Formation and crystallization of ZrCuTi metallic glasses

We report the suction casting of Zr₆₅Cu₂₇Ti₈ bulk metallic glasses with diameters up to 1?mm. While the substitution of Ti for Cu increases the glass forming ability significantly, the onset crystallization temperature and the width of the supercooled liquid region decrease. This decrease is due to the appearance of an icosahedral quasicrystal phase, which crystallises from the glass at a lower temperature than the Zr₂Cu devitrification product in the Zr₆₅Cu₃₅ glasses. Based on the results of recent structural studies of undercooled Ti/Zr-based alloys, this likely reflects the formation of icosahedral order in the undercooled liquid, which increases the nucleation barrier for the Zr₂Cu phase during the quench, making glass formation easier.     

Effect of Fe on the glass-forming ability,structure and devitrification behavior of Zr–Cu–Al bulk glass-forming alloys

We report on the glass-forming ability and devitrification behavior of Zr₆₀Cu₃₀Al₁₀, Zr₆₀Cu₂₅Al₁₀Fe₅ and Zr_62.5Cu_22.5Al₁₀Fe₅ bulk glass-forming alloys on heating. The effect of Fe addition on the structure of Zr–Al–Cu alloys is also discussed. Crystallization kinetics and structural changes in the glassy alloys were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The results indicate that good glass-formers, such as Zr_62.5Cu_22.5Al₁₀Fe₅, are located somewhat beyond the equilibrium eutectic point. Possible phase separation in the supercooled liquid on heating and electron beam-induced in situ crystallization are observed and discussed.     

非晶态Cu56Zr44合金的结构及其等温退火晶化过程的研究

利用X射线衍射技术、差示扫描量热分析技术和透射电子显微镜研究了非晶态Cu₅₆Zr₄₄合金的结构及其等温退火条件下的晶化过程.实验结果表明,非晶态Cu₅₆Zr₄₄合金在室温下的短程结构类似于硬球无规密堆积分布.在703K过冷液相区内等温退火时发现,当退火时间为3min时,晶化产物主要为Cu₈Zr₃相;当退火时间为6min时,Cu₈Zr₃关键词： 非晶态 56Zr₄₄合金')" href="#">Cu₅₆Zr₄₄合金 结构 等温退火     

Structural relaxation and viscous flow in amorphous ZrAlCu

The ternary metallic glass Zr₆₅Al_7.5Cu_27.5 offers a wide temperature range between glass transition temperature and crystallization temperature and is therefore well suited for investigation of the glass transition and the state of the super cooled liquid. The non-linear viscosity change caused by structural relaxation has been measured caused by structural relaxation has been measured using tensile creep experiments on as quenched samples. The increase of viscosity can be described by bimolecular annihilation kinetics of flow defects. The Arrhenius plot of equilibrium viscosity shows a kink at a temperature which seems to be the glass transition temperature. The activation energies of viscous flow below and above that glass transition temperature differ by nearly a factor two. Different microscopic processes responsible for viscous flow in the two regimes of temperature are therefore conceivable. This view is also encouraged by Dynamic-Mechanical-Analysis on relaxed samples, a method to examine the viscoelastic behaviour of glassy materials on different time scales and by recent diffusion measurements on a different system.     

Structural relaxation and viscous flow in amorphous ZrAlCu

The ternary metallic glass Zr₆₅Al_7.5Cu_27.5 offers a wide temperature range between glass transition temperature and crystallization temperature and is therefore well suited for investigation of the glass transition and the state of the super cooled liquid. The non-linear viscosity change caused by structural relaxation has been measured caused by structural relaxation has been measured using tensile creep experiments on as quenched samples. The increase of viscosity can be described by bimolecular annihilation kinetics of flow defects. The Arrhenius plot of equilibrium viscosity shows a kink at a temperature which seems to be the glass transition temperature. The activation energies of viscous flow below and above that glass transition temperature differ by nearly a factor two. Different microscopic processes responsible for viscous flow in the two regimes of temperature are therefore conceivable. This view is also encouraged by Dynamic-Mechanical-Analysis on relaxed samples, a method to examine the viscoelastic behaviour of glassy materials on different time scales and by recent diffusion measurements on a different system.     

