Mechanical properties and thermal stability of a Cu-based bulk metallic glass microalloyed with silicon

(Cu₄₂Zr₄₂Al₈Ag₈)_{100? x} Si _x (x?=?0?～?1) amorphous alloy rods of 2–6?mm diameter were prepared by Cu-mold drop casting. The thermal properties, microstructure evolution, and mechanical properties were studied by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), transmission electron microscopy (TEM), hardness test, and compression test. The XRD result revealed that all as-quenched (Cu₄₂Zr₄₂Al₈Ag₈)_100?x Si _x alloy rods exhibited a broad diffraction pattern in the amorphous phase. The (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 alloy was found to possess the highest glass forming ability (GFA) as well as the best thermal stability among all tested samples. In addition, both its hardness and yield strength were increased by the microalloyed Si content. The fracture strength and the plastic strain of (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 amorphous alloy can reach 2000?MPa and 3.5 %.     

Effect of Er on properties of Zr-based bulk metallic glasses

(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)_100-xEr_x(x?=?0～6) bulk metallic glasses were fabricated by copper mould suction casting method, and the effect of Er on properties was studied. The compressive plastic strain (ε_p) and compressive strength (σ_max) at room temperature increases first and then decreases with the increase of Er content. The compressive plastic strain (ε_p) of the specimen is 35.1% when x?=?2.6, which is about eight times than that of the specimen with x?=?0. The compressive strength (σ_max) is 2513?MPa, which is much higher than that of the specimen with x?=?0. It indicates that Zr-based bulk metallic glasses could be strengthened and toughened by adding Er. The thermal stability decreases gradually and the glass-forming ability increases first and then decreases with the increase of Er content.     

Composition and size dependent torsion fracture of metallic glasses

The fracture of metallic glasses(MGs)of different compositions and sizes down to micrometers under torsion loading were systematically investigated.Contrary to the flat shear fracture along the circumfer-ential plane as commonly supposed under torsion,we find that the torsion fracture of metallic glasses can deviate from flat shear plane,and the fracture angle is closely dependent on the composition and the size of MG samples.With a conversion method,we show that the torsion fracture of both millimeter-and micrometer-sized MGs can be described by the ellipse fracture criterion as originally proposed for the tension fracture.The deviation from the circumferential shear plane under torsion is further shown to intrinsically relate to the fracture toughness of MGs.The tougher MG tends to have a smaller fracture angle with respect to the maximum shear plane,and vice versa,indicating a correlation between the fracture toughness and pressure/normal stress sensitivity in MGs.Our results provide new insights on the fracture mechanism and are helpful to design and control the deformation and fracture behavior of MGs under torsion loading.     

Mechanical behavior of Zr-based bulk metallic glasses

Bulk metallic glasses have a very high corrosion resistance and mechanical strength. Bulk metallic glasses show elastic-perfectly plastic behavior with an extended region of elastic strain (≈ 2%). But at room temperature their macroscopic plasticity is weak even though a local plastic strain is observed in shear bands. A relaxation analysis allowed studying micro-mechanisms of plastic deformation and estimating the apparent activation volume (≈ 2000 ų). __________ Translated from Problemy Prochnosti, No. 1, pp. 167–170, January–February, 2008.     

Application of Fe-based metallic glasses in wastewater treatment

This work pioneered the use of the Fe₇₈Si₉B₁₃ metallic glass ribbons in wastewater treatment. Fe₇₈Si₉B₁₃ metallic glass was employed to remediate wastewater contaminated with a mixture of organic dyes. The removal rate of chemical oxygen demand (COD) with Fe₇₈Si₉B₁₃ metallic glass and metallic Fe⁰ was up to 23 ± 0.93% in 30 min and 21 ± 0.67% with in 45 min, respectively. The dosage of Fe-based metallic glass was only 1/25 of that of metallic Fe⁰ to obtain equivalent effects. The mechanism of wastewater treatment through Fe-based metallic glasses is discussed.     

