Bulk metallic glass formation in Cu–Zr–Ti ternary system

The formation of bulk metallic glasses (BMG) in the Cu-rich Cu–Zr–Ti ternary system is studied by using the ‘e/a-variant line criterion’. Three such lines, (Cu₉Zr₄)_1−xTi_x, (Cu_61.8Zr_38.2)_1−xTi_x and (Cu₅₆Zr₄₄)_1−xTi_x, are defined in the Cu–Zr–Ti system by linking three binary compositions Cu₉Zr₄, Cu_61.8Zr_38.2 and Cu₅₆Zr₄₄ to the third element Ti. The binary compositions Cu₉Zr₄, Cu_61.8Zr_38.2 and Cu₅₆Zr₄₄ correspond to specific Cu–Zr binary clusters. BMGs are obtained by copper mould suction casting method with Ti contents of 7.5–15 at.%, 7.5–12.5 at.% and 5–12 at.%, respectively along the (Cu₉Zr₄)_1−x Ti_x, (Cu_61.8Zr_38.2)_1−xTi_x and (Cu₅₆Zr₄₄)_1−xTi_x lines. The BMGs on each composition line manifest decreased thermal stabilities and glass forming abilities (GFAs) with increasing Ti contents. The maximum GFA appears at Cu₆₄Zr_28.5Ti_7.5, with characteristic thermal parameters of T_g = 736 K, T_x = 769 K, T_g/T_l = 0.627 and γ = 0.403, which are all superior to those reported for the known Cu₆₀Zr₃₀Ti₁₀ BMG.     

Isochronal crystallization kinetics of Cu60Zr20Ti20 bulk metallic glass

Isochronal crystallization kinetics of Cu₆₀Zr₂₀Ti₂₀ bulk metallic glass has been investigated by differential scanning calorimetry. By means of the Kissinger, Ozawa, Kempen, Matusita and Gao methods, average effective activation energies for the first and second crystallization reactions in Cu₆₀Zr₂₀Ti₂₀ are calculated to be about 375 ± 9 and 312 ± 11 kJ mol⁻¹, respectively, which are smaller than the values deduced from isothermal experiments. Meanwhile, average Avrami exponents, 3.0 ± 0.1 and 3.4 ± 0.2, for two crystallization reactions in isochronal anneals, differ from the value about 2.0 in isothermal anneals. The nonidentity of the Avrami exponents and effective activation energies may be contributed to different crystallization mechanisms and the nature of non-isokinetic between isochronal and isothermal experiments. The values of frequency factor k₀ for the first and second crystallization reactions of Cu₆₀Zr₂₀Ti₂₀ are (1.7 ± 0.3) × 10²⁴ and (7.0 ± 0.8) × 10¹⁸ s⁻¹, respectively, and the large value of k₀ has been discussed in terms of the atomic configuration and interaction.     

Determination of activation energies for nucleation and growth from isothermal differential scanning calorimetry data

Differential scanning calorimetry (DSC) is usually adopted to analyze solid-state phase transformation incorporating nucleation, growth and impingement. Then, for isothermal transformation, time-dependent Avrami exponent and overall effective activation energy can always be deduced using recipes, which are derived from an analytical phase transformation model. On this basis, a concise and reliable approach to determine time-independent activation energies for nucleation and growth is proposed. Numerical calculations have demonstrated that the new approach is sufficiently precise under different conditions of transformation (e.g. nucleation: mixed nucleation and Avrami nucleation; growth: interface-controlled growth and diffusion-controlled growth; impingement: randomly nuclei dispersed, anisotropic growth and non-random nuclei distributions). Application of the approach in crystallization of Zr₅₅Cu₃₀Al₁₀Ni₅, Zr₅₀Al₁₀Ni₄₀ and Cu₄₆Zr₄₅Al₇Y₂ bulk amorphous alloys as measured by isothermal DSC was performed.     

Crystallization processes in amorphous Zr54Cu46 alloy

The crystallization of amorphous Zr₅₄Cu₄₆ alloy was investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The experimental results show that an endothermic peak in DSC traces for amorphous Zr₅₄Cu₄₆ alloy exists at about 1006 K, indicating following eutectoid reaction occurs, namely, Cu₁₀Zr₇+CuZr₂↔CuZr in amorphous Zr₅₄Cu₄₆ alloy during heating. With increasing the heating rate, the glass transition temperature T_g and onset crystallization temperature T_x of amorphous Zr₅₄Cu₄₆ alloy increase in parallel, and the supercooled liquid region ΔT_x (=T_x−T_g) holds almost constant with an average value of 44 K. Both XRD and TEM results prove that Cu₁₀Zr₇ and CuZr₂ are main crystallization products for amorphous Zr₅₄Cu₄₆ alloy under continuous heating conditions. No CuZr phase is identified because of its small precipitation amount. Finally, the crystallization processes of amorphous Zr₅₄Cu₄₆ alloy were summarized.     