Thermal expansion of amorphous Zr Al Cu Ni in the vicinity of the glass transition

The thermal expansion of non-crystalline Zr₆₅Al_7.5Cu_17.5 Ni₁₀ has been studied in the range of the glass transition and in the undercooled liquid using a dilatometric device. The measuring technique used permits reliable experimental results up to 40 K above the glass transition temperature. The linear thermal expansion coefficient obtained is almost constant in the glassy state with a value of . It discontinuously increases at the glass transition temperature yielding a value of in the undercooled liquid. The results are compared with specific heat measurements of the amorphous material in this temperature range and are interpreted in the framework of a cluster model. Received 5 March 1999 and received in final form 11 June 1999     

AgxCu50-xZr50非晶态合金及其晶化

采用高频熔炼后的真空单辊急冷技术制备了Ag_xCu_50-xZr₅₀金属玻璃,发现在x<12的范围内都可得到完全的非晶态。测量了x=2,4,6和10的Ag_xCu_50-xZr₅₀金属玻璃的玻璃转变温度和晶化温度,并采用Kissinger方法测定了晶化激活能E_a。发现在金属玻璃Ag_xCu_50-xZr_{50关键词：}     

Crystallization behaviour in a new multicomponent Ti16.6Zr16.6Hf16.6Ni20Cu20Al10 metallic glass developed by the equiatomic substitution technique

A new amorphous Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ alloy has been developed using the novel equiatomic substitution technique. Melt spinning Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ forms an amorphous phase with a large supercooled liquid region, ΔT=70°C. After isothermal annealing within the supercooled liquid region for 3 h at 470°C, the amorphous alloy crystallizes to form a fine-scale distribution of 2–5 nm nanocrystals, and the supercooled liquid region increases to ΔT=108°C. Atomic-scale compositional analysis of this partially crystalline material using a three-dimensional atom probe (3DAP) is unable to detect any compositional difference between the nanocrystals and the remaining amorphous phase. After annealing for 1 hr at 620°C, the amorphous alloy crystallizes to form 20–50nm equiaxed grains of a hexagonal-type C14 Laves phase with lattice parameters a = 5.2Å and c = 9.0 Å. 3DAP analysis shows that this Laves phase has a composition very close to that of the initial amorphous phase, suggesting that the alloy crystallizes via a polymorphic rather than a primary crystallization mechanism, despite the complexity of the alloy composition.     

Effects of niobium on thermal stability and corrosion behavior of glassy Cu-Zr-Al-Nb alloys

The corrosion behavior of Cu_95−xZr_xAl₅ (x=40, 42.5 and 45 at.%) in 1 N HCl, 3 mass% NaCl and 1 N H₂SO₄ solutions was studied. As Zr content increases, the corrosion resistance is slightly enhanced. In order to improve the corrosion resistance of the Cu-Zr-Al glassy alloy, Nb was selected to substitute Cu. Although the supercooled liquid region ΔT_x of the Cu-Zr-Al glassy alloys decreases with increasing Nb content, the alloys still retain high glass-forming ability and bulk glassy samples with 1.5 mm diameter can be obtained when up to 5 at.% Nb was added. It is found that the addition of Nb results in improvement of the corrosion resistance of the glassy Cu-Zr-Al alloys.     

Increasing Superplasticity and Strong Dynamic Behaviour of Zr--Cu--Ni--Al Bulk Metallic Glass

The plasticity and the dynamic fragility of bulk metallic glass of a Zr62 CuxsNiloAllo alloy are studied by three- point beam bending methods. We find that the alloy behaves super plastic not only at room temperature, but also at high temperatures. More importantly, it is found that the superplasticity increases with increasing temperature. In addition, the dynamic fragility parameter m for the supercooled liquid of this alloy is measured to be 34.87 and the supercooled liquid of Zr62 CuxsNixoAlxo alloy behaves as a strong liquid.     

