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1.
L. Xia  S.K. Kwok  P. Yu 《Journal of Non》2011,357(5):1469-1472
In this work, a Zr50Cu48Al2 bulk metallic glass (BMG) with improved glass forming ability and mechanical properties was synthesized by adding a small amount of Al to a Zr-Cu binary glass-forming alloy. The as-cast Zr50Cu48Al2 glassy rod does not exhibit macroscopic failure under compression at room temperature indicating the excellent plasticity of the BMG. The deformation behavior of the BMG was studied intensively by examining the true stress-strain curve and the surface morphology of the post-deformation sample. The effect of minor Al addition on the mechanical properties including the fracture stress, the modulus, and the kinetic characteristics of the BMG was also investigated. The enhanced plasticity of the BMG is considered to be related to its reduced fragility parameter m value.  相似文献   

2.
G. Li  Y.C. Li  T. Xu  J. Liu  R.P. Liu 《Journal of Non》2009,355(9):521-524
The existence of special covalently bonded short-range ordering structures in a Mg65Cu25Tb10 bulk metallic glass (BMG) is confirmed by thermal expansion and compression behavior. Under ambient conditions the linear thermal expansion coefficient obtained is almost constant in the glassy state with a value of 4.0 × 10−5 K−1. By fitting the static equation of state at room temperature under ambient conditions we find the value for bulk modulus B of 48.7 GPa, which is in excellent agreement with the experimental study by pulse-echo techniques of 44.7 GPa. Unlike many bulk metallic glasses, such as Zr- and Pd-based, which bulk modulus is much larger than 100 GPa, the value B of Mg65Cu25Tb10 BMG falls into the range of SiO2 and fluorozirconate glass ZBLAN. Moreover, the elastic constant of the Mg65Cu25Tb10 BMG is almost the same as those of ZBLAN. No evidence for the high-pressure phase transitions of the Mg65Cu25Tb10 BMG has been found up to 31.19 GPa at room temperature.  相似文献   

3.
H.S. Chen 《Journal of Non》1981,46(3):289-305
Structural relaxation processes are investigated calorimetrically for a pre-conditioned Pd48Ni32P20 glass over a wide temperature range from well below to just above the glass transition. The low temperature anneals further stabilize the glassy structure. Upon heating, the annealed sample shows an excess endothermic specific heat ΔCp above the annealing temperature and completely recovers the initial enthalpy before any manifestation of glass transition, Tg. Significantly the ΔCp peak evolves in a continuous manner with annealing time. A physically reasonable activation energy spectrum N01(Q) is obtained with the proper choice of coupling constants which are dependent on annealing temperature. Results suggest the existence of localized relaxation modes which do not contribute to macroscopic flow. A concept of distribution in glass transition temperatures H(Tg,m) is conceived to account for the reversible relaxation with temperature. A model glass transition based on percolation theory is proposed and is found to reproduce the calorimetric relaxation phenomena well.  相似文献   

4.
The ionic and optical transports of 50Li2O–50B2O3 glass were investigated. Time-resolved current spectra (TRCS) showed repetitions of typical charge and discharge processes. The model circuit and equation for the TRCS and the equation for the relation between the turning times of polarization (TTP) and configuration energy (CE) have also been suggested. Equations were satisfied by the experimental results, and the potential and temperature dependence of the configuration energy (CE) and the dipole length from the TTP were investigated in detail. Kink phenomena showed that three or more types of charges were involved in the polarizations. The bi-exponential conductivity equation was applied to obtain the temperature dependence of the ac conductivity (TDAC). Complex impedance spectra (CIS) consisted of a semi-arc and a spur due to the electrode-specimen polarization. The shift of inflection points and peak frequencies in complex modulus spectra (CMS) showed non-Debye type relaxations, and the activation energy for relaxation was consistent with the relaxation for the temperature dependence of the dc conductivity (TDC). The migration concept (MC) applied to the CMS was satisfied at the dispersion and peak region, but slightly swerved at the tail. The fractal dimensionality displayed a three-dimensional character. The band gap, Urbach energy and optical indexes were obtained from optical spectra using Kramers–Kronig analysis (KKA).  相似文献   

