Al Bulk Metallic Glasses Research Articles

Structural origins for the high plasticity of a Zr–Cu–Ni–Al bulk metallic glass

The structural origins for the high plasticity of a Zr53Cu18.7Ni12Al16.3 (at.%) bulk metallic glass are explored. Under plastic flow conditions, in situ synchrotron high-energy X-ray diffraction reveals that the atomic strain saturates to the closest packing in the longitudinal direction of the applied load while atoms yield in the transverse plane. Scanning electron microscopy investigation reveals that global plasticity benefits from abundant shear band multiplication and interactions. Atomic level flows are seen to accompany profuse shear bands. The plasticity enhancement of this metallic glass benefits from such atomic level flows. Atomic level flow facilitates the activation of shear transformation zones that further self-assemble to promote shear band multiplication. On the other hand, it also mitigates the shear band propagation that prevents catastrophic shear band extension.

A Zr–Co–Al Bulk Metallic Glass Derived from the Atomic-Cluster-Plus-Glue-Atom Model and Its Mechanical Properties

In the present work we have studied the formation of bulk metallic glass in the Zr–Co–Al system. Using the atomic-cluster-plus-glue-atom model, a cluster formula composition, [Co2Al2Zr7](Co2Zr) = Zr57.1Co28.6Al14.3), was derived to explore bulk metallic glass formation. Glass rod of 10 mm diameter can be made at this composition by copper mold casting. The glass alloy exhibited an undercooled liquid span of 43 K at a constant differential calorimetric heating rate of 40 K/min. Under uniaxial compression at room temperature, the alloy exhibited a yield strength of 2,100 MPa and a plastic strain of 10 %.

On the low-temperature absorption of longitudinal ultrasound in Zr52.5Ti5Cu17.9Ni14.6Al10 bulk metallic glass

Ultrasonic absorption and attenuation in Zr52.5Ti5Cu17.9Ni14.6Al10 bulk metallic glass have been investigated at frequencies of 20, 50 and 150 MHz and temperatures from 80 to 300 K. Using the obtained data the activation energy spectrum of defects responsible for the ultrasonic attenuation is estimated. The results are discussed in the framework of the Debye relaxation model.

Pronounced ductility in CuZrAl ternary bulk metallic glass composites with optimized microstructure through melt adjustment

Microstructures and mechanical properties of as-cast Cu47.5Zr47.5Al5 bulk metallic glass composites are optimized by appropriate remelting treatment of master alloys. With increasing remelting time, the alloys exhibit homogenized size and distribution of in situ formed B2 CuZr crystals. Pronounced tensile ductility of ∼13.6% and work-hardening ability are obtained for the composite with optimized microstructure. The effect of remelting treatment is attributed to the suppressed heterogeneous nucleation and growth of the crystalline phase from undercooled liquid, which may originate from the dissolution of oxides and nitrides as well as from the micro-scale homogenization of the melt.

Formation of Zr–Co–Al bulk metallic glasses with high strength and large plasticity

A series of Zr56Co44−xAlx (x = 12, 14, 16 and 18, respectively) bulk metallic glasses (BMGs) are obtained using water-cooled copper mold casting technique. With increasing Al/Co ratio, the BMGs exhibit a better thermal stability of the supercooled liquid, higher strength and larger plasticity. The origin of the high specific fracture strength lies in the increased strength and reduced mass density (more Al). Among them, Zr56Co26Al18 BMG has a high fracture strength (∼2477 MPa), small density (∼6.31 g/cm3) and very high specific fracture strength (∼3.92 × 105 Nm kg−1) exceeding the values of commercial stainless steel, light alloys as well as some popular BMGs. It seems to be a promising structural material owning to its excellent GFA, large plasticity and high specific strength.

