High-Entropy Metallic Glasses

The high-entropy alloys are defined as solid-solution alloys containing five or more than five principal elements in equal or near-equal atomic percent. The concept of high mixing entropy introduces a new way for developing advanced metallic materials with unique physical and mechanical properties that cannot be achieved by the conventional microalloying approach based on only a single base element. The metallic glass (MG) is the metallic alloy rapidly quenched from the liquid state, and at room temperature it still shows an amorphous liquid-like structure. Bulk MGs represent a particular class of amorphous alloys usually with three or more than three components but based on a single principal element such as Zr, Cu, Ce, and Fe. These materials are very attractive for applications because of their excellent mechanical properties such as ultrahigh (near theoretical) strength, wear resistance, and hardness, and physical properties such as soft magnetic properties. In this article, we review the formation and properties of a series of high-mixing-entropy bulk MGs based on multiple major elements. It is found that the strategy and route for development of the high-entropy alloys can be applied to the development of the MGs with excellent glass-forming ability. The high-mixing-entropy bulk MGs are then loosely defined as metallic glassy alloys containing five or more than five elements in equal or near-equal atomic percent, which have relatively high mixing entropy compared with the conventional MGs based on a single principal element. The formation mechanism, especially the role of the mixing entropy in the formation of the high-entropy MGs, is discussed. The unique physical, mechanical, chemical, and biomedical properties of the high-entropy MGs in comparison with the conventional metallic alloys are introduced. We show that the high-mixing-entropy MGs, along the formation idea and strategy of the high-entropy alloys and based on multiple major elements, might provide a novel approach in search for new MG-forming systems with significances in scientific studies and potential applications.     

金属玻璃弛豫行为及其机理的模拟研究进展

金属玻璃的弛豫动力学研究非常复杂,极具挑战性。弛豫（α弛豫、慢β弛豫和快β弛豫）发生在不同的温度下。利用模拟可观测微观原子信息的优势,评述了模拟中3种典型弛豫的特征和机理,并讨论了它们对材料力学性能的影响。讨论了近年来通过模拟方法获得的与弛豫相关的动力学、结构和物理机理方面的研究进展。本综述有助于认识玻璃的本质,建立玻璃材料的动力学-结构-性能关联。     

金属玻璃薄膜的研究进展

金属玻璃因具有良好的软磁特性、塑性好、耐磨损、耐腐蚀、表面光滑等特点,近几十年来受到广泛关注。块体状金属玻璃在室温下具有宏观脆性和加工性能差的缺点,限制了其应用,而薄膜态金属玻璃易于实现,并且可以克服块体玻璃本身的脆性缺陷,因而成为研究热点。综述了近十年来金属玻璃薄膜的研究成果,介绍了金属玻璃薄膜的制备方法,包括已经在工业中投入使用的物理气相沉积技术和电镀法,其中磁控溅射方法和电弧离子镀应用较多。阐述了金属玻璃薄膜的不粘性、抗疲劳性、耐腐蚀性、生物相容性、耐磨性、光学性能和催化性能以及相关影响因素,发现Zr基MGTF能够同时表现出多种性能,综合性能最佳,薄膜的不粘性值得特殊关注。表述了金属玻璃薄膜在改善合金性能、生物医疗领域和半导体领域的应用,在生物医用材料上镀膜可提高生物医用材料的不粘性和抗菌性,加速伤口愈合,具有很大潜力。最后,通过总结金属玻璃薄膜投入使用可能会面临的挑战和需要解决的问题,对今后的研究趋势进行了展望。     

金属玻璃纳米晶化机制研究进展

金属玻璃是一类具有结构和功能应用前景的新型金属材料,是目前物理和材料学科最为活跃的研究领域之一。由于处于热力学亚稳态,金属玻璃在合适的外界条件下会自发地向相应的晶态相发生转变,导致晶化事件的发生。研究金属玻璃的纳米晶化不仅有重要的科学意义,同时也可对金属玻璃的应用提供理论指导。简要介绍了目前几种代表性的金属玻璃纳米晶化微观机制：经典形核理论、基于耦合通量模型的形核机制、基于相分离的纳米晶形核长大机制、有序原子集团沉积机制、非经典形核理论、大过冷度条件下纳米晶化的微观机制等,同时结合作者课题组近年来在这方面的研究进展,对各种机制进行了评述,最后对未来金属玻璃纳米晶化机制研究中需要重视的几个问题进行了简单展望。     