5.
The kinetics of structural relaxation and of glass transition of the 45Na2O-40B2O3-10Al2O3-5In2O3 glassforming melt is studied by means of standard DSC and of temperature modulated DSC. In this way the dependence of the fictive temperature on cooling rate is determined simultaneously with the determination of the dependence of the dynamic glass transition temperature on modulation frequency. Both sets of data are fitted together in terms of the equation of Ritland-Bartenev. It was found that the activation energy of the structural relaxation exhibits a moderate dependence on temperature with the dimensionless fragility parameter α=3.3 (for strong systems, α is about 1 and increases to about 8 for some very fragile polymeric systems).  相似文献   

6.
Ti40Zr25Ni8Cu9Be18 bulk metallic glass has a unique quenched-in nuclei/amorphous matrix structure. The crystallization of quenched-in nuclei, when the experimental isothermal annealing time is within its incubation time, may not disturb the enthalpy relaxation, which makes it have the accordingly common enthalpy relaxation behavior with amorphous materials. The alloy's annealing time dependence of recovery enthalpy follows a stretched exponential function with the mean relaxation time obeying an Arrhenius law. The equilibrium recovery enthalpy ΔHTeq, mean relaxation time τ and stretching exponent β are all dependent on the annealing temperature, and generally, a higher annealing temperature comes with a lower value of ΔHTeq, τ and a higher value of β. Two parameters, βg and τg, representing the stretching exponent and the mean structural relaxation time at the calorimetric glass transition temperature, respectively, are correlated with glass forming ability and thermal stability, respectively. For Ti40Zr25Ni8Cu9Be18 BMG, the high value of βg, which is much higher than 0.84 and approaches unity, reveals its good glass forming ability, while, on the other hand, the low value of τg indicates a worse thermal stability compared with typical BMGs.  相似文献   

7.
The load relaxation behavior within the supercooled liquid region of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass has been investigated. To explain the relationship between normalized stress and relaxation time, two different stress relaxation modes such as a Kohlrausch-Williams-Watts (KWW) behavior and a simple power law were applied to the short and long relaxation time regimes, respectively. The apparent activation energy for stress relaxation is 126 ± 10 kJ/mol. Flow curves were obtained by converting load-displacement data into a flow stress-strain rate relation, resulting in three different deformation characteristics through a wide strain rate region interpreted in terms of strain rate sensitivity. A prediction of hot workability has also been attempted by constructing a power dissipation map based on a dynamic materials model.  相似文献   

8.
Refractory bulk metallic glasses and bulk metallic glass composites are formed in quaternary Ni-Nb-Ta-Sn alloy system. Alloys of composition Ni60(Nb100−xTax)34Sn6 (x = 20, 40, 60, 80) alloys were prepared by injection-casting the molten alloys into copper molds. Glassy alloys are formed in the thickness of half mm strips. With thicker strips (e.g., 1 mm), Nb2O5 and Ni3Sn phases and the amorphous phase form an in situ composite. Glass transition temperatures, crystallization temperatures, and ΔTx, defined as Tx1 − Tg (Tx1: first crystallization temperature, Tg: glass transition temperature) of the alloys increase dramatically with increasing Ta contents. These refractory bulk amorphous alloys exhibit high Young’s modulus (155-170 GPa), shear modulus (56-63 GPa), and estimated yield strength (3-3.6 GPa).  相似文献   

9.
The a.c. and d.c. conductivities of PbOSiO2 glass with 0–10 mole% Fe2O3 additions were measured in the temperature range 77–700 K. Two relaxation processes were noted. The relaxation mechanism at lower temperatures is due to polaron hopping between ferric-ferrous ion pairs with a distribution of relaxation times which is energy independent. The second relaxation phenomenon, at higher temperatures is polaron hopping along iron ion chains in the glass of which the pairs responsible for the first process are a part. A theoreticalmodel is proposed and additional evidence for this model is presented in the form of magnetic susceptibility and electron spin resonance (esr) data.  相似文献   

