Calorimetric measurement of structural relaxation in chalcogenide and metallic glasses

Some special characteristics of the structural relaxation (SR) in chalcogenide and metallic glasses are presented and the current theories dealing with the physical nature of the SR are recalled. The type of experiments used to measure SR by differential scanning calorimetry are reviewed and some rules to be taken into account when measuring calorimetrically the SR are stressed.

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Zusammenfassung Es werden einige spezielle Charakteristiken der Strukturrelaxation (SR) von Chalkogeniden und Metallgläsern vorgestellt und die gegenwärtigen Theorien über die physikalische Natur der SR zitiert. Die Art von Experimenten zur Messung von SR mittels DSC wurden kritisch besprochen und einige inbetrachtzuziehende Regeln für die kalorimetrische Bestimmung der SR hervorgehoben.

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This work was supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT) project MAT88-0439.     

Enthalpic study of structural relaxation and crystallization in some metallic glasses

Structural relaxation and crystallization have been studied in the metallic glasses Fe₃₉Ni₃₆Cr₅P₁₄B₆, Fe₈₁B₁₉, Fe₇₆Co₄B₂₀ and Fe₇₅V₄B₂₁ by DSC.Different coefficients of calibration of the DSC cell were determined for the two phenomena.The enthalpy of relaxation increases with increasing quenching rate for Fe₃₉Ni₃₆Cr₅P₁₄B₆ and with increasing number of alloy components for Fe-B-based glasses. In the latter systems. relaxation is never completed before the start of crystallization.The enthalpy of crystallization does not depend on the quenching rate for Fe₃₉Ni₃₆Cr₅P₁₄B₆, and does not change during annealing within the relaxation field before crystallization.

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Zusammenfassung Strukturelle Relaxation und Kristallisation der metallischen Gläser Fe₃₉Ni₃₆Cr₅P₁₄B₆, Fe₈₁B₁₉, Fe₇₆Co₄B₂₀ und Fe₇₅V₄B₂₁ wurden mittels DSC untersucht. Verschiedene Koeffizienten zur Kalibrierung der DSC-Zelle wurden für die zwei Phänomene bestimmt. Die Entalpie der Relaxation steigt mit zunehmender Abkühlungsgeschwindigkeit im Falle von Fe₃₉Ni₃₆Cr₅P₁₄B₆ und mit zunehmender Zahl der Legierungskomponenten im Falle der Fe-B-Gläser an. In den letztgenannten Systemen ist die Relaxation niemals vor Beginn der Kristallisation beendet. Die Entalpie der Kristallisation ist im Falle von Fe₃₉Ni₃₆Cr₅P₁₄B₆ unabhängig von der Abkühlungsgeschwindigkeit und ändert sich auch nicht beim Tempern im Relaxationsgebiet vor der Kristallisation.

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Fe₃₉Ni₃₆Cr₅P₁₄B₆, Fe₈₁B₁₉, Fe₇₆Co₄B₂₀ Fe₇₅V₄B₂₁. . Fe₃₉Ni₃₆Cr₅P₁₄B₆ , Fe-B — . . Fe₃₉Ni₃₆Cr₅P₁₄B₆ .

     

Flow and fracture in Zr-based bulk metallic glasses

Effects of atomic-scale open-volume regions in metallic glass structure on the flow and fracture behavior of a Zr-Ti-Ni-Cu-Be bulk metallic glass were examined. Metallic glass structure was changed by annealing at 300 °C. Studies of relaxation time scales showed that atomic arrangement processes for viscous flow were significantly retarded with annealing. Plane strain fracture toughness was significantly decreased and fatigue crack-growth rates were dramatically increased, indicating degradation of resistance to crack extension as a result of annealing. Fracture morphology completely changed from vein patterns to cleavage-like features with little evidence of plasticity with annealing. The positron lifetime and Doppler broadening experiments revealed decreased open-volume regions as a result of annealing. The observed variation of the viscoelastic relaxation time scales with annealing was well described in terms of the anneal-out of open-volume regions. The current metallic glass was found to posses a low fractional free volume of the order of 0.1% indicating dense-packed structure which contributes to the excellent glass forming ability. The loss of stress relief ability by retarded crack tip viscous flow as a result of the anneal-out of open-volume regions is believed to contribute to subsequent embrittlement.     