Development of quaternary Fe-based bulk metallic glasses

Fe-based bulk metallic glasses have been designed using several modeling criteria. Quaternary alloys were successfully developed in the Fe-rich compositional region where the only solutes used were Cr, Nb, and B. Furthermore, the exceedingly high level of Fe, exceeding 75 wt.% in some alloys, makes this series of alloys, compositionally very close to conventional steel alloys. Therefore, their production using conventional facilities and materials is more easily attainable than previously developed bulk metallic glasses. The modeling criteria used, simultaneously analyzes the thermodynamics and kinetics of the vitrification behavior in a potential glass-forming alloy. A liquidus model, which determines and ranks the presence of deep eutectics, is used to determine the optimal compositional region. This criterion is cross-checked with an elastic strain model. Alloys compositionally located near a deep eutectic, while simultaneously containing a topology that induces significant elastic strain in a developing crystalline lattice exhibits experimentally good glass forming ability.     

Ultra-high strength Mg-Li based bulk metallic glasses: Preparation and performance research

In this paper, new Mg-Li based bulk metallic glasses (BMGs) are prepared by conventional copper mold injection casting method. The alloys exhibit excellent mechanical properties, such as ultra-high compressive fracture strength (maximal 729 MPa), high Vickers hardness (>2 GPa) and low elastic modulus (∼35 GPa). Compared with the corresponding crystal alloys, the density of the amorphous alloy samples is reduced by about 1.5% due to their free volume. Thus, it is believed that this new BMGs with these outstanding properties will broaden Mg-Li based alloys’ application fields.     

Vibrational dynamics of Zr-based bulk metallic glasses

The vibrational dynamics of some Zr-based bulkmetallic glasses were studied at room temperature in terms of phonon eigen frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS). The well recognized model potential is employed successfully to explain electron-ion interaction in the metallic glass. The present findings of phonon dispersion curve are found to be in fair agreement with available theoretical as well as experimental data. The thermodynamic properties obtained by the HB and TG approaches are found to be much lower than those obtained by the BS approach.     

Characterization and modeling of breaking-induced spontaneous nanoscale periodic stripes in metallic glasses

Stripes with a period of 87 nm appear in the mirror region of the fracture surface of metallic glasses. Two competing failure mechanisms of immediate meniscus instability and cavitation mechanism near the crack tip control the fracture process of metallic glasses and the formation process of nanostripes.     

Bulk metallic glasses: A new class of engineering materials

Bulk glass-forming alloys have emerged over the past fifteen years with attractive properties and technological promise. A number of alloy systems based on lanthanum, magnesium, zirconium, palladium, iron, cobalt and nickel have been discovered. Glass-forming ability depends on various factors like enthalpy of mixing, atomic size and multicomponent alloying. A number of processes is available to synthesise bulk metallic glasses. The crystallisation behaviour and mechanical properties of these alloys pose interesting scientific questions. Upon crystallisation many of these glasses transform to bulk nanocrystals and nanoquasicrystals. A detailed study of the structure and the crystallisation behaviour of glasses has enabled the elucidation of the possible atomic configuration in liquid alloys. Their crystallisation behaviour can be exploited to synthesise novel nanocomposite microstructures and their mechanical properties can be enhanced. A broad overview of the present status of the science and technology of bulk metallic glasses and their potential technological uses is presented.     

The potential of Zr-based bulk metallic glasses as biomaterials

Zr-based bulk metallic glasses (BMGs) are a new type of metallic materials with disordered atomic structure that exhibit high strength and high elastic strain, relatively low Young’s modulus, and excellent corrosion resistance and biocompatibility. The combination of these unique properties makes the Zr-based BMGs very promising for biomaterials applications. In this review article, the authors give an overview of the recent progress in the study of biocompatibility of Zr-based BMGs, especially the relevant work that has been done in the metallic glasses group in Huazhong University of Science and Technology (HUST), including the development of Ni-free Zr-based BMGs, the mechanical and wear properties, the bio-corrosion resistance, the in vitro and in vivo biocompatibility and the bioactive surface modification of these newly developed BMGs.     

