Zirconium-based Bulk Metallic Glass Research Articles

Bioinspired nacre-like alumina with a bulk-metallic glass-forming alloy as a compliant phase

Bioinspired ceramics with micron-scale ceramic “bricks” bonded by a metallic “mortar” are projected to result in higher strength and toughness ceramics, but their processing is challenging as metals do not typically wet ceramics. To resolve this issue, we made alumina structures using rapid pressureless infiltration of a zirconium-based bulk-metallic glass mortar that reactively wets the surface of freeze-cast alumina preforms. The mechanical properties of the resulting Al2O3 with a glass-forming compliant-phase change with infiltration temperature and ceramic content, leading to a trade-off between flexural strength (varying from 89 to 800 MPa) and fracture toughness (varying from 4 to more than 9 MPa·m½). The high toughness levels are attributed to brick pull-out and crack deflection along the ceramic/metal interfaces. Since these mechanisms are enabled by interfacial failure rather than failure within the metallic mortar, the potential for optimizing these bioinspired materials for damage tolerance has still not been fully realized.

Microstructures in the joint of zirconium-based bulk metallic glass and copper

Using the pulse laser beam welding-brazing technique, we form a joint between Zr44Ti11Ni10Cu10Be25 (at%) bulk metallic glass (BMG) and copper. Scanning electron microscopy with energy dispersive spectroscopy and x-ray diffraction are used to characterize the microstructures and chemical composition of the joint. There are fusion zone (FZ) and heat-affected zone (HAZ) formed across the joint. The XRD pattern of the FZ exhibits a broad diffraction halo, and no peaks of crystalline phases are present. There is a diffusion layer formed between the FZ and copper, suggesting the migration of copper towards the FZ across the FZ/Cu interface during the welding. The Vickers hardness of the joint is slightly larger than that of the BMG. The C-curve and thermal cycle curves associated with the welding are used to discuss the mechanism controlling the evolution of the structures in the FZ and HAZ.

Extreme rejuvenation and softening in a bulk metallic glass

Rejuvenation of metallic glasses, bringing them to higher-energy states, is of interest in improving their plasticity. The mechanisms of rejuvenation are poorly understood, and its limits remain unexplored. We use constrained loading in compression to impose substantial plastic flow on a zirconium-based bulk metallic glass. The maximum measured effects are that the hardness of the glass decreases by 36%, and its excess enthalpy (above the relaxed state) increases to 41% of the enthalpy of melting. Comparably high degrees of rejuvenation have been reported only on microscopic scales at the centre of shear bands confined to low volume fractions. This extreme rejuvenation of a bulk glass gives a state equivalent to that obtainable by quenching the liquid at ~1010 K s–1, many orders of magnitude faster than is possible for bulk specimens. The contrast with earlier results showing relaxation in similar tests under tension emphasizes the importance of hydrostatic stress.

Simulation of Solidification Parameters during Zr Based Bulk Metallic Glass Matrix Composite’s (BMGMCs) Additive Manufacturing

After a silence of three decades, bulk metallic glasses and their composites have re-emerged as a competent engineering material owing to their excellent mechanical properties not observed in any other engineering material known till date. However, they exhibit poor ductility and little or no toughness which make them brittle and they fail catastrophically under tensile loading. Exact explanation of this behaviour is difficult, and a lot of expensive experimentation is needed before conclusive results could be drawn. In present study, a theoretical approach has been presented aimed at solving this problem. A detailed mathematical model has been developed to describe solidification phenomena in zirconium based bulk metallic glass matrix composites during additive manufacturing. It precisely models and predicts solidification parameters related to microscale solute diffusion (mass transfer) and capillary action in these rapidly solidifying sluggish slurries. Programming and simulation of model is performed in MATLAB®. Results show that the use of temperature dependent thermophysical properties yields a synergic effect for multitude improvement and refinement simulation results. Simulated values proved out to be in good agreement with prior simulated and experimental results.

An experimental investigation and modeling of micro array replication with Zr-based bulk metallic glass using a hot embossing process

Zirconium-based bulk metallic glass (Zr-based BMG) is a potential material for micro/nano molds. In this study, we investigated the flow characteristics of Zr-based BMG in the supercooled liquid region (SLR) with a series of uniaxial compression tests. The Newtonian viscosity model of Zr-based BMG is constructed by fitting with the experimental results based on the Arrhenius equation. The hot embossing process which can be seen as a combination of two kinds of simultaneous flows is theoretically analyzed based on Navier-Stokes (N-S) equations. The velocity and pressure fields in a BMG sample have been evaluated. Two kinds of filling modes are proposed considering the interfacial tension and oxide layer that forms on the BMG surface. The exact solutions are obtained when the cavities of the micro arrays are circular, triangular and rectangular in shape based on N-S equations. The theoretical solutions, considered surface resistance, are in good agreement with our experimental results. These models can be used to describe the fillings of metallic glass in micro hot embossing process. Finally, we studied the effects of micro cavity size and shape on BMG filling, and found that the cavities of micro rectangular array are easier filling in same feature size, however, the cavities of micro circular array are easier filling in same area. The exact models developed in this paper can be used to calculate the BMG filling heights in the cavities of micro arrays and verify the reliability of simulation results in future mold designs.