10.
G. Paramesh 《Journal of Non》2011,357(5):1479-1484
Transparent glasses in the system 0.5Li2O-0.5M2O-2B2O3 (M = Li, Na and K) were fabricated via the conventional melt quenching technique. The amorphous and glassy nature of the samples was confirmed via the X-ray powder diffraction and the differential scanning calorimetry, respectively. The frequency and temperature dependent characteristics of the dielectric relaxation and the electrical conductivity were investigated in the 100 Hz-10 MHz frequency range. The imaginary part of the electric modulus spectra was modeled using an approximate solution of Kohrausch-Williams-Watts relation. The stretching exponent, β, was found to be temperature independent for 0.5Li2O-0.5Na2O-2B2O3 (LNBO) glasses. The activation energy associated with DC conduction was found to be higher (1.25 eV) for 0.5Li2O-0.5K2O-2B2O3 (LKBO) glasses than that of the other glass systems under study. This is attributed to the mixed cation effect.  相似文献   

11.
Electrical resistivity and thermal expansion measurements were made to elucidate the structural relaxation of Ni78Si8B14 metallic glass, especially, the topological short range ordering. The decrease of the resistivity and the increase of its temperature coefficient were observed, and these changes due to the structural relaxation were discussed on the basis of the extended Ziman theory for metallic glasses proposed by Nagel. The densification of about 0.25% and the decrease of 4% in the thermal expansion coefficient were observed in the considerably relaxed sample. The topological short range ordering in Ni78Si8B14 metallic glass occurs rapidly at the annealing temperature above 200°C.  相似文献   

12.
Viscosity of (GeSe2)x(Sb2Se3)1−x undercooled melts (x = 0.4-0.8) was measured using parallel-plate method and penetration method. By using these two techniques viscosity of the whole measurable region of undercooled melt and of the part of glass region can be measured. In this relatively broad viscosity interval (seven orders of magnitude) all measured samples show Newtonian behavior and the dependence of their viscosity on temperature can be described by a simple Arrhenius equation. The kinetic fragilities calculated from these dependencies show similar compositional dependence as heat capacity changes at glass transition measured by DSC.  相似文献   

13.
Krzysztof Ziewiec 《Journal of Non》2008,354(33):4019-4023
The Cu68.5Ni12P19.5 alloy was cast into the ribbons using melt spinning (23 m/s). The amorphous ribbon in the as-cast state was investigated by differential thermal analysis (DTA), dynamic mechanical analysis (DMA), resistivity measurements and X-ray diffraction ‘in situ’ at different temperatures. The work presents attempts to find correlation between the changes of the mechanical properties presented by DMA cycles and during the other tests. The measurements of the relative resistivity R/R0 versus temperature for repeated heating and cooling cycles to different temperatures show changes of the temperature coefficient of resistivity (TCR) indicating reversible and irreversible transformations in the studied alloy.  相似文献   

14.
K. Russew  F. Sommer 《Journal of Non》2003,319(3):289-296
The density changes of bulk amorphous Pd40Cu30Ni10P20 due to structural relaxation under isothermal heat treatment were measured using the buoyancy method. The corresponding length changes of amorphous Pd40Cu30Ni10P20 ribbons applying non-isothermal heat treatment are determined applying dilatometry. The measured density changes Δρ(T=const.,t)/ρo as a function of isothermal heat treatment increase close to the glass transition up to 0.18%. The measured density changes as a function of temperature and time are furthermore reversible. The experimental data validate the model predictions of the free volume model for length and density changes of amorphous alloys due to structural relaxation applying isothermal and non-isothermal heat treatment.  相似文献   

15.
The structure and elastic properties of a series of xNa2O · MgO · 4SiO2 glasses have been studied using both Raman and Brillouin spectroscopy. Relative to Na2O-SiO2 glasses, the maximum abundance for phyllosilicate structural units in the present glasses shows a lag of 0.5 units in the number of non-bridging oxygen per silicon atom (NBO/Si). This phenomenon has been attributed to the decrease in the average coordination number of modifying cations due to the presence of Mg2+. It has also been found that the decomposition of both metasilicate and disilicate (dimerized SiO4) anionic structural units in Na2O-SiO2 glasses are enhanced by the addition of MgO. However, the presence of Mg2+ does not cause a considerable effect on the decomposition of phyllosilicate structural unit. The acoustic data have revealed that both shear and Young’s moduli of the present glasses decrease with increasing NBO/Si (the variation in bulk modulus is reversed, however). The resistance to shear deformation for the anionic structural units in silicate glasses has been found to decrease in the following order: tectosilicate > phyllosilicate > metasilicate > disilicate > orthosilicate. The relative contribution of the various anionic structural units to the bulk modulus of a glass remains to be determined. The ideal mixing model using Makishima-Mackenzie’s relationship for predicting Young’s modulus is not applicable to the present glasses.  相似文献   