Machinability of BMG

This chapter covers the series of machinability evaluation test result and discussions of Zr52.5Ti5Cu17.9Ni14.6Al10bulk metallic glass (BMG). These tests are lathe turning, drilling, milling and preliminary level grinding tests. In the continuous machining methods such as turning, drilling and grinding of BMG, above a threshold cutting speed, the low thermal conductivity of BMG leads to chip temperatures high enough to cause the chip oxidation and associated light emission. The high temperature produced by this exothermic chemical reaction causes crystallization within the chips. Chips morphology suggests that increasing amounts of viscous flow control the chip-removal process. Moreover, viscous flow and crystallization can occur during the machining of the bulk metallic glass, even under the high temperature gradient and strain rate. High cutting speed significantly reduced the forces for BMG machining due to thermal softening. However, in intermittent cutting process which is milling, there is no high temperature problem, special burr formations the rollover and the top burr were observed along the slot and achieved good surface roughness, Ra= 0.113 μm, using conventional WC-Co cutting tool. In each method, tests repeated for the conventional materials for comparison purpose. This study concludes the precision machining of BMG is possible with the selection of feasible tools and process parameters for each method.

Crack-resistance curve of a Zr–Ti–Cu–Al bulk metallic glass with extraordinary fracture toughness

For the emerging bulk metallic glasses (BMGs), damage tolerance is a key mechanical property needed for their practical applications. To reach a fracture toughness on a par with, or even better than, conventional engineering alloys, the only route reported so far is to compositionally base the BMG on high-cost palladium (Pd), which has a very high Poisson’s ratio (∼0.42). Here we report the discovery of a Zr61Ti2Cu25Al12 (ZT1) BMG that has a toughness as high as the Pd-based BMG, but at the same time consists of common engineering metals and has robust glass-forming ability. The new BMG, while having an unimpressive Poisson’s ratio of 0.367, derives its high toughness from its high propensity for crack deflection and local loading-mode change at the crack tip due to extensive shear band interactions. The crack-resistance curve (R-curve) of this BMG has been obtained from fatigue pre-crack samples, employing standard “single-specimen” and “multiple-specimen” techniques.

Lightweight Ti–Zr–Be–Al bulk metallic glasses with improved glass-forming ability and compressive plasticity

A series of lightweight Ti–Zr–Be–Al bulk metallic glasses (BMGs) have been developed through the addition of Al to Ti–Zr–Be ternary glassy alloy. By replacing Be with Al, the critical size of the glassy rod has been increased from 5mm for Ti41Zr25Be34 alloy to 7mm for Ti41Zr25Be29Al5 alloy, while the yield strength of Ti41Zr25Be34−xAlx (x=2–10) has been greatly enhanced, resulting in a significant increase of the specific strength which is defined as yield strength/density. Among these newly developed Ti–Zr–Be–Al BMGs, Ti41Zr25Be26Al8 glassy alloy exhibits a high specific strength of 4.33×105Nm/kg and a very large compressive plastic strain of 47.0%, which are much larger than those (3.69×105Nm/kg and 2.9%, respectively) for Ti41Zr25Be34 glassy alloy. The present results show that Al is an effective alloying element for improving the glass-forming ability (GFA) and mechanical properties of Ti-Zr-Be glassy alloy.

Undercooling behavior of Zr–Cu–Ni–Al bulk metallic glasses investigated by in situ synchrotron high energy X-ray diffraction

Three quaternary Zr–Cu–Ni–Al bulk metallic glasses are undercooled via the containerless aerodynamic levitation technique and investigated by using in situ high energy X-ray diffraction. By tracing the temperature T dependent evolutions of the maximum diffraction peak position Qmax(T) and the integrated maximum diffraction peak intensity Imax(T), glass transition and/or crystallization is identified occurring at the temperature that corresponds to the slope change of the linear functions Qmax(T) and Imax(T). Glass transition temperature Tg, onset crystallization temperature Tx,c, critical cooling rate Rc, and the volumetric thermal expansion coefficient of the three alloy in liquid state αV,l are evaluated during melt cooling.

The pitting corrosion behavior of shear bands in a Zr-based bulk metallic glass

Multiple nearly parallel shear bands were induced by cold-rolling Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass. Immersion measurements, chronopotentiometry and anodic polarization tests for as-rolled samples before and after annealing or electropolishing are conducted to analyze the pitting behavior on shear bands. It is demonstrated that the shear bands indeed act as preferential sites for pitting initiation under certain conditions, a finding attributed mainly to the structural changes in shear bands rather than surface shear offset or residual stress.