Effect of annealing and cobalt content on relaxation and crystallization behavior of zirconium based bulk metallic glasses

The effects of annealing and cobalt content on relaxation and the crystallization process of Zr 64 Ni 10 Al 7 Cu 19 bulk metallic glasses were investigated. β-relaxation occurs during annealing, leading to increased endotherm before crystallization. α-relaxation during high temperature annealing (higher than Tg) affects the crystallization process. The introduction of cobalt leads to an inhomogeneous amorphous structure and two-step crystallization due to the positive mixing enthalpy between cobalt and copper. Non-affine thermal strain arising from low temperature annealing of heterogeneous structure leads to a reduced endotherm phenomenon during relaxation on the DSC curves and a reduction in hardness.

Analysis of surface texture of bulk metallic glass in micro electrical discharge drilling

The influences of machining parameters has a like gap voltage, capacitance and spindle speed on machining performances for surface finish Ra and Sa of high aspect ratio through micro holes drilled in zirconium-based bulk metallic glass Vitreloy 1 or Vit 1 with cylindrical tungsten tool electrodes in micro electrical discharge drilling were studied. The experimentation was carried out adopting Taguchi's L27 (313) orthogonal array. The simultaneous effects of machining parameters on machining performance were studied by applying response surface methodology. Adopting analysis of variance technique, it was observed that the machining parameters selected have great significant effects on responses. Second order regression models were developed for responses and found excellent for acceptance. Predicted optimal designed value for responses was computed using Taguchi's algorithm. Validity of the models was checked statistically and found acceptable. The proposed model could be considered as valuable tools for process planning for cost effective machining of Vit 1. Tool electrode material tungsten was deposited on the hole surface as observed from energy dispersive X-ray spectroscopy study.

Electrochemical Corrosion of As-Cast and Annealed Zr<sub>48</sub>Cu<sub>36</sub>Al<sub>8</sub>Ag<sub>8</sub> BMG in 0.1 M NaCl Solution

Electrochemical corrosion of as-cast and annealed zirconium-based bulk metallic glass (BMG) Zr48Cu36Al8Ag8 in 0.1 M NaCl solution was investigated in this work. The as-cast specimen, in complete amorphous form, contained null percent of crystal phase (denoted as 0C); however, the annealed ones contained 11, 25, 50, 75 and 100 % crystal phase (denoted as 11C, 25C, 50C, 75C and 100C, respectively) determined by the annealing duration of 0C specimen at 471 °C. Through monitoring of open circuit potential (OCP), measurements of direct-current polarization resistance (PR), Tafel plot (TP), cyclic anodic potentiodynamic polarization (CAPD), and electrochemical impedance spectroscopy (EIS), we found that the corrosion behavior of the Zr48Cu36Al8Ag8 was detremined by the the crystal phase present in the specemns dominated by the annealing durations. The corrosion resistance decreased in the order: 25C > 11C > 0C > 50C > 75C > 100C. This result revealed that the corrosion resistance inclined to be better and reached a mxmium with increasing the percentgae of the crystal phase from 0 to 25%; however, it decreased with further increasing the crystal phase over 25%. A corrosion mechanism is proposed to rationalize the sequence of corrosion resistance. According to the mechanism, the remained free volume and residual strain energy are responsible for the specimens containing crystal phase less than 25% (i.e., 0C, 11C and 25C); whereas crystal defects such as grain boundaries governed the corrosion of those containing crystal phase more than 25 % (i.e., 50C, 75C and 100C).

