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.     

Strain rate induced crystallization in bulk metallic glass-forming liquid

We report on the solidification of Au49, Ag5.5, Pd2.3, Cu26.9, Si16.3 bulk metallic glass under various strain rates. Using a copper mold casting technique with a low strain rate during solidification, this alloy is capable of forming glassy rods of at least 5 mm in diameter. Surprisingly, when the liquid alloy is splat cooled at much higher cooling rates and large strain rates, the solidified alloy is no longer fully amorphous. Our finding suggests that the large strain rate during splat cooling induces crystallization. The pronounced difference in crystallization behavior cannot be explained by the previously observed strain rate effect on viscosity alone. A strain rate induced phase separation process is suggested as one of the explanations for this crystallization behavior. The strain-rate-dependent critical cooling rate must be considered in order to assess the intrinsic glass forming ability of metallic liquid.     

Phase separating bulk metallic glass: a hierarchical composite

Phase separating systems present a unique opportunity for designing composites with hierarchical microstructure at different length scales. We report here our success in synthesizing phase separating metallic glasses exhibiting the entire spectrum of microstructural possibilities expected from a phase separating system. In particular, we report novel core shell and hierarchical structures of spherical glassy droplets, resulting from critical wetting behavior and limited diffusion. We also report synthesis of a bulk phase separating glass in a metallic glass system. The combination of unique core shell and hierarchical structures in metallic glass systems opens a new avenue for the microstructure design of metallic glasses.     

Crystallization Kinetics of Co48Cr15Mo14C15BaEr2 Bulk Metallic Glass with High Thermal Stability

We investigate the crystallization kinetics of Co48Cr15Mo14C15B6Er2 bulk metallic glass. It is found that Co48Cr15Mo14C15B6Er2 alloy shows extraordinary glass-forming ability, and a fully glassy rod with a diameter of 10mm can be formed, Thermal analysis exhibits that this glassy alloy has a high thermal stability, Johnson-Mehl-Avrami analysis of isothermal differential scanning calorimetry demonstrates that the crystalline phases homogeneously nucleates at a constant rate and grows linearly at a constant rate in three dimensions in the supercooled liquid of the glassy alloy.     

非晶材料与物理近期研究进展

由于结合了金属和玻璃的特性,非晶合金表现出许多新奇和优异的力学和物理性质,在很多领域具有广泛的应用前景.非晶合金具有连续可调的成分、简单无序的原子结构、丰富多变的材料性质,为研究非晶态物理中的许多共性科学问题提供了理想的模型材料.块体非晶合金的发展更是将玻璃和液体及其相关科学问题的研究推进到凝聚态物理和材料科学的研究前沿.中国科学院物理研究所极端条件物理重点实验室亚稳材料合成、结构及性能研究组(EX4组)近二十年来一直致力于非晶材料和物理的研究,在新型非晶合金的制备、物性以及相关机理的研究上取得了许多重要成果.本文介绍团队最近在非晶材料和物理机理方面取得的研究成果,包括非晶合金的动力学行为和调控、非晶合金的表面动力学、功能应用以及材料探索新方法等.     

块体非晶合金的韧塑化

块体非晶合金因其独特的原子结构而具有许多优异的力学性能,成为近年来材料领域的研究热点之一,但是由于其在变形过程中的室温脆性和应变软化等关键问题一直制约着其实际工程应用.为解决此问题,块体非晶合金领域的研究者们提出了多种方案,包括通过在非晶合金中调控其内禀特性如弹性常数、结构不均匀性,通过外加手段改变其应力及缺陷状态,通过外加和内生的方法在非晶基体中引入晶态增强相等方式,获得了一系列力学性能优异的块体非晶合金及其复合材料.特别是利用"相变诱导塑性"(transformation-induced plasticity,TRIP)概念研制出的块体非晶合金复合材料,同时具有大的拉伸塑性和加工硬化能力.本文围绕块体非晶合金的韧塑化这个关键科学问题,对单相非晶及非晶复合材料的韧塑化方案及机理进行了综述,着重介绍了TRIP韧塑化块体非晶合金复合材料的制备、性能、组织调控及韧塑化机理等,并对此领域的未来发展进行了展望.     

Glass formation and magnetic properties of Fe-C-Si-B-P-(Cr-Al-Co) bulk metallic glasses fabricated using industrial raw materials

Formation of Fe-C-Si-B-P-(Cr-Al-Co) bulk metallic glasses with enhanced glass-forming ability (GFA) and magnetic properties fabricated using industrial pig-iron and Fe-P alloys as raw materials has been studied. It was found that GFA of the pig-iron (Fe_79.5C_18.0Si_2.3P_0.2, at%) could be improved by proper additions of only metalloids C, Si, P and B, and fully glassy structure was obtained in the Fe_75.5C_7.0Si_3.3B_5.5P_8.7 alloy with a critical diameter of 1 mm. With suitable additions of metallic elements Cr, Co and Al, the GFA is further increased and fully amorphous rods in 4 mm diameter can be prepared for the Fe_68.2C_7.0Si_3.3B_5.5P_8.7Cr_2.3Al_2.0Co_3.0 alloy that shows a unique combination of good soft-magnetic properties (M_s=1.03 T, H_c=9.39 A/m), high GFA and high fracture strength. These low-cost Fe-based bulk metallic glasses fabricated using industrial raw materials have a potential to be utilized as engineering materials.     

