Heredity of clusters in the rapidly cooling processes of Al-doped Zr_(50)Cu_(50) melts and its correlation with the glass-forming ability

The heredity of clusters in rapidly cooled(Zr_(50)Cu_(50))_(100-x)Al_x melts and its correlation with glass-forming ability(GFA) are studied via molecular dynamics simulations. Pair distribution function and the largest standard cluster(LSC)are adopted to characterize the local atomic structures in the(Zr_(50)Cu_(50))_(100-x)Al_x systems. The [12/555] icosahedra and their medium-range order(IMRO) play an important role in forming(Zr_(50)Cu_(50))_(100-x)Al_x metallic glasses(MGs). The fraction of [12/555], the number of IMRO, and the maximum size of IMRO in MGs increase significantly with increasing x. A tracking study further reveals that the configuration heredity of icosahedral clusters starts from supercooled liquids.No direct correlation exists between the GFA and the onset temperature of continuous or stated heredity. Instead, a larger hereditary supercooled degree of icosahedra matches with better GFA of Al-doped Zr_(50)Cu_(50) alloys.     

Glass formation criterion for various glass-forming systems

A conceptual approach to evaluate glass-forming ability for various glass-forming systems has been proposed from a physical metallurgy point of view. It was found that the glass-forming ability for noncrystalline materials was related mainly to two factors, i.e., 1/(T(g)+T(l)) and Tx (wherein Tx is the onset crystallization temperature, T ( g) the glass transition temperature, and T(l) the liquidus temperature), and could be predicated by a unified parameter gamma defined as T(x)/(T(g)+T(l)). This approach was confirmed and validated by experimental data in various glass-forming systems including oxide glasses, cryoprotectants, and metallic glasses.     

Structural evolution in deformation-induced rejuvenation in metallic glasses: A cavity perspective

Classical molecular dynamics simulations have been performed to investigate the structural evolution in deformationinduced rejuvenation in Cu_(80)Zr_(20) metallic glass. Metallic glasses obtained by different cooling rates can be rejuvenated into the glassy state with almost the same potential energy by compressive deformation. The aging effect in different metallic glasses in cooling process can be completely erased by the deformation-induced rejuvenation. The evolution of cavities has been analyzed to understand the structural evolution in rejuvenation. It is found that as metallic glasses are rejuvenated by mechanical deformation, a lot of cavities are created. The lower the potential energy is, the more the cavities are created. The cavities are mainly created in the regions without cavities or with small cavities populated, indicating that the irreversible rearrangements induced by deformation are accompanied by the creation of cavity. This finding elucidates the underlying structural basis for rejuvenation and aging in metallic glasses from the cavity perspective.     

Minor alloying behavior in bulk metallic glasses and high-entropy alloys

The effect of minor alloying on several bulk metallic glasses and high-entropy alloys was studied. It was found that minor Nb addition can optimize the interface structure between the W fiber and the Zr-based bulk metallic glass in the composites, and improve the mechanical properties. Minor Y addition can destabilize the crystalline phases by inducing lattice distortion as a result to improve the glass-forming ability, and the lattice distortion energy is closely related to the efficiency of space filling of the competing crystalline phases. A long-period ordered structure can precipitate in the Mg-based bulk metallic glass by yttrium alloying. For the high-entropy alloys, solid solution can be formed by alloying, and its mechanical properties can be comparable to most of the bulk metallic glasses.     

Glass-forming ability in laser quenched transition-metal Alloys

The glass-forming ability by laser quenching is investigated for several transition metal systems (Au-Ti, Co-Ti, Cr-Ti, Zr-Ti). Metallic glasses are obtained in the systems Au-Ti, Co-Ti, and Cr-Ti. The results are compared to predictions by several semiempirical criteria of glass-forming ability. Our results indicate that at the cooling rates typical to laser quenching glasses in binary metallic systems form whenever diffusionless crystallization is excluded.     

