Metallic glasses

Metallic glasses are a new class of materials produced by rapidly quenching the melts at rates often exceeding a million deg/sec. These have been found to display an optimum combination of properties such as high strength, good bend ductility, improved corrosion resistance and excellent soft magnetic properties. Thus, metallic glasses are emerging as economically viable competitors to conventional engineering materials. A clear understanding of the atomic structure of metallic glasses and its change during annealing are of prime importance. Although techniques such as field-ion microscopy (fim) x-ray diffraction and small angle x-ray scattering have been employed for this purpose, high resolution electron microscopic (hrem) investigations conducted during the last few years aided greatly in deriving information on the atomic scale. Availability of high-voltage high-resolution electron microscopes has been mainly responsible for this happy situation. Studies on several metallic glasses have revealed thathrem images contain well-defined pattern of fringes over local regions, even though the diffraction pattern is that of a typical amorphous structure. The details of structure in the early stages of crystallization derived throughhrem, fim and analytical microscopic techniques are presented and discussed.     

Ferromagnetic resonance in metallic glasses: study of fracture,stress and thermal stability

Effects of fracture, stress and isothermal annealing of Fe-Ni based metallic glasses have been investigated using the ferromagnetic resonance technique.fmr linewidth is quite sensitive to changes in the magnetic and structural order in metallic glasses, andfmr lineshape seems to provide useful qualitative information on the mechanical state of these systems. Our observations are compared with recent work of Baianu and co-workers.     

Elektronenstrahlschweißen von massiven metallischen Gläsern

Electron‐Beam‐Welding of bulk metallic glasses Because of their excellent mechano‐technological properties bulk metallic glasses form a promising, relatively new class of materials. Due to their low thermal stability the weldability of bulk metallic glasses is subject to narrow limits, in case the joining zone shall be prevented from crystallization. The paper at hand describes the status‐quo of the research work on electron beam welding of beryllium‐free, zirconium‐based bulk metallic glasses (Zr_52,5Ti₅Cu_17,9Ni_14,6Al₁₀) carried out at the Welding and Joining Institute at RWTH Aachen University. So far, high quality joints free from defects could be produced, however, it has not beenaccomplished to avoid the crystallization of the joining zone completely. Further research is in progress.     

Diffusion in metallic glasses

Rutherfordα-particles backscattering technique was employed for measurements of diffusion rates in metallic glasses. Effects of relaxation, crystallization and plastic deformation on diffusion rates were also investigated. It has been observed that the diffusion rates of a metallic solute are of the same orders of magnitude in both metal-metal and metal-metalloid glasses. A higher diffusivity is likely if there is a large difference between melting points of the solute and matrix. Relaxation has no effect on diffusion, however, diffusivity increases on crystallization. An increase in diffusivity is also observed on plastic deformation of metallic glass.     

Inverse ductile–brittle transition in metallic glasses?

There is evidence that metallic glasses can show increased plasticity as the temperature is lowered. This behaviour is the opposite to what would be expected from phenomena such as the ductile–brittle transition in conventional alloys. Data collected for the plasticity of different metallic–glass compositions tested at room temperature and below, and at strain rates from rate 10^?5 to 10³ s^?1, are reviewed. The analogous effects of low temperature and high strain rate, as observed in conventional alloys, are examined for metallic glasses. The relevant plastic flow in metallic glasses is inhomogeneous, sharply localised in thin shear bands. The enhanced plasticity at lower temperature is attributed principally to a transition from shear on a single dominant band to shear on multiple bands. The origins of this transition and its links to shear bands operating ‘hot’ or ‘cold’ are explored. The stress drop on a shear band after initial yielding is found to be a useful parameter for analysing mechanical behaviour. Schematic failure mode maps are proposed for metallic glasses under compression and tension. Outstanding issues are identified, and design rules are considered for metallic glasses of improved plasticity.     

Phase relations and activities in the Co-Ni-O system at 1373 K

The tie-lines delineating equilibria between CoO-NiO and Co-Ni solid solutions in the ternary Co-Ni-O system at 1373 K have been determined by electron microprobe andedax point count analysis of the oxide phase equilibrated with the alloy. The oxygen potentials corresponding to the tie-line compositions have been measured using a solid oxide galvanic cell with calcia-stabilized zirconia electrolyte and Ni + NiO reference electrode. Activities in the metallic and oxide solid solution have been derived using a new Gibbs-Duhem integration technique. Both phases exhibit small positive deviations from ideality; the values ofG ^E/X ₁ X ₂ are 2640 J mol⁻¹ for the metallic phase and 2870 J mol⁻¹ for the oxide solid solution.     

Corrosion behaviour of metallic glasses

A review is presented concerning the current experimental information on the corrosion behaviour of metallic glasses, particularly of iron-base glasses of metal-metalloid-type obtained by using electrochemical measurements and scanning electron microscopy. The corrosion characteristics of glasses of metal-metal-type, such as Cu-Ti, are also compared with those of known, highly corrosion-resistant metallic glasses. Compositional and structural effects, such as the addition of metallic or metalloid elements, amorphous phase structure effects, passive film formation and stress corrosion cracking, are also discussed.     