16.
Eun-Sub Lim 《Journal of Non》2006,352(8):821-826
A BaO-B2O3-SiO2 glass system was chosen as a candidate composition for the application to Pb-free low temperature sinterable glass. The effect of BaO content on the crystallization, sintering behavior, and properties of the glasses was examined. Both the glass transition temperature and crystallization temperature decreased as the BaO content increased. Crystallization easily occurred during sintering with a BaO content of more than 50 mol%, which effectively inhibited the over-firing phenomenon. The dielectric characteristics and thermal expansion coefficient of the glasses were examined and the results were explained on the basis of the crystallization and densification of the specimens.  相似文献   

17.
I. Dyamant  E. Korin 《Journal of Non》2008,354(27):3135-3141
Glasses in the La2O3−CaO−B2O3 ternary system were studied. The glass forming range as determined by the appearance of the annealed cast was found to match previously published findings. Clear glasses were formed in the composition range of 5.7−19.1 mol% La2O3 with constant B2O3 content of 71.4 mol%, and in glasses of constant La2O3:CaO ratio of 1:4 with B2O3 content in the range of 71.4-55.0 mol%. The non-linear optical crystalline phase La2Ca2B10O19 was crystallized from the clear glasses after heat treatments, as determined by powder XRD. Two types of the LaBO3 crystalline phases were detected in the partially and the fully crystallized glass compositions outside the glass forming range. Data are reported for the glass transition temperature (Tg), dilatometric softening point (Td), linear coefficient of expansion (α), onset crystallization temperature (Tx), exothermal peak temperature (TP), density (ρ) and index of refraction (nD) in the clear glasses.  相似文献   

18.
Calcium phosphate based bioactive quaternary glass systems P2O5-CaO-Na2O-K2O were prepared by melt growth technique. Glasses were prepared in five different compositions by fixing P2O5 at 47 mol% and CaO at 30.5 mol% and by varying the K2O and Na2O concentrations. The structural properties of the glasses are analyzed using X-ray diffraction (XRD) studies and scanning electron microscopy (SEM) studies; and the composition of the glasses are studied using energy dispersive X-ray spectrum (EDS). The microhardness of the glass systems are studied by Vickers hardness measurements and the bioactivity of the glasses are studied using in vitro study. The thermal properties have been examined by means of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The ultrasonic velocity measurements show that the addition of K2O contents produces non-bridging oxygen ion and hence weaken of the glass structure. The weakening of the glass structure reduces the ultrasonic velocity and hence an increase in attenuation.  相似文献   

19.
The compressive stress relaxation modulus of a container glass composition was investigated over a wide range of strain, time, modulus, and temperature. It is shown that the glass behaves in a linear viscoelastic manner up to a 2% strain level, and that the relaxation modulus is a smooth function of time, with no pseudo-rubbery plateau apparent down to a modulus of 108 dyn/cm2. The data cover roughly five decades of modulus, five decades of time, and a temperature range of 150° C above the glass transition, Tg = 536°C. Within experimental error, the effect of temperature on the stress relaxation behavior is to simply shift the modulus-time curves along the time axis with no change in shape. Temperature dependent shift factor data are expressed in terms of the WLF relation, and are shown to be in good agreement with data found in the literature for other silicate compositions. Viscosity data derived from the generated stress relaxation data agree well with data obtained by more direct methods.  相似文献   

20.
The Li replacement including the Li2O replaced by other oxides and the expensive Li2CO3 replaced by low-cost spodumene mineral was studied to lower the product cost of (Li2O-Al2O3-SiO2, LAS) glass ceramic, and the effects of Li replacement on the nucleation, crystallization and microstructure of LAS glass were investigated by the differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that Li2O replacement increases the crystallization activation energy, lowers the crystal growth, and increases the nucleation and crystallization temperature by restraining the formation of crystalline phases. The Li2CO3 replacement decreases the crystallization activation energy, promotes the crystal growth, without affecting the nucleation, and lowers the crystallization temperature by adding some beneficial compositions with mixed alkali effect.  相似文献   

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