Devitrification behaviour of Cu-Zr-Ti-Pd bulk glassy alloys

The glass formation, mechanical properties and devitrification of the Cu-Zr-Ti-Pd glassy alloys are studied. The formation of a nanoscale icosahedral phase in Cu-based alloys is observed. The nanoscale particles with icosahedral symmetry are primarily formed in the Cu-Zr-Ti-Pd glassy alloys in the initial stage of the devitrification process. As the icosahedral phase is metastable it transforms to the equilibrium oC68 (Cu, Pd)₁₀(Zr, Ti)₇ single phase or its mixture with the oP44 Cu₈Zr₃ phase, depending upon the alloy composition, through an intermediate crystalline compound. The structure changes on heating were studied by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and isothermal calorimetry.     

PAC Studies on Zr-Based Intermetallic Compounds

The Zr₂Al, Zr₃Al₂ and Zr₆NiAl₂ intermetallic compounds were characterized by means of time differential perturbed angular correlation (TDPAC) and X-ray diffraction. Our interest in these Zr(Hf) aluminides comes from crystallization studies of Zr(Hf)-based bulk metallic glasses which have a wide supercooled liquid region.     

Formation,thermal stability and mechanical properties of Ti<Subscript>42.5</Subscript>Zr<Subscript>7.5</Subscript>Cu<Subscript>40</Subscript>Ni<Subscript>5</Subscript>Sn<Subscript>5</Subscript> bulk metallic glass

Ti_42.5Zr_7.5Cu₄₀Ni₅Sn₅ bulk metallic glass with a critical diameter of 4 mm was fabricated by the conventional copper mould casting method. The supercooled liquid region ΔT _x, reduced glass transition temperature T _rg, γ parameter, and δ parameter of the alloy were measured to be 63.9 K, 0.561, 0.393, and 1.400, respectively, implying that the alloy has an excellent glass-forming ability. The bulk metallic glass exhibits high compressive fracture strength of 2162 MPa with distinct plastic strain of 0.9%. The fracture surface consists mainly of vein-like patterns, typical of bulk glassy alloys. Supported by the Program for New Century Excellent Talents in University of China and the National Natural Science Foundation of China (NSFC)(Grant No. 50771040)     

Recovery of the deformability of the aged metallic glass Pd40Cu30Ni10P20 under conditions of testing for shear stress relaxation

It has been established that quenching from the supercooled liquid state of the aged metallic glass Pd₄₀Cu₃₀Ni₁₀P₂₀ causes the recovery of its deformability, which manifests itself in measurements of the torque relaxation under conditions of isochronous heating.     

Formation and structure of nanocrystals in bulk Zr<Subscript>50</Subscript>Ti<Subscript>16</Subscript>Cu<Subscript>15</Subscript>Ni<Subscript>19</Subscript> metallic glass

The possible formation of a nanocrystalline structure in controlled crystallization of a bulk Zr₅₀Ti₁₆Cu₁₅Ni₁₉ amorphous alloy has been studied using differential scanning calorimetry, transmission and high-resolution electron microscopy, and x-ray diffraction. It was established that crystallization of the alloy at temperatures above the glass formation point occurs in two stages and brings about the formation of a nanocrystalline structure consisting of three phases. Local spectral x-ray analysis identified the composition and structure of the phases formed.     

Observation and analysis of a glass transition in amorphous frozen solutions of iron-II chloride

This paper deals with Mössbauer investigations, X-ray diffraction studies and differential calorimetric measurements of the amorphous state of frozen solutions of FeCl₂ in water. This glassy state persists from at least ?180 °C until ?90 °C. All three experimental methods reveal the existence of a glass transition at ?110 °C from an amorphous state to a supercooled liquid. It is shown that for such transitions important conclusions can be drawn from a comparison between the Mössbauer and X-ray diffraction Debye-Waller factor respectively by determining the transmitted Mössbauer intensity far off resonance. Out of the analysis we conclude that the glassy state of quenched ice is due to the hexaquo complexes as implanted impurities which prevail their surrounding from a regular crystallisation. These impurities are also responsible for the glass transition into a supercooled liquid state by releasing new degrees of freedom as e.g. hindered rotational modes.     