Evaluation of the elastic properties of bulk metallic glasses

The development of bulk metallic glasses as a prominent class of functional and structural materials has attracted considerable interest in the last years. One of the fundamental physical quantities necessary to describe the mechanical properties of the materials is the bulk modulus. In the present article, a simple method to estimate the bulk modulus and its pressure derivative is proposed. It is shown that these quantities can be estimated from the values of the constituent elements and their compositions. Comparison with measured data shows good agreement. The physical background of the method is discussed based on the jellium model of metals.     

On non-isothermal kinetics of two Cu-based bulk metallic glasses

In this paper, two Cu-based bulk metallic glasses, Cu₅₅Zr₃₇Ti₈ and Cu₆₁Zr₃₄Ti₅, have been evaluated in thermodynamics and kinetics. The activation energies with the constant values were generalized by different theoretical models. The E _x of Cu₅₅Zr₃₇Ti₈ and Cu₆₁Zr₃₄Ti₅ are 319 ± 12 and 359 ± 12 kJ mol^?1, respectively, implying that the as-cast alloys have a good stability in thermodynamics. On the other hand, variable activation energies were also determined using Kissinger–Akahira–Sunose method, Ozawa–Flynn–Wall method, and Friedman’s method. The results showed that the Ea(x) at the beginning of the crystallization are higher than that at the end of the crystallization in the first exothermic peak. By introducing the local Avrami exponent, n(x), the growth and nucleation mechanisms were discussed. Furthermore, the effects of different activation energies on local Avrami exponent were also given a discussion.     

Spatial scale-dependent tracer diffusion in bulk polycarbonate studied by holographic relaxation

The diffusion of a photochromic dye tracer in polycarbonate was studied by a holographic relaxation technique (forced Rayleigh scattering) at temperatures close to the glass transition temperature. By varying the holographic grating period the results could be interpreted via the spatial scale dependence of apparent diffusion coefficients within a two-state diffusion model. This indicates inhomogeneities on the scale of a few micrometers in the polymer glass.     

Using fluctuation microscopy to characterize structural order in metallic glasses.

We have used fluctuation microscopy to reveal the presence of structural order on length scales of 1-2 nm in metallic glasses. We compare results of fluctuation microscopy measurements with high resolution transmission electron microscopy and electron diffraction observations on a series of metallic glass samples with differing degrees of structural order. The agreement between the fluctuation microscopy results and those of the other techniques is good. In particular, we show that the technique used to make thin specimens for electron microscopy affects the structure of the metallic glass, with ion thinning inducing more structural order than electro-polishing. We also show that relatively minor changes in the composition of the alloy can have a significant effect on the medium-range order; this increased order is correlated with changes in mechanical behavior.     

A new correlation between the characteristics temperature and glass-forming ability for bulk metallic glasses

Journal of Thermal Analysis and Calorimetry - A new criterion or parameter χ given by $$\left( {\frac{{T_{\text{x}} - T_{\text{g}} }}{{T_{\text{l}} - T_{\text{x}} }}} \right) \times \left(...     

Unified approach to ion transport and structural relaxation in amorphous polymers and glasses

Kinetic data for structural relaxation in silver iodomolybdates at the glass transition temperature (Tg) are obtained by high-pressure differential scanning calorimetry (HP-DSC) and are compared with activation energies (EA) and volumes (VA) obtained earlier from conductivities below Tg. The results are fitted to an empirical equation, EA = MVA, and displayed in the form of a master plot of EA versus VA, an approach previously applied to strongly coupled systems, including polymer electrolytes and molten salts above their glass transition temperatures. The parameter M emerges as a localized modulus, expressive of interatomic forces within the medium, linking together EA,sigma, VA,sigma and EA,s, VA,s, the "apparent" activation parameters for ionic conductivity and structural relaxation, respectively. The VA and EA values for ion transport are much smaller than the corresponding values for structural relaxation. However, remarkably close agreement emerges between the "process parameters", Ms and Msigma, both close to 8 GPa, thus establishing a quantitative link between ion transport and structural relaxation in this highly decoupled system. A new EA versus VA master plot is constructed, which points the way to a unified approach to ion transport in polymers and glasses.     

