Bulk Metallic Glass Formation Research Articles

Sub-second thermoplastic forming of bulk metallic glasses by ultrasonic beating.

The work proposed a novel thermoplastic forming approach–the ultrasonic beating forming (UBF) method for bulk metallic glasses (BMGs) in present work. The rapid forming approach can finish the thermoplastic forming of BMGs in less than one second, avoiding the time-dependent crystallization and oxidation to the most extent. Besides, the UBF is also proved to be competent in the fabrication of structures with the length scale ranging from macro scale to nano scale. Our results propose a novel route for the thermoplastic forming of BMGs and have promising applications in the rapid fabrication of macro to nano scale products and devices.

Atomic structure and formation of CuZrAl bulk metallic glasses and composites

Cu47.5Zr47.5Al5 metallic glass is studied experimentally by high-energy X-ray diffraction, neutron diffraction with isotopic substitution, electron diffraction and X-ray absorption spectroscopy. The atomic structure of the glass is modeled by reverse Monte-Carlo and molecular dynamics simulations. RMC modeling of seven experimental datasets enabled reliable separation of all partial pair distribution functions for Cu47.5Zr47.5Al5 metallic glass. A peculiar structural feature of the ternary alloy is formation of the strong Al–Zr bonds, which are supposed to determine its high viscosity and enhanced bulk glass formation. Analysis of the local atomic order in Cu47.5Zr47.5Al5 glass and Cu10Zr7, CuZr2 and CuZr B2 crystalline structures elucidates their similarities and differences explaining the phase formation sequence by devitrification of the glass.

On the formation, mechanical properties and crystallization behaviors of a Zr56Co24Al20 bulk metallic glass

An amorphous Zr56Co24Al20 alloy, prepared by water-cooled copper mold suction casting technique, showed high yield strength of approximately 2177 MPa and a pronounced plastic strain. Comparative research indicated that the compression strength and specific strength improved obviously with the increasing Al/Co ratio in Zr56Co44−xAlx (x = 12, 16 and 20) bulk metallic glasses (BMGs). Moreover, the width of the super-cooled liquid region increased, indicating a better thermal stability of the super-cooled liquid. However, more Al content enhanced the crystallization process and hence reduced the activation energy. This work might have some implications for designing high specific strength BMGs with high glass forming ability.

Protocols for multi-step thermoplastic processing of metallic glasses

Temperature profiles of multi-step thermoplastic forming of bulk metallic glasses were simulated by isothermal annealing at multiple temperatures and sequences. For a single annealing temperature, the time to crystallize is additive. When the sample is first annealed at a higher temperature and quenched to a lower temperature, time till crystallization is gained, and vice versa. These findings can be explained by the temperature dependence of nucleation and growth rates, which suggests the maximum nucleation temperature is below thermoplastic forming temperatures.

Effects of Metalloid B Addition on the Glass Formation, Magnetic and Mechanical Properties of FePCB Bulk Metallic Glasses

Low-cost Fe80P12−xC8Bx (x = 0, 1, 2, 3 and 4 at.%) bulk metallic glasses (BMGs) with good soft magnetic and mechanical properties were prepared, and effects of metalloid B addition on the glass-forming ability (GFA) as well as thermal, magnetic, and mechanical properties of the BMGs were investigated. It was found that the proper B substitution for P improves the GFA of the Fe–P–C BMGs. The alloy with 2 at.% B addition manifests the highest GFA with critical diameter for glass formation of 2 mm. Besides, these BMGs exhibit good soft magnetic properties featured by high saturation magnetization of 1.35–1.57 T and low coercivity of 2.2–7.7 A/m as well as unique mechanical properties of high fracture strength of ∼3.3 GPa and visible plastic strain of 0.4%–2.5%. The combination of high GFA, good soft magnetic and mechanical properties as well as low cost makes the present Fe–P–C–B BMGs promising as soft magnetic materials for industrial applications.