Correlation between flow characteristics and interfacial friction behaviour of a Zr-based metallic glass during micro-extrusion

The interfacial friction behaviour of Zr₃₅Ti₃₀Be_26.75Cu_8.25 metallic glass during micro-extrusion was investigated at various strain rates and temperatures in the supercooled liquid region. A friction mechanism map that distributes adhesion regime, furrow regime and mechanical engagement regime was constructed. These regimes respectively correspond to Newtonian flow, non-Newtonian flow and inhomogeneous flow by comparing with the typical deformation map. The correlation between flow characteristics and interfacial friction behaviour is well analysed by combining the viscosity theory with the finite-element simulations.     

A STUDY OF THE CRYSTALLIZATION OF AMORPHOUS Cu60Zr40 ALLOY

The crystallization of the amorphous Cu₆₀Zr₄₀ alloy has been studied by differential scanning calorimetry (DSC), scanning Auger microprobe (SAM) and transmission electron microscopy (TEM). The DSC trace showed that the sample exhibited a glass transition at 750 K and a strong exothermic effect beginning from 782 K. An enrichment of the element Zr and significant oxygen contamination in a zone near the surface to a depth of about 10 nm were revealed by SAM in the analysis of surface competition and depth profiles of the Cu₆₀Zr₄₀ sample. Also, the change of concentration ratio of Ca to Zr in amorphous matrix at the clean Cu₆₀Zr₄₀ surface as a function of annealing temperature was examined in detail, and it was found that the concentration of Zr at the surface is slightly higher than that in the bulk until 780K and that the concentration ratio of Cu to Zr in matrix has an abrupt increase in the temperature range of 780-800K. The observations by high resolution TEM revealed the appearance of cluster-like regions of approximately 1.5-2.0 nm in size just before crystallization and they distributed randomly throughout the sample. This phenomenon is analogous to the results obtained using field ion microscopy (FIM) by the present authors. The microstructural changes of the sample daring heating show the gradual crystallization of the amorphous matrix.     

Deformation behavior of Zr-based bulk metallic glass and composite in the supercooled liquid region

A Zr-based bulk metallic glass (BMG) with a composition of (Zr₇₅Cu₂₅)_78.5Ta₄Ni₁₀Al_7.5 and a bulk metallic glass matrix composite (BMGC) with a composition of (Zr₇₅Cu₂₅)_74.5Ta₈Ni₁₀Al_7.5 have been prepared by copper-mold casting. The compressive deformation behavior of the BMG and BMGC was investigated in the supercooled region at different temperatures and various strain rates ranging from 8×10⁻⁴ s⁻¹ to 8×10⁻² s⁻¹. It was found that both the strain rate and test temperature significantly affect the deformation behavior of the two alloys. The deformation follows Newtonian flow at low strain rates but non-Newtonian flow at high strain rates. The deformation mechanism for the two kinds of alloys was discussed in terms of the transition state theory. Supported by the National Natural Science Foundation of China (grant Nos. 50471060 and 50635020)     

Effect of TiO2 addition on the crystallization of quenched glasses in the SiO2–Al2O3–ZrO2 system

The glass formation in the SiO₂-rich region of the ternary oxide system Al₂O₃–ZrO₂–SiO₂ with MgO, CaO, and TiO₂ as melting aids was analyzed. The crystallization of glasses with different content of TiO₂ and phase evolution with the temperature was studied by X-ray diffraction, infrared, laser Raman spectroscopy and transmission electron microscopy. The use of TiO₂ favored formation and crystallization of the glasses due to the decrease of the viscosity of melts and acting as a nucleating agent. The crystalline phase of t-ZrO₂ was developed at temperatures as low as 880°C whereas in as prepared specimens without TiO₂ its presence was not detected. For the specimens with TiO₂, t-ZrO₂ and mullite were the principal phases at 1000°C. TiO₂ addition did not change the crystallization sequence but decreased the formation temperature of the crystalline phases. Most of Ti⁴⁺ ions entered into t-ZrO₂ and only a small portion in mullite, but the surplus was detected in ZrTiO₄.