Crystallization kinetics of metallic glasses

In this study, the temperature-heating rate diagram of the main crystallization process of two metallic glasses, Fe₇₄Ni_3.5Mo₃B₁₆Si_3.5 and Fe₄₁Ni₃₈Mo₃B_18, was obtained from one experimental differential scanning calorimetry (DSC) scan and the knowledge of their activation energy as determined by an isoconversional method. A good concordance was observed between the diagram curves obtained by calculation (isoconversional approach) and the experimental data, which verifies the reliability of the method and the validity of the kinetic approach in these alloys.     

Biocorrosion and biocompatibility of Zr–Cu–Fe–Al bulk metallic glasses

Owing to their unique chemo‐physical and structural characteristics, amorphous bulk metallic glasses (BMGs) are of great demand for fabrication of variety of advanced and innovative products including surgical and biomedical tools and devices. In this study, a series of Ni‐free Zr‐based BMGs in Zr–Cu–Fe–Al system are fabricated using copper‐mold casting technique, and their biocorrosion and biocompatibility are evaluated with respect to their corrosion behavior in the phosphate buffered saline (pH = 7.4) solution. Anodic polarization curves, scanning electron microscopy combined with energy‐dispersive X‐ray, and wettability analyses are conducted to characterize the surfaces of BMG samples. The biocompatibility of the BMG and control samples is studied by comparing cell–substrate interactions among different samples. It is found that Zr₆₀Cu₂₀Fe₁₀Al₁₀ displays a higher passive region compared with that of Zr₆₀Cu_22.5Fe_7.5Al₁₀, but both BMGs exhibit lower corrosion resistance compared with Ti–6Al–4V alloy. By addition of titanium to Zr–Cu–Fe–Al system (Zr₆₀Ti₆Cu₁₉Fe₅Al₁₀), a significant increase in the passive region of the polarization curve is detected. The cell culture experiments reveal that the number of attached and grown cells is significantly higher on the surface of the treated BMGs as compared with Ti–6Al–4V substrates and the culture plate as controls. There is no noticeable difference in cellular morphology among the BMG samples, and no cytotoxicity is detected. We speculate that the interaction of water molecules and matrix proteins with the surfaces of BMGs plays an important role in cell–substrate interactions and improved cell response. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigation of structural relaxation of Fe85B15 amorphous metallic alloy by thermomagnetization

Thermomagnetometry was used to determine the Curie temperature of Fe₈₅B₁₅ amorphous alloy. Measurements were made with a TGS-1 Perkin-Elmer thermobalance in a permanent magnetic field. Armosphous material with a thickness of 25 m was prepared by melt spinning.In the temperature region 300 to 800 K the sample is characterized by one Curie transformation in the amorphous matrix atT _c570 K. A broad region of primary crystallization of -Fe begins at approximately 660 K, followed closely by the rapid crystallization of Fe₃B phase with maximum atT _cr2 750 K. Amorphous material which is unstable due to quenching is relaxed by annealing. The structural relaxation causes ageing of the Curie temperature in the metallic glass.The observed phenomena might be explained in terms of certain changes in local atomic arrangement.

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Zusammenfassung Die thermomagnetometrische Methode wurde zur Bestimmung der Curie-Temperatur der amorphen Legierung Fe₈₅B₁₅ herangezogen. Die Messungen wurden mit einer Perkin-Elmer-Thermowaage des Typs TGS-1 unter Anwendung eines permanenten Magnetfeldes ausgeführt. Das 25 m dicke amorphe Material wurde nach dem Schmelzspinnverfahren dargestellt. Im Temperaturbereich von 300 bis 800 K ist für die Probe eine Curie-Transformation in der amorphen Matrix beiT _c570 K charakteristisch. Ein breiter Bereich der primÄren Kristallisation von -Fe beginnt bei etwa 660 K, dem sofort eine schnelle Kristallisation der Fe₃B-Phase mit maximaler Geschwindigkeit beiT _cr2 750 K folgt. Die durch Abschrecken eintretende InstabilitÄt des amorphen Materials wird durch Tempern aufgehoben. Die strukturelle Relaxation verursacht eine Alterung der Curie-Temperatur im metallischen Glas. Die beobachteten PhÄnomene können durch VerÄnderungen der lokalen Anordnung der Atome erklÄrt werden