From closed-packed B3(Fe, Co, Ni)8 clusters to bulk metallic glass formation

Bulk metallic glasses are known to have a close relationship with some special clusters and can be designed within the framework of the cluster-plus-glue-atom model. So the key issue in applying this model lies in the determination of the appropriate clusters. In this paper, the atomic density radial distribution is proposed to define the closed-packed cluster. As examples B–Fe, B–Co and B–Ni alloy phases are analyzed from the viewpoint of coordination polyhedral clusters. Then capped octahedral antiprism B3(Fe, Co, Ni)8 clusters are highlighted because of the most close packing. Finally the relationship between B3(Fe, Co, Ni)8 clusters and bulk metallic glass formation is discussed and indeed verified by experiments.

Crystal growth limitation as a critical factor for formation of Fe-based bulk metallic glasses

In the present work we study the formation mechanism and crystallization behavior of Fe-based bulk metallic glasses influenced by the addition of rare-earth elements. Samples are characterized by conventional X-ray diffractometry, optical microscopy, and high-resolution field-emission-gun scanning and transmission electron microscopy. In the rare-earth-containing alloys, bulk metallic glasses are formed with populations of quenched-in nuclei. Consequently, crystallization on isothermal annealing occurs without any incubation period. This behavior, not typical of bulk metallic glasses in general, implies that in the rare-earth-containing alloys glass formation is possible only because of restricted crystal growth: both on cooling from the molten and on heating from the glassy state, growth of the primary χ-Fe36Cr12Mo10 crystals is too slow to be significant on a reasonable timescale. The low growth rate is connected with large inhomogeneous strain in the growing nanoparticles, while nucleation of eutectic colonies is hampered by slow diffusion of a rare-earth alloying element.

Evolution of shear bands into cracks in metallic glasses

In the present work, the cracks formation and propagation behavior of a ductile Zr-based bulk metallic glass with single dominant shear band deformation was investigated. From the ideal compressive load–displacement curve of the sample with single shear band deformation, the instant at which the shear band turns into cracks and the total area of cracked-regions prior to failure were analyzed. Further investigations revealed that the micro-cracks might have originated from the local planar faults or defects within the shear plane along the shear direction. The existence of such planar faults (steps) was consistent with the observations of the surfaces of unfractured and fractured samples. Based on these results, a new interpretation of how shear bands evolve into the present micro-cracks was proposed. These novel results provide a new perspective to understand the deformation behavior of metallic glasses.

Formation of Bulk Metallic Glasses from Cu-Zr Based Alloys with Yttrium Addition

Abstract Cu46Zr46Al8 bulk metallic glass (BMG) was prepared by low purity sponge zirconium instead of high purity crystal bar zirconium, and via the microalloying of adding a small amount of yttrium. The results show that the glass forming ability (GFA) and the thermal stability of the Cu46Zr46Al8 alloy are improved by yttrium addition. When the addition amount of Y is 2at% and 3at%, the enhancement of GFA is most significant. The compressive fracture strength of Y microalloyed BMG is more than 2 GPa, which is much higher than that of BMG alloy produced with high purity raw materials, but its plasticity deteriorates obviously.

Effect of Nb on formation, mechanical and corrosion properties of (Zr0·55Al0·1Ni0·05Cu0·3)100-xNbx bulk metallic glasses

The (Zr0·55Al0·1Ni0·05Cu0·3)100−xNbx alloys have been prepared using an in situ suck casting method in a copper mould. The effect of Nb on the microstructure, mechanical and corrosion properties of the (Zr0·55Al0·1Ni0·05Cu0·3)100−xNbx alloys has been investigated using X-ray diffraction, scanning electron microscopy, compressive and corrosion tests. It has been found that the appropriate addition of Nb enhanced the formation of the crystalline phases. All the alloys had excellent corrosion resistance in the alkaline solution. An appropriate addition of Nb greatly improved the corrosion resistance of the alloys in the 1N HCl solution. The average corrosion rate in the 1N HCl solution was 4·57 μg cm−2 h−1 for the Zr55Al10Ni5Cu30 alloy, 0·95 μg cm−2 h−1 for the (Zr0·55Al0·1Ni0·05Cu0·3)99Nb1 alloy, and 0·071 μg cm−2 h−1 for the (Zr0·55Al0·1Ni0·05Cu0·3)95Nb5 alloy.