Glass formation and non-isothermal crystallization of Zr62.5Al12.1Cu7.95Ni17.45 bulk metallic glass

Glass forming ability (GFA) and non-isothermal crystallization kinetics of Zr_62.5Al_12.1Cu_7.95Ni_17.45 bulk metallic glass were investigated. Its critical dimension is up to 7.5 mm and its critical cooling rate is less than 40 K s⁻¹, indicating its better GFA. It manifests two crystallization procedures and the second crystallization peak is more sensitive to heating rate than the first crystallization peak. The glass transition and crystallization both have remarkable kinetics effects. The apparent activation energies derived from the Kissinger plots are 175.24 ± 27.59 KJ mol⁻¹ for glass transition E_g, 212.84 ± 15.84 KJ mol⁻¹ for onset crystallization E_x, 230.51 ± 23.85 KJ mol⁻¹ for the first crystallization peak E_p1 and 124.85 ± 15.15 KJ mol⁻¹ for the second crystallization peak E_p2.     

Pressure and heating rate dependence of the crystallization temperature for amorphous (Fe65Ni35)75P16B6Al3 and Ti50Be40Zr10

The crystallization temperature, T_x, was determined at constant heating rate, $\text{R =}\text{T}\text{?}\text{? 7}\text{K min}{}^{\mathrm{?1}}$, by monitoring the electrical resistance. Such experiments were carried out under pressures up to 2.5 GPa, and the resulting dT_x/dP was 15.9 K GPa^?1 for (Fe₆₅Ni₃₅)₇₅P₁₆B₆Al₃ and 8.7 K GPa^?1, 8.1 K GPa^?1 for the two crystallization processes in Ti₅₀Be₄₀Zr₁₀. The activation energies of crystallization under atmospheric pressure were obtained from measurements of T_x at rates from 0.05 K min^?1 ?55 K min^?1, analysed by plotting ln(T_x²R^?1) versus T_x^?1.     

Study of the local structure of CuZr amorphous alloys by exafs. Effect of a structural relaxation

A structural investigation of Cu_xZr_1?x amorphous alloys has been made using EXAFS (x = 0.33, 0.46, 0.60). The partial radial distribution functions of the first shell of neighbours were derived from the study of the Cu and Zr K absorption edges. The distribution of the CuCu pairs remains almost constant in the whole range of concentration while the distribution of the unlike atom pairs varies drastically, becoming more asymmetric with increasing Cu content. In the meantime, the chemical ordering increases.A study of structural relaxation has been done for the Cu₆₀Zr₄₀ and Cu₄₆Zr₅₄ glasses by DTA and EXAFS. An additional endothermic phenomenon appears at T_g on DTA curves after annealing. No drastic change was observed by EXAFS. A slight increase of the spectrum was however obtained on the Cu edge for Cu₆₀Zr₄₀.     

Precipitation of icosahedral quasicrystalline and crystalline approximant phases in Zr-Cu-(Co, Rh or Ir) metallic glasses

Zr₇₀Cu₃₀, Zr₇₀Cu₂₀Co₁₀, Zr₇₀Cu₂₀Rh₁₀ and Zr₇₀Cu₂₀Ir₁₀ glassy alloys were prepared by the single roller melt-spinning method and the crystallization process was studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy, with an emphasis on the initial stage. The Zr₇₀Cu₃₀ metallic glass crystallizes through the direct precipitation of the stable crystalline phase from the matrix. The addition of Co, Rh and Ir to the Zr₇₀Cu₃₀ metallic glass induces the precipitation of metastable phases prior to the formation of the stable ones. The metastable phases are a Ti₂Ni-type compound for Zr₇₀Cu₂₀Co₁₀, a mixture of the Ti₂Ni-type compound and an icosahedral quasicrystalline phase (I-phase) for Zr₇₀Cu₂₀Rh₁₀, and the I-phase for Zr₇₀Cu₂₀Ir₁₀ metallic glasses. The different effects of Co, Rh and Ir addition are explained based on their difference in atomic radius.     