Research on deformation behavior of zirconium-based bulk metallic glasses containing hydrogen with different deformability

Bulk metallic glasses (BMGs) have absorbed much attention for their potential applications as high-strength materials. However, they are notorious for being extremely brittle, failing in a catastrophic manner. A large number of researches indicated that, BMGs deform through the formation of highly localized shear bands under loading at room temperature, i.e., deformation of the BMGs take places just within very narrow shear bands. However, whether or not all the BMGs, including BMGs with high global deformability and poor plasticity, have the same deformation manner at room temperature is not very clear. In present paper, two Zr-based BMGs, marked by T1 and T2, were prepared via copper-mold vacuum suction casting under the gaseous mixture of hydrogen and argon, of which, T2 presents a large plasticity at room temperature, while T1 is prone to brittleness. The uniaxial compression experiments of T1 and T2 BMGs were carried out under a quasistatic condition to investigate the deformation manners of BMGs with different deformability at room temperature. The results showed that the differences of initiation and propagation of shear bands result in the different deformation behavior of T1 and T2 BMGs at room temperature.

バルク金属ガラスのピストンシリンダーへの応用

This article reviews required properties for cylinder material for piston-cylinder high pressure apparatuses, and show that zirconium-based bulk metallic glass (Zr-BMG) has outstanding properties as a cylinder material. The piston-cylinder made of the Zr-BMG cylinder sustains pressures up to ～2 GPa, which is estimated by the pressure dependence of superconducting temperature of lead. The Zr-BMG cylinder is particularly useful for neutron scattering experiments owing to its remarkable transparency for neutron, and also potentially useful for SQUID measurements owing to its relatively low magnetic susceptibility.

Mechanical and tribological properties of Zr-based bulk metallic glass for sports applications

The microstructure, and mechanical and tribological properties of zirconium-based bulk metallic glass (Zr-BMG) were investigated for golf club heads. The Zr-BMG had a fully amorphous structure without any detectable crystalline phases. The hardness and Young's modulus of the Zr-BMG were relatively high even though they were lowered by about 36% and 28% respectively by the increased indentation depth from 200 to 1000nm due to strain softening during the nanoindentation test. The tribological behaviour of the Zr-BMG was investigated by sliding against alumina (Al2O3), 100Cr6 steel or polymethyl-methacrylate (PMMA) balls under normal loads of 1–3N. The wear of the Zr-BMG tested against the Al2O3 and 100Cr6 balls became higher with higher normal loads while a higher wear resistance of the Al2O3 ball than that of the 100Cr6 ball caused a higher wear of the Zr-BMG. A much lower wear resistance of the PMMA ball than that of the Zr-BMG resulted in a preferential wear of the PMMA ball without generating any apparent wear of the Zr-BMG during the testing. The Zr-BMG tested against the Al2O3 ball exhibited the highest wear under all the normal loads due to the highest wear resistance of the Al2O3 ball among the counter balls.

Thermodynamics and kinetics of laser induced transformation in zirconium based bulk metallic glass

Laser-material interaction for a Zirconium based bulk metallic glass was investigated. The change in glass transition, crystallization temperature and enthalpies along with microstructure of the amorphous alloy was explained by the non-isothermal history experienced during processing. Varying volume fractions of amorphous and crystalline phases were found through the cross-section. A finite element based multi-physics modeling approach was employed to predict the temperature history and associated cooling rates during laser processing. Maximum devitrification occurred in sub-surface regions that experienced suitable combination of thermodynamic and kinetic conditions during laser treatment. It was demonstrated that the location and length scale of crystallized zone can be controlled by tailoring the laser processing parameters.

Corrosion behavior of ZrTiCuNiBe bulk metallic glass subjected to friction stir processing

The corrosion behavior of a Zirconium-based bulk metallic glass subjected to friction stir processing was evaluated. Processing was done at the tool rotational speeds of 300rpm, 500rpm and 900rpm. Potentiodynamic polarization and electrochemical impedance spectroscopy studies were carried out in 0.1M NaCl solution. A strong correlation was found between the corrosion rate and enthalpy of structural relaxation, which is a measure of free volume. Electrochemical impedance spectroscopy measurements showed lower polarization resistance for processed samples as compared to as-cast metallic glass which is consistent with the DC polarization results. Shear bands in processed specimens were found to be preferred nucleation sites for the formation of corrosion pits. In contrast, pitting was more stochastic for the as-cast metallic glass.

Evolution of atomic distribution during devitrification of bulk metallic glass investigated by atom probe microscopy

Evolution of atomic distribution during devitrification of a zirconium-based bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for the as-cast alloy, with no phase separation. The metallic glass was annealed at different temperatures to study the crystallization pathways and the length scale, distribution, and morphology of the phases formed. Devitrification was found to proceed via the formation of a metastable icosahedral phase. The devitrification pathway is explained based on “strong-liquid” behavior of this alloy.

