragility value, unlike other phase-change chalcogenides such as liquid Ge-Sb-Te. There is clear evidence for a fragile-to-strong crossover on cooling liquid AIST, similar to that analyzed in Te85Ge15. The change in fragility associated with the crossover in both these cases is rather weak, giving a broad temperature range over which η(T) is near-Arrhenius. We discuss how such behavior may be beneficial for the performance of phase-change memory. Consideration of the fragile-to-strong crossover in liquid chalcogenides may be important in tuning compositions to optimize the device performance.

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].

Crystallization from a melt and from a metallic glass both occur in an undercooled liquid. In this way identical nucleation mechanisms can operate in the two cases. However, in metallic glasses, unlike conventional solidification at low undercooling, the low atomic mobility permits the resolution and microscopical study of nucleation processes on added particles. Conventional aluminium grain-refiner based on Al-Ti-B has been used to obtain nucleant particles embedded in a glassy matrix of Al85Y8Ni5Co2 (at%). During crystallization from the glassy state, nucleation and growth of α-Al can be observed on TiB2 particles coated with a layer of Al3Ti Empirical relations found in casting practice of Al-alloys, such as excess Ti necessary for grain refinement, can be related to the observed nucleation mechanism, which is found to be very sensitive to both crystallographic and chemical factors.

Al13Fe4, Al6Fe and AlmFe are common intermetallics in commercial AA1XXX series Al alloys. Grain-refining additions (based on either Al-Ti-B or Al-Ti-C) are usually added to such alloys during solidification processing to aid the grain structure development. They also influence the favoured intermetallic and, hence, can affect the materials’ properties. This work simulates commercial casting practices in an attempt to determine the mechanisms by which one intermetallic phase is favoured over another by the introduction of grain-refining additions. Directional solidification experiments on Al-0.3wt.%Fe-0.15wt.%Si with and without grain refiner are conducted using Bridgman apparatus. The type, amount and effectiveness of the grain-refining additions are altered and the resulting intermetallic phase selection followed. The materials are characterised using optical microscopy, scanning electron microscopy and X-ray diffraction. AlmFe is seen to form when Al-Ti-B grain-refiner is introduced but only when the refinement is successful; reducing the effectiveness of the refiner led to Al6Fe forming under all conditions. Al-Ti-C refiners are seen to promote AlmFe at lower solidification velocities than when Al-Ti-B was used even though the grain structure was not as refined. These trends can be explained within existing eutectic theory, by considering growth undercooling.

Homogenisation of direct chill (DC)-cast AA3104 can beverage stock aluminium alloy causes intermetallic constituent particles to transform from a tetragonal Al6(Fe,Mn) phase to cubic α-Al-(Fe,Mn)-Si phase. Electron microscopy techniques have been used to investigate this transformation in samples of a model Al-0.5Fe-1.0Mn-0.2Si (wt.%) alloy during isothermal heat treatments at 500°C. Elemental mapping using energy-filtered transmission electron microscopy, together with convergent-beam electron diffraction, has revealed that transformation is eutectoid; diffusion of silicon from the aluminium matrix into the Al6(Fe,Mn) particles causes transformation to an α-Al-(Fe,Mn)-Si/aluminium eutectoid. Nucleation appears to be a key factor controlling the overall transformation rate. After transformation, intragranular eutectoid aluminium coalesces and ripens to become intergranular ‘Al-spots’. The particle morphologies have been observed by examining deep-etched samples in a FEGSEM. In addition, manganese diffuses into transformed particles, segregating to grain boundaries.

Foundry alloys with Al-based matrices have a wide range of uses in today's global economy and there is a high demand for castings of Al alloys, including Al-Zn alloys. In this paper, investigations on the grain refinement of high-Zn aluminium cast alloys are presented. Aluminium alloys with relatively high zinc content have a tendency to be coarse-grained, especially in the case of castings with low cooling rates such as are found in sand moulds. The coarse-grained structure degrades the plasticity, specifically the elongation. Therefore, for aluminium alloys of high (10-30 wt.%) zinc content, inoculation is attractive, aiming to break up the primary dendrites of the a-phase solid solution of zinc in aluminium. Such dendrites are the principal microstructural component in these alloys. On the other hand, a finer grain structure usually reduces the damping (e.g. as measured by attenuation of ultrasound) in these alloys. In the present investigations, a binary sand-cast Al-20 wt.% Zn alloy was inoculated with different additions of AlTi3C0.15 (TiCAl) and ZnTi-based master alloys. The sand-cast samples were subjected to mechanical-property measurements (tensile strength and elongation), image analysis to determine grain size, and measurements of the attenuation of 1 MHz ultrasound. It is found that both of the master alloys used cause significant refinement of the a-AlZn primary dendrites and change their morphology from linear-branched to semi-globular, increase the elongation by about 40%, and decrease the attenuation coefficient by about 25% in comparison with the initial alloy without inoculation.

Development of cast alloys with good mechanical properties and involving less energy consumption during their melting is one of the key demands of today's industry. Zinc foundry alloys of high and medium Al content, i.e. Zn-(15-30) wt.% Al and Zn-(8-12) wt.% Al, can satisfy these requirements. The present paper summarizes the work [1-9] on improving properties of sand-cast ZnAl10 (Zn-10 wt.% Al) and ZnAl25 (Zn-25 wt. % Al) alloys by melt inoculation. Special attention was devoted to improving ductility, whilst preserving high damping properties at the same time. The composition and structural modification of medium- and high-aluminium zinc alloys influence their strength, tribological properties and structural stability. In a series of studies, Zn - (10-12) wt. % Al and Zn - (25-26) wt.% Al - (1-2.5) wt.% Cu alloys have been doped with different levels of added Ti. The melted alloys were inoculated with ZnTi-based refiners and it was observed that the dendritic structure is significantly finer already after addition of 50 - 100 ppm Ti to the melted alloys. The alloy's structure and mechanical properties have been studied using: SEM (scanning electron microscopy), LM (light microscopy), dilatometry, pin-on-disc wear, and tensile strength measurements. Grain refinement leads to significant improvement of ductility in the binary high-aluminium Zn-(25-27) Al alloys while in the medium-aluminium alloys the effect is rather weak. In the ternary alloys Zn-26Al-Cu, replacing a part of Cu with Ti allows dimensional changes to be reduced while preserving good tribological properties. Furthermore, the high initial damping properties were nearly entirely preserved after inoculation. The results obtained allow us to characterize grain refinement of the examined high-aluminium zinc alloys as a promising process leading to the improvement of their properties. At the same time, using low melting ZnTi-based master alloys makes it possible to avoid the excessive melt overheating needed for TiCAl or TiBAl refiners and reduces the possibility of gas pick-up and material loss.