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Abstract: A series of Zr–Cu glassy ribbons were fabricated, and the compositional dependence of microhardness in the as-quenched and annealed state was systematically investigated. The as-quenched microhardness exhibits a positive deviation from linearity at the compositions which correspond to local maximum in glass forming ability (GFA). Upon annealing, the microhardness change is relatively smaller for the high GFA compositions. High atomic packing density at the special compositions should be responsible for the microhardness behavior. [Copyright &y& Elsevier]

We report a family of Sr-based bulk metallic glasses (BMGs) with good glass-forming ability and many unique properties, such as ultralow glass transition temperature T g, elastic moduli and less fragility than known BMGs. The T g of Sr60Li11Mg9Zn20 BMG is at room temperature (∼299K). Remarkably, the BMGs have tunable degradation behavior in water and the corrosion rate can be controlled by simply minor alloying, so that the full degradation time can be effectively modulated from minutes to more than weeks. [Copyright &y& Elsevier]

Abstract: The microstructural evolution of the Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass during annealing and rolling deformation was studied. After annealing at 680K for 0.5h, phase separation is observed, and nanocrystallization is further induced by the subsequent rolling deformation. Increasing annealing time to 1.5h leads to the formation of both nanocrystals and large-size particles of the Zr–Cu fcc phase. After rolling, the volume fraction of nanocrystals increases slightly while the Zr–Cu particles disappear. The presence of phase separation and nanocrystals during annealing reduce the thermal stability of the glass and accelerate the subsequent crystallization driven by rolling. During rolling the two annealed specimens exhibit the good ductility. [Copyright &y& Elsevier]

Abstract: The microstructure and stored energy of Cu60Zr20Ti20 bulk metallic glass rolled at cryogenic temperature in a wide strain rate range 1.0×10−4 −5.0×10−1 s−1 have been investigated. As the specimen is rolled to be thinner, the stored energy first increases linearly, and then saturates above a critical thickness reduction at lower strain rates, or decreases at high strain rates. At the initial stage of rolling, no phase transformation except shear bands appears in the glass. Phase transformation occurs only when the specimen is severely deformed at strain rates higher than 1.0×10−4 s−1. As strain rate increases, the critical strain for the stored energy to saturate increases, but the critical strain for phase separation to occur decreases, and meanwhile the type of the phase transformation changes from phase separation to nanocrystallization. The stored energy does not change with the occurrence of phase separation, but decreases due to nanocrystallization. It is proposed that coalescence of more free volume in shear bands into nano-voids should be principally responsible for the saturation of the stored energy, which balances the results from the increase in shear band number at higher strains. [Copyright &y& Elsevier]

Bulk Cu47.5Zr47.5Al5 metallic glass was rolled at different strain rates and temperatures. No phase transformation occurs in the as-rolled specimens except for shear bands. Free volume monotonously increases with increasing strain, and the rate of increase becomes larger with increasing strain rate or decreasing temperature. However, after an initial rise, the microhardness drops when the strain exceeds a critical value dependent on the rolling conditions. The increase in hardness is proved to result from the interaction of shear bands. [Copyright &y& Elsevier]

Abstract: The microstructure and hardness evolutions of the as-cast and annealed Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass during rolling deformation were studied. It is revealed that nanocrystals and new glassy phases with sizes in the range of 5–20nm form in the as-cast/rolled sample when the reduction in thickness exceeds 90%. If the glass is isothermally pre-annealed, the deformability decreases due to the precipitation of the crystalline phases. However, the samples with the fraction of crystalline phases less than 36% still possess a good ductility during rolling. The hardness of the material decreases with the rolling proceeding, and the decrease is more significant in the pre-annealed samples. [Copyright &y& Elsevier]

Abstract: Mechanical strength evolutions during rolling the Cu60Zr20Ti20 bulk metallic glass (BMG) at room temperature (RT) and cryogenic temperature (CT) have been investigated by measuring the microhardness. The hardness slightly increases during the initial rolling stage as a result of the gradually enhanced microinhomogeneity of chemical composition, and then dramatically rises owing to phase separation at CT or phase separation plus nanocrystallization at RT. It is revealed that the Cu-rich separated amorphous phases from the matrix possess higher strengths than the original and Cu-poor separated amorphous phases. As the deformation-induced nanocrystallites contain lots of crystal defects, their resistance to yielding is deteriorated. Consequently, as partial phase-separated regions crystallize during RT-rolling, the increase rate of microhardness slows down as compared with that in CT-rolling. It is proposed that phase separation may be a more effective way to strengthen the BMG than the incorporation of the nanocrystallites with crystal defects. [Copyright &y& Elsevier]

