Bulk Metallic Glass Formation Research Articles

Three-Dimensional Shell Fabrication Using Blow Molding of Bulk Metallic Glass

A blow molding method based on thermoplastic forming of bulk metallic glasses (BMGs) is used to fabricate 3-D microshells. The 3-D microshells are attached to the Si wafer through mechanical locking, which is achieved in the same processing step. Versatile sizes and shapes of the 3-D shells can be precisely controlled. High strength ( >; 1 GPa), elasticity (~ 2%), and controlled surface roughness (<; 2 nm), which are achievable for BMGs, suggest their potential use in devices, including resonators, microlenses, microfluidic, and packaging.

Formation and mechanical properties of Ni-free Zr-based bulk metallic glasses

Glass formation and mechanical properties of Zr–Al–Co–Cu–Ag bulk metallic glasses (BMGs) were investigated. The glass-forming ability (GFA) of Zr 55Al 20Co 20Cu 5 alloy is significantly improved with minor addition of Ag, indicating by the impressive increase of the critical diameter of glass formation from 5 mm for Zr 55Al 20Co 20Cu 5 to 16 mm for (Zr 0.55Al 0.20Co 0.20Cu 0.05) 97Ag 3 and (Zr 0.55Al 0.20Co 0.20Cu 0.05) 95Ag 5 alloys. The Zr–Al–Co–Cu–Ag BMGs exhibit high compressive strength of 2160–2280 MPa and distinct plasticity of 0.6–2.5%. The Zr-based BMGs with outstanding GFA and mechanical properties as well as low-level cytotoxicity elements are expectative for industrial and biological applications.

Role of Alloying Additions in Glass Formation and Properties of Bulk Metallic Glasses.

Alloying addition, as a means of improving mechanical properties and saving on costs of materials, has been applied to a broad range of uses and products in the metallurgical fields. In the field of bulk metallic glasses (BMGs), alloying additions have also proven to play effective and important roles in promoting glass formation, enhancing thermal stability and improving plasticity of the materials. Here, we review the work on the role of alloying additions in glass formation and performance improvement of BMGs, with focus on our recent results of alloying additions in Pd-based BMGs.

Effect of elements with positive enthalpy of mixing on mechanical properties of bulk metallic glasses

Samples of (Cu 46Zr 46Al 8) 100− x Z x metallic glass forming alloys with diameters 2–6 mm were prepared by injection casting. The effect of minor amounts of elements Z = Gd, Co and Re with positive enthalpy of mixing within the Gd–Zr, Cu–Co and Cu–Re terminal systems was compared. The addition of Gd up to x = 2 slightly enhances the glass forming ability, Co reduces the critical diameter of bulk metallic glass formation, whereas even for small fractions of Re bulk samples were crystalline, but only amorphous splats can be prepared. Both Gd and Co diminish the crystallization temperature T x with respect to the Cu 46Zr 46Al 8 master alloy, but in Re-bearing splats T x is increased. Alloying with optimum amounts of Gd and Co up to x = 2 leads to plastic deformability of rods, 2 and 3 mm in diameter, in comparison with the brittle Cu 46Zr 46Al 8 bulk metallic glass.

Formation and properties of two-phase bulk metallic glasses by spark plasma sintering

Using a mixture of the gas-atomized Ni 52.5Nb 10Zr 15Ti 15Pt 7.5 and Fe 73Si 7B 17Nb 3 glassy alloy powders, we produced the two-phase bulk metallic glass (BMG) with high strength and good soft magnetic properties as well as satisfying large-size requirements by the spark plasma sintering (SPS) process. Two kinds of glassy particulates were homogeneously dispersed each other. With an increase in sintering temperature, density of the produced samples increased, and densified samples were obtained by the SPS process at above 773 K. Good bonding state among the Ni- and Fe-based glassy particulates was achieved.