Possible link of the V-shaped phase diagram to the glass-forming ability and fragility in a water-salt mixture

Water is a very poor glass former, but its link to the thermodynamic and kinetic anomalies remains elusive. We experimentally reveal that the glass-forming ability and fragility of a water-salt mixture are closely related to its equilibrium phase diagram. We propose that frustration between local and global orderings controls both the glass-forming ability and the fragility. Relying on the same role of salt and pressure, which commonly break tetrahedral order, we apply this idea to pure water under pressure. This scenario not only explains unusual behavior of water-type liquids such as water, Si, and Ge but also provides a mechanism for a link between the equilibrium phase diagram, glass-forming ability, and fragility for various materials including oxides, chalcogenides, and metallic glasses.     

非晶中结构遗传性及描述

非晶态物质广泛存在于人们的日常生活和工业生产活动中,但人们对其原子结构及其结构与性能关系的认识还远不如对晶体材料那样充分.非晶态物质的原子结构不具备空间平移对称性,这使得传统针对晶体材料的实验技术和手段无法直接有效地应用到非晶态物质的结构分析中.用常规的衍射实验数据分析方法并不能直接地观察到非晶态物质的本征结构特征,但这些实验衍射数据往往隐含有极其重要的微观结构信息.本文简要综述了这些衍射数据背后所隐含的与金属玻璃中程序相关的结构信息.研究发现,非晶态物质中的一类隐含序与晶体结构中的球周期序紧密相关,意味着非晶态物质与晶体材料之间在原子结构上存在着非凡的同源性.进一步的研究结果还表明,不同隐含拓扑序之间纠缠的强弱与体系本身的玻璃形成能力存在明显的对应关系,这为衡量金属合金玻璃形成能力强弱的经验规律——混乱原理提供了微观结构上的理解,同时为进一步深入认识和理解非晶态材料衍射数据所隐含的微观结构信息提供了新的分析思路和方法.     

A New Cu-Based Metallic Glass Composite with Excellent Mechanical Properties

A new Cu-based bulk metallic glass composite of nominal composition(at.%) Cu_(41)Ni_(27)Ti_(25)Al_7 with excellent plasticity and a strong work-hardening behavior is fabricated. Strength above 1859 MPa and plasticity more than 11% are achieved under compression and tension modes. The deformation mechanism is proposed to the structural heterogeneities of the composite that promotes multiple shear bands meanwhile inhibits their free propagation,which results in the macroscopically plastic strain and work hardening. The alloy contains relatively cheap metals and has a low cost, which is beneficial to industrial applications.     

新型远红外Ge-Te-I硫系玻璃性能研究

采用传统的熔融-淬冷法制备了系列Ge20Te80－xIx(x=2,4,6,8 mol%) 玻璃样品.利用X射线衍射仪、扫描电子显微镜、差热分析仪等设备系统测试了玻璃结构和物化性质,分析了卤素I对玻璃形成及稳定性的影响|利用分光光度计、红外光谱仪等研究了玻璃光谱性质,分析了I对玻璃的短波吸收及红外透过光谱的影响|利用Tauc方程计算了样品的直接和间接光学带隙.实验结果表明:I的引入,降低了Te的金属性,提高了Te基硫系玻璃的成玻能力|随着卤素I含量的增加,玻璃的密度减小,摩尔体积增大,且短波吸收截止边发生红移,光学带隙减小|I的引入提高了玻璃的热稳定性,其中玻璃组分为Ge20Te72I8样品热稳定性最好,其特征温度（ΔT）达到121℃|各Ge-Te-I玻璃样品均具有良好的红外透过性能,其红外透过范围为1.8~25 μm.     

