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1.
Mg based bulk metallic glasses: Glass transition temperature and elastic properties versus toughness
In this work, optimal compositions for bulk metallic glasses (BMGs) formation in the ternary Mg-Cu-Nd and Mg-Ni-Nd systems are located at the Mg57Cu34Nd9 and Mg64Ni21Nd15, respectively, with the critical diameter of 4 mm for the rods fabricated by copper mold casting. As indicated by notch toughness testing, Mg64Ni21Nd15 BMG (KQ = 5.1 MPa√m) manifests higher toughness with respect to the Mg57Cu34Nd9 (KQ = 3.6 MPa√m), even though both BMGs have similar compressive fracture strength of 870-880 MPa. Such an improvement in toughness for Mg BMGs correlates with the reduction of shear modulus and the enhancement of thermal stability to resist to the structural relaxation at room temperature, which is indicated by the elevated glass transition temperature Tg. Under the Mode I loading condition, morphology in fracture surface of the Mg64Ni21Nd15 BMG varies along the crack propagation path. Fractographic evolution of the fracture surface follows the Taylor's meniscus instability criterion. For the Mg-based BMGs, shear modulus scales with the glass transition temperature, and can be expressed as μ = 4.7 + 625Tg/Vm[1-4/9(T/Tg)2/3]. Meanwhile, correlation between the calorimetric Tg and elastic properties at Tg can be rationalized with Egami's model. 相似文献
2.
R. Risti? E. Babi? A. Kuršumovi? I.A. Figueroa I. Todd I. Bakonyi 《Journal of Non》2011,357(15):2949-2953
We provide new data for the stiffness, hardness, Debye temperatures and crystallization and glass transition temperatures for fourteen Ti-TL and Hf-TL amorphous alloys (TL = Ni,Cu) covering wide composition range (x(TL) ≤ 70). These data increase linearly with x, as was previously observed for Zr-TL glassy alloys. Thus, the strength of interatomic bonding (reflected in stiffness) in all TE-TL amorphous alloys (TE = Ti,Zr,Hf) increases with x for x ≤ 65. The actual variations of studied properties depend on TE, being feeble for TE = Ti. The approximately linear variation of mechanical, vibrational and thermal parameters with x enables one to estimate these parameters for pure amorphous TEs, but does not indicate compositions at which bulk metallic glasses (BMG) form in these alloy systems. The reduced glass transition temperature Trg is the property which roughly correlates with the formation of BMGs in glassy TE-TL alloys. 相似文献
3.
W.K. An A.H. Cai J.H. Li Y. Luo T.L. Li X. Xiong Y. Liu Y. Pan 《Journal of Non》2009,355(34-36):1703-1706
Glass forming ability (GFA) and non-isothermal crystallization kinetics of Zr62.5Al12.1Cu7.95Ni17.45 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 Eg, 212.84 ± 15.84 KJ mol−1 for onset crystallization Ex, 230.51 ± 23.85 KJ mol−1 for the first crystallization peak Ep1 and 124.85 ± 15.15 KJ mol−1 for the second crystallization peak Ep2. 相似文献
4.
The crystallization behavior of Zr65.0Al7.5Ni10.0Cu17.5 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 Zr65.0Al7.5Cu27.5 specimen, while microstructures consisting of finer nanocrystalline bct-Zr2Cu, fcc-Zr2Ni and Zr6Al2Ni formed in the Zr65.0Al7.5Ni10.0Cu17.5 specimen. The oxidation resistance of the melt-spun Zr65.0Al7.5Ni10.0Cu17.5 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 Zr65.0Al7.5Ni10.0Cu17.5 specimen was lower, which was probably due to suppressed oxygen diffusion in ZrO2. 相似文献
5.
D. Meng 《Journal of Non》2011,357(7):1787-1790
Ta-based bulk metallic glasses with high strength (2.7 GPa) and hardness (9.7 GPa), high elastic modulus (170 GPa) and high density (12.98 g/mm3) were developed. The best glass forming ability so far for a Ta-Ni-Co system reaches a critical diameter of 2 mm by the copper mold casting method. It shows an exceptionally high glass transition temperature of 983 K and a high crystallization temperature up to 1023 K. The unique mechanical and physical properties make them a promising high strength material. 相似文献
6.