Developing aluminum-based bulk metallic glasses

This paper details a systematic investigation of the formation of Al-based bulk metallic glasses, expanding on an earlier brief report [Scripta Mater. 61 (2009) p.423]. We discuss an approach for designing and predicting the best glass-forming composition in the Al–TM–RE systems, based on the atomic cluster packing model for the internal structure of the glass. The effects of additional elements in quaternary and quinary systems on the glass-forming ability and thermal stability of the glasses are also discussed. Three new compositions, Al86Ni6Y4.5Co2La1.5, Al86Ni7Y5Co1La1 and Al86Ni7Y4.5Co1La1.5, are capable of forming fully glassy rods of 1 mm in diameter; their glass transition and other thermal properties are systematically characterized.

Ni-rich Ni–Pd–P bulk metallic glasses with significantly improved glass-forming ability and mechanical properties by Si addition

We report the significant effect of a small amount of Si on glass formation and mechanical properties of Ni-based bulk metallic glasses. It was found that only 2 at.% silicon dramatically enhances the glass-forming ability of Ni-based Ni–Pd–P alloys and the critical sample diameters can be improved from smaller than 7 mm of Ni 60Pd 20P 20 to 15 mm of Ni 60Pd 20P 18Si 2. The new Ni-based bulk metallic glass also exhibits excellent mechanical properties with both high strength and good compression plasticity.

The effect of cooling rates on the apparent fragility of Zr-based bulk metallic glasses

We investigate the behavior of the kinetic fragility parameter D∗ as different cooling rates are applied to samples of the Zr57Cu15.4Ni12.6Al10Nb5 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 bulk metallic glass formers. The glassy samples are heated into the supercooled liquid region using differential scanning calorimetry (DSC) and cooled back into the glassy state with sets of different cooling rates, qC. The shifts in the glass transition are measured by determining the onset glass transition temperature, Tgonset, as well as the limiting fictive temperature, Tf′, upon reheating with a set of heating rates, qH. We then model the data by assuming a Vogel–Fulcher–Tammann-type behavior in the structural relaxation time, τ, and observe an apparent increase in the kinetic fragility parameter for slower cooling rates. These results show that fragilities calculated from DSC scans, where qH=qC are in good agreement with those from equilibrium viscosity data recently obtained by three-point beam-bending.

Formation and corrosion properties of Fe-based bulk metallic glasses

Bulk metallic glass (BMG) formation was explored in the Fe-B-Si-Nb alloy system though combined use of the atomic cluster line approach and the minor alloying strategy. The basic ternary compositions in the Fe-B-Si system were determined by the intersection points of two cluster lines, namely, Fe-B cluster to Si and Fe-Si cluster to B. 3at%–4at% Nb was added to the quaternary Fe-B-Si-Nb alloy. The casting experiments revealed that good glass-forming ability (GFA) occurred at the (Fe73.4Si8.2B18.4)96Nb4 composition, and 3-mm diameter BMG samples were made. The glass transition temperature (T g), crystallization temperature (T x), and supercooled liquid region (ΔT x=T x−T g) of this BMG were measured to be 866, 889, and 23 K, respectively. The BMG shows a high Vickers hardness of about Hv 1164, a Young’s modulus of 180 GPa, and a good corrosion resistance in the solutions of 1 mol/L HCl and 3wt% NaCl.

The influence of the cooling rate on bulk metallic glass formation in Mg80Cu15Y5 and Mg80Cu10Y10

The Mg–Cu–Y system is known to be one of the best glass formers among the various existing magnesium alloys. The compositions chosen for the current study were Mg80Cu15Y5 and Mg80Cu10Y10. Different casting processes yielded four different microstructures that were analyzed by means of X-ray diffraction, scanning electron microscopy, high resolution scanning electron microscopy, and energy-dispersive X-ray spectroscopy chemical analysis. The different casting procedures were gravity castings of 3 mm diameter specimens into a copper mold held at different temperatures (cooled to −195 °C with the aid of liquid nitrogen, held at room temperature and heated up to 300 °C) and melt-spinning. Detailed microstructure study was then performed on the melt-spun specimen using transmission electron microscopy and high resolution transmission electron microscopy. The above-mentioned investigation revealed a crystalline rather than amorphous structure. The observed microstructure could not be explained on the basis of current models referring to the frequency of nucleation events.