The relationship between shear bands and deformability in bulk metallic glasses

It has been well documented that the plastic deformation of bulk metallic glasses (BMGs) is localized in narrow shear bands, resulting in rapid propagation of these shear bands and catastrophic failures of BMGs subjected to loads. Shear bands in BMGs play a dominant role in their deformation behavior and macroscopic properties. In order to comprehensively understand the deformation mechanism of BMGs, it is necessary to investigate the formation of shear bands and consequent deformation. In present paper, Zr62.55Cu17.55Ni9.9Al10 and Zr64.80Cu14.85Ni10.35Al10 BMGs were prepared and the effect of indentation on the formation of shear bands was studied at room temperature. The results showed that Zr62.55Cu17.55Ni9.9Al10 BMG deforms through formation of radiation-like and circular shear bands, while for Zr64.80Cu14.85Ni10.35Al10 BMG, basically only radiation-like shear bands can be found after indentation deformation. The density of shear bands in the former is larger than that in the latter with a same loading condition. The different indentation deformation behavior in the two BMGs might be attributed to the differences in thermodynamic stabilities and intrinsic natures. The formation mechanism of the shear bands as well as the deformation mechanism of the BMGs were analyzed and discussed.

Effects of Cr addition on glass-forming ability and mechanical properties of Cu–Zr–Al bulk metallic glass

Effects of a small amount addition of Cr on glass-forming ability (GFA) and mechanical properties of Cu–Zr–Al bulk metallic glass were investigated. The GFA of (Cu46Zr46Al8)100−x Cr x (x = 0, 0.25, 0.5, 0.75, and 1 at%) alloys tends to decrease with the increasing Cr content. A good correlation between the GFA and the temperature interval of supercooled liquid region ΔT x or parameter γ exists in these alloys. Addition of an appropriate amount of Cr can significantly improve the plasticity of the alloys. The bulk metallic glass with x = 0.5 exhibits promising mechanical properties with high fracture strength of 1870 MPa and obvious plastic strain of 2.23%.

Enhanced glass forming ability in Zr-based bulk metallic glasses with Hf Addition

We report on the partial substitution of Hf for Zr in Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass (BMG) and the resulting enhanced glass forming ability and processability. Critical casting thickness increased from less than 14 mm for Zr57Nb5Cu15.4Ni12.6Al10 to more than 16 mm for Zr45Hf12Nb5Cu15.4Ni12.6Al10. This improvement contrasts with earlier reports of reduced glass forming ability with partial substitution of Hf for Zr. Furthermore, the new BMG alloy exhibited one of the best bend ductility reported to date for BMG samples that are more than 4 mm thick. The improved glass forming ability with Hf substitution is presented and the underlying factors for improved glass forming ability are discussed.

Characterization of shear bands/cracks induced by fatigue experiment in a Zr–Cu–Al bulk metallic glass

A Zr50Cu40Al10 bulk metallic glass was deformed by three-point bending fatigue experiments. Shear bands/cracks appeared on the tensile and compressive regions of the sample surfaces. Characterizations of these shear bands/cracks cross sections by transmission electron microscopy reveal that a composition change occurred within the shear bands/cracks. Additionally, nanocrystallites with a higher copper content formed within the cracks. The composition change of the shear bands/cracks and formation of nanocrystallites are attributed to the diffusion of oxygen and copper atoms, respectively.

Glass-forming ability and corrosion resistance of Zr-based Zr–Ni–Al bulk metallic glasses

Zr–Ni–Al metallic glass samples with diameters above 10mm could be produced in a wide composition range of 54–64at.% Zr, 21–27at.% Ni, and 11–21at.% Al by a copper mold casting method. The best glass-forming ability was obtained for Zr60Ni25Al15 and Zr58Ni27Al15 alloys, and the glassy samples with diameters up to 15mm were fabricated. The Zr60Ni25Al15 bulk metallic glass possesses high compressive yield strength of over 1740MPa with large plastic strain above 3.0%, and the mechanical properties and fracture mode are almost independent of the cast sample size or the position within the rod where the samples have been machined. In addition, the bulk metallic glass shows high corrosion resistance in chloride-ion-containing solutions.