Zr-based bulk metallic glass as a cylinder material for high pressure apparatuses

Zirconium-based bulk metallic glass (Zr-based BMG) has outstanding properties as a cylinder material for piston-cylinder high pressure apparatuses and is especially useful for neutron scattering. The piston-cylinder consisting of a Zr-based BMG cylinder with outer/inner diameters of 8.8/2.5 mm sustains pressures up to 1.81 GPa and ruptured at 2.0 GPa, with pressure values determined by the superconducting temperature of lead. The neutron attenuation of Zr-based BMG is similar to that of TiZr null-scattering alloy and more transparent than that of CuBe alloy. No contamination of sharp Bragg reflections is observed in the neutron diffraction pattern for Zr-based BMG. The magnetic susceptibility of Zr-based BMG is similar to that of CuBe alloy; this leads to a potential application for measurements of magnetic properties under pressure.

Tribological behavior of Zr-based bulk metallic glass sliding against polymer, ceramic, and metal materials

The tribological properties of zirconium-based bulk metallic glass (BMG) sliding against polymers, steels, and ceramics at different loads and speeds were investigated. Acoustic emission (AE) technology was used to analyze wear states. The frictional coefficients of the BMG slid against the steel and ceramic balls were high but decreased with increased applied normal load and sliding speed. As the steel balls were more ductile than the ceramic ones, the steel–BMG sliding pairs generated weaker AE signals and exhibited larger wear rates. The BMG tested against the polymer balls had much lower and more stable frictional coefficients than the ones against the steel or ceramic balls because of transferred polymer layers on the BMG surfaces. The BMG against the polymer balls also exhibited the highest AE signals among the three types of counter materials used, indicating that abrasive wear dominated in the polymer-BMG sliding pairs. These results demonstrated the potential application of the BMG as a new tribomaterial that could be an alternative to the traditional crystalline metals for various counter materials.

Structural relaxation driven increase in elastic modulus for a bulk metallic glass

The change in elastic modulus as a function of temperature was investigated for a zirconium-based bulk metallic glass. High temperature nano-indentation was done over a wide temperature range from room temperature to the glass-transition. At higher temperature, there was a transition from inhomogeneous to homogeneous deformation, with a decrease in serrated flow and an increase in creep displacement. Hardness was found to decrease, whereas elastic modulus was found to increase with temperature. The increase in elastic modulus for metallic glass at higher temperature was explained by diffusive rearrangement of atoms resulting in free volume annihilation. This is in contrast to elastic modulus increase with temperature for silicate glasses due to compaction of its open three dimensional coordinated structure without any atomic diffusion.

Structural changes in amorphous metals from high-strain plastic deformation

Abstract Structural changes in a bulk metallic glass subjected to high-strain plastic deformation was investigated. A zirconium-based bulk metallic glass was friction stir processed at different tool rotational speeds. The alloy retained its fully amorphous structure at lower speed. At higher tool rotational speed there was partial nano-crystallization with nearly three times increase in surface hardness. Changes in the glass transition temperature, relaxation and crystallization enthalpies were analyzed to explain the physics of high-strain deformation in amorphous metals.

Surface Texture and Elemental Characterization of High Aspect Ratio Blind Micro Holes on Different Materials in Micro EDM

Micro features machined through micro electrical discharge machining (micro EDM) are adversely affected by tool wear. Tool electrode and machined parts are deformed due to stochastic behaviour of discharge processes. Deposition of tool electrode material on workpiece deteriorates the surface quality of the micro part. Study of the surface quality of blind micro hole is very difficult in non-destructive method due to its miniature size. In this communication, attempts have been made to study the surface quality of high aspect ratio blind micro holes by opening the holes in destructive method. High aspect ratio blind micro holes were drilled in wear resistant high grade steel (block gauge material), zirconium based bulk metallic glass (BMG) Vit 1, titanium super alloy Ti-6Al-4V, oxygen free high thermal conductivity (OFHC) copper, Monel 400 and hard anodized aluminium alloy 6082 T6 in micro EDM by cylindrical tungsten (W) electrode and opened the holes axially through wire EDM (WEDM) to study the surface texture of the opened holes using 3D optical profilometry technique. Elemental analysis of materials of tips of tool electrode and surfaces of the opened micro holes were studied by using energy dispersive X-ray spectroscopy (EDS) technique in scanning electron microscope (SEM). Deformations of tool electrode and tool profile on the workpiece were also studied.

Investigation and simulation of crystallization of bulk zirconium-based metallic glasses

This article is devoted to the investigation and simulation of the crystallization kinetics of zirconium-based bulk metallic glasses under heating with a constant rate, as well as under isothermal holding at an elevated temperature. The investigation into crystallization kinetics with time can provide a deeper under-standing of the crystallization mechanism of bulk metallic glasses and promote the scientifically substantiated selection of thermal treatment modes to form the desired structure and properties of composite materials on their basis.