Processing of Bulk Metallic Glass

Bulk metallic glass (BMG) formers are multicomponent alloys that vitrify with remarkable ease during solidification. Technological interest in these materials has been generated by their unique properties, which often surpass those of conventional structural materials. The metastable nature of BMGs, however, has imposed a barrier to broad commercial adoption, particularly where the processing requirements of these alloys conflict with conventional metal processing methods. Research on the crystallization of BMG formers has uncovered novel thermoplastic forming (TPF)-based processing opportunities. Unique among metal processing methods, TPF utilizes the dramatic softening exhibited by a BMG as it approaches its glass-transition temperature and decouples the rapid cooling required to form a glass from the forming step. This article reviews crystallization processes in BMG former and summarizes and compares TPF-based processing methods. Finally, an assessment of scientific and technological advancements required for broader commercial utilization of BMGs will be made.

A four-step approach to the multicomponent bulk-metallic glass formation

A four-step approach to fabricate the multicomponent bulk-metallic glasses is presented: (1) deep eutectics, (2) mutual solubility, (3) atomic-size- and thermodynamic effects, and (4) micro-alloying. Based on this alloying strategy, a detailed route to fabricate Ni-based bulk-metallic glasses is outlined.

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.

Improving plasticity and toughness of Cu-Zr-Y-Al bulk metallic glasses via compositional tuning towards the CuZr

In this work, we propose a simple approach for designing plastic bulk metallic glasses (BMGs) by exploiting the ductility of intermetallic compounds involved in the BMG-forming system. Its validity was examined by investigating a series of quaternary Cu-Zr-Y-Al alloys along the composition tie-line between Cu42Zr44.4Y3.6Al10 (Y1) and the B2 CuZr phase, expressed as (Cu0.5Zr0.5)x(M)100-x (M = Zr0.15Y0.225Al0.625, 84≤x≤93). When tuning the composition towards the CuZr, the glass-forming ability of alloys is dramatically degraded, showing a reduction of critical diameter Dc for BMG formation from 16 mm at x = 84 (Y1) to 2 mm at x = 93. As the composition of BMGs shifts to the CuZr terminal, the shear modulus μ of the BMGs decreases, whereas the Poisson's ratio ν increases. With respect to the Y1 BMG, compressive plasticity and toughness of the Y2 BMG (x = 92, Dc = 4 mm) with a higher concentration of the CuZr are improved, which is consistent with its lower μ and higher ν values.

Bulk metallic glass formation in the Mg–Cu–Y system

The influence of the cooling rate on 80Mg–15Cu–5Y was investigated. Four different cooling rates yielded different microstructures that were characterised by means of X-ray diffraction (XRD), SEM, high-resolution SEM, energy dispersive spectroscopy chemical analysis, TEM and high-resolution TEM. The different casting procedures were gravity castings of 3 mm diameter specimens into a copper mould held at different temperatures (cooled to −195°C with the aid of liquid nitrogen, held at room temperature and heated to 300°C) and melt spinning. Only the melt spun specimen yielded what appeared to be an amorphous XRD spectrum; however, a detailed TEM analysis showed that this specimen was characterised by a micro- or even nanocrystalline rather than amorphous structure.

