Effects of ion irradiation on Zr52.5Cu17.9Ni14.6Al10Ti5 (BAM-11) bulk metallic glass

Bulk metallic glasses are intriguing candidates for nuclear applications due to their inherent amorphous structure, but their radiation response is largely unknown due to the relatively recent nature of innovations in bulk metallic glass fabrication. Here, microstructural and mechanical property evaluations have been performed on a Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass (BAM-11) irradiated with 3 MeV Ni⁺ ions to 0.1 and 1.0 dpa at room temperature and 200 °C. Nanoindentation hardness and Young's modulus both decreased by 6–20% in samples irradiated at room temperature, with the sample irradiated to 1.0 dpa experiencing the greatest change in mechanical properties. However, no significant changes in properties were observed in the samples irradiated at 200 °C, and transmission electron microscopy showed no visible evidence of radiation damage or crystallization following ion irradiation at any of the tested conditions. These results suggest that BAM-11 bulk metallic glass may be useful for certain applications in nuclear environments.     

Nano-porous surface states of Ti–Y–Al–Co phase separated metallic glass

A novel nano-porous state was fabricated at the surface of the Ti-based metallic glass by selective etching technique. By transforming the surface of the Ti₄₅Y₁₁Al₂₄Co₂₀ phase separated alloy from smooth towards rough with nano-pores in an oxidised state, the passivation behaviour of the glassy alloy in simulated body fluid condition was remarkably improved leading to corrosion resistance significantly higher than that of the Ti–6Al–4V alloy, one of the favourite candidate materials for implant applications.     

Electron irradiation induced phase transformation in Zr66.7Cu33.3 and Zr66.7Pd33.3 metallic glass

Crystallization and phase selection in Zr_66.7Cu_33.3 and Zr_66.7Pd_33.3 metallic glass during thermal annealing and electron irradiation were examined. During thermal annealing an equilibrium C11_b–Zr₂Cu phase directly precipitated in the amorphous phase of Zr_66.7Cu_33.3 metallic glass while a thermal equilibrium C11_b–Zr₂Pd phase formed after icosahedral quasi-crystalline phase precipitation in Zr_66.7Pd_33.3 metallic glass. The amorphous phase was not stable under electron irradiation and metastable crystalline phases with face-centered cubic-based structure formed in both kinds of metallic glass by electron irradiation induced crystallization. The unique phase selection in electron irradiation induced crystallization is due to a change in the phase stability of crystal, quasi-crystal and amorphous phase under electron irradiation.     

Low-temperature brazing of titanium by the application of a Zr–Ti–Ni–Cu–Bebulk metallic glass (BMG) alloy as a filler

Titanium (Ti) was successfully brazed at low temperatures below 800 °C by employing a Zr_41.2Ti_13.8Ni_10.0Cu_12.5Be_22.5 (at.%) bulk metallic glass (BMG) alloy as a filler. Through the use of this alloy filler, the detrimental segregation of Zr–Cu–Ni filler elements was completely eliminated by heating to well below 800 °C, so the resultant joint was quite homogeneous with a coarse acicular structure. The disappearance of the Zr–Cu–Ni segregated region was rate-controlled by the diffusion of the filler elements in the Ti base metal. Remarkably, the mechanical property and corrosion resistance of the homogeneous joint brazed at 800 °C for 10 min were mostly comparable to those of bulk Ti.     

Precision die-casting of optical MU/SC conversion sleeve

The performance of MU/SC conversion sleeve produced by bulk metallic glass (Zr₅₅Al₁₀Ni₅Cu₃₀) was examined. A precision die-casting method was applied to improve size accuracy. The size accuracy of the conversion sleeve produced by the precision die-casting method was ±1 μm, and optical insertion loss (Li) was less than 0.3 dB for a standard value. The wear resistance of metallic glass is improved by surface oxidation treatment in air at 673 K. The MU/SC conversion sleeve produced from bulk metallic glass has superior characteristics for optical parts.     

Effect of mischmetal substitution on the glass-forming ability of Mg–Ni–La bulk metallic glasses

The effect of La substitution by LaMM (lanthanum mischmetal) on the glass-forming ability of a Mg–Ni–La metallic glass has been studied. For compositions close to the eutectic Mg₆₉Ni₁₈La₁₃, the LaMM substitution improved the glass-forming ability, for instance up to a critical amorphous diameter of 2 mm for the Mg₆₅Ni₂₀LaMM₁₅ alloy. However, of all the alloys studied, it has been observed that La-containing alloys have higher GFA for compositions further from the eutectic and a maximum critical amorphous diameter of 2.5 mm was obtained for the Mg₆₀Ni_23.6La_16.4 alloy.     