Study of superconducting state parameters of ternary metallic glasses through pseudopotential approach

A theoretical investigation on the screening dependence of the superconducting state parameters (SSPs) viz. the electron-phonon coupling strength λ, the Coulomb pseudopotential μ∗, the transition temperature T_C, the isotope effect exponent α and the effective interaction strength N₀V of some ternary metallic glasses such as Ti₅₀Be₃₄Zr₁₀, (Mo_0.6Ru_0.4)₇₈B₂₂, (Mo_0.6Ru_0.4)₈₀B₂₀, (Mo_0.4Ru_0.6)₈₀P₂₀, (Mo_0.6Ru_0.4)₇₀Si₃₀, (Mo_0.6Ru_0.4)₈₄B₁₆, (Mo_0.6Ru_0.4)₇₂Si₂₈, (Mo_0.6Ru_0.4)₈₆B₁₄, (Mo_0.6Ru_0.4)₇₆Si₂₄, (Mo_0.6Ru_0.4)₇₈Si₂₂, (Mo_0.6Ru_0.4)₈₀Si₂₀, (Mo_0.6Ru_0.4)₈₂Si₁₈ and (Mo_0.6Ru_0.4)₈₀P₂₀ is reported for the first time using Ashcroft''s empty core (EMC) model potential. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al (F) and Sarkar et al (S) are used in the present investigation to study the effect of screening on the aforesaid properties. It is observed that λ and T_C are reasonably sensitive to the selection of the local field correction functions, whereas μ∗, α and N₀V show weak dependences on the local field correction functions. The transition temperature T_C obtained from the H-local field correction function is found to be in excellent agreement with available experimental data. Also, the present results are found to be in qualitative agreement with other earlier reported data, which confirms the existence of the superconducting phase in the above ternary metallic glasses.     

低温弛豫对Mge5 Cu25 Gd10大块非晶合金热稳定性及力学行为影响

Mg65 Cu25 Gd10非晶合金的热稳定性关系到其作为结构材料的实用性及发展前景。利用差示扫描量热法（DSC）研究了预先低温弛豫处理后Mg65 Cu25 Gd10非晶的特征转变温度和晶化激活能，分析了低温弛豫对其热稳定性的影响，通过Kissinger方程计算其晶化激活能、频率因子、反应速率系数进一步说明此非晶的晶化过程。同时，通过比较其力学性能的变化，发现非晶压缩性能受非晶稳定性影响不大，抗压强度下降很小。但其断裂方式及断面微观特征有明显变化。     

Melt-spinning technique for preparation of metallic glasses

Rapid solidification of metallic melts at a rate ≳10⁵ °K/sec has gained considerable interest for casting non-equlibrium crystalline structures in general and metallic glasses in particular. Of the variety of techniques used for rapid solidification, melt-spinning and melt-extraction are widely used. This paper describes the design and development of a melt-spinning technique in our laboratory. Optimization of spinning parameters for smooth and continuous ribbons is discussed. Glassy ribhons of Cu-Zr and Pd-Ge alloys have been made under optimized conditions. A brief account of some of the structural and electronic properties of these glasses is illustrated.     

Internal friction and elastic modulus of bulk metallic glasses

The mechanical relaxation in binary, ternary, quaternary, and quitary bulk metallic glasses with widely different glass-forming ability, or the critical cooling rate, has been studied. A single-roller melt-spinning apparatus was used for preparing thin specimens. The internal friction Q⁻¹ and the oscillation frequency f of the specimens were measured using an inverted torsion pendulum with the free decay method. The measurements were performed from room temperature, through the glass transition temperature T_g, up to the crystallization temperature T_x. As the temperature is increased, the background Q⁻¹ increases, and peaks can usually be seen near T_g and T_x. The shear modulus, which is proportional to f², is changed near the Q⁻¹ peak. The experimental data are presented and overall features of the results are discussed.     

Strengthening and toughening of Mg-Cu-(Y, Gd) bulk metallic glasses by minor addition of Be

Mg₆₅Cu₂₅Re₁₀ and Mg₆₅Cu₂₄Be₁Re₁₀ (Re = Y, Gd) bulk metallic glasses (BMGs) were successfully fabricated by conventional Cu-mold casting method. By the addition of 1 at.% Be, the compressive strengths of Mg₆₅Cu₂₄Be₁Y₁₀ and Mg₆₅Cu₂₄Be₁Gd₁₀ alloys are increased from 760 MPa and 860 MPa to 930 MPa and 1025 MPa, respectively. The fracture morphology is changed from nanometer scale corrugation to micrometer scale dimple and vein pattern, indicating that the addition of minor Be obviously improves the toughness of the alloys. The fracture morphologies with different size of plastic zone in Mg-based BMGs provide probability for understanding the fracture mechanism of BMGs.     