Fabrication of Cu rich bulk metallic glass composites via solidification method

Abstract

Cu based bulk metallic glasses and composites with tiny crystalline phases embedded in metallic glass matrix have been successfully fabricated by solidification technique in the present work. The formation of crystalline phases and structure inhomogeneity in bulk metallic glasses was characterised. Al is used as the minor alloying element to partly substitute Cu element in 61Cu–34Zr–5Ti. The results show that quarternary 60Cu–34Zr–5Ti–1Al alloy exhibits monoamorphous feature, and 56Cu–34Zr–5Ti–5Al alloy has a few crystalline peaks superimposed on a broad diffraction peak, suggesting that a composite structure forms in certain solidification conditions. To further identify the microstructure of the as cast rod, all samples were characterised by scanning electron microscopy (SEM). Small size phases are found in 2 mm diameter 56Cu–34Zr–5Ti–5Al rod, which has larger plastic deformation. The composition of those crystalline phases is also investigated. All results indicate that the presence of certain phases in metallic matrix benefits the mechanical properties of the as cast bulk metallic glasses.     

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.     

Influence of alkali content and alkali mixing on the chemical durability of fluorozirconate glasses

The corrosion of alkali-containing fluorozirconate glasses in water and acidic and alkaline solutions was studied with glasses of the compositions (100–x) (0.6ZrF₄·0.1AlF₃·0.3BaF₂)· xLiF and 48ZrF₄·8AlF₃·24BaF₂·xLiF·(20–x)NaF. The corrosion of the glasses in deionized water and 0.1 n HCl solution is mainly controlled by diffusion with an inductive period due to the passage from reaction-controlled to diffusion-controlled mechanisms, and the weight loss of glass increases with increasing LiF content in the single-alkali glasses. There was no appreciable effect of alkali mixing on the corrosion of glasses in deionized water and 0.1 n HCl solution. The glasses exhibited good stability in alkaline solution. The weight loss due to corrosion of the glasses in acidic buffered solution increased exponentially with increasing LiF content.     

Non-ohmic electric conduction in polycrystalline thulium oxide

The current voltage behaviour of polycrystalline Tm₂O₃ has been investigated at 77 K and 300 K to 350 K. At low voltages, the conduction is ohmic while at higher voltages the current has a quadratic dependence on voltage. The voltageV _T at which the transition from ohmic to non-ohmic conduction takes place changes from 180 V to 100 V as temperature increases from 77 K to 350 K. The results are interpreted in terms of the Rose theory of space charge limited currents (sclc) in defect insulators containing shallow traps.     

Effects of Mechanical Load and Ionizing Radiation on Glass

This paper develops an approach to investigation of a solid as an integral system whose fundamental properties are determined by the energetics of its structure. Addressing the subject from a unified viewpoint, we consider the formation, accumulation, and transformations of defects in silicate and aluminophosphate glasses, which emit electromagnetic waves in a wide frequency range as a result of cracking. It has been shown that electron irradiation causes spontaneous electrical discharges, whose magnitude depends on the electron energy and irradiation time. The discharges occur at surface defects. Brush discharges develop in a layer where charged particles are distributed. In a thin layer of a charged dielectric, we observe a breakdown effect. The electrical discharge concentrates at surface defects, which can be produced in advance. A discharge can be initiated by approaching a grounded metallic tip to a charged surface even some time after irradiation. A discharge, mechanical loading, cooling, or heating of glass is accompanied by not only a light burst but also electromagnetic emission (EME), which correlates well with a polymorphic transformation process, thermoluminescence, etc. Thus, the release of accumulated energy from unirradiated and irradiated inorganic glasses on heating and cooling is accompanied by pulsed EME, whose intensity depends on the energy stored in the material.     

Nanocrystallization in Ni60Ta40 and Ni60Nb40 metallic glasses below calorimetric glass transition

Crystallization of Ni₆₀Ta₄₀ and Ni₆₀Nb₄₀ metallic glasses at temperatures well below their respective calorimetric glass transition temperatures has been studied by differential scanning calorimetry, nanodiffraction, and electron microscopies. Nanometer-scaled metastable FCC phases were found to grow out from the glass structures. The Z-contrast images reveal that the nanocrystals are enriched in Ta or Nb in comparison with the surrounded amorphous structures. The experimental evidence is suggestive of the decoupled cooperative diffusion of Ni atoms in these fragile glasses.     

Characterization of defects in amorphous type II superconductors using the collective flux pinning properties

As in crystalline materials, flux pinning in type II superconducting metallic glasses arises from the interaction of the flux-line lattice with defects that locally change the superconducting properties of the sample. The nature of these defects is still subject of numerous investigations. In this paper we demonstrate that the collective pinning properties of weak pinning, type II superconductors provide an ideal additional tool for probing defects of sizes comparable to the coherence length . Our results obtained from sputtered Nb _X Ge and Mo _X Si layers sketch a straightforward relation between the sputter conditions, the resulting defects, and the pinning behavior. A classification of the defects that provide the pinning is given and estimates on their sizes and densities are derived. They are in excellent agreement with other (direct) observations.     