Crystallization of amorphous Cu60Zr40 prepared by magnetron sputter deposition

The crystallization of amorphous Cu₆₀Zr₄₀ prepared by magnetron sputter deposition was studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. Calorimetric results were similar to those reported in the literature for liquid-quenched Cu₆₀Zr₄₀, including the manifestation of a glass transition. Crystallization above and below the glass transition temperature, T_g, occurred by nucleation and growth of the equilibrium phase, Cu₁₀Zr₇. This phase was characterized by convergent beam electron diffraction. With isothermal annealing below T_g, the time scale for crystallization indicated that the vapor-quenched alloy was kinetically more stable than the liquid-quenched alloy. This was interpreted as a difference in the quenched-in structures, produced by the different synthesis methods. During longer anneals, TEM analysis indicated that the structure was being contaminated by oxygen.     

Heat Capacity and Thermodynamic Properties of p'-Substituted p-n-Hexyloxybenzylideneaniline. I. p-n-Hexyloxybenzylideneamno-p'-Benzonitrile (HBAB)

Abstract

The heat capacity of the nematogenic liquid crystal, HBAB, has been measured between 15 K and 385 K by using an adiabatic calorimeter. The crystal-crystal phase transition has been discovered at 27 K below the crystal-nematic phase transition temperature. The transition temperatures, the enthalpies and the entropies of the three phase transitions have been determined: T ₁ = 306.98 K, ΔH _t = 5.11 kJ mol^?1, ΔS _t = 16.7 JK^?l; T _m = 334.05 K, ΔH _m = 23.77 kJ mol^?1, ΔS_m = 71.2 J K^?l mol^?1; and T _c = 375.10 K, ΔH _c = 1.75 kJ mol^?1, ΔS _c = 3.2 J K^?1 mol^?1, respectively. The thermodynamic functions of HBAB from 0 K to 385 K have been determined from the heat capacity data and the enthalpies of the transitions. Two crystal modifications, one yellow and granular form and the other white and needle-like form, have been obtained during the course of the preparation of the sample. It turned out that the yellow form was the stable crystal and the white the metastable modification. The crystal-crystal phase transition has been discussed as an onset of partial melting from the entropy consideration. In this connection the total entropies of the transitions, 91.1 J K^?1 mol^?1 has been proposed to be an important measure of melting.     

Etude par Calorimetrie,Diffraction des Rayons X et Diffusion Raman d'une Transition de Phase dans (C4 H4P) Mn (CO)3

Abstract

Heat capacity measurements (95-300K), X-ray diffraction (78-300K) and low frequency Raman spectroscopy (10-350K) have evidenced an order-disorder phase transition in phosphacymantrene, (C₄ H₄P) Mn (CO)₃. This transition has been characterized by a monoclinic ←→ triclinic structural change at about 110 K and by a pretransitional phenomenon. The measured transition enthalpy and entropy are 480 ± 10J.mil^?1 and 4.17 ± 0.08J.K^?1 mol^?1, at 115 K, respectively.

A complete assignment of the observed Raman bands in h₄ and d₄ derivatives is proposed. From the temperature dependence of frequencies, intensities and half-widths of some Raman bands we have discussed the order, the nature and the mechanism of the phase transition: intermolecular interactions appear to be mainly involved in the mechanism and an activation energy roughly equal to 2100 ± 840 J. mol^?1 has been determined.     

Effect of Ni-addition on the crystallization behavior and the oxidation resistance of Zr-based metallic glasses below the crystallization temperature

The crystallization behavior of Zr_65.0Al_7.5Ni_10.0Cu_17.5 metallic glasses by addition of Ni with 753 K annealing treatment and its effect on the oxidation resistance around the supercooled liquid region at 663 K were studied. By annealing at 753 K, the nanocrystalline phase of bct-Zr₂Cu precipitates was observed in the Zr_65.0Al_7.5Cu_27.5 specimen, while microstructures consisting of finer nanocrystalline bct-Zr₂Cu, fcc-Zr₂Ni and Zr₆Al₂Ni formed in the Zr_65.0Al_7.5Ni_10.0Cu_17.5 specimen. The oxidation resistance of the melt-spun Zr_65.0Al_7.5Ni_10.0Cu_17.5 specimen was improved by addition of Ni, which is evidenced by less mass gain and thin oxide scale. The microstructural refinement by the formation of numerous nanocrystalline phases of bct-Zr₂Cu, fcc-Zr₂Ni and Zr₆Al₂Ni from the matrix resulted in an improvement of the oxidation resistance, whereas a relative coarse nanocrystalline phase consisting of bct-Zr₂Cu exhibited fast oxidation along grain boundaries. Although the oxide species for both specimens were composed of a large amount of CuO/Cu₂O, some tetragonal and monoclinic-ZrO₂ as well as a minor amount of the oxide state of Cu³⁺, the amount of oxides especially for ZrO₂ in the Zr_65.0Al_7.5Ni_10.0Cu_17.5 specimen was lower, which was probably due to suppressed oxygen diffusion in ZrO₂.     

