具有优良玻璃形成能力添加Al的CuZr基大块金属玻璃

在CuZr二元大块金属玻璃的基础上，利用铜模吸铸方法制备出了添加Al组元的CuZr 基大块 金属玻璃.CuZr基大块金属玻璃在很宽的成分范围内有很强的玻璃形成能力，在Al含量从4％ 到8％之间，CuZr基大块金属玻璃都可以做出直径至少5 mm的非晶样品.通过实验分析，解释 了CuZr基大块金属玻璃具有良好玻璃形成能力的物理机理.CuZr基金属玻璃组分简单、成本 低廉，有潜在的应用价值；同时，制备CuZr基金属玻璃的方法为开发新的大块金属玻璃体系 提供了一条切实有效的途经. 关键词： 大块金属玻璃 玻璃形成能力 CuZr基金属玻璃     

Magnetic properties of Sm-based bulk metallic glasses

We perform detailed investigation on the magnetization and specific heat of Sm-based ternary bulk metallic glasses with different Co contents at low temperature. A low temperature cluster spin-glass phase below T_f ∼25 K is evidenced for all samples. This cluster spin-glass behavior is ascribed to competition among the multi-fold magnetic interactions and the intrinsic structural inhomogeneity. The magnetic relaxation behavior of the spin-glass phase can be well described using the stretched exponential dynamics. The magnetic hysteresis under field-cooling condition and spin dynamics further demonstrate the low temperature cluster spin-glass behavior. It is revealed that the Co atoms play an important role in modulating the physical properties of the present Sm-based ternary metallic glasses.     

Thermodynamical properties of Zr-based bulk metallic glasses

The temperature dependence of Gibb's free energy difference (ΔG), entropy difference (ΔS) and enthalpy difference (ΔH) between the undercooled melt and the corresponding equilibrium solid phases of bulk metallic glass (BMG) forming melts has been proved to be very useful in the study of their thermodynamical behavior. The present study is made by calculating ΔG, ΔS and ΔH in the entire temperature range T_m (melting temperature) to T_g (glass transition temperature) for three Zr-based samples of BMGs: Zr₅₇Cu_15.4Ni_12.6Al₁₀Nb₅, Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5 and Zr_58.5Cu_15.6Ni_12.8Al_10.3Nb_2.8. The study is made on the basis of Taylor's series expansion and a comparative study is also performed between the present result and the result obtained in the framework of expansions proposed by earlier workers, and also with the experimental results. An attempt has also been made to study the glass forming ability for BMGs.     

脆性金属玻璃断面上的奇妙图案

文章简要介绍了脆性块体金属玻璃(简称BMG)断裂面上几种主要的图案花样：河流花样、“韧窝”结构花样和自组装条纹结构花样,并总结了目前对上述各种形貌形成机理的可能的物理解释.对BMG断裂面上形貌的研究可以揭示材料的断裂机理,有助于更深刻地理解材料的力学性能, 开发高性能金属玻璃材料,并为工程选材提供安全标准.     

脆性金属玻璃断面上的奇妙图案

文章简要介绍了脆性块体金属玻璃(简称BMG)断裂面上几种主要的图案花样:河流花样、"韧窝"结构花样和自组装条纹结构花样,并总结了目前对上述各种形貌形成机理的可能的物理解释.对BMG断裂面上形貌的研究可以揭示材料的断裂机理,有助于更深刻地理解材料的力学性能,开发高性能金属玻璃材料,并为工程选材提供安全标准.     

Effect of the ultrasound action on the acoustic emission and mechanical properties of zirconium-based bulk metallic glasses

The effect of preliminary ultrasound action on the mechanical properties and features of the structure of zirconium-based bulk metallic glasses has been studied by the method of acoustic emission under uniaxial compression. Results of studies have been interpreted using the polycluster model of the structure of amorphous metallic alloys. Analysis of the obtained data has allowed us to substantiate the mechanism of the change in the structure and strength of metallic glasses as a result of alternating-sign mechanical loading with an ultrasound frequency of 20 kHz.     