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Fe₈₅B₁₅. -1 -, . 25 . 300–800 . -Fe 660 , Fe₃B T _cr2750 . , , . . .

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We wish to thank P. Duhaj for the preparation of glassy ribbons.     

Investigations of the solid state reaction process in mechanically alloyed Zr-Al-Cu-Ni bulk metallic glasses by analytical transmission electron microscopy

Starting with elemental powders, the progress of amorphization in mechanically alloyed Zr₆₅Al_7.5Cu_17.5Ni₁₀ has been investigated by x-ray diffractometry and transmission electron microscopy (TEM). Detailed investigations of the microstructural evolution during milling indicate that the amorphization proceeds by solid state reaction, similar to other well known binary or multicomponent systems.     

Thermal evolution of ferromagnetic metallic glasses

A traditional TG apparatus was modified by placing two permanent magnets producing a controlled magnetic field (TG(M): Magneto Thermogravimetry). This technique proved to be useful to study both structural relaxation and crystallisation of ferromagnetic metallic glasses. Results obtained for the amorphous alloys Fe₄₀Ni₄₀P₁₄B₆ and Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅, are reported in this paper. Structural relaxation can be evaluated by measuring changes in Curie temperature induced by thermal treatments. Crystallisation in TG(M) is detected through a change in the measured apparent mass (difference between the sample mass and magnetic force driving it upward). These results were confirmed by DSC analysis. Whether the obtained crystalline phase is ferromagnetic, it can be identified through its Curie temperature, measured by TG(M). In fact the value of 770°C measured as Curie temperature of crystallised Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅led to conclude that the only ferromagnetic crystalline phase is a-Fe. These hypothesis was confirmed by XRD analysis, showing that the first crystallisation yields to a-Fe nanocrystals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of structural factors on the reversible 1,5-diketone — Hydroxydihydropyran conversion

It is shown that -bicyclanones with five-membered rings have less of a tendency to undergo conversion to cyclohemiacetals than the analogous compounds with six-membered rings.Communication XXVIII from the series Reactions of 1,5-Diketones. See [1] for communication XXVII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1315–1319, October, 1977.     

Nuclear techniques characterization of short-range order in Zr-TM-Cu-Al-Ni (TM=Hf,Ti, Fe) bulk metallic glasses

In this paper an overview of recent and new perturbed angular correlation (PAC), Mössbauer (MS) and positron annihilation (PAS) experiments on Zr- and Hf-based bulk metallic glasses is presented. PAC results showed that all samples in their as-prepared amorphous state, irrespective of the preparation method used, are well described by a dense random packing of ions (DRP). Hf-based samples showed a greater electric field gradient (EFG) value than Zr-based ones for same composition. A general observation is that the relaxed amorphous and supercooled liquid has the same local arrangements than the initial amorphous state. The crystallization behaviour is not preparation-method dependant but composition and impurities have a major influence on it. Preliminary positron annihilation lifetime measurements on amorphous samples yielded one characteristic lifetime, with a value intermediate between those for the well-annealed and defected metallic constituents of the alloys. Mössbauer spectra of as-prepared amorphous alloys consist of a broad asymmetric doublet, originating from a distribution of electric field gradients characteristic for amorphous samples.     

Effects of crystals on the mechanical properties of Zr52.5Ti5Cu17.9Ni14.6Al10 bulk metallic glasses

In this paper the mechanical properties of fully amorphous and partially cystalline Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ alloys were investigated. The changes in hardness and ductiity caused by the presence of crystals in the amorphous matrix is presented.