The correlations between the pressure sensitivity and the fragility/glass transition temperature have been addressed in various bulk metallic glasses in the present work. The results demonstrate that the pressure sensitivity of bulk metallic glasses is closely related to both the fragility index (m) and the glass transition temperature (Tg). The physical origin of the correlations has been discussed from their disordered structure, which is determined by the glass transition behavior and the glass transition temperature. 相似文献
7.
Transitions into, and out of intermediate phases (IPs) with minimal strain have been identified to date by Boolchand and co-workers, in bulk glasses, primarily by the extraordinary low values of the change in enthalpy, ΔHnr, associated with non-reversible heat flow, and by Lucovsky and coworkers in deposited thin films, and at dielectric–semiconductor interfaces by combining spectrographic characterizations, primarily synchrotron X-ray absorption and X-ray photoemission, and electrical measurements. This paper emphasizes chemical bonding self-organizations that minimize macroscopic strain within the IP windows, and identifies for the first time the necessary and sufficient conditions for IP windows to open, and to close, as a function of changes in the alloy composition. Percolation theory, and in particular competitive and synergistic double percolation provide a quantification of IP window first and second transition compositions that account for many of the experimentally determined IP window threshold transitions and IP window widths identified to date. 相似文献
8.
Amorphous Mg50Ni50 alloy was produced by mechanical alloying (MA) of the elemental powders Mg and Ni using a SPEX 8000D mill. The alloyed powders were microstructurally characterized by X-ray diffraction (XRD). The thermal transformation of amorphous Mg50Ni50 into stable intermetallics (Mg50Ni50 → remaining amorphous + Mg2Ni → Mg2Ni + MgNi2) was analyzed using the Kissinger and isoconversional methods based on the non-isothermal differential scanning calorimetry (DSC) experiments. The apparent activation energies (Ea) and the transformation diagrams, temperature-time-transformation (T-T-T) and temperature-heating rate-transformation (T-HR-T), were obtained for both processes. A good agreement was observed between the calculated transformation curves and the experimental data, which verifies the reliability of the method utilized. 相似文献
9.
Recently, a series of quaternary Zr-based bulk metallic glasses (BMGs), i.e., Zr53Cu18.7Ni12Al16.3, Zr51.9Cu23.3Ni10.5Al14.3 and Zr50.7Cu28Ni9Al12.3, have been developed and their glass-forming ability (GFA) increases with Cu concentration. In this work, atomic structures of the three BMGs were rebuilt by reverse Monte Carlo simulations based on the reduced pair distribution functions measured by high energy X-ray diffraction. The results show that a certain amount of substitution of short Zr-Cu, Cu-Cu pairs with long Zr-Zr and Zr-Al pairs enhances the local denser packing of Kasper polyhedral centered by Zr and Al atoms. A cell sub-divided method is proposed to describe the fluctuation of local number density which is found to follow the normal distribution function. The largest possible free volume in the three alloys is found to approaches to 3.8 Å. For the three alloys, the enhancement of GFA with increasing Cu content is due to the increase in the fluctuation degree of local density instead of the dense packing. 相似文献
10.
A surface softening effect induced during copper-mould suction casting of bulk metallic glass is investigated as a function of rod diameter and glass fragility index, m, by nanoindentation. A reduction in hardness and reduced modulus at the rod surface is found to be favoured in small diameter castings and in fragile systems, respectively resulting from limited in-situ annealing and from a greater diversity of metastable atomic environments in the potential energy landscape of fragile glasses. Enhanced propensity for shear transformation zone nucleation in the low moduli surface is explained in terms of reduced atomic connectivity arising from a reduction in local co-ordination number and a lowering of the shear modulus. Finally, the structure and mechanical diversity that is possible in as-cast bulk metallic glass rods is explored through a relative quantification of shear modulus and plastic zone size across the whole as-cast state and in a single rod. These findings illustrate the sensitivity of bulk metallic glass to preparation, especially in respect of thermal history, potentially making replication of mechanical data between researchers problematic. 相似文献
11.