LaGa-based bulk metallic glasses

We report the formation of La Ga-based bulk metallic glasses. Ternary La–Ga–Cu glassy rods of 2–3 mm in diameter can be easily formed in a wide composition range by the conventional copper mold casting method. With minor addition of extra elements such as Co, Ni, Fe, Nb, Y, and Zr, the critical diameter of the full glassy rods of the La–Ga–Cu matrix can be markedly enhanced to at least 5 mm. The characteristics and properties of these new La Ga-based bulk metallic glasses with excellent glass formation ability and low glass transition temperature are model systems for fundamental issues investigation and could have some potential applications in micromachining field.     

Effects of cooling rates on the mechanical properties of a Ti-based bulk metallic glass

Mechanical properties of the glassy specimens fabricated at different cooling rates with a composition of Ti40Zr25Cu12Ni3Be20 were systematically investigated. It was confirmed that faster cooling rates caused not only a larger amount of frozen-in free volume but also a higher glass transition temperature in the bulk glassy alloy. Increase in the free volume was found to favor plastic deformation and then to give rise to larger compressive plasticity, whilst the rise in the glass transition temperature seem...     

Ni-based Ni-Fe-B-Si-Ta bulk metallic glasses

The glass-forming ability and properties of Ni-based Ni-Fe-B-Si-Ta bulk metallic glasses are explored in this work. The alloy compositions are determined by using a combination of the cluster line approach, the multi-alloying strategy and the substitutions of similar elements. Bulk metallic glasses with diameters of 3 mm take shape at compositions formulated under the clus- ter-plus-glue-atom model [M9B]B~[(Ni1-xFex)7.71(Si0.66Ta0.34)1.29B]B0.94=(Ni1-xFex)70.5B17.7Si7.8Ta4, x=0.35–0.45, where the bracketed part is the cluster and the unbracketed part is the glue atoms. These alloys exhibit good magnetic properties. The maximum Is is found in the (Ni0.55Fe0.45)70.5B17.7Si7.8Ta4 alloy which reaches 0.51 T, with its Hc as low as 8.5 A/m. Interestingly, these alloys display dual glass transitions at (Ni0.65Fe0.35)70.5B17.7Si7.8Ta4, (Ni0.60Fe0.4)70.5B17.7Si7.8Ta4 and (Ni0.55Fe0.45)70.5B17.7- Si7.8Ta4 as unveiled by Temperature-Modulated Differential Scanning Calorimetry.     

Developing aluminum-based bulk metallic glasses

This paper details a systematic investigation of the formation of Al-based bulk metallic glasses, expanding on an earlier brief report [Scripta Mater. 61 (2009) p.423]. We discuss an approach for designing and predicting the best glass-forming composition in the Al–TM–RE systems, based on the atomic cluster packing model for the internal structure of the glass. The effects of additional elements in quaternary and quinary systems on the glass-forming ability and thermal stability of the glasses are also discussed. Three new compositions, Al₈₆Ni₆Y_4.5Co₂La_1.5, Al₈₆Ni₇Y₅Co₁La₁ and Al₈₆Ni₇Y_4.5Co₁La_1.5, are capable of forming fully glassy rods of 1 mm in diameter; their glass transition and other thermal properties are systematically characterized.     

金属玻璃的热塑性成型

金属玻璃在其过冷液相区内表现出随着温度升高黏度逐渐降低的特性,因此可以对其进行热塑性加工.该性质颠覆了传统金属的加工成型方式,使得其在远低于传统金属材料加工的温度和应力作用下可以按照人们的要求进行成型.因此,一些具有低玻璃转变温度的金属玻璃又被称作金属塑料.另外,由于金属玻璃是一种无序结构材料,不存在位错、晶界等晶体缺陷,且热膨胀系数小,在热塑性成型中具有优异的尺寸精度,因此被认为是理想的微成型材料,有广阔的应用前景.本文系统介绍了金属玻璃的热塑性成型性质及其应用,从热塑性成型的基本概念出发,阐述了金属玻璃热塑性成型能力的评估指标、热塑性成型技术、热塑性微成型及其理论、热塑性微成型的应用等,对认识金属玻璃的热塑性及扩展其应用有重要的意义.     

