Binary Metallic Glasses Research Articles

Medium-range icosahedral order in quasicrystal-forming Zr2Pd binary metallic glass

Medium-range order in Zr2Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of Zr2Pd metallic glass.

Binary Ni-Ta Bulk Metallic Glasses Designed by Using a Cluster-Plus-Glue-Atom Model

With the aid of the atomic-cluster-plus-glue-atom model (ACPGA model) proposed by Dong et al [1] for bulk metallic glasses (BMGs), the formation and characteristic of Ni-Ta binary BMGs were investigated in this work. Binary glass-forming compositions containing 56.3–62.5 at.%-Ni were obtained by a composition formula [M-Ni6Ta6]Ni3based on the ACPGA model. It was found that Ni-Ta BMGs with a diameter of 2 mm was obtained over a composition range of 59 ~ 62 at.%-Ni by copper mold casting method, which are in good agreement with our model prediction. Newly-developed Ni–Ta BMGs are a kind of extreme materials, which exhibit superior thermal stability (Tg= 993K) and a ultrahigh fracture strength of about 3.5 GPa.

Atomic structure of Zr48Cu45Al7 bulk metallic glass

Atomic structures of Zr48Cu45Al7 ternary and Zr50Cu50 binary metallic glasses were investigated by performing reverse Monte Carlo (RMC) simulation upon synchrotron radiation based X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) data. Bond shortening in Zr-Al and Cu-Al atomic pairs was detected in Zr48Cu45Al7, which is attributed to strong interactions between Al atoms and its neighbors. Subsequently, their atomic structure was further analyzed by Voronoi tessellation method, it was found that all kinds of Voronoi clusters have smaller volume in Zr48Cu45Al7 than their counterparts in Zr50Cu50. Accordingly it is suggested that atoms may be more densely packed in atomic structure of Zr48Cu45Al7 ternary than in corresponding Zr50Cu50 binary MG at cluster scale, which may be the structural origin of high glass-forming ability of CuZr-based bulk metallic glass prepared by Al addition.

Concentration fluctuations and boson peak in a binary metallic glass: A generalized collective modes study

It is shown that longitudinal and transverse concentration dynamic structure factors of a metallic binary glass ${\text{Mg}}_{70}{\text{Zn}}_{30}$ obtained by molecular dynamics (MD) simulations contain pronounced low-frequency peaks, that correspond to boson-peak modes. With a purpose of theoretical analysis of MD-derived time-correlation functions an extended approach of generalized collective modes (EGCM) is proposed, that permits treatment of slow collective processes in glasses. The EGCM eigenvalues are analyzed for estimation of dispersion of collective excitations in the binary glass. Low-frequency collective eigenmodes with very flat dispersion corresponding to the region of boson peak are obtained among the EGCM eigenvalues. An eigenvector analysis, performed for estimation of contributions from the collective modes to dynamic structure factors, supports strong contribution of boson-peak modes to concentration dynamic structure factors of ${\text{Mg}}_{70}{\text{Zn}}_{30}$ glass.

Networked interpenetrating connections of icosahedra: Effects on shear transformations in metallic glass

The local structures of metallic glasses have been analyzed previously in term of various types of short-range order (SRO). However, the SRO alone, neglecting the interconnection of neighboring icosahedra to medium range and beyond, is insufficient to account for the structure–property relationship in metallic glasses. In this study, we use molecular dynamics (MD) simulations of Cu–Zr binary metallic glasses to examine the effects of the next level of structural hierarchy: the interpenetrating connection of icosahedra (ICOI) and the linkage of the medium-range ICOI patches to form networks of icosahedra over extended range. The mechanical properties of these metallic glasses, especially the shear transformations that mediate plasticity, are found to be dependent on the degree of ICOI and development of the ICOI network. The evolution of the ICOI network during shear deformation, as well as the composition dependence, has been monitored and discussed.

