共查询到20条相似文献,搜索用时 13 毫秒
1.
We report the formation of a family of bulk metallic glasses (BMGs) based on rare earth element of ytterbium and alkaline earth element of calcium. The glass-forming ability, atomic packing density and corrosion behaviors of the BMGs show an extremum around the eutectic point with the change of the concentration of Yb and Ca. 相似文献
2.
J.Q. Wang 《Journal of Non》2011,357(1):220-222
By statistically analyzing 48 kinds of metallic glasses, we report clear correlations between the dimensionless ratio of glass transition temperature/Debye temperature (Tg/ΘD) and density (ρ), and between Young's modulus or shear modulus and Tg/ρ, for the glasses consisting of only metal elements, while the metallic glasses alloyed with metalloid elements exhibit distinct deviation from the correlations. It is suggested that the alloying of metalloid elements would show covalent-like bonding characteristics in metallic glass, and the found correlations can be used to distinguish different bonding characteristics in metallic glasses. 相似文献
3.
We report that both shear and bulk moduli, not only shear modulus, are critical parameters involved in both homogeneous and inhomogeneous flows in metallic glass. The flow activation energy (?F) of various glasses when scaled with average molar volume Vm, which is defined as flow activation energy density ρE = ?F/Vm, can be expressed as: . The extended elastic model is suggestive for understanding the glass transition and deformation in metallic glasses. 相似文献
4.
Studies on the formability of Al-based metallic glasses/nanocomposites based on isochronal DSC analysis 总被引:1,自引:0,他引:1
Longchao Zhuo 《Journal of Non》2010,356(43):2258-2262
The Al86Si0.5Ni4.06Co2.94Y6Sc0.5 metallic glass of highly improved glass-forming ability (GFA) has been investigated by isochronal differential scanning calorimetry measurements, as well as the Al85Ni5Co2Y8 for comparison. The experimental results indicate that the Al86Si0.5Ni4.06Co2.94Y6Sc0.5 exhibits enlarged temperature interval between the first and second crystallization onsets (termed as primary fcc-Al/glass region), as well as enlarged second activation energy (Ep2) against the nucleation and the growth of intermetallic compounds besides fcc-Al. The variation of the Avrami exponent demonstrates that the primary crystallization process is a rapid two- and three-dimensional diffusion-controlled nucleation and growth mechanism initially, and the whole process is strongly controlled by the growth of fcc-Al crystals. According to the analysis on the basis of atomic mobility of alloy components, it demonstrates that the enlarged primary fcc-Al/glass region obtained through proper coexistence of dissimilar and similar elements would be in favor of preparing Al-based metallic glasses or nanocomposites in greater size. 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.
We have studied the influence of the arc melting procedure of Nb-containing Zr-based bulk metallic glasses (BMGs) on their thermal and mechanical properties. We found that the strength and plastic strain to failure, determined at room temperature, increases by the addition of a few percentage of Nb into the Zr-based BMGs. High-resolution transmission-electron microscopy results show that the addition of 2 at.% Nb introduces the formation of as-cast nanocrystals. At the same time, thermal analyses indicate an increase in glass forming ability with the small addition of Nb. Contrary to the reported results in other amorphous alloys, we found that the plastic strain increases further after heat-induced structural relaxation in the Zr-based BMGs. 相似文献
7.
X.Q. Gao 《Journal of Non》2011,357(21):3557-3560
Bulk metallic glasses (BMGs) are usually based on a single principal element such as Zr, Cu, Mg and Fe. In this work, we report the formation of a series of high mixing entropy BMGs based on multiple major elements, which have unique characteristics of excellent glass-forming ability and mechanical properties compared with conventional BMGs. The high mixing entropy BMGs based on multiple major elements might be of significance in scientific studies, potential applications, and providing a novel approach in search for new metallic glass-forming systems. 相似文献
8.
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
9.
The crystallization behavior of Zr-Cu-Al metallic glasses was studied using thermophysical property measurements. When the Zr content of Zr-Cu-Al metallic glass decreased from 65 at.% to 45 at.%, the thermal conductivity gradually increased and the maximum value obtained was the composition of Zr:Cu:Al = 50:39.3:10.7(at.%). These metallic glasses were not crystallized upon heat treatment below the glass transition temperature Tg, and the thermophysical properties of these metallic glasses were almost constant. In contrast, these metallic glasses started to crystallize upon heat treatment above Tg after a certain derived time, and their thermal conductivity increased with the crystallinity of the metallic glass. 相似文献
10.
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
11.
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
12.
A significant enhancement in plasticity was achieved by the micro-addition of Cu in Fe-based bulk metallic glasses (BMGs) which have high strength at room-temperature. It was found that the nanocrystallization caused by the formation of the α-Fe phase is responsible for the improvement in plasticity of the Fe-based BMGs. Our results suggest that the micro-addition of Cu is a promising approach to enhancing the plasticity of Fe-based BMGs through compositional and structural design by microalloying. 相似文献
13.
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
14.
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
15.
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
16.
Rare earth based bulk metallic glasses 总被引:1,自引:0,他引:1
Q. Luo 《Journal of Non》2009,355(13):759-714
Recently, the rare earth based bulk metallic glasses (REBMGs) have attracted increasing interest due to their unique properties and potential applications as functional glassy materials. These REBMGs display many fascinating properties such as heavy fermion behavior, thermoplastic properties near room temperature, excellent magnetocaloric effect, hard magnetism, and polyamorphism, all of which are of interest not only for basic research but also for metallurgy and technology. These characteristics and properties are ascribed to the unique electronic, magnetic and atomic structures of the REBMGs. In this review paper, the fabrication, glass-forming ability, polyamorphism, elastic, thermal, and physical properties are summarized and discussed. Owing to the unique electronic structure of rare earth elements, the electric and magnetic properties of the REBMGs are especially addressed. The works have implications for seeking novel metallic glasses with controllable properties and for understanding the nature of glass formation. The development of REBMGs as functional materials might promote and extend the commercial applications of metallic glasses. 相似文献
17.
Dynamic mechanical properties of two metallic glasses, Fe40Ni40P14B6 and Fe32Ni36Cr14P12B6, have been studied at frequencies ranging from 0.1 to 3 kHz and at temperatures between ? 160 and 390°C. Each of the samples exhibits an internal friction maximum at about ?20°C with activation energies of 25 and 34 kcal/mol. A possible mechanism for the low-temperature internal friction peak is suggested. 相似文献
18.
Metallic glasses (MGs) combined with copper cores possess many advantages in precision casting and coring of alloys. In this study, inner holes with different dimensions and complex sectional shapes were fabricated through direct casting and coring in MGs. The MG castings show good surface finish and the cored inner holes exhibit high aspect ratios larger than 80 while holding a tight dimension tolerance. The dimensional deviation was proved to originate mainly from the contraction disagreement between castings and copper cores by comparing their thermal expansion coefficients and simulating the solidification and cooling processes, while other factors may also contribute to it. The results are expected to provide a convenient and economical way in the near net-shape fabrication of inner holes in metallic devices and in the assembly of MG components. 相似文献
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20.
The relationships between the elastic moduli, glass forming ability and response to deformation of bulk metallic glasses are investigated. Five bulk metallic glasses are prepared from high purity elements via suction casting. The results confirm that there exists a correlation between energy absorbed to failure during compression testing and the bulk to shear modulus ratio. This finding is developed such that it corresponds only to the elastic component of energy absorption, and that the bulk modulus dominates this. Plastic deformation appears to be favored by a reduced shear modulus, although it shows greater dependence on structural features that are frozen in during the glass transition, and so may well be dependent on the liquid fragility. 相似文献