Imaging the diffusion pathway of Al~(3+) ion in NASICON-type(Al_(0.2)Zr_(0.8))_(20/19)Nb(PO_4)_3 as electrolyte for rechargeable solid-state Al batteries

Among all-solid-state batteries, rechargeable Al-ion batteries have attracted most attention because they involve threeelectron-redox reactions with high theoretic specific capacity. However, the solid Al-ion conductor electrolytes are less studied. Here, the microscopic path of Al~(3+)-ion conduction of NASICON-type(Al_(0.2)Zr_(0.8))_(20/19)Nb(PO_4)_3 oxide is identified by temperature-dependent neutron powder diffraction and aberration-corrected scanning transmission electron microscopy experiments.(Al_(0.2) Zr_(0.8))_(20/19) Nb(PO_4)_3 shows a rhombohedral structure consisting of a framework of(Zr,Nb)O_6 octahedra sharing corners with(PO_4) tetrahedra; the Al occupy trigonal antiprisms exhibiting extremely large displacement factors. This suggests a strong displacement of Al ions along the c axis of the unit cell as they diffuse across the structure by a vacancy mechanism. Negative thermal expansion behavior is also identified along a and b axes, due to folding of the framework as temperature increases.     

New criterion in predicting glass forming ability of various glass-forming systems

It has been confirmed that glass-forming ability （GFA） of supercooled liquids is related to not only liquid phase stability but also the crystallization resistance. In this paper, it is found that the liquid region interval （T1 - Tg） characterized by the normalized parameter of Tg/T1 could reflect the stability of glass-forming liquids at the equilibrium state, whilst the normalization of supercooled liquid region △Tx=（Tx - Tg）, i.e. △Tx/Tx （wherein T1 is the liquidus temperature, Tg the glass transition temperature, and Tx the onset crystallization temperature） could indicate the crystallization resistance during glass formation. Thus, a new parameter, defined as ζ = Tg/T1＋△Tx/Tx is established to predict the GFA of supercooled liquids. In comparison with other commonly used criteria, this parameter demonstrates a better statistical correlation with the GFA for various glass-forming systems including metallic glasses, oxide glasses and cryoprotectants.     

New criterion in predicting glass forming ability of various glass-forming systems

It has been confirmed that glass-forming ability (GFA) of supercooled liquids is related to not only liquid phase stability but also the crystallization resistance. In this paper, it is found that the liquid region interval ($T_{\rm l}-T_{\rm g})$ characterized by the normalized parameter of $T_{\rm g}$/$T_{\rm l}$ could reflect the stability of glass-forming liquids at the equilibrium state, whilst the normalization of supercooled liquid region $\Delta T_{\rm x}$=($T_{\rm x}-T_{\rm g})$, i.e. $\Delta T_{\rm x}$/$T_{\rm x}$ (wherein $T_{\rm l}$ is the liquidus temperature, $T_{\rm g}$ the glass transition temperature, and $T_{\rm x}$ the onset crystallization temperature) could indicate the crystallization resistance during glass formation. Thus, a new parameter, defined as $\xi =T_{\rm g}$/$T_{\rm l}+\Delta T_{\rm x}$/$T_{\rm x}$ is established to predict the GFA of supercooled liquids. In comparison with other commonly used criteria, this parameter demonstrates a better statistical correlation with the GFA for various glass-forming systems including metallic glasses, oxide glasses and cryoprotectants.     

Preparation and properties of Ce-doped Na–Gd phosphate glasses

Rare earth-doped sodium–gadolinium phosphate glasses with increased luminescence efficiency are promising materials for the detection of neutrons, γ- and X-rays. Their main advantages are low cost, high radioluminescence light output, high quality and chemical durability. The glasses were prepared by a rapid quenching technique in air. The radioluminescence intensity maximum was achieved for a Ce concentration of 3 mol% and that of Gd around 30%. Glass transition temperatures were above 300°C for the tested samples and this guarantees that the glass can be utilised in a sufficiently broad temperature range. The glass-forming ability of this glass system is high. However, until now high-quality glass has been only prepared with a Gd concentration of 40 mol% in the starting batch. The glasses containing at least 30 mol% Gd were moisture resistant, while those with lower Gd concentrations were slightly hygroscopic.     

Structural amorphous steels

Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist's dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.     