A short-range ordering description of amorphous metal alloys using the central atoms model

A description of the atomic structural properties of a binary metallic glass is developed by employing the central atoms model (CAM). The original CAM, derived for crystalline materials, is extended to the amorphous phase by utilizing the short-range order (SRO) inherent in the glassy structure. CAM is then validated through comparison of calculated short-range atomic structure with calculation from other models, as well as with experimental data. Predicted partial coordination numbers are in general agreement with those determined by neutron and X-ray scattering experiments. When applied to Zr- and Fe-based binary metallic glasses, chemical ordering is observed, occurring most prominently at compositions experimentally shown to possess the best glass-forming ability. The model suggests the observed differences in glass stability between Cu– and Ni–Zr binary alloys are a result of the local atomic arrangements around Cu and Ni atoms.

An assessment of binary metallic glasses: correlations between structure, glass forming ability and stability

<title/>This manuscript explores the influence of atomic structure on glass forming ability and thermal stability in binary metallic glasses. A critical assessment gives literature data for 628 alloys from 175 binary glass systems. The atomic structure is quantified for each alloy using the efficient cluster packing model. Comparison of atomic structure with amorphous thickness and thermal stability gives the following major results. Binary glasses show a strong preference for discrete solute to solvent atomic radius ratios R*, which give efficient local atomic packing. Of 15 possible R* values, only five are common and only four represent the most stable glasses. The most stable binary glasses are also typically solute rich, with enough solute atoms to fill all the solute sites and roughly one-third of the solvent sites. This suggests that antisite defects, where solutes occupy solvent atom sites, are important in the glass forming ability of the most stable glasses. This stabilising effect results from an increase in the number of more stable solute-solvent bonds in solute rich glasses. Solute rich glasses also enable efficient global atomic packing. Together, these structural constraints represent only a narrow range of topologies and thus give a useful predictive tool for the exploration and discovery of new binary bulk metallic glasses (BMGs).

Microscale deformation behavior of amorphous/nanocrystalline multilayered pillars

Metallic glasses have recently been extended their research and application in micro-electro-mechanical systems (MEMS). However, the brittle nature of metallic glasses in the bulk and thin film forms inevitably imposes limitation. The current study applies the new idea to adopt a thin layer of nanocrystalline metal film beneath the brittle binary ZrCu thin film metallic glass (TFMG) layer. This metal film needs to be sufficiently strong in modulus and strength and needs to be deposited with the appropriate film orientation. The face-centered cubic Cu {111} film appears to be too soft, the body-centered cubic Mo {110} film behaves to be too brittle, but the hexagonal close-packed Zr {0001} film matches all above requirements. The shear bands initiated in the ZrCu thin film metallic glass layer can be absorbed and accommodated by the nanocrystalline Zr {0001} layer via the nano-twinning mechanism. The original brittle ZrCu TFMG, with the inclusion of a Zr layer beneath, can behave highly ductile with semi-uniform plastic deformation of 55%, even more ductile than most pure metals. The amorphous-crystalline interface exhibits good strain compatibility after appreciable plastic deformation. This finding can impose great impact on the TFMG/metal multilayer structures useful for MEMS design.

Interatomic potential to predict the binary metallic glass formation

Interatomic potentials are constructed for eight representative binary metal systems covering various structural combinations and thermodynamic characteristics. On the basis of the constructed interatomic potentials, molecular dynamics simulations reveal that the physical origin of metallic glass formation is the crystalline lattice collapsing while solute atoms are exceeding the critical value, thus determining two critical solid solubilities for the system. For a binary metal system, the composition range bounded by the two determined critical solid solubilities is therefore defined as its intrinsic glass-forming range, or quantitative glass-forming ability.

Nanoindentation analysis of time-dependent deformation in as-cast and annealed Cu–Zr bulk metallic glass

The room-temperature time-dependent deformation of a Cu–Zr binary bulk metallic glass was investigated by performing nanoindentation creep experiments. Experimental results show that creep is much more pronounced in the as-cast sample than in the annealed sample. In both cases, the amount of creep displacement was found to increase with the loading rate. From the results, the influence of structural state and indentation rate on the creep behavior is discussed. Additionally, the stress exponent for the steady-state creep is estimated from the curve of creep displacement vs. holding time.