On the anelasticity and strain induced structural changes in a Zr-based bulk metallic glass

We report on the anelastic behavior of a cyclically loaded Zr62.5Fe5Cu22.5Al10 bulk metallic glass well below its yield strength. The dynamic mechanical behavior of the glass is discussed on the basis of its structural and thermodynamic properties before and after tests. We show how the kinetically frozen anelastic deformation accumulates at room temperature and causes a structural relaxation and densification of the glass and further leads to its partial crystallization.

Internal stresses induced by plastic shear deformation of Zr–(Cu,Ag)–Al bulk metallic glasses

Effective internal shear stress σi induced by torsional deformation of Zr46(Cu4/5Ag1/5)46Al8 and Zr46Cu46Al8 bulk metallic glasses different by the glass-forming ability of the maternal melts has been determined by measurements of stress relaxation upon stepwise unloading. It has been found that the ratio σi/σ0 (σ0 is the initially applied shear stress) decreases upon increasing the temperature from ≈0.8 at T=450K (T≈0.64×Tg) to ≈0.08 at T=638K (T≈0.91×Tg) independently of σ0 and glass composition. The obtained result is in good agreement with earlier data obtained on ribbon metallic glasses. The origin of deformation-induced internal stresses and their connection with deformation mechanisms of metallic glasses has been briefly discussed.

High glass forming ability and good mechanical properties of Cu–Zr–Al bulk metallic glasses

For developing bulk metallic glasses with high glass forming ability (GFA) and good mechanical properties, Cu92−xZrxAl8 (x = 35–65 at-%) alloys have been studied by means of tilt mould casting method. The largest glassy rod with a critical diameter of 18 mm in this alloy series was obtained for Cu42Zr50Al8 alloy. The Hruby factor is appropriate for evaluating GFA in the cast Zr–Cu–Al bulk glassy alloy. The bulk metallic glasses with high GFA exhibit good mechanical properties, i.e. compressive fracture strength of 1783–2240 MPa, Young’s modulus of 90–123 GPa and plastic strain of 0–0·73%.

Effects of Ni addition on the glass-forming ability, mechanical properties and corrosion resistance of Zr–Cu–Al bulk metallic glasses

The thermal stability, glass-forming ability (GFA), mechanical properties and corrosion resistance of Zr60Cu25−xAl15Nix (x = 0–25 at.%) bulk metallic glasses (BMGs) were systematically investigated. The additional Ni greatly enhances the thermal stability and GFA of BMGs. For alloy with x = 15, a fully glassy rod with a critical diameter up to 18 mm can be obtained by copper mold casting. In addition, the strength and plasticity of BMGs are effectively improved by adding Ni, and they show remarkable correlations with glass transition temperature and Poisson's ratio or G/B value, respectively. A Zr60Cu5Al15Ni20 BMG exhibits largest compressive plastic strain of 5.5%, yielding strength of 1755 MPa and Young's modulus of 83 GPa at ambient temperature. Moreover, the electrochemical potentiodynamic polarization curves demonstrate that replacement of Cu by Ni improves the corrosion resistance in chloride-ion-containing solutions significantly.

Wetting of bulk metallic glass forming liquids on metals and ceramics

Contact wetting angle of Pd43Ni10Cu27P20, Pt57.5Cu14.7Ni5.3P22.5, Au49Ag5.5Pd2.3Cu26.9Si16.3, and Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass forming alloys have been determined on materials that are used in micro and nano fabrication. Employing the sessile drop technique at a temperature above the corresponding melting temperatures, three kinds of wetting behaviors are observed, spanning from θ ≈ 140°, over neutral wetting, θ ≈ 80°, to almost complete wetting, θ < 5°. The origin for complete wetting is the formation of an interface phase promoting wetting. Estimations of the contact wetting angles are presented for temperatures in the supercooled liquid region where micro and nano fabrication is typically carried out. Consequences of the observed wetting behaviors for nanoforming are discussed.