Isomechanical groups in bulk metallic glasses

Isomechanical groups are, as defined by Frost and Ashby [H.J. Frost and M.F. Ashby, Deformation–Mechanism Maps, Pergamon Press, Oxford, 1982], separate classes of materials that exhibit similar deformation and transport properties when normalised by an appropriate parameter. Fundamentally, this separation results from significant differences in material structure and bonding. Here, such an analysis is applied to 40 bulk metallic glasses (BMGs) grouped into three classes according to their Poisson's ratio, which is known to be an indicator of intrinsic toughness. Through rigorous statistical analysis, it is found that isomechanical groups are present and that they may result from (1) variation in the tendency for directional bonding, and (2) how liquid-like the structure is, which may be characterised by a quantification of local volumetric strain. These results suggest that, although experimentally observed properties from BMGs in different isomechanical groups are all typically considered within the same framework, differences in atomic packing and inter-atomic bonding mean that they should in fact be treated separately. These fundamental differences in bonding and structure may explain the known large variation in the tendency for toughness and plasticity in BMGs.     

Collective dynamics of Zr-based bulk metallic glasses

The collective dynamics for the longitudinal as well as the transverse modes of the phonon eigenfrequencies are carried out for three Zr-based bulk metallic glasses (BMGs) in the present paper by employing pseudopotential theory. The theoretical phonon models proposed by Hubbard-Beeby (HB), Takeno-Goda (TG) and Bhatia-Singh (BS) are used to generate the phonon dispersion curves (PDC). The elastic and thermodynamic properties have also been investigated for the said BMGs by using the elastic limit of the phonon dispersion curves. The screening impact was also observed by using five different forms of local field functions due to Hartree (H), Taylor (T), Ichimaru and Utsumi (IU), Faridet al. (F) and Sarkaret al. (S) for the aforesaid properties. The derived results are seen to be in qualitative agreement with the available experimental and theoretically calculated data, as they confirm the applicability of Shaw's constant core model potential and self-consistent phonon theory for such studies.     

超高强块体非晶合金的研究进展

研制具有极限力学性能的金属材料一直是材料研究人员的梦想.超高强块体非晶合金是一类具有极高断裂强度(4 GPa)、高热稳定性(玻璃化转变温度通常高于800 K)和高硬度(通常高于12 GPa)的新型先进金属材料,其代表合金材料Co-Ta-B的断裂强度可达6 GPa,为目前公开报道的块体金属材料的强度记录值.本文系统地综述了该类超高强度块体非晶合金的组分、热学性能、弹性模量及力学性能,阐述了该类材料的研发历程;以弹性模量为联系桥梁,阐明了该类超高强块体非晶合金材料各物理性能的关联性,并揭示了其高强度、高硬度的价键本质.相关内容对于材料工作者了解该类超高强度金属材料的性能和特点,并推进该类材料在航空航天先进制造、超持久部件、机械加工等领域的实际应用有着重要意义.     

Extraordinary plasticity of ductile bulk metallic glasses

Shear bands generally initiate strain softening and result in low ductility of metallic glasses. In this Letter, we report high-resolution electron microscope observations of shear bands in a ductile metallic glass. Strain softening caused by localized shearing was found to be effectively prevented by nanocrystallization that is in situ produced by plastic flow within the shear bands, leading to large plasticity and strain hardening. These atomic-scale observations not only well explain the extraordinary plasticity that was recently observed in some bulk metallic glasses, but also reveal a novel deformation mechanism that can effectively improve the ductility of monolithic metallic glasses.     