Ni–Ta binary bulk metallic glasses

Two millimeter Ni-Ta bulk metallic glasses (BMGs) were realized over a composition range of 59-62 at.% Ni. According to the cluster-plus-glue-atom model, this composition range can be expressed by a cluster formula [MNi(6)Ta(6)]Ni(3), where M ranges from Ni to Nb. These alloys show a glass transition temperature T(g) of about 993 K, the highest among known BMG alloys. They also have a wide undercooled liquid region Delta T(x) = T(x) - T(g) exceeding 50 K. These BMGs exhibit ultrahigh strengths of about 3.5 GPa. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Study on crystallization kinetics of binary alloys through model colloidal mixtures

Since the discovery of amorphous alloys, extensive attentions have been paid to understand the mechanism of glass-forming. The structural studies on its underlying mechanism have met challenge on direct structural characterization. It has been shown that the phase behavior of colloids dispersed in a solvent is thermodynamically equivalent to that of atoms and small molecules, however, colloids can be studied with optical microscopy due to their relatively large size. In this work, we use a binary colloidal model system with the particle size ratio comparable to atomic ratio of reported binary bulk metallic glasses to study the topological effect on crystallization and glass-forming ability of binary metallic alloys (Cu–Hf and Cu–Zr systems). The crystallization kinetics and structure of the colloid system were studied by real-time optical examination and light scattering technique. The results exhibit that there are two confined regions in the mixing ratio (composition) range in the colloid system with an enhanced glass-forming ability and retarded crystallization kinetics. The agreement between results of the model system and the experimental data on the binary bulk metallic glass formation suggests that purely topological factor plays an important role in determining the glass-forming ability.

Thermal stability and fragility of Pd–Si binary bulk metallic glasses

The thermal stability of the glassy structure and the supercooled liquids of Pd 80+ x Si 20− x ( x = 0, 1, and 2) binary bulk metallic glasses were investigated by differential scanning calorimetry. It is found that Pd–Si binary metallic glasses exhibit large activation energy for glass transition and crystallization, indicating the glassy structure and the supercooled liquids possess high thermal stability. Based on the kinetic nature of the glass transition and thus the resulted heating rate dependence, the fragility index of the Pd–Si binary glassy alloys has been obtained, and compared with other bulk metallic glasses.

Volume and thermal studies for tellurite glasses

Binary tellurite glass systems of the forms TeO2(100 − x) − xAnOm where AnOm = La2O3 or V2O5 and x = 5, 7.5, 10, 12.5, 15, 17.5, and 20 mol% for La2O3 and 10, 20, 25, 30, 35, 40, 45, and 50 mol% for V2O5 were prepared. Density and molar volume of each glass were measured and calculated. The compressibility model has been used to find the difference volume Vd due to the exchange of one formula unit between Te and both of La and V in the binary glass system and the mean volume VA per formula unit in the present binary glass in order to check whether or not it is independent of the percentage of the modifier for a glass series and also different from series to another. Differential scanning calorimetric at different heating rates was used to gain some insight into the thermal stability and calorimetric behavior of the present binary transition metal and rare-earth tellurite glasses. The glass transformation temperature Tg and glass crystallization temperature Tc were recorded at different heating rates to calculate both of the glass transition activation and the glass crystallization activation energies by using different methods.

Atomic-Scale Heterogeneity of a Multicomponent Bulk Metallic Glass with Excellent Glass Forming Ability

We report the atomic structure of a multicomponent Cu45Zr45Ag10 bulk metallic glass investigated by state-of-the-art experimental and computational techniques. In comparison with a binary Cu50Zr50 metallic glass, Zr-rich interpenetrating clusters centered by paired and stringed Ag atoms and Cu-rich icosahedra are widely observed in the ternary Cu45Zr45Ag10 alloy. The atomic-scale heterogeneity caused by chemical short- and medium-range order is found to play a key role in stabilizing the liquid phase and in improving the glass forming ability of the multicomponent alloy.