镁基块体非晶合金的研究进展

Mg基块体非晶合金因其低成本和高比强度而有望成为轻质高强度结构材料,引起人们研究的极大兴趣.通过对Mg基决体非晶合金发展情况的综述研究,尤其是介绍了新成分设计和力学性能改善等方面的研究现况,发现Mg基块体非晶合金的研究主要集中在Mg-Cu基,成分设计以元素替代和合全体系元素优化为主,Mg基非晶合金塑性的改善是当前研究的重点和难点.     

大块非晶合金的制备方法

介绍目前大块非晶态合金材料的制备方法及其特色,并对各种制备方法的优缺点进行了讨论,最后对大决非晶合金制备方法的研究方向进行了展望.现阶段要想实现大块非晶态合金产品的工业化生产及应用需要开发新的制备方法或设备,对原有制备技术不断优化,改善现有的冷却环境,以及降低对原料纯度的要求.     

Relating Dynamic Properties to Atomic Structure in Metallic Glasses

Atomic packing in metallic glasses is not completely random but displays various degrees of structural ordering. While it is believed that local structures profoundly affect the properties of glasses, a fundamental understanding of the structure–property relationship has been lacking. In this article, we provide a microscopic picture to uncover the intricate interplay between structural defects and dynamic properties of metallic glasses, from the perspective of computational modeling. Computational methodologies for such realistic modeling are introduced. Exploiting the concept of quasi-equivalent cluster packing, we quantify the structural ordering of a prototype metallic glass during its formation process, with a new focus on geometric measures of subatomic “voids.” Atomic sites connected with the voids are found to be crucial in terms of understanding the dynamic, including vibrational and atomic transport, properties. Normal mode analysis is performed to reveal the structural origin of the anomalous boson peak (BP) in the vibration spectrum of the glass, and its correlation with atomic packing cavities. Through transition-state search on the energy landscape of the system, such structural disorder is found to be a facilitating factor for atomic diffusion, with diffusion energy barriers and diffusion pathways significantly varying with the degree of structural relaxation/ordering. The implications of structural defects for the mechanical properties of metallic glasses are also discussed.     

Zr-Al-Co块状非晶的成分优化

运用等电子浓度和变电子浓度线判据实现了Zr—Al—Co块状非晶合金的成分优化．在(Al50Co50)-Zr等电子浓度线(e／α=1．5)和(Zr9Co4)—Al及(Zr78．5Co21．5)—Al变电子浓度线上设计成分，并通过吸铸法制备块状合金．实验结果表明，在(Al50Co50)—Zr等电子浓度线和(Zr9Co4)—Al变电子浓度线上可形成块状非晶合金，且非晶合金的热稳定性与非晶形成能力随电子浓度的增大而单调递增．其中，(Al50Co50)-Zr等电子浓度线和(Zr9Co4)—Al变电子浓度线交点处形成的Zr53Al23．5Co23．5非晶合金，具有最大的热稳定性和非晶形成能力，特征热力学参数Tg=783K，Tx=849K，Tg／Tm=0．637，Tg／Ti=0．590。     

Evaluation of Cu-Zr-Ti-In Bulk Metallic Glasses via Nanoindentation

In this paper, the mechanical properties of two bulk metallic glasses, Cu₆₀Zr₃₄Ti₅In₁ and Cu₅₈Zr₃₄Ti₅In₃, have been evaluated by nanoindentation tests. The hardness and Young’s modulus of as-cast Cu₆₀Zr₃₄Ti₅In₁ bulk metallic glass increase from the center to the edge of the rod, but Cu₅₈Zr₃₄Ti₅In₃ shows an inverse trend. The Young’s modulus of Cu₅₈Zr₃₄Ti₅In₃ is lower than that of Cu₆₀Zr₃₄Ti₅In₁. For both bulk metallic glasses, serrations on the nanoindentation load-displacement curves depend not only on loading rate but also on the maximum load. Alternatively, the onset position of the appearance of serrations on the curves increases with the loading rate. In addition, the hardness of both samples decreases as the size of the indent increases due to indentation size effects.     