Evaluation of glass-forming ability for bulk metallic glasses based on characteristic temperatures

A new criterion ω 2, defined as T g/(2 T x− T g)− T g/ T l (wherein T g is the glass transition temperature, T x the onset crystallization temperature, and T l the liquidus temperature), has been proposed to assess the glass-forming ability (GFA) of bulk metallic glasses (BMGs) based on the classical crystallization theory and the crystallization resistance. The analysis indicates that the factors T g/(2 T x− T g) and T g/ T l could reflect the crystallization resistance and liquid phase stability of metallic glasses, respectively. From the available experimental data in literatures, the new criterion ω 2 has a better correlation with the GFA of metallic glasses than all other existing criteria such as T rg(= T g/ T l), Δ T x(= T x− T g), γ(= T x/( T g+ T l)), Δ T rg(=( T x − T g)/( T l − T g)), α(= T x/ T l), β(= T x/ T g + T g/ T l), δ( =T x /( T l − T g)), φ( =T rg(Δ T x /T g) 0.143), γ m(=(2 T x − T g)/ T l), β(= T x × T g/( T l − T x) 2) and ξ(=Δ T x/ T x+ T g/ T l). It has also been demonstrated that this ω 2 parameter is a simple and efficient guideline for exploring new BMG formers.

Bulk metallic glass formation near intermetallic composition through liquid quenching

Metallic glass is typically formed either by liquid quenching near deep-eutectics or by solid-state reaction near the intermetallic in center of the phase diagram. In our research, two optimum bulk glass formers are synthesized in the vicinity of the intermetallic compound of Cu–Zr system through liquid quenching. It is shown that such a pair of unique glass formation is only feasible in a narrow composition range close to but clearly separated by the intermetallic composition where both the kinetic and thermodynamic conditions for the amorphous formation are matched. The discovery of this “intermetallic glass” pair through quenching allows us to find a potentially applicable host of metallic glass systems. This is followed by a discussion on its impact on understanding the formation and physics of bulk metallic glasses.

A model of atom dense packing for metallic glasses with high-solute concentration

Taking the chemical ordering in the metallic glasses into consideration, we have extended the efficient cluster packing model to predict the composition in high-solute concentration alloys with atomic dense packing. Its validity is supported by the good agreements between the predicted compositions with the maximum packing efficiency and the experimentally optimized bulk metallic glass formers in the Cu–Zr, Cu–Hf, and Ni–Nb binary systems. Despite its simplicity, it seems that the structure predicted by our model reflects in certain way the averaged structural configuration of metallic glasses.

Enhancement of plasticity in Zr-base bulk metallic glass by soft metal plating

We investigated the effect of Cu plating with micron-size grains on the shear band formation and plasticity of a Zr-base bulk metallic glass (BMG). We found that the plasticity of the BMG can be efficiently enhanced and the detrimental effect of surface scratches on ductility can be overcome by the application of Cu plating. The proliferation of shear bands and the enhanced plasticity in Cu-plated BMG was linked to the absorption of elastic energy release in the soft Cu layer.

Bulk metallic glass formation, composite, and magnetic propertiesof Fe-B-Nd based alloys

The glass formation in Fe-rich ternary Fe-B-Nd and quaternary (Fe,B,Nd)96Nb4alloys has been studied and the best ternary and quaternary glass formers are located at Fe67B23Nd10and (Fe68B25Nd7)Nb4with critical diameters of 1 and 4 mm, respectively. For (Fe,B,Nd)96Nb4alloys, the competing phases with glass were identified by monitoring the microstructure change. Fe14Nd2B was discovered to be one competing phase, which is the principle magnetic phase for Nd-Fe-B hard magnets. Composites with uniformly distributed Fe14Nd2B were formed for quaternary alloys with a diameter of 1.5 to 3 mm. Bulk hard magnets could be obtained by directly annealing the composites in a compositional area. A hard magnet with a coercivity of 1,100 kAm−1and a maximum energy product, (BH)max, of 33 kJm–3was obtained at (Fe67B23Nd10)96Nb4by annealing. The combination of hard magnetic properties and the large critical sample size may make these alloys a commercially viable candidate for industrial applications.