Local atomic structures in Zr–Ni metallic glasses

Local atomic structures of Zr 100 − x Ni x ( x = 33.3 , 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr–Ni bond length, R Zr – Ni , keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr 64Ni 36 metallic glass consist of Zr 2Ni-like and ZrNi-like CSROs.

Geometrical aspects of the glass-forming ability of dense binary hard-sphere mixtures

Non-crystalline dense binary hard-sphere mixtures are generated where the size ratio of the spheres and the fraction of small spheres are varied from 1.0 to 2.0 in steps of 0.1 and from 0 to 100% in steps of 10%, respectively. A confined region within this parameter space is defined where non-crystalline structures are stabilized. Comparison of the present results with experimental data for binary bulk metallic glasses supports the validity of geometrical arguments regarding glass-forming ability of binary metallic melts.

Theoretical study of superconducting state parameters of binary metallic glasses by a pseudopotential method

The theoretical investigations of the superconducting state parameters (SSP) viz. electron–phonon coupling strength λ, Coulomb pseudopotential μ ∗, transition temperature T C , isotope effect exponent α and effective interaction strength N 0 V of binary metallic glasses have been reported using Ashcroft’s empty core (EMC) model potential for the first time. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are used in the present investigation to study the screening influence on the aforesaid properties. It is observed that λ and T C are quite sensitive to the selection of the local field correction functions in comparisons with μ ∗, α and N 0 V. The T C obtained from H-local field correction function is found in qualitative agreement with available experimental data and show linear nature with the concentration ( C). A linear T C equation is proposed by fitting the present outcomes for H-local field correction function, which is in conformity with other results for the experimental data. Also, the present results are found in qualitative agreement with other such earlier reported data, which confirms the superconducting phase in the metallic glasses.

Evaluation of glass-forming ability of binary metallic glasses with liquidus temperature, crystallographic data from binary phase diagrams and molecular dynamics simulations

The glass-forming ability (GFA) of binary metallic glasses was analyzed with data for the liquidus temperature ( T l) acquired as a function of composition from binary phase diagrams, assisted by crystallographic data combined with amorphous-forming composition range (AFCR) and molecular dynamics (MD) simulations. A necessary condition for the formation of bulk metallic glasses (BMGs) was determined as Δ T l ≥ 300 K where Δ T l was defined as a decrease in T l due to eutectic reaction. The crystalline compounds with structure types of bcc or its derivative type, such as CsCl (B2), CrB (B f), Al 2Cu (C16) and MoSi 2 (C11 b), tended to be found in AFCR frequently. The total pair-distribution and interference functions revealed a high forming tendency of a noncrystalline Cu 10Zr 7 structure created by MD. Simultaneous achievements of the Cu 10Zr 7 structure for crystallographic features resulting from the bcc family structure and geometrical features in phase diagram for T l affect the formation of Cu 61.8Zr 38.2 BMG.

Nano quasicrystal formation and local atomic structure in Zr–Pd and Zr–Pt binary metallic glasses

Abstract Formation of the nanoscale icosahedral quasicrystalline phase (I-phase) in the melt-spun Zr70Pd30 and Zr80Pt20 binary metallic glasses were reported. Local atomic structure in the glassy and quasicrystal (QC)-formed states were also analyzed by XRD and EXAFS measurements in order to investigate the formation mechanism of QC phase. The distorted icosahedral-like local structure can be identified around Zr atom in the Zr70Pd30 metallic glass. In the QC formation process, a change of local environment around Zr is detected, in which the approximately one Zr atom substitutes for one Pd atom. In contrast, since the local environment around Pt atom is remaining during the QC precipitation, it is suggested that the stable icosahedral local structure is mainly formed around a center Pt atom in the glassy state in Zr80Pt20. We also found that the local environment around Zr atom significantly changes during the quasicrystallization in the alloy. These results differ from those in the Zr70Pd30 metallic glass.