Controlling shear band behavior in metallic glasses through microstructural design

Plastic deformation in metallic glasses is governed by the initiation and propagation of shear bands. The successful use of bulk metallic glasses in structural applications will depend on controlling these processes to improve ductility and toughness. In Zr–Cu–Ni–Al metallic glasses, the addition of Ta can influence the structure of the material and hence the shear band behavior in two ways. At low Ta contents (<4 at.%), the material is amorphous but has enhanced order over length scales of 5–15 Å Higher levels of Ta result in the precipitation of bcc Ta-rich solid solution particles in a metallic glass matrix. Under uniaxial compression, both of these materials show greater apparent plastic strain to failure than the glass without Ta. This appears to be the result of the influence of the structure on the initiation and propagation of shear bands in the amorphous matrix.     

Structural bulk metallic glasses with different length-scale of constituent phases

Bulk metallic glass composites containing constituent phases with different length-scales are prepared via an in situ method by copper mold casting homogeneous Zr–Ti–Nb–Cu–Ni–Al melts. The phase formation and the microstructure of the composite materials are investigated by X-ray diffraction, optical, scanning and transmission electron microscopy, and microprobe analysis. The composition of the melt as well as the cooling conditions realized during casting determine the type and the morphology of the phases present in the composite. The mechanical properties of composite materials with quasicrystalline or ductile bcc phase reinforcements are tested in uniaxial compression at room temperature, showing that the deformation is controlled by the type of the constituent phases and their morphology. Ductile phase-containing metallic glass composites demonstrate improved work hardening and ductility compared to monolithic metallic glasses. Similar results are obtained for composites with ductile bcc phase dendrites embedded in a nanocrystalline matrix. The improved ductility of the composites is due to the presence of the ductile second phase, which counteracts catastrophic failure by shear localization.     

Localized corrosion behavior of a zirconium-based bulk metallic glass relative to its crystalline state

To date, few detailed corrosion studies of the new bulk metallic glasses (BMGs) have been presented. In the present work, the aqueous electrochemical corrosion properties of BMG-11, 52.5Zr–17.9Cu–14.6Ni–5.0Ti–10.0Al (atomic percent), were investigated. Cyclic-anodic-polarization tests were conducted on amorphous and crystalline specimens in a 0.6 M NaCl solution (simulated seawater) and on amorphous specimens in a 0.05 M Na₂SO₄ solution (simulated moisture condensation, as related to ongoing fatigue experiments in humid air), all at room temperature. In the NaCl solution, both amorphous and crystalline materials were found to exhibit passive behavior with low corrosion rates (15 μm/year or less). However, susceptibilities to pitting corrosion were observed. The amorphous material was found to be more resistant to the onset of pitting corrosion under natural corrosion conditions. In the 0.05 M Na₂SO₄ solution, the amorphous BMG-11 was found to exhibit passive behavior with a very low corrosion rate (0.4 μm/year), and to be immune to pitting corrosion. Furthermore, when the protective passive film was removed by scratching with a diamond stylus, it was found to quickly reform. This result suggested that a corrosion influence on the fatigue properties of BMG-11 in humid air would be minimal.     

Thermal stability and crystallisation of a Zr55Cu30Al10Ni5 bulk metallic glass studied by in situ ultrasonic echography

An original in situ ultrasonic echography technique was used to study the thermal stability and crystallisation of a Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass between RT and 630 °C. Changes in Young's modulus with temperature were reported allowing to study the supercooled-liquid state and the crystallisation process. Investigations of viscoelastic properties gave information on the correlation factor (hierarchically correlated motion theory) and three distinct crystallisation stages were observed. Their kinetics were studied using Voigt's and Reuss' approximations for a two-phase material and comparisons with the Johnson–Mehl–Avrami–Kolmogorov theory allowed us to consider a mixed surface/internal nucleation for the first stage and a surface nucleation for the two last stages.     