Abstract: Bulk Cu60Zr20Ti20 metallic glass has been rolled at room temperature (RT) and cryogenic temperature (CT) up to 97% in thickness reduction, and the dependences of microstructure on the strain and temperature have been investigated. It is revealed that as the deformation proceeds below a critical thickness reduction, which is 87% at RT and 89% at CT, only the shear band density and the free-volume content increase, whereas the thermal stability of the deformed glass remains unchanged. Deformation above the critical thickness reduction results in phase separation plus nanocrystallization at RT, but only phase separation at CT, indicating that lowering the temperature can effectively retard the deformation-driven crystallization, and that phase separation is the precursor of crystallization. The appearances of phase separation and especially nanocrystallization reduce the thermal stability of the glass since they create advantages in chemical composition and topological structure for the primary crystalline phase to nucleate and grow. [Copyright &y& Elsevier]

This letter reports the effect of repeated melting of the ingots on the glass-forming ability (GFA) of Zr60Al15Ni25 and Zr65Al7.5Ni10Cu17.5 alloys. The results indicate that the glass transition temperature Tg and the onset temperature of crystallization Tx of Zr60Al15Ni25 alloy increase as melting times increase. However, the repeated melting of the ingot brings only a little change to Zr65Al7.5Ni10Cu17.5 glassy alloy. Within the framework of structure heredity and thermodynamics, the reason for the improvement of the GFA of alloys is discussed. [Copyright &y& Elsevier]

Previous work suggests that the size factor may be the most crucial one on the glass forming ability (GFA). But the alloys in a system have significant deference for GFA. A criterion λn is defined in the present work to comprehensively evaluate concentration dependence of GFA of alloys in a system. It is found that the values of λn of bulk glass formers with greatest GFA in Zr-, Pd-, Mg-, Nd- and Fe-based systems are nearly constant of 0.18. Based on the mathematical description of regular polytopes and the dense random packing of hard sphere (DRPHS) model, a cluster model is suggested. This model provides the physical meaningful origin of the λn from the view of free volume. The glass structure of bulk glass formers with λn≈0.18 has optimum defect concentration within the framework of the cluster model. In the term of λn criterion, an alloy with λn of about 0.18 will be one of bulk glass former candidates, which is verified by the experimental result of Zr&z.sbnd;Al&z.sbnd;Ni system. [Copyright &y& Elsevier]

In order to unravel the effect of free volume on the bending plasticity of Zr 55 Al 10 Ni 5 Cu 30 bulk metallic glass (BMG) with monolithic amorphous structure, a series of samples with different free volume content and structural disorder degree were prepared by varying the remelting times of the master alloy ingots and annealing the as-cast samples at 673 K. It is shown that both free volume and structural disorder degree influence the plasticity of the monolithic BMGs. Annihilating the excessive free volume from the BMG has a larger influence on the plasticity of the BMG that is more disordered in structure. [ABSTRACT FROM AUTHOR]

Alloys around eutectic points are thought to be good glass formers. However, the glass-forming ability (GFA) as a function of composition from pure metals to the eutectic alloy has not been quantified and the underlying microstructural and dynamical origins are unclear. In this work, the GFA of Cu–Ag alloys at various compositions was thoroughly investigated by using molecular dynamics simulations. According to the results, the critical cooling rate for glass formation R c (K/s) varies with solute content x ′ (at%), following R c ≈ A exp(kx ′) where A = 4.61 × 1012 and k = -0.25 on the Cu side and A = 4.43 × 1012 and k = -0.19 on the Ag side. The R c of the eutectic alloy is about 5 orders of magnitude lower than that of the pure metals. Structurally, the number of densely packed icosahedral-like clusters in Cu–Ag metallic glasses increases with increasing solute content, resulting in the most densely packed structure at the eutectic composition. The dynamical properties of Cu–Ag melts are basically independent on composition at high temperatures, but obviously change with composition at low temperature. Besides the largest reduced glass transition temperature, the highest five-fold symmetry (FFS) local structure and more importantly the retarded dynamics of liquid atoms below the liquidus temperature around the eutectic composition impart the eutectic alloy with the best glass-forming ability. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The composition dependences of crystallization, microstructure and mechanical properties have been investigated. When the Ag content is in the range of 0–8at%, the BMGs with two or three-step of crystallization process exhibit remarkable plasticity, of which primary phase is an icosahedral phase. However, when the Ag concentration reaches 12–16at%, the BMGs with single-step of crystallization mode display relatively limited plasticity, whose precipitation phase is Zr2Cu and/or Zr2Ni intermetallic compounds. Structural analyses reveal that the presence of icosahedral medium-range order clusters, which, in turn leads to the heterogeneity of free volume distribution, is responsible for the improvement of plasticity. The present results suggest that, under appropriate microstructural design by the introduction of icosahedral medium-range order clusters, BMG has extensive application prospect as structural material. [Copyright &y& Elsevier]