Formation of different surface reliefs of metallic glasses under mechanical stress

The micro- and nanoreliefs of loaded lateral surfaces and fracture surfaces of foils of the Fe₇₇Ni₁Si₉B₁₃, Fe₅₈Ni₂₀Si₉B₁₃, and Fe₇₀Cr₁₅B₁₅ amorphous alloys have been investigated using scanning tunneling and atomic force microscopy. The isotropic and anisotropic surface reliefs have been examined. The fractal dimensions of the surfaces of loaded specimens and the fracture surfaces along and across the direction of crack propagation have been estimated using the box counting method. Fractal characteristics of the surfaces, such as the Hölder exponent and the half-width of the singularity spectrum, have been calculated using the wavelet transform method. It has been found that, on the topographies with a clearly pronounced anisotropy of the relief, the surface is fractal in only one direction, and the surface is fractal in two directions on the topographies with a less pronounced anisotropy of the relief. The fractal characteristics of the lateral surfaces and the fracture surfaces with allowance made for their anisotropy have close values. It has been shown that the formation of two types of fracture surfaces is adequately described in terms of the model of a cellular automaton.     

Effects of surface characteristics on the change of metallic glass structure and magnetoelastic properties induced by laser heat treatment

Laser annealing of amorphous alloy ribbons was performed by irradiating either their smooth or rough side. Experimental results such as hyperfine field distributions, average orientation of the magnetic moment, X-ray diffractography, initial permeability, magnetic anistropy, and low field magnetization, show the influence of the surface characteristics on the effects induced by the laser treatment. In particular, the effects of an applied tensile stress are compared to eachother and with previously obtained results. Many results are explained by means of the crystallization occurrence (at surface and also bulk) and taking into account its dependence on the irradiated surface properties and interaction time.     

Excimer laser surface treatment of bulk ceramics

Changes of surface morphology following excimer laser (KrF, ArF) irradiation were investigated for three technical ceramic materials (TZP, PSZ, Si₃N₄). Zirconia samples exhibit a smooth and glass-like surface at the low power density regime, while at higher power densities colour changes were observed due to changes in the chemical composition of the bulk material. In the silicon nitride samples new crystals of specific orientation are formed, which could be crystalline silicon.     

Three-point bending fracture characteristics of bulk metallic glasses

This paper presents the SEM micrographs for the three-point bending fracture surfaces of Zr-based, Ce-based and Mg-based bulk metallic glasses (BMGs), which show the dimple structures in the three kinds of BMGs. The shapes of the giant plastic deformation domain on the fracture surface are similar but the sizes are different. The fracture toughness KC and the dimple structure size of the Zr-based BMG are both the largest, and those of the Mg-based BMG are the smallest. The fracture toughness KC and the dimple structure size of the Ce-based BMG are between those of the Zr-based and the Mg-based BMG. Through analyzing the data of different fracture toughnesses of the BMGs, we find that the plastic zone width follows w = (KC/σY)2/(6π).     

Fe-B-Y-Nb bulk metallic glasses in relation to clusters

Bulk metallic glass formations in the Fe-B-Y-Nb quaternary alloy system were investigated by using the cluster line rule in combination with the minor alloying principle. The Fe-B-Y ternary system was selected as the basic system and the intersections of cluster lines were taken as the basic ternary compositions. The basic compositions were further alloyed with minor amounts of Nb. After 3–5 at.% Nb was added, the basic composition Fe_68.6B_25.7Y_5.7, which was developed from the most densely packed cluster Fe₈B₃, formed 3 mm bulk metallic glasses. These quaternary bulk metallic glasses (Fe_68.6B_25.7Y_5.7)_100−x Nb _x (x = 3–5 at.%) are expressed approximately with a unified simple composition formula: (Fe₈B₃)₁(Y, Nb)₁. The (Fe_68.6B_25.7Y_5.7)₉₇Nb₃ bulk metallic glass has the largest glass forming ability with the following characteristic parameters T _g = 907 K, T _x = 1006 K, T _g/T _l = 0.644, γ = 0.434, and longness t = 22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses. Supported by the National Natural Science Foundation of China (Grant Nos. 50671018, 50631010 and 50401020) and the National Basic Research Program of China (Grant No. 2007CB613902)