Synthesis of La-based in-situ bulk metallic glass matrix composite

An in-situ dendritic crystalline α-La reinforced bulk metallic glass matrix composite was successfully synthesized by chill casting a La₆₆Al₁₄Cu₁₀Ni₁₀ alloy into copper mould with a rod diameter as large as 12 mm in diameter. The critical cooling rates for the formation of the in-situ composite determined by Bridgman solidification and for complete glass formation are 15 K/s and 450 K/s respectively. The thermal stability of the residual amorphous in the composite is higher than that of the fully amorphous sample of the same alloy.     

Influence of Small Amounts of Impurities on Copper Oxidation at 600–1050°C

In order to study the influence of small amount of impurities on the copper oxidation kinetics, the oxidation was examined at 600–1050°C in 0.1 MPa oxygen atmosphere using 99.5% (2N) and 99.9999% (6N) pure copper specimens. The influence of impurities has been discussed considering the roles of the nonprotective CuO layer, the impurity layer at the Cu₂O–Cu interface, and the diffusion of copper in the Cu₂O layer. The nonprotective CuO layer for 2N copper can greatly enhance copper oxidation. However, the impurities concentrated at the region near the Cu₂O–Cu interface for 2N copper can slow oxidation. Contrary to the presence of metallic impurities, such as Ni, Sb, and Pb, the nonmetallic elements As and Se dissolved in Cu₂O have a deleterious influence on the outward diffusion of copper. Grain-boundary diffusion in Cu₂O can somewhat contribute to 2N copper oxidation at 850–1050°C, but its effect in enhancing oxidation at 600–800°C is weaker than the effect of the impurity layer at the Cu₂O–Cu interface in impeding oxidation.     

Kinetic peculiarities of anodic dissolution of silver and Ag–Au alloys under the conditions of oxide formation

The kinetics of anodic dissolution of silver and Ag–Au alloys (X_Au = 0.1–30 at.% Au) in aqueous alkaline solution under the conditions of the formation of silver oxides has been examined. The techniques of cyclic voltammetry, chronoammetry, and photopotential measurements have been used. It was established that the anodic formation and cathodic reduction of Ag₂O on silver and alloys are controlled by migration in the oxide layer. Ag₂O oxide is an n-type semiconductor with an excess of silver atoms. Oxide layers formed on monocrystalline Ag(1 1 1) and Ag(1 1 0) are more stoichiometric than the layer formed on polycrystalline Ag.     

Concept of chemical short range order domain and the glass forming ability in multicomponent liquid

The concept of multicomponent chemical short-range order (MCSRO) domain is systematically developed by the experimental investigation of Zr–Ti–Cu–Ni–Al bulk metallic glass (BMG) and thermodynamic modeling and calculation. The existence of MCSRO domains in Zr-based BMG is verified by the observations of high-resolution transmission electron microscopy (HRTEM) images and the analysis of nano-beam electron diffraction patterns. The size of the nano-beam used in this work is 0.5 nm in diameter. Thermodynamic evaluation of the melt composed of multiple-MCSRO domains and glass-forming ability (GFA) based on the concept of MCSRO domains has also been conducted. It is indicated that the thermodynamic calculation of the GFA based on MCSRO model is consistent with the experimental data of crystallization activation energy and glass transition temperature for Ni-Zr and Zr-Cu binary alloys, and with supercooled liquid region (ΔT_x) for Zr–Ni–Al ternary alloy. The existence of MCSRO domain lowers the free energy of the melt (ΔG_MCSRO), resulting in a large undercooling and a larger energy barrier to the nucleation of a critical crystalline nucleus. Large ΔG_MCSRO, low melting point as well as co-existence of multiple MCSRO domains are valid criterion for the valuation of GFA.     

Laser welding of annealed Zr55Cu30Ni5Al10 bulk metallic glass

Laser welding is one of the promising ways for manufacturing metallic glass products with complicated shape and geometry. In this work we focus on the effect of annealing treatment and welding parameters on laser welding of annealed Zr₅₅Cu₃₀Ni₅Al₁₀ bulk metallic glass as intended and unintended heat treatment occurs in the process. We find that laser welding can produce well welded specimen plates with no obvious welding defects in the joints and high welding speed may lead to better joints. Although higher annealing temperature or longer annealing time leads crystallization, bulk metallic glass material still remains largely amorphous in the heat affected zone. Compared with the welded joint without annealing, the micro-hardness and bending strength are enhanced due to the presence of the nanocrystals occurred in annealed welding joint. Therefore, appropriate annealing treatment with the annealing temperature near the glass transition temperature and annealing time as long as that in hot embossing of BMG parts may play a beneficial role in laser welding of metallic glasses.     