Influence of melt temperature on the Invar effect in (Fe71.2B24Y4.8)96Nb4 bulk metallic glass

The influence of melt temperature on the glass formation, physical properties and local structure of (Fe71.2B24Y4.8)96Nb4 bulk metallic glass (BMG) was investigated through X-ray diffractometry, differential scanning calorimetry, thermal dilatation, and Mossbauer spectra tests. Amorphous alloys were formed by fast cooling of the melt from the temperature range of 1573–1773 K. BMG cast from 1623 K has lower Curie temperature and larger spontaneous volume magnetostriction, i.e., stronger Invar effect. The abnormality, which can not be eliminated by annealing, is attributed to the higher amount of Fe–Fe pairs indicated by the hyperfine field distribution. This special local structure is inherited from the melt, which has a liquid–liquid change manifested by an exothermic step region at the temperature range of 1615–1650 K. Through a slow-cooling process, the melt in the liquid–liquid change is frozen to a crystalline structure contained Y2Fe17 phase with a high intensity signal. These findings help explain the correlation between the liquid–liquid change and the structure of cooling products.

New insight on glass-forming ability and designing Cu-based bulk metallic glasses: The solidification range perspective

In this paper, a new equation was rationally generalized from the reduced glass transition temperature. This equation indicates that solidification range can be used for describing glass-forming ability, which can be calculated with the aid of computational thermodynamic approach. Based on this scenario, several new Cu-based bulk metallic glasses in the ternary Cu–Zr–Ti alloy system were discovered. The as-cast samples were characterized by X-ray diffraction and transmission electronic microscopy. The results indicate that as-cast samples have monolithic amorphous nature. Thermal analysis validates that the smaller solidification range is closely related to the higher glass-forming ability, which is contributed to the effect of solidification time on the formation of bulk metallic glasses. This work also suggests that solidus can influence glass formation.

Looking for footprint of bulk metallic glass in electronic and phonon heat capacities of Cu55Hf45−xTix alloys

We report on the heat capacity investigation of Cu55Hf45−xTix metallic glasses. The most appropriate procedure to estimate low temperature electronic and phonon contributions has been determined. Both contributions exhibit monotonous Ti concentration dependence, demonstrating that there is no relation of either the electron density of states at the Fermi level or the Debye temperature to the increased glass forming ability in the Ti concentration range x = 15–30. The thermodynamic parameters (e.g., reduced glass temperature) remain better indicators in assessing the best composition for bulk metallic glass formation.

Formation and Mechanical Properties of Pd-Si Binary Bulk Metallic Glasses

Glassy spherical samples in the diameters up to 10 mm were produced in a binary Pd-Si alloy system. These Pd-Si bulk metallic glasses (BMGs) combine high strength of about 1600 MPa and superplasticity of over 70% together. In addition to abundant micrometer-scale shear bands, 10–20 nanometer-sized shear bands were also observed on the side surface of the deformed sample. The excellent ductility shown by the Pd-Si BMGs is suggested to arise from the nanoscale structural inhomogeneity.

Indenter Geometry Affecting Indentation Behaviors of the Zr-Based Bulk Metallic Glass

Indenter dependent indentation behaviors of the Zr-based bulk metallic glass, such as adhesion, serrated flows, shear bands, residual indent morphologies, were found and analyzed in this paper. An interesting phenomenon is presented that adhesion of the Zr-based bulk metallic glass appears during the indentation test using the cube-corner indenter but it’s not observed when using the Berkovich indenter. Corresponding to the adhesion behavior, “dirty” but new surfaces with the nano-scale dimple structure are formed by the cube-corner indenter while relatively smooth surfaces with few discrete shear bands are obtained by the Berkovich indenter. Indentation experiments indicate that the adhesion force between the cube-corner indenter and the Zr-based bulk metallic glass depends on the loading rate, the maximum penetration load and the cyclic loading number. These phenomena will enhance understanding of shear band formation, shear-induced softening, and adhesion of bulk metallic glasses. [doi:10.2320/matertrans.M2014136]

Direct measurement of the kinetics of volume and enthalpy relaxation of an Au-based bulk metallic glass

Structural relaxation of glasses below their glass transition is a well-studied phenomenon that still poses several open issues. With the advent of bulk metallic glasses with exceptionally low glass transition temperatures, new options are available that are based on the experimental assessment of the time dependence of several different thermodynamic quantities by direct measurements with high accuracy. In this contribution the first direct measurement of the isothermal relaxation of the volume and the enthalpy of an Au-based bulk metallic glassformer are reported and discussed with respect of the characteristics describing the underlying processes.