Metallic liquids and glasses: atomic order and global packing

In this Letter, we have revealed the common structural behavior of metallic glasses through scrutinizing the evolution of pair distribution functions from metallic liquids to glasses and statistically analyzing pair distribution functions of 64 metallic glasses. It is found that the complex atomic configuration in metallic glasses can be interpreted globally as a combination of the spherical-periodic order and local translational symmetry. The implications of our study suggest that the glass transition could be visualized mainly as a process involving in local translational symmetry increased from the liquid to glassy states.     

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.     

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.     

Metallic glassy fibers

A review on the formation and unique physical and mechanical properties of metallic glassy fibers (MGFs) with the diameter ranging from micro to nano scales fabricated by a supercooled liquid extraction method (SLEM) is given. The SLEM method, through driving metallic glass rods in their supercooled liquid region via superplasticity, can fabricate MGFs with precisely designed and controlled size and properties, high structural uniformity and surface smoothness and extreme flexibility. The SLEM method is efficient and the MGFs can be continuously prepared by this method. A parameter f based on the thermal and rheological properties of MG-forming alloys is proposed to control the preparation and size of the fibers. We show that the novel MGFs with superior properties may attract intensive scientific interests and propel more engineering and functional applications.     

Fracture of brittle metallic glasses: brittleness or plasticity

We report a brittle Mg-based bulk metallic glass which approaches the ideal brittle behavior. However, a dimple structure is observed at the fracture surface by high resolution scanning electron microscopy, indicating some type of "ductile" fracture mechanism in this very brittle glass. We also show, from the available data, a clear correlation between the fracture toughness and plastic process zone size for various glasses. The results indicate that the fracture in brittle metallic glassy materials might also proceed through the local softening mechanism but at different length scales.     

永磁性Pr55Al12Fe30Cu3 大块金属玻璃

报道一个新的Pr55Al12Fe30Cu3 大块金属玻璃.采用铜模吸铸法制备了直径为5 mm、长度达100 mm的Pr55Al12Fe30Cu3 大块金属玻璃.差示扫描量热分析结果表明在该Pr基大块金属玻璃体系具有宽达64 K左右的过冷液相区，而且该合金呈非晶态时的熔化温度要比相应晶态样品的熔化温度高约140 K.磁滞回线测量表明非晶态Pr55Al12Fe30Cu3 块体合金在室温下呈现永磁特性，而完全晶化后样品在室温下呈现软磁特性. 关键词： 大块金属玻璃 玻璃转变 晶化 永磁性     

Shear band formation and ductility in bulk metallic glass

The variations in the chemical compositions of the metallic glasses reported in the literature, as well as the overall lack of experimental data concerning the inhomogeneous deformation behaviour of metallic glass, make the evaluation of the effects of shear band/fracture behaviour on the mechanical properties of metallic glasses difficult. Isolating the effect of local shear band formation on bulk inhomogeneous flow would appear to be a first step in approaching this problem. The mechanical behaviour of Vitreloy metallic glass at room temperature and at various strain rates in tension and compression was investigated. The formation of multiple shear bands was observed at high strain rates. An increase in strain rate leads to enhanced ductility in tension and compression. Some aspects of the deformation processes in tension and compression are discussed.     

Effect of Yttrium Addition on Glass Forming Ability of ZrCuAlSi Alloy

The effect of yttrium addition on glass formation of a ZrCuAlSi alloy is investigated. The maximum diameter 8mm of the glassy rods for （Zr46.3Cu43.3Al8.9Si1.5）100-xYx alloy with x = 2.5 is obtained by copper mould casting. Apparent enhancement of the glass formation ability is found with addition of yttrium, mainly due to the purification of the alloy melt and the suppression of formation of the primary phases by yttrium.     

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.     

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.     

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     

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,thermal stability and mechanical properties of Ti<Subscript>42.5</Subscript>Zr<Subscript>7.5</Subscript>Cu<Subscript>40</Subscript>Ni<Subscript>5</Subscript>Sn<Subscript>5</Subscript> bulk metallic glass

Ti_42.5Zr_7.5Cu₄₀Ni₅Sn₅ bulk metallic glass with a critical diameter of 4 mm was fabricated by the conventional copper mould casting method. The supercooled liquid region ΔT _x, reduced glass transition temperature T _rg, γ parameter, and δ parameter of the alloy were measured to be 63.9 K, 0.561, 0.393, and 1.400, respectively, implying that the alloy has an excellent glass-forming ability. The bulk metallic glass exhibits high compressive fracture strength of 2162 MPa with distinct plastic strain of 0.9%. The fracture surface consists mainly of vein-like patterns, typical of bulk glassy alloys. Supported by the Program for New Century Excellent Talents in University of China and the National Natural Science Foundation of China (NSFC)(Grant No. 50771040)