Unusual Glassy Smectic-G Liquid Crystal: Heat Capacity of N-p-n-Pentyloxybenzylidene-p'-n-butylaniline between 11 and 393 K

Abstract

The heat capacities of the title compound (C₃H₁₁,O—C₆H₄,- CH=N—C₆H₄,—C₄H₉, abbreviation 5O ? 4) with a purity of 99.92 mole percent have been measured with an adiabatic-type calorimeter between 11 and 393 K. The transition temperature and the enthalpy and entropy of phase transition for stable crystal → S_G, S_G → N and N → isotropic liquid were T _c = 299.69 K/ΔH = 22.68 kJ mol^?1/ΔS = 75.70 JK^?1 mol^?1, 325.72/7.11/21.79 and 342.48/1.78/5.22, respectively. The crystal which melts at 285.5 K is a metastable modification. The S_A phase hitherto reported in between S_G and N does not exist. The glassy So state was realized by rapid cooling of the specimen from the So phase. The molar enthalpy of the glassy S_G state at 0 K was by (10.1±0.1) kJ mol^?1 higher than that of the stable crystalline state and the residual entropy of the glassy state was (9.40±0.83) JK^?1 mol^?1. The relaxational heat-capacity anomaly was observed from as low as 100 K and double glass transition phenomenon occurred around 200 K; a quite unusual phenomenon which has never been observed for the glassy states of nematic and cholesteric liquid crystals. The present results give a fair evidence that the unusual glass transition phenomenon previously found for the S_G state of 6O?4 (a homologous compound) is not exceptional at all but common to the smectic glasses; at least common to the glassy S_G states. Two possible origins responsible for the double glass transitions have been discussed.     

The effect of structural relaxation on the local structure of Cu40Zr60 amorphous alloys

Structural relaxation phenomena associated with heat treatments near the glass transition temperature range were investigated in liquid-quenched amorphous Cu₄₀Zr₆₀ alloys by means of differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and EXAFS. A kinetic study was performed by DSC in order to determine the evolution of the configurational enthalpy ($\text{3 H}{}_{\mathrm{\sigma }}$) against temperature (upon continuous heating or during isothermal annealing treatments) and to define the heat treatment suitable to obtain highly relaxed samples.SAXS results show that the structure of the relaxed samples remains homogeneous at the intermediate range of order up to at least 100 Å, whatever be the previous heat treatment. EXAFS detects a slight change in the local structure only for the most highly relaxed samples; this change could be interpreted by a variation of 0.5 atom in the coordination numbers (probably of the ZrZr pairs) or by a change of the disorder parameter of about 0.01 Å.No phase separation is detected in the relaxed amorphous Cu₄₀Zr₆₀ specimens.     

Fabrication and characterization of metallic glasses with a specific microstructure for micro-electro-mechanical system applications

Metallic glass microstructures with high aspect ratios for micro-electro-mechanical system applications have been fabricated by micro-electro-discharge machining and selective electrochemical dissolution methods. Micro-holes and three-dimensional microstructures machined on the La₆₂Al₁₄Ni₁₂Cu₁₂, Zr₅₅Al₁₀Ni₅Cu₃₀ and Cu₄₆Zr₄₄Al₇Y₃ bulk metallic glasses by micro-electro-discharge machining are evaluated by using X-ray diffraction, scanning electron microscopy, and nanoindentation. The experimental results demonstrate that the machined samples kept their amorphous structure without devitrification, and their machining characteristics are related to the thermo-physical properties of the alloys and the electrode diameters. Porous, single-pore and thin-walled Zr-based metallic glass tubes with micro-pore structures can be prepared by selective electrochemical dissolution method. The high aspect ratio microstructures fabricated by the two methods have the potential applications as micro-nozzles, polymer micro-injection molding tools, micro-channels or micro-flow meters in micro-electro-mechanical system devices.     