Abstract: Isochronal crystallization kinetics of Cu60Zr20Ti20 bulk metallic glass has been investigated by differential scanning calorimetry. By means of the Kissinger, Ozawa, Kempen, Matusita and Gao methods, average effective activation energies for the first and second crystallization reactions in Cu60Zr20Ti20 are calculated to be about 375±9 and 312±11kJmol−1, respectively, which are smaller than the values deduced from isothermal experiments. Meanwhile, average Avrami exponents, 3.0±0.1 and 3.4±0.2, for two crystallization reactions in isochronal anneals, differ from the value about 2.0 in isothermal anneals. The nonidentity of the Avrami exponents and effective activation energies may be contributed to different crystallization mechanisms and the nature of non-isokinetic between isochronal and isothermal experiments. The values of frequency factor k 0 for the first and second crystallization reactions of Cu60Zr20Ti20 are (1.7±0.3)×1024 and (7.0±0.8)×1018 s−1, respectively, and the large value of k 0 has been discussed in terms of the atomic configuration and interaction. [Copyright &y& Elsevier]

A superamphiphobic (both superhydrophobic and superoleophobic) CaLi-based bulk metallic glass (BMG) surface was constructed by etching the surface with water and modifying the etched surface with fluoroalkylsilane coating. The modified surface exhibits high corrosion resistance and stable superamphiphobicity with a high static contact angle of more than 150°; these properties could extend the practical applications of BMGs. The superamphiphobicity mechanism of the BMG is discussed. The facile method can be used to form other BMG surfaces with special wettability. [Copyright &y& Elsevier]

Abstract A series of Al 100-a-b Ni a (La 1-x Gd x) b metallic glass ribbons, where a = 9–10, b = 4.5–5.5 and x = 0–1, were prepared by melt-spinning under identical conditions for investigating the dependence of crystallization behavior on the mutual substitution between La and Gd. In general, as the rare earth gradually changes from full La to full Gd, the thermal stability decreases and the formation of α-Al as primary phase is favored. A parameter taking the number and strength of various solvent-solute bonds into account was proposed to evaluate the thermal stability of present and other Al-TM-RE (TM-transition metal and RE-rare earth) metallic glasses, and good agreement was achieved between the theory and experimental results. Substitution of La by Gd releases additional "free Al atoms" and enhances the segregation of solvent Al atoms, therefore promoting the formation of α-Al at the first crystallization stage. Highlights • The optimal glass former and its neighbors in Al-Ni-La systems were base alloys. • La was substituted by Gd in each base metallic glass to study crystallization behavior. • A parameter was proposed for predicting thermal stability of Al-Ni-(La-Gd) metallic glasses. • The inhomogeneity with free-Al volume dominates the type of primary phase. [ABSTRACT FROM AUTHOR]

Atomic structures of Cu 100− x Zr x ( x  = 41.18–66.67) metallic glasses were investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy and molecular dynamics (MD) simulations. It is demonstrated that both the fraction and average volume of the typical atomic clusters, characterized by Voronoi cells, are of compositional dependence. With the increasing of Zr content, the fraction of Cu and Zr centered Voronoi clusters with coordination number lower than 11 and 14 respectively increases, while that of clusters with larger coordination numbers reduces. Among the major Voronoi clusters, the Cu-centered icosahedra are distinctive. Their average volume is far smaller than that of the other Cu-centered Voronoi cells with the same coordination number. More importantly, they prefer to interlink into pentagon-rich icosahedral super-clusters. However, compared with their neighbors, the glasses with x = 44 and x = 50 exhibit no other particularity in Cu-centered icosahedra than a slightly enhanced interlink at x = 50 although glass forming ability (GFA) reaches a local maximum at these two compositions, indicating that there are other factors dominating the GFA change with composition. A significant reduction in free volume for the loosely packed regions takes place at x = 44 and x = 50, due to which the corresponding Cu-Zr metallic glasses have the maximum microhardness. [ABSTRACT FROM AUTHOR]