Wire arc spraying process was used to deposit FeBSiCrNbMnY amorphous/nanocrystalline alloy coating onto stainless steel substrate. The microstructure of the coating was characterized by using X-ray diffraction (XRD), scanning election microscopy (SEM) equipped with energy dispersive X-ray analysis (EDXA) and transmission electron microscopy (TEM). The coating is about 500 μm in thickness with fully dense and low porosity. The microstructure of the coating is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of α Fe, Cr nanoscale particles with a scale of 30–60 nm in a residual amorphous matrix region. The formation mechanism of the amorphous and nanocrystalline alloy was discussed. Mechanical properties, such as microhardness and wear resistance of the coating were also analyzed. The Vickers hardness of the coating is around Hv = 900–1050. The relatively wear resistance of the amorphous/nanocrystalline alloy coating is about 3× than that of crystalline structure 3Cr13 martensite stainless steel coating under the same wear testing condition. The FeBSiCrNbMnY amorphous/nanocrystalline alloy coating has high microhardness and excellent wear resistance. 相似文献
12.
Based on some of our earlier dielectric relaxation studies during structural relaxation of molecular glasses, we describe certain features specific to the change in the Johari-Goldstein (JG) relaxation and examine their consequences for understanding of the molecular mechanism of the JG process. The parameter for the distribution of relaxation times increases slightly (loss curve becomes narrower) and the relaxation rate either remains constant or increases on ageing. In all cases, contribution to permittivity from the JG relaxation, ΔεJG decreases with time, with a rate constant k according to a relation, ΔεJG (t) = ΔεJG (t → ∞) − [ΔεJG (t = 0) − ΔεJG ( t → ∞)][1− exp[−(kt)]. This reduces to an equation of the type ΔεJG(t) = a + b exp(− kt) where a and b are constants of the glass as well are dependent on the thermal history of quenching of the glassy system. On decreasing the temperature, the relaxation rate for a rigid molecular glass follows the Arrhenius equation in a range that extends from liquid to glass, but deviates from it as a result of structural relaxation of the two alcohols, while the distribution of relaxation times decreases. The variation of ΔεJG with temperature shows an increase in slope on heating through Tg or else a deep and broad minimum before Tg is reached and the slope increases are remarkably similar to the changes observed for volume and thermodynamic properties on heating a glass. These findings need to be considered for a molecular mechanism in the potential energy view of JG relaxation, in analyzing the physical ageing of the α-relaxation process. It is argued that a recent suggestion for considering the JG relaxation within the picture of potential energy landscape may not be inconsistent with its molecular origin and dynamics in localized regions of structurally inhomogeneous glass. But there is still need to determine how the apparent dynamic heterogeneity evident from the broad distribution of the JG relaxation times can be reconciled with the dynamic heterogeneity used to explain less-broad spectra of the α − relaxation process. 相似文献
13.
In this paper, the effects of annealing and nanocrystallization on the mechanical properties of a Zr55Al10Ni5Cu30 metallic glass have been studied. It has been shown that the high volume fractioned nanocrystals facilitate the formation of shear bands and thus decrease the yield stress. At the same time, the nanocrystals also facilitate the formation of interfacial voids during compression, resulting in substantial decrease in the plasticity of the metallic glass. 相似文献
14.
Erbium doped chalcogenide glasses are of great interest in the integrated optoelectronic technology due to their Er3+ intra-4f emission at the standard telecommunication wavelength of 1.54 μm. In this paper, the photoluminescence (PL) of a series of (GeS2)x(Ga2S3)100−x (x = 75 and 67) glasses doped with high amounts of Er2S3 (1.8, 2.1, 2.4 and 2.7 mol%) under excitation with 1064 nm light has been studied. A quenching PL effect at 1.22 аt.% Er-doped (GeS2)75(Ga2S3)25 and 1.39 аt.% Er-doped (GeS2)67(Ga2S3)33 glasses has been established. The relative changes in PL line-shape at around 1540 nm have been estimated by deconvoluting the spectra to Gaussian sub-bands centered at 1519 ± 1, 1537 ± 1, 1546 ± 1, 1555 ± 1 and 1566 ± 4 nm, which correspond to F21, F11, F22, F12 and F13 transitions in the 4I13/2 and 4I15/2 energy levels and have intensity and manifestation that are strongly depend on the Er-doping level. The influence of gallium on the PL efficiency has been evaluated with a view to enhanced emission cross-section. 相似文献
15.