Low frequency Raman scattering in chalcogenide glasses

Low frequency Raman spectra of chalcogenide glasses are analyzed in terms of matrix element effects and modes of a layered structure. The spectra of GeSe₂ at low temperature shows no peaks which can be assigned to layer modes. The reduced spectra indicates that the density of states exhibits nearly ω² dependence for ω < 60 cm^?1, and the coupling constant approaches ω² dependence at frequencies less than 20 cm^?1.     

Crystallization kinetics of the Zr61Al7.5Cu17.5Ni10Si4 alloy using isothermal DSC and TEM observation

The crystallization behavior and microstructure development of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During isothermal annealing of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy at 703 K, Zr₂Cu crystals with an average size of about 5 nm were first observed during the early stages (30% crystallization) of crystallization by TEM. The Zr₂Cu crystal size increased with annealing time and attained an average size of 20 nm corresponding to the stage of 80% crystallization. In addition, the change in particle size with increasing annealing time exhibited a linear relationship between grain growth time and the cube of the particle size for the Zr₂Cu type crystalline phase. This indicates that the crystal growth of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy belongs to a thermal activated process of the Arrhenius type. The activation energy for the grain growth of Zr₂Cu is 155 ± 20 kJ/mol in the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ amorphous alloy. The lower activation energy for grain growth in compared to that for crystallization in Zr₆₅Cu₃₅ 440 kJ/mol crystal corresponds to the rearrangement of smaller atoms in the metallic glass, Al or Si (compare to Zr).     

Monotonic and jumpwise deformation of bulk amorphous Zr<Subscript>46.8</Subscript>Ti<Subscript>8</Subscript>Cu<Subscript>7.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>27.5</Subscript> alloy in nanoindentation

The study is aimed at the establishment of regions of stable (monotonic) and unstable (jumpwise) plastic flow in bulk amorphous Zr_46.8Ti₈Cu_7.5Ni₁₀Be_27.5 alloy under the conditions of local deformation. The characteristics of the jumpwise plastic flow in bulk amorphous Zr_46.8Ti₈Cu_7.5Ni₁₀Be_27.5 alloy are studied by the method of continuous nanoindentation (depth-sensing testing) in the range of strain rates \(\dot \varepsilon \) from 10^?2 to 10⁴ s^?1. The boundaries between the regions of homogeneous and localized plastic strain are established and the fractions of monotonic and jumpwise plastic strain under the indenter are determined.     

Potentiodynamic polarization studies on amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr65Cu17.5Ni10Al7.5, Zr67Ni33 and Ti60Ni40 in aqueous HNO3 solutions

Potentiodynamic polarization studies were carried out on virgin specimens of Zr-based bulk amorphous alloys Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 and Zr₆₅Cu_17.5Ni₁₀Al_7.5, and conventional-type binary amorphous alloys Zr₆₇Ni₃₃ and Ti₆₀Ni₄₀ in solutions of 0.2 M, 0.5 M and 1.0 M HNO₃ at room temperature. The values of the corrosion current density (I_corr) for the bulk amorphous alloy Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 were found to be comparable with those of Zr₆₅Cu_17.5Ni₁₀Al_7.5 in 0.2 M and 0.5 M HNO₃, but the value of I_corr for the former was almost three times more than that of the latter in 1.0 M HNO₃. In the case of conventional binary amorphous alloys, Ti₆₀Ni₄₀ showed lower value of I_corr as compared to Zr₆₇Ni₃₃ in 0.5 M and 1.0 M HNO₃ and a comparable value of I_corr in 0.2 M HNO₃. In general, the binary Ti₆₀Ni₄₀ displayed the best corrosion resistance among all the alloys in all the cases and the corrosion current density (I_corr) for all the alloys was found to increase with the increasing concentration of nitric acid. It is noticed that the bulk amorphous alloys do not possess superior corrosion resistance as compared to conventional binary amorphous alloys in aqueous HNO₃ solutions. The observed differences in their corrosion behavior are attributed to different alloy constituents and composition of the alloys investigated.     

Growth and spectral properties of Er:Gd2SiO5 crystal

Er³⁺-doped Gd₂SiO₅ (Er:GSO) single crystal with dimensions of ? 35×40 mm³ has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd–Ofelt theory, and the intensity parameters Ω₂, Ω₄ and Ω₆ are obtained to be 6.168×10^?20, 1.878×10^?20, and 1.255×10^?20 cm², respectively. The emission cross-section has been calculated by Fuechtbauer–Ladenbury formula.