Metallic glasses (MGs) with various geometrical notches have been one of the most attractive research topics because of their interesting mechanical behavior. In this work, molecular dynamics simulations were employed to examine the effect of internal notch depth on the mechanical behavior of Cu 50 Zr 50 MGs. It is shown that both the strength and the deformation mode are sensitive to the notch depth, and in particular to the inter-void ligament distance. With increasing the notch depth, the notch intensification gets enhanced, while the deformation mode is seen to change from shear banding dominated to mixed mode and then to necking governed. Detailed stress distribution analysis reveals that the notch intensification and the deformation mode transition result from the stress state change induced by the presence of notches. The critical effective shear stress corresponding to local/atomic yielding in the MGs is identified to be around 1.9 GPa. In addition, the intrinsic size confinement effect also influences the deformation process. The findings are expected to provide useful guidance for materials design and investigation of yielding in MGs based on atomistic simulations. [ABSTRACT FROM AUTHOR]

The mechanical behavior of metallic glasses shows similar size dependences as fine grained crystals, yet the strengthening mechanism is quite different. Tensile deformations of Cu 50 Zr 50 metallic glass thin films by molecular dynamics simulation reveal that surface effects play an important role in affecting the deformation mode and ductility of the films. The presence of surfaces promotes the activation of shear transformation zones upon deformation, facilitating homogeneous plastic flow. While surface relaxation helps to annihilate the excess free volume generated in the film, and in turn retards the nucleation and/or propagation of shear bands, and consequently enhances the ductility of the films. The surface area to volume ratio is larger for thinner films and therefore the annihilation effect overwhelms the generation effect due to deformation, enabling the “smaller is stronger” phenomenon. Meanwhile, a transition of deformation mode from shear fracture dominated to mixed mode and then to homogeneous deformation is observed with the decreasing of film thickness. The findings suggest that the ductility and strength of metallic glass samples could be improved effectively by reducing the sample size or increasing its surface area to volume ratio. [ABSTRACT FROM AUTHOR]

• Dynamic property of Cu 54.2 Ag 45.8 eutectic melt under different pressure was investigated. • External pressure is favorable for formation of crystal-like clusters but not icosahedra. • Pressure induced an inverse structure-energy relationship in the relaxed metallic glass. • Lower temperature decreases potential energy, but higher pressure does not. The effects of pressure on the dynamic property and glass transition of Cu 54.2 Ag 45.8 eutectic melt were systematically studied by extensive molecular dynamics simulations. It is shown that an increasing external pressure can slow down the dynamics of the melt and enhances the dynamic heterogeneity. As the pressure increases, the dynamic crossover temperature and glass transition temperature monotonously increase. Application of an external pressure to the melt is conducive to formation of <0, 3, 6, 4> and <0, 3, 6, 3> polyhedrons in the metallic glass, but unfavorable for formation of <0, 0, 12, 0> clusters. The increase of pressure results in an inverse structure-energy relationship in the relaxed glass, i.e., the potential energy increases with increasing atomic packing density, because the relaxation of local structure into the low-energy configuration is restricted. Finally, the effects of temperature and pressure on the microstructure evolution during glass formation were compared. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were performed to investigate the atomic structure and thermal stability of interfaces formed between amorphous Cu 50 Zr 50 matrix and embedding B2 CuZr nano-crystallites. The interfaces are found to be rather abrupt, and their widths show negligible dependence on the nano-crystallite size. Local atomic configuration in the interfacial region is dominated by geometry characterized by Voronoi polyhedra <0,5,2,6> and <0,4,4,6>, and the contents of these polyhedra also exhibit apparent size dependence, which in turn results in an increasing trend in the interfacial energy against the nano-crystallite size. Annealing of the interface models at elevated temperatures will also enrich these characterizing polyhedra. While when the temperature is as high as the glass transition temperature of the matrix, growth of the nano-crystallites will be appreciable. The growth activation energy also shows size dependence, which is lower for larger nano-crystallites, suggesting that large nano-crystallites are prone to grow upon thermal disturbance. [ABSTRACT FROM AUTHOR]

A series of Al 100 – a – b Ni a (La 1 – x Gd x ) b alloys, where a = 9–10, b = 4.5–5.5 and x = 0–1, were suction cast under identical conditions into a wedge-shaped copper mold for investigating the compositional dependence of glass-forming ability (GFA). The GFA of the ternary alloys, except for the optimal glass former (Al 85.5 Ni 9.5 La(Gd) 5 ), is enhanced when a given rare earth element (La or Gd) is partially substituted by the other. The mutual substitution content between La and Gd for the optimal GFA increases with a decrease in Ni content. The enhancement of GFA by the mutual substitution between La and Gd was interpreted based on Miracle’s model of atom packing efficiency. [ABSTRACT FROM AUTHOR]