Superplasticity in a bulk amorphous Pd-40Ni-20P alloy:a compression study

Compressive deformation behavior of a cast Pd₄₀Ni₄₀P₂₀ bulk metallic glass in the supercooled liquid region (589–670 K) was investigated at strain rates ranging from 10⁻⁴ to 10⁻² s⁻¹. The material exhibited excellent mechanical formability in the supercooled liquid region. However, in contrast to a Newtonian behavior generally observed in oxide glasses, the present alloy also showed a non-Newtonian behavior, depending upon the temperature and applied strain rate. Specifically, the alloy is like a Newtonian fluid at high temperatures, but becomes non-Newtonian at low temperatures and high strain rates. Structures of the amorphous material, both before and after deformation, were examined using X-ray diffraction and high-resolution transmission electron microscopy. The non-Newtonian behavior is proposed to be associated with the glass instability during deformation.     

Glass coatings on stainless steels for high-temperature oxidation protection: Mechanisms

The oxidation behavior of a martensitic stainless steel with or without glass coating was investigated at 600–800 °C. The glass coating provided effective protection for the stainless steel against high-temperature oxidation. However, it follows different protection mechanisms depending on oxidation temperature. At 800 °C, glass coating acts as a barrier for oxygen diffusion, and oxidation of the glass coated steel follows linear law. At 700 or 600 °C, glass coating induces the formation of a (Cr, Fe)₂O₃/glass composite interlayer, through which the diffusion of Cr³⁺ or Fe³⁺ is dramatically limited. Oxidation follows parabolic law.     

Anisotropic nanocrystallization of a Zr-based metallic glass induced by Xe ion irradiation

Structural modification in a Zr-based metallic glass caused by irradiation with 7 MeV Xe²⁶⁺ ions was investigated. Needle-like nanocrystalline structures, formed under ion irradiation, consist of Cu₁₀Zr₇ phase (primary) and/or minor (Ni_xCu_1−x)₁₀Zr₇ phase. The formation of needle-like nanocrystals suggested an anisotropic atomic diffusion caused by ion irradiation.     

Fatigue behavior of Zr52.5Al10Ti5Cu17.9Ni14.6 bulk metallic glass

In the present study, fatigue tests were conducted on a zirconium-based bulk metallic glass (BMG), BMG-11 (Zr–10Al–5Ti–17.9Cu–14.6Ni, atomic percent), in air and vacuum to elucidate the possible environmental effects. In air, the fatigue endurance limit and the fatigue ratio were found to be 907 MPa and 0.53, respectively. These values are better than many conventional high-strength crystalline alloys. Unexpectedly, the fatigue lifetimes in vacuum were found to be lower than in air. Additional testing indicated that dissociation of residual water vapor to atomic hydrogen in the vacuum via a hot-tungsten-filament ionization gauge, and subsequent hydrogen embrittlement of the BMG-11, could have been a factor causing the lower fatigue lifetimes observed in vacuum.     

Oxidation of γ-Ni−Al−Si alloys at 1073 K

The formation and development of oxides in Ni–4Al and Ni–4Al–xSi (at.%, x=1, 3, 5) alloys at 5–9×10^–6 and 1 atm oxygen pressure at 1073 K have been studied. The oxidation rate increased with an increase of silicon content in the alloy at the early stage of oxidation, but decreased after longer time exposure due to formation of an intermediate layer composed of NiO and spinel (NiAl₂O₄ and Ni₂SiO₄) between the top NiO layer and the internal-oxidation zone. This intermediate layer became a barrier for releasing stress, generated by the volume expansion associated with oxidation of solute atoms, resulting in high dislocation density and severe distortion in the internal-oxidation zone for the Ni–Al–Si alloys. In Ni–4Al alloy where no complete intermediate-layer formation occurred, stress was easily released by an enhanced vacancy gradient, and therefore an enhanced vacancy-injection rate into the alloy, resulting in a higher oxidation rate than the situation where a sample was oxidized at an oxygen pressure associated with the dissociation of NiO.