Ti-Zr-Be-Fe quaternary bulk metallic glasses designed by Fe alloying

A series of Ti-Zr-Be-Fe bulk metallic glasses(BMGs)with good glass-forming ability(GFA)and high specific strength have been developed.With different alloying routes and content of Fe,it is found that these alloys exhibit different GFA and mechanical properties.The effects of Fe addition on the GFA and mechanical properties of Ti-Zr-Be alloy are systemically investigated.The possible mechanisms for the improvement or damage to the GFA by addition of Fe can be interpreted in view of the mixing enthalpy,atomic size differences and electronegativity differences of the alloys,while the mechanical properties strongly depend on the Poisson’s ratio and free volume concentration.The experimental results also show that alloying technology is an effective method to improve the GFA and mechanical properties of Ti-Zr-Be glassy alloy.     

NANOSTRUCTURED Zr-BASED ALLOYS-PHASE FORMATION AND MECHANICAL PROPERTIES

Newly developed nanostructured Zr/Ti-Al-TM multiphase alloys can provide a large bandwidth of interesting properties, such as mechanical properties. Bulk materials with nanocrystalline/ amorphous and (nano)quasicrystalline/ amorphous microstructure with different volume fractions of nanophases and with different grain sizes can be obtained by slowly cooling the melt as well as by solid state reactions. Multiphase structures are realized either by partial de-vitrification of bulk glass-forming alloys or by defined addition of inert compounds upon alloying. Special preparation techniques e.g. copper mould casting and subsequent controlled annealing and mechanical alloying combined with hot consolidation of powders are described. The phase formation and transformation processes and the thermal stability of such materials in dependence on alloy composition and processing parameters are discussed in detail. Currently, the exploration of properties with respect to potential applications of these nanostructured alloys is still at the beginning. First investigations on the contributions of different phases/ volume fractions to the overall mechanical behaviour will be shown. At room temperature, the deformation behaviour of amorphous/crystalline bulk samples is governed by contributions of all existing phases yielding a high strength of the material.     

Microstructure and mechanical properties of a partially crystallized La-based bulk metallic glass

The evolution of microstructure upon partial crystallization and its influence on the mechanical properties such as hardness, elastic modulus and viscosity in a La 55 Al 25 Cu 10 Ni 5 Co 5 bulk metallic glass alloy are studied. Specimens with various volume fractions of crystalline phases were obtained by annealing the as-cast amorphous alloy above its glass transition temperature and were characterized by transmission electron microscopy. Microscopic examination of the heat-treated samples shows short-range-ordered domains prior to nanocrystallization within the amorphous matrix, followed by the growth and impingement of the crystallites. Whereas the hardness of the annealed samples increases linearly with increasing crystallinity, the elastic modulus and the viscosity both increase abruptly when the crystalline volume fraction is about 40 vol.%, with a only minor variation on either side of this range. The sudden rises in the modulus and viscosity are similar to those in the literature data on the fracture strength of partially crystallized bulk amorphous alloys that shows a steep drop in strength at 30-50 vol.% crystallinity. On the basis of the microscopic observations, it is suggested that the interaction and formation of rigid networks of crystalline phases upon the attainment of a critical second-phase volume fraction may be the possible reason for the sudden change in mechanical properties. Percolation theory is utilized in further substantiating this hypothesis.     

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.     

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.     

铜基大块非晶合金添加微量元素对腐蚀行为的影响机理研究

通过分子动力学方法模拟了Cu-Al合金液相,然后模拟降温过程得到Cu-Al非晶合金.通过计算机编程建立了Cu-Al-M非晶基体、Cu-Al-M非晶表面及吸附O原子Cu-Al-M非晶表面原子结构模型.利用实空间连分数方法,研究了添加微量合金元素Zr,Nb,Ta,V,Y,Sc对Cu基大块非晶合金的腐蚀行为的影响机理.研究发现合金元素Zr,Nb,Ta,V,Sc不向清洁Cu基非晶表面偏聚,但除Y外向有氧吸附的表面偏聚,说明有氧吸附后Cu基非晶表面偏聚发生逆转.键级积分计算表明Zr,Nb,Ta,V,Y,Sc元素均增大与氧之间的结合力,易形成氧化膜,提高Cu基大块非晶的耐蚀性.稀土Y提高Cu基大块非晶的耐蚀性可能是由于它向合金与氧化膜界面偏聚并提高了合金与氧化膜的结合力.     

NMR signature of evolution of ductile-to-brittle transition in bulk metallic glasses

The mechanical properties of monolithic metallic glasses depend on the structures at atomic or subnanometer scales, while a clear correlation between mechanical behavior and structures has not been well established in such amorphous materials. In this work, we find a clear correlation of (27)Al NMR isotropic shifts with a microalloying induced ductile-to-brittle transition at ambient temperature in bulk metallic glasses, which indicates that the (27)Al NMR isotropic shift can be regarded as a structural signature to characterize plasticity for this metallic glass system. The study provides a compelling approach for investigating and understanding the mechanical properties of metallic glasses from the point of view of electronic structure.     

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.     