Highlights: [•] Wedge-shaped samples were suction cast with casting conditions controlled. [•] Partial substitution of La by Ce decreases the GFA of Al85.5Ni9.5La5. [•] Partial substitution of La by Ce increases the GFA of other Al–Ni–La alloys. [•] The GFA was analyzed from the thermodynamic and topological points of view. [Copyright &y& Elsevier]

Abstract: Atomic size may change due to the interaction between different elements when pure metals are synthesized into alloys. In present paper, the effective atomic radii instead of the nominal radii were introduced in the cluster line method to predict the optimum glass forming compositions in Al-based Al–Ni–RE (RE = La, Y, Ce, Gd, Dy) systems. Wedge-shaped samples of the alloys were suction cast under well-controlled condition to experimentally determine the dependence of the glass forming ability (GFA) on the composition. It is found that such a modification to the method makes the prediction very close to the experimental results. When the effective atomic radii are used to calculate the topological instability parameter originally proposed by Egami and Waseda, λ′, the λ′ corresponding to the best GFA in each Al–Ni–RE system linearly changes with the radius of the RE element. Meantime, the onset temperature of crystallization and mixing enthalpy linearly increase with the λ′. [Copyright &y& Elsevier]

Abstract: The composition dependence of glass-forming ability (GFA) of Ni–P binary alloys was systematically examined by fabricating ribbons of different thicknesses, and the microhardness of the glassy ribbon was measured. The eutectic alloy Ni80.4P19.6 has the best GFA and the highest microhardness in glassy state. As the alloy composition is deviated from the eutectic composition, both GFA and microhardness decrease, accompanied with an increasing full width at half maximum of the main broad peak in the X-ray diffraction spectrum of the glassy ribbon. All these results indicate a close correlation among microstructure, GFA and microhardness for the metallic glass. [Copyright &y& Elsevier]

Abstract: The effect of cooling rate on the bending plasticity of Zr55Al10Ni5Cu30 bulk metallic glass was investigated by varying the thickness of the as-cast sample. It turned out that as the thickness of the as-cast sample increases from 1 to 3mm, short-range ordering in the microstructures is enhanced until noticeable nanocrystallization occurs in the thickest sample, but the bending plasticity measured under the same test specification first decreases and then increases. It is suggested that both free volume and structural heterogeneity dominate the plasticity of metallic glasses. [Copyright &y& Elsevier]

Abstract: Most reported bulk metallic glasses (BMGs) contain multiple constituent elements but only one of them is the principal element. Here we report that a senary Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy bulk metallic glass (HE-BMG) with a critical diameter larger than 15mm has been successfully prepared by copper mold casting. It shows that newly developed HE-BMG possesses large glass-forming ability, together with the supercooled liquid region ΔT (=T x−T g), reduced glass transition temperature T rg (=T g/T l) and γ parameter (=T x/(T g+T l)) of 70K, 0.619 and 0.422, respectively. The present result indicates that high entropy alloys, even for senary alloys or metal–metal type, could also possess large glass-forming ability. And the present HE-BMG could serve as a model material for studying the fundamental issues both of high entropy alloys and bulk metallic glasses. [Copyright &y& Elsevier]

The atomic packing structure of Al 90.5 Y 9.5 , Al 89.5 Fe 4.5 Y 6 , Al 85.5 Ni 9.5 Y 5 , Al 89 Co 5.5 Y 5.5 and Al 85.5 Co 9.5 Y 5 metallic glasses (MGs) was studied using the extended X-ray absorption fine structure (EXAFS) technique, and the atomic packing efficiency (APE) of solute-centered clusters was calculated. The results indicated that both Co- and Y-centered clusters possess higher APE in Al 89 Co 5.5 Y 5.5 MG than in Al 85.5 Co 9.5 Y 5 MG, due to which the former has the best glass-forming ability (GFA) in Al–Co–Y system. The chemical property of transition metals (TMs) influences the medium range ordering, i.e. the connection of solute-centered clusters. As TM element changes from Fe, Co to Ni, the TM-centered clusters tend to share more and more Al atoms, resulting in the sequential increase of the concentration ratio of TM/Y in Al 89.5 Fe 4.5 Y 6 , Al 89 Co 5.5 Y 5.5 and Al 85.5 Ni 9.5 Y 5 MGs that have the best GFA in their respective alloy system. • EXAFS of several Al–Y, Al-TM-Y (TM = Fe, Ni, Co) metallic glasses are measured. • Coordination numbers of Al around TM and Y atoms and interatomic distance were determined. • Atomic packing efficiency of solute-centered clusters was evaluated. • The way for TM-centered clusters to connect depends on the type of TM. • Difference in glass-forming ability was analyzed. [ABSTRACT FROM AUTHOR]