热双金属稳定化热处理效果的电阻分析

通过电阻和X-Ray衍射分析方法，研究了热双金属5J20110及其组元在稳定化热处理过程中电阻率和残余应力随循环次数的变化。研究结果表明经第一次循环热处理后，热双金属的残余应力下降最显著，与合金电阻率的变化趋势相同。通过电阻率的分析可以确定稳定化热处理的效果。     

Multiresolution atomistic simulations of dynamic fracture in nanostructured ceramics and glasses

Multimillion atom molecular-dynamics (MD) simulations are performed to investigate dynamic fracture in glasses and nanostructured ceramics. Using multiresolution algorithms, simulations are carried out for up to 70 ps on massively parallel computers. MD results in amorphous silica (a-SiO₂) reveal the formation of nanoscale cavities ahead of the crack tip. With an increase in applied strain, these cavities grow and coalesce and their coalescence with the advancing crack causes fracture in the system. Recent AFM studies of glasses confirm this behavior. The MD value for the critical stress intensity factor of a-SiO₂ is in good agreement with experiments. Molecular dynamics simulations are also performed for nanostructured silicon nitride (n-Si₃N₄). Structural correlations in n-Si₃N₄ reveal that interfacial regions between nanoparticles are amorphous. Under an external strain, nanoscale cavities nucleate and grow in interfacial regions while the crack meanders through these regions. The fracture toughness of n-Si₃N₄ is found to be six times larger than that of crystalline -Si₃N₄. We also investigate the morphology of fracture surfaces. MD results reveal that fracture surfaces of n-Si₃N₄ are characterized by roughness exponents 0.58 below and 0.84 above a certain crossover length, which is of the order of the size of Si₃N₄ nanoparticles. Experiments on a variety of materials reveal this behavior. The final set of simulations deals with the interaction of water with a crack in strained silicon. These simulations couple MD with a quantum-mechanical (QM) method based on the density functional theory (DFT) so that chemical processes are included. For stress intensity factor K=0.4 MPa m^1/2, we find that a decomposed water molecule becomes attached to dangling bonds at the crack or forms a Si-O-Si structure. At K=0.5 MPa m^1/2, water molecules decompose to oxidize Si or break Si-Si bonds.     

Relationship between dealloying conditions and coarsening behaviors of nanoporous copper fabricated by dealloying Cu-Ce metallic glasses

Monolithic nanoporous copper(NPC) with tunable ligament size(107–438 nm) was synthesized by dealloying a new Cu-Ce binary glassy precursor in dilute H_2SO_4 aqueous solution. The effects of the dealloying conditions on the morphologies of NPC were evaluated comprehensively. The results show that the ligaments of NPC can significantly coarsen with the increase of acid concentration, elevation of reaction temperature or prolongation of immersion time. These coarsening behaviors can be well described by a diffusion based growth kinetic model. Moreover, the surface diffusivity and activation energy for diffusion of Cu atoms were also estimated to investigate the formation mechanism of NPC, which is mainly governed by dissolution of Ce element in the glassy precursor coupled with nucleation and growth of Cu clusters via the precursor/solution interface. In the experiment of the degradation of methyl orange(MO) dye, the NPC fabricated by Cu-Ce metallic glasses exhibits superior sono-catalytic activity.     

Evolutionary intelligence in design and synthesis of bulk metallic glasses by mechanical alloying

The present work demonstrates a new approach of a combinatorial design of Bulk Metallic Glasses using evolutionary intelligence of genetic programming (GP) and genetic algorithm (GA). A glass-forming potential expression, carrying similar sense as the glass-forming ability (GFA) indicator expression, has been identified by principal component analysis and GP, enabling one to map the fitness of the composition from the multidimensional attribute space of the alloy in the course of GA search. The genetically inspired alloy compositions are evolved by GA search and subsequently validated through existing empirical knowledge. Two randomly chosen compositions are subjected to experimental trial where the glass-forming potential has been evaluated by amorphization potential through mechanical alloying. A literature-reported good glass -forming composition has been studied as a reference alloy and comparison was made for the proposed designed alloys.