非晶及纳米结构钛合金研究进展

综述了钛基大块非晶的成分-非晶形成能力的对应关系，总结了已知的钛基大块非晶的一次结晶相及力学性能，并阐述了钛基大块非晶的塑性变形机制，以及造成低塑性的因素和改善塑性的方法，着重介绍了铸造纳米结构钛合金的成分、组织和力学性能。通过精巧的成分设计，结合金属模铸造技术，制备出了直径小于5mm，并具有微米尺度β-Ti（M）一次树枝晶相＋纳米尺度棒状β-Ti／γ-TiCu共晶结构的复合组织，其中棒状β-Ti相尺寸在30nm～300nm范围；γ-TiCu共晶基体相由小于10nm的晶粒或亚晶粒组成，这种多层次纳米结构的钛合金具有高强度，同时县有明显的延伸性。     

A Concordant Shift Model for Flow in Bulk Metallic Glasses

The homogeneous plastic flow in bulk metallic glasses(BMGs) must be elucidated by an appropriate atomistic mechanism. It is proposed that a so-called concordant shifting model, based on rearrangements of five-atom subclusters,can describe the plastic strain behaviour of BMGs in a temperature range from room temperature to the supercooled liquid region. To confirm the effectiveness of the atomic concordant shifting model, a comparative investigation between the vacancy/atom model and the concordant shifting model is carried out based on the estimation of the strain rate deduced from two models. Our findings suggest that the atomic concordant shifting model rather than the vacancy/atom exchange model can well predict the large strain rate in the superplasticity of BMGs.     

Impact Conditions for Cold Spraying of Hard Metallic Glasses

As compared to thermal spray techniques, cold spraying allows to retain metastable phases of the feedstock material like amorphous structures, due to lower process gas temperatures. Compared to crystalline metals, metallic glasses are brittle at ambient temperature but viscous at higher temperatures. Therefore, cold spray parameters must be optimized for conditions that allow softening of the amorphous spray material for successfully producing coatings. For this study, a FeCoCrMoBC metallic glass was used that in comparison to others offers advantages with respect to higher hardness, less costly feedstock powder, and minimum reactivity with the environment. Necessary impact conditions were investigated to meet the window of deposition in cold gas spraying. According to calculations and cold spray experiments, neither the glass transition temperature T _g nor the melting temperature T _m can describe required conditions for bonding. Thus, a so called softening temperature between the glass temperature and the melting temperature had to be defined to calculate the critical velocity of metallic glasses. With respect to the bonding mechanism, impact morphologies could prove that a transition to viscous flow gets more prominent for harsher spray conditions. By sufficiently exceeding the critical condition for bonding, coatings with rather dense microstructures can be processed at deposition efficiencies of about 70%. The coatings have a hardness of 1100?HV 0.3, but the results also demonstrate that further work is still needed to explore the full potential for bulk metallic glasses.     

三种ZrAlNiCu大块金属玻璃的力学性能

采用真空氩弧熔炼加铜模吸铸的方法成功制备了3种ZrAlNiCu全非晶材料。通过Instron-3369力学性能试验机测试了3种金属玻璃的压缩力学性能,并采用FEINano230型场发射扫描电镜(SEM)研究了压缩断口特征。研究表明,增加Ni含量和降低Cu含量将降低ZrAlNiCu金属玻璃的断裂强度和弹性模量,并使得ZrAlNiCu金属玻璃的断口由扩展良好的"脉络状"花纹转变为完全脆性特征。Ni含量的增加以及Cu含量的降低减少了ZrAlNiCu金属玻璃中自由体积的密度,降低了合金的变形能力,增加了合金的变形局域化程度,从而降低了ZrAlNiCu金属玻璃的断裂强度、塑性和弹性模量。     

Nanoindentation Mechanical Properties of Indium-Alloyed Cu-Based Bulk Metallic Glasses