Crystallization Kinetics and Magnetic Properties of Fe<sub>40</sub>Ni<sub>40</sub>B<sub>20</sub> Bulk Metallic Glass

Fe-based bulk metallic glasses (BMGs) have been extensively studied due to their potential technological applications and their interesting physical properties such as a low modulus of elasticity, high yielding stress and good magnetic properties. In the present work, the bulk metallic glass (BMG) formation of Fe40Ni40B20 (numbers indicate at %) with a ribbon form was fabricated by the single roller melt-spinning method. Rapid solidification leads to a fully amorphous structure for all compositions. The thermal properties associated with crystallization temperature of the glassy samples were measured using differential scanning calorimetry (DSC) at a heating rate of 10℃/mn. The microstructure and constituent phase of the alloy composite have been analyzed by using X-ray diffractometry (XRD). The effect of high temperature on the isothermal crystallization of Fe40Ni40B20 ribbon was investigated by HTX-ray diffraction. In addition, these ribbon glasses also exhibit good soft magnetic properties with M-H curvature measured under the magnetic fields between –1 kOe and 1 kOe.

Comment on “Comparative analysis of glass-formation in binary, ternary, and multicomponent alloys” [J. Appl. Phys. 108, 103511 (2010)

Best ternary bulk metallic glass formers A44B38C18, A44B43C13, A65B25C10, A56B32C12, A55B28C17, A70B20C10, and A65B20C15 are quantitatively explained using the cluster-plus-glue-atom model.

A connection between the structural α-relaxation and the β-relaxation found in bulk metallic glass-formers

New metallic glasses containing La or Ce have been introduced having dynamic properties bordering on two extremes of conventional metallic glasses. This provides opportunity to test if the trends or correlations established before in molecular and polymeric glass-formers also exist in the broader family of metallic glasses. Due to the drastically different chemical and physical structures of metallic glass-formers than soft matter, there is no guarantee that any correlation found in the latter will hold in the former. If the trends and correlations are found, the result brings metallic glasses closer to the much wider classes of glass-formers in the similarity of properties. In non-metallic glass-formers, a general and fundamental connection has been established between the non-exponentiality parameter of the structural α-relaxation and the separation between its relaxation time τα and the β-relaxation time τβ. In this paper, we explore the experimental data of metallic glass-formers and show the correlation applies. An explanation of this correlation is given by the Coupling Model. The establishment of the correlation may facilitate the understanding of the roles played by the β-relaxation in macroscopic properties of metallic glasses including the relations to shear transformation zone, ductile-brittle transition in deformation, crystallization, and diffusion.

Glass-forming ability of Al-Co alloy under rapid annealing

By using molecular dynamics method, transition of Al-Co alloy from liquid to amorphous structure has been investigated theoretically. The structure parameters, pair distribution functions (PDF), bond-angle distribution functions, and Voronoi polyhedra analysis are adopted as indicators of the evolution of clusters in Al-Co alloy during the rapid cooling processes. We found that below transition temperature, the second peak of PDF curves splits into two pronounced subpeaks, while at all temperature the PDF curves gradually converge to unity at large distance. This indicates that the amorphous alloy exhibits local ordering structure and has no long-range ordering. Besides, the bond-angle distribution function predicts that the degrees in the vicinity of 63.4 and 113.4 are dominated in the system during the processes of rapid annealing, which represent that the icosahedral structures are dominant. Together with the cluster structures observed in simulation, Voronoi polyhedra analysis shows that the most popular polyhedron is full icosahedron with the Voronoi index 〈0, 0, 12, 0〉, which is always predominant in bulk metallic glass (MG) formers with excellent glass forming ability. Our studies indicated that doping of cobalt atoms in the Al-based alloy should have a better capacity of forming MG.