超声波筛选激光增材制造非晶合金

目的 快速优化出无缺陷非晶合金激光增材制造工艺。方法 以Zr51Ti5Cu25Ni10Al9非晶合金为模型材料,利用超声波对金属内部缺陷的衰减,来快速筛选激光增材制造非晶合金的最佳工艺组合（激光功率和扫描速度）。结果 超声波检测可以准确有效地检测出非晶合金试件的晶化比例,并且当激光功率为1 300 W、扫描速度为600 mm/min时超声波衰减系数降至最低。进一步对该工艺下获得的样品分析发现,该工艺成型的Zr51Ti5Cu25Ni10Al9非晶合金缺陷最少、晶化程度最低、性能最佳。结论 超声波技术是快速筛选激光增材制造非晶合金等高性能金属最佳工艺参数的有效技术手段。     

Study of Superconducting State Parameters of Binary Metallic Glasses by Pseudopotential Method

The theoretical calculation of the superconducting state properties (SSP) viz electron–phonon coupling strength λ, Coulomb pseudopotential μ ^*, transition temperature T _C , isotope effect exponent α and effective interaction strength N _O V of 50 binary metallic glasses of simple, non-simple, and transition metals have been carried out using a well-recognized model potential. We have employed here five different types of local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F), and Sarkar et al. (S) to study the exchange and correlation effects on the present investigations. Instead of using Vegard’s law, a pseudo-alloy-atom model (PAA) in the present investigation is proposed and found successful. The present results of the SSP are found to be in qualitative agreement with other such earlier reported data wherever they exist, which confirms the superconducting phase in the metallic glasses.     

Microstructure and optical absorption of silver granules in oxide glasses produced by ion-exchange and reduction treatments

An electron micrographic investigation has been carried out on two oxide glasses containing alkali ions and subjected to a sodiumsilver ion-exchange followed by reduction treatments at various temperatures. The presence of metallic silver in the silver-rich droplet phases has been confirmed by selected-area electron diffraction. The silver-rich phases are found to have diameters ranging from 3 to 50 nm. The nucleus density of these particles is found to have a maximum value at temperatures in the range 250 to 300° C. The optical absorption spectra of the reduced glasses show a maximum around a wavelength of 400 nm. Maxwell-Garnett theory has been used to calculate the optical absorption and the predicted wavelength for maximum absorption is in reasonable agreement with the experimental value.     

Simulated body fluid electrochemical response of Zr-based metallic glasses with different degrees of crystallization

The bio-electrochemical response in simulated body fluid of the Zr₅₃Cu₃₀Ni₉Al₈ metallic glasses with different degrees of partial crystallization was systematically examined and discussed. Through thermal annealing, the volume fractions of the crystalline phases are determined to be 0, 34, 63, and near 100%. Based on the bio-corrosion voltage and current, as well as the polarization resistance, it is concluded that the fully amorphous alloy exhibits the highest bio-electrochemical resistance. With an increasing degree of partial crystallization, the corrosion resistance becomes progressively degraded. The passive current reveals that the fully amorphous metallic glasses can form a more protective and denser passive film on the metallic glass surface. The formation of reactive nanocrystalline phases in the amorphous matrix would reduce the bio-corrosion resistance.     

Structural investigation of amorphous iron-nickel-boron alloys

Accurate X-ray diffraction investigation has been made of ten amorphous alloys having the compositions (Fe_0.6Ni_0.4)_100–x B _x with x=14 to 24 and (Fe_100–y Ni _y )₈₀B₂₀ with y=30 to 70 which were obtained by rapid quenching from the melt. Using the common Fourier analysis, the radial distribution function was calculated from which the distance and its number of the near neighbour atoms were derived. The present results indicate that the atomic distribution of metallic glasses with low boron content differs slightly from that observed previously for a number of metallic glasses of transition metalmetalloid type. The compositional effect, in particular the boron concentration effect, on the structure and characteristic structural features of amorphous Fe-Ni-B alloy glasses is discussed together with the mean atomic volume and the partial atomic volume of metalloid elements using the measured density data.     

Preparation and properties of iron-boron metallic glass ribbons melt spun in air

The preparation of metallic glass ribbons by melt spinning is a simple technique; however, a researcher often faces many problems when undertaking the preparation of such ribbons. The difficulties encountered are oxidation of the melt, choking of the nozzle by the solidified metal, formation of metal globules or ribbon fragments, oxidation of the ribbons, etc. These problems are particularly severe when working with high melting point alloys. This report describes certain experimental techniques used to overcome problems in preparation of metallic glass ribbons of iron-boron and other high melting point alloys. The ribbons thus produced have been characterized by transmission electron microscopy, mechanical tests and differential thermal analysis. The mechanical strength of the ribbon is comparable to the best recorded strength for ribbons of similar composition. Thedta data support the view that the formation of the phase Fe₂₃B₆ takes place upon crystallization of the eutectic alloy.