In this paper, two Indium-alloyed Cu-based bulk metallic glasses, Cu₅₄Zr₃₇Ti₈In₁ and Cu₅₀Zr₃₇Ti₈In₅, have been evaluated with nanoindentation testing. Both bulk metallic glasses have homogenous nature in structure. Both hardness and Young’s modulus of bulk metallic glasses do not show a loading rate-dependent. Addition of In decreases hardness and Young’s modulus, but increases creep-resistance of bulk metallic glasses. Indentation creep of two bulk metallic glasses has also been investigated. The displacement-time curves of creep processes were described with generalized Kelvin model. The creep displacement, compliance spectrum, and retardation spectrum for each bulk metallic glass were discussed comparatively. The results showed that Cu₅₀Zr₃₇Ti₈In₅ has better creep-resistance at room temperature and a more relaxed state.     

Serrated Flow Model for Metallic Glasses under Compressive Loading

A rheological model is proposed that incorporates the serrated flow nature of metallic glasses. It involves the process of the nucleation, propagation and the arrest of a shear bands in the samples subjected to compressive deformation at room temperature. Numerical resolution of the constitutive equations resulting from the model is compared with the stress-strain curve obtained from in-situ nano-compression test in SEM of Zrbased metallic glass. Parametric identification method was applied and enabled us to release the physical parameters of the model. The obtained results showed that the model is adequately valid to describe the experimental data and the almost adjustable model parameters are physically meaningful and comparable to literature.     

Co(-Fe)-B-Si-Nb块体非晶合金

利用团簇线方法和微合金化原理研究了Co基Co(-Fe)-B-Si-Nb多组元合金体系中块体非晶合金的形成。首先,确定Co-B-Si三元体系为基础体系,利用团簇线(体现在三元体系中为二元特殊团簇与第三组元的连线)在Co-B-Si体系中确定基础合金成分;然后添加少量的Nb对基础三元成分进行合金化以提高合金的玻璃形成能力。利用铜模吸铸法制备直径为3mm的合金棒,结果表明能够形成块体非晶的合金成分为(Co8B3-Si)100-xNbx(x=4～5at%),其中,Co8B3为密堆附半八面体的阿基米德反棱柱团簇结构。并且这些非晶成分可近似地用(团簇)1(胶粘原子)1模型表达,为(Co8B3)1M1(M=(Si,Nb)),即非晶成分由一个团簇连接一个胶粘原子组成,其中胶粘原子M为Si和Nb原子的组合。最后用Fe替代部分Co可进一步提高合金的玻璃形成能力,得到的Co-Fe-B-Si-Nb五元块体非晶合金具有很好的软磁性能,其饱和磁化强度(Ms)最大可达0.98T,矫顽力(Hc)低于6A/m。     

金属玻璃的功能性应用及相关基础研究

金属玻璃是一类具有热力学非平衡特征和亚稳特性、以金属元素为主要组分、原子排列处于无序结构的固体材料。近年来,随着金属玻璃研究领域的蓬勃发展,涌现出很多新的研究方向和热点。简要综述了近期金属玻璃在化学反应中表现出的优异催化性能和高反应速率等相关的功能性应用和基础研究进展,主要介绍了金属玻璃在降解污水中的偶氮染料方面的功能性应用和基础研究。实验结果表明,镁基和铁基金属玻璃粉降解偶氮染料的效率分别达到商业晶态铁粉的1000倍和200倍以上。而且,相对于液体雾化法制备的金属玻璃粉,用球磨粉碎法制备的金属玻璃粉反应活性更高,这可能与球磨金属玻璃粉比表面积增加、残余应力导致的反应激活能降低有关。最后对金属玻璃的功能性应用和相关基础研究的未来研究前景进行了展望。     

新型Y-Fe-Co-B大块非晶合金的制备与磁性能研究

用水冷铜模吸铸方法制备了最大截面直径为2mm的Y6Fe60.5Co11.5B22铁基大块非晶合金，研究了冷却速率对合金磁性能的影响，分析并计算了合金的临界冷却速率。大块Y6Fe6.5Co11.5B22非晶合金具有良好的软磁性能：其矫顽力Hc=2．53A／m，饱和磁化强度Ms=1．24T，初始磁化率明显高于相同成分的晶态合金。热稳定性分析表明，该合金具有较高的非晶形成能力，其形成非晶的临界冷却速率（Rc）约为119K／s。