Glasses exhibit intriguing physical and mechanical properties resulting from their structure. We have investigated metal-glass dynamics using inelastic X-ray scattering and ultrasonic techniques for several Pd-, Pt-, and Zr-based glasses with varying fragility. In some cases we have observed a faster phase velocity at short wavelengths than long wavelengths, or positive dispersion. Here we apply elastic wave scattering theory to suggest that the behavior of acoustic phonons can be understood by considering the presence of intrinsic nanoscale elastic inhomogeneity with a certain correlation length, i.e., “static heterogeneity”. Furthermore, we suggest that such an elastic inhomogeneity could be the origin of many of the interesting physical and mechanical properties of metallic glasses. 相似文献
16.
Moritz Schwabe 《Journal of Non》2011,357(2):490-493
Creep/recovery measurements of amorphous PdCuSi ribbons have been performed. From these data we calculated the activation volume of relaxation processes in the temperature range from the glass transition temperature (Tg) to crystallization. The results indicate a correlation between applied stress and the activation volume of clusters in temperature regime close to Tg. With these results it is possible to compare molecular dynamic simulations for microscopic loss processes in metallic glasses with experimental values for mobile clusters. 相似文献
17.
The temperature dependent structure of Ni81P19 metallic glasses, rapidly quenched from melts which have undergone different heat treatments, has been investigated by small angle neutron scattering and neutron diffraction. All samples contain in the as-quenched state particles or clusters of a very wide range of sizes. These are amorphous regions of different compositions in a large composition range and/or crystallites of another Ni composition than the matrix, such as Ni3P, Ni5P2 or Ni12P5, or even “voids”. The results can be interpreted within the concept of a heterogeneous structure existing in eutectic melts in a certain temperature range. Comparison is made with results from the literature on samples from the same ribbons investigated by calorimetry as well as by fractography and Weibull analysis of mechanical properties. 相似文献
18.
An investigation was made into the thermal stability and mechanical behavior under nanoindentation of a new glassy alloy with composition Ni50Nb28Zr22, produced in the form of melt-spun ribbons and copper mold-cast wedges. The alloy composition was designed based on the lambda criterion combined with the electronegativity difference among the elements. X-ray diffraction and scanning electron microscopy confirmed that the ribbons and wedges (up to 200 μm in thickness) are amorphous. The thermal properties of these samples were evaluated by differential scanning calorimetry (DSC). Nanoindentation revealed that the hardness of this alloy, around 10 GPa, is among the highest reported for metallic glasses. Remarkably, the cast wedge exhibits greater hardness and higher elastic modulus than the ribbon. This correlates with the larger amount of frozen-in free volume in the ribbons than in the cast wedges, as evidenced by DSC. In addition, finite element simulations of nanoindentation curves were performed. The Mohr-Coulomb yield criterion allows for better adjustment of the experimental data than the pressure-independent Tresca yield criterion. The simulations also reveal that the cohesive stress in the ribbons is lower than in the wedges, which explains the difference in hardness and Young's modulus between the two samples. 相似文献
19.
The crystallization behavior and microstructure development of the Zr61Al7.5Cu17.5Ni10Si4 alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During isothermal annealing of the Zr61Al7.5Cu17.5Ni10Si4 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 Zr61Al7.5Cu17.5Ni10Si4 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 Zr61Al7.5Cu17.5Ni10Si4 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). 相似文献
20.
The absolute contents of free volume in the as-cast and annealed Zr45.0Cu39.3Al7.0Ag8.7 bulk metallic glass (BMG) samples were quantified by density measurements and reverse Monte Carlo (RMC) simulation using the total structural factors F(Q) determined by X-ray diffraction (XRD) experiments as fitting constraints. The densities of the as-cast, annealed and crystallized samples measured by Archimedes method are 7.319, 7.327 and 7.342 g/cm3 (precision ± 0.003 g/cm3), respectively. A new approach was used in the RMC simulation to define the free volume as the difference between the volume of the Voronoi polyhedron and the volume of the Wigner-Seitz cell of the constituent atoms. Two types of initial configurations were constructed: (1) in configuration A, all types of potential atomic pairs are allowed; (2) in configuration B, Al-Al and Ag-Ag atomic pairs are excluded. The contents of free volume in the as-cast and annealed samples were found to be 0.59% and 0.39% (configuration A), 0.55% and 0.34% (configuration B), respectively (precision ± 0.03%). The probability distribution of the as-calculated free volume can be well-fitted by the equation proposed by Turnbull and Cohen. Finally, it is shown that the contents of free volume determined by density measurements and RMC are comparable, while the discrepancy of the results is discussed. 相似文献