新型GeS_2-Ga_2S_3-KI玻璃性能的研究

用传统熔融淬冷法制备了新型硫卤玻璃(100-x)(80GeS2-20Ga2S3)-xKI(x=0,10,20mol%).利用差热分析、可见/近红外吸收光谱、红外透射光谱等技术对准三元硫卤玻璃体系GeS2-Ga2S3-KI的组成、结构和性能关系进行了研究.分析结果表明:GeS2-Ga2S3-KI三元系统玻璃具有较宽的玻璃形成区;当KI的含量为10mol%时,玻璃热稳定性最好;随着KI的加入,玻璃的红外截止波长无明显变化,皆为12.5μm;然而随着局域电位场的增大,玻璃的短波吸收限向短波方向发生了移动,光学带隙存在增大趋势.     

非晶合金中的低温电阻率极小行为研究

研究了非磁非晶合金Cu₆₀Zr₂₀Hf₁₀Ti₁₀和铁磁非晶合金Fe₆₁Co₇Zr₁₀Mo₅W₂B₁₅的低温电阻，用不同的模型对电阻温度曲线进行拟合.对两个样品中出现的极小值行为进行分析，探讨了无序结构和磁性状态对极小值行为的影响. 关键词： 非晶合金 电阻 极小值     

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.     

Calorimetric study of characteristic temperatures and crystallization behavior in Ge-As-Se-Te glass system

Results of differential scanning calorimetry of high purity Ge_xAs_40−xSe₄₀Te₂₀ (x=0-40) chalcogenide glasses are reported. The glass transition temperatures and crystallization behavior were studied under non-isothermal conditions at different heating rates (2.5-35 K/min). The glass transition temperature changes from 140 °C up to 320 °C with increasing the Ge content in Ge_xAs_40−xSe₄₀Te₂₀ glass. The studied glasses with x≤35 have no exothermal peaks of crystallization, indicating their high glass-forming ability. The glass of Ge₄₀Se₄₀Te₂₀ composition has one-stage glass transition and double-stage crystallization process during phase change. The activation energy of the glass transition (E_g), the activation energy of crystallization (E_c), the Avrami exponent (n), the frequency factor (K₀) and the crystallization criteria of Ge₄₀Se₄₀Te₂₀ glass were determined.     

Self-organization and the physics of glassy networks

Network glasses are the physical prototype for many self-organized systems, ranging from proteins to computer science. Conventional theories of gases, liquids and crystals do not account for the strongly material-selective character of the glass-forming tendency, the phase diagrams of glasses or their optimizable properties. A new topological theory, only 25 years old, has succeeded where conventional theories have failed. It shows that (probably all slowly quenched) glasses, including network glasses, are the result of the combined effects of a few simple mechanisms. These glass-forming mechanisms are topological in nature and have already been identified for several important glasses, including chalcogenide alloys, silicates (window glass and computer chips) and proteins.     

稀土掺杂P2O5-Al2O3-BaO玻璃的制备及其结构研究

稀土掺杂磷酸盐玻璃具有优异的光学和光谱特性,在激光介质、有色滤光材料等领域中有着重要的应用。在P2O5_Al2O3_BaO_Sm2O3(PABS)玻璃形成能力研究的基础上,借助MAS NMR、红外光谱等分析手段,研究了玻璃的结构、玻璃组成与热处理等对玻璃结构的影响。结果表明:不同组成PAB(S)玻璃的31P MAS NMR谱在-20ppm~-25ppm范围内均存在单一的特征信号峰,对应于磷氧多面体[PO4]的Q2型结构;在18ppm、-12ppm和-36ppm处27Al的MAS NMR谱的三个特征信号峰分别对应于27Al的[AlO5][、AlO6]、[AlO6]配位结构,稀土离子的掺入以及热处理均使得[AlO6]向[AlO5]转变;玻璃的网络结构主要由Q2型[PO4]、[AlO5]和[AlO6]构成,并P_O_P、P_O_Al的形式相连接。玻璃在1383 cm-1处出现的吸收峰可能是玻璃结构中形成了P_O_Sm键所致。