非晶合金的高通量制备与表征

非晶合金是一种不同于传统合金材料的新型合金,其突出的机械、物理、化学等性能在工程应用领域备受关注.作为一种具有无序原子结构的新型合金,非晶合金中蕴含的丰富的物理现象在基础研究领域也备受瞩目.非晶合金往往由多个组元构成,这给成分优化和性能调制带来了巨大的挑战.材料基因组方法是最近发展起来的新方法,通过高通量制备和结构表征以及性能筛选有望加快新型非晶合金材料的探索,在高通量表征中获得的大量实验数据可以帮助人们理解非晶合金中的科学问题.本文主要介绍高通量制备和表征在非晶合金中的应用,通过列举典型案例,展示通过高通量方法探索新型非晶合金材料的作用.     

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.     

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.     

Amorphous metallic plastic

We report cerium-based bulk metallic glasses with an exceptionally low glass transition temperature Tg, similar to or lower than that of many polymers. We demonstrate that, in near-boiling water, these materials can be repeatedly shaped, and can thus be regarded as metallic plastics. Their resistance to crystallization permits extended forming times above Tg and ensures an adequate lifetime at room temperature. Such materials, combining polymerlike thermoplastic behavior with the distinctive properties of metallic glasses, are highly unusual for metallic alloys and have great potential in applications and can also facilitate studies of the supercooled liquid state.     

High-entropy alloy and amorphous alloy composites fabricated by ultrasonic vibrations

We successfully fabricate high-entropy alloys and amorphous alloy composites by adopting the proposed ultrasonic vibration method. The low-stress, low-temperature method enables us to create composites that combine both amorphous and crystalline properties. Microscopic observations and computed tomography measurements indicate good bonding quality without pores or cracks in the composites. Due to the unique structure which mixes soft and rigid phases, the composite exhibits improved mechanical performance compared to that obtained from a pure single phase. Our results are promising for the manual design and fabrication of smart materials containing multiple phases and compositions.     

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.     

Amorphous Coatings and Surfaces on Structural Materials

Metallic glasses show a unique combination of high strength, excellent corrosion, and wear resistances because of their amorphous structure having a short-range order. In spite of excellent properties, the application of metallic glasses is restricted because of their inherent limitations in the bulk form, including limited tensile ductility. Using metallic glasses as the coatings for structural applications is an attractive way of taking advantage of their superior properties. Additionally, metallic glass-based composites having crystalline phases embedded in a amorphous matrix have also shown improved properties. Thus, metallic glasses can be synthesized as the coatings or subjected to surface modification to provide functionally superior surfaces. This article is a review of metallic glass-based coatings and surface modification of metallic glasses to achieve functionally superior surfaces for structural applications. Essential theoretical concepts were discussed which influence the processing. Common ways of processing along with the influence of various processing parameters were explored. Some non-conventional techniques which emerged as a result of continued efforts were also taken into account. Corrosion and wear properties of these materials along with the underlying mechanisms were discussed in detail. Focus was given to the recent product level applications explored in the open literature. Current challenges in the field were reviewed and guidelines for the future developments were provided.     

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.     

Effect of annealing on the deformation and fracture of metallic glass under local loading

An investigation is undertaken into the variations observed in the cracking resistance, the plasticity, and the structure of an 82K3KhSR metallic glass upon annealing. A method of evaluating the mechanical properties and the structural state of metallic glasses is proposed. This method is based on the indentation of the metallic glass deposited onto a substrate prepared from a polyester material and a metal. The critical annealing temperature that corresponds to drastic changes in the mechanical properties of the metallic glass is determined. It is found that dependences of the cracking resistance of metallic glasses on the indenter load exhibit a linear behavior at annealing temperatures above the critical point. An exponential decrease in the cracking resistance upon indentation is observed with an increase in the annealing temperature of metallic glasses.     

An Attempt to Prepare Metallic Glasses from Quasicrystals

Icosahedrons in supercooled liquids and glasses are considered to be of significance for the glass formation in alloy systems.Starting from the similarity of the local structure of quasicrystals to the icosahedrons in metallic glasses,a scheme is put forward to prepare metallic glasses based on a well-known quasicrystal Zr_(40)Ti_(40)Ni_(20).A series of(Zr_(40)Ti_(40)Ni_(20))_(100-x)Co_x metallic glasses are fabricated,and the optimized glass forming composition is determined at(Zr_(40)Ti_(40)Ni_(20))_(92)Co_8.The results show that the glass-forming ability of the alloys is closely related to the quasicrystalline phases.The mechanism of the enhanced glass-forming ability is discussed.     

Microstructure controlled shear band pattern formation and enhanced plasticity of bulk metallic glasses containing in situ formed ductile phase dendrite dispersions

Results are presented for a ductile metal reinforced bulk metallic glass matrix composite based on glass forming compositions in the Zr-Ti-Cu-Ni-Be system. Primary dendrite growth and solute partitioning in the molten state yields a microstructure consisting of a ductile crystalline Ti-Zr-Nb beta phase, with bcc structure, in a Zr-Ti-Nb-Cu-Ni-Be bulk metallic glass matrix. Under unconstrained mechanical loading organized shear band patterns develop throughout the sample. This results in a dramatic increase in the plastic strain to failure, impact resistance, and toughness of the metallic glass.     

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.