Bending-fatigue behavior of bulk metallic glasses and their composites

Amorphous alloys with high glass-forming ability and thermal stability were discovered in the 1990s. In the following years, the alloy design increased the critical casting thickness to several centimeters, and a homogeneous dispersion of nanoscale particles was found to improve the ductility. Therefore, bulk metallic glasses (BMGs) are being studied widely because of their potential as structural materials. The fatigue behavior is an important characteristic of structural materials. The current review documents the bending-fatigue studies of BMGs and their composites. The fatigue characteristics of these alloys in different loading conditions and environments are summarized and compared in this paper. The factors affecting the fatigue behavior of BMGs and their composites are discussed. The mechanisms of fatigue-crack initiation and propagation in BMGs are addressed in this review. In order to broaden the scope of applications of BMGs, a fundamental understanding of the fatigue behavior is critical for the design of new alloy systems and the development of the processing techniques.     

Compositional design and microstructure analysis of Zr-based bulk metallic glasses

The systematical studies of Zr-based BMGs were summarized in terms of their compositional design and their structural characterization. In particular, several key issues of BMG materials were focused, including initial alloy design and subsequent composition optimization, solidification microstructure characterization and crystallization process specification. The results show that a compositional designing approach is successfully developed and, through extensive microstructure characterization using transmission electron microscopy, several new crystalline phases are discovered in these newly developed Zr-based BMG alloys. Crystallization behavior ofZr-based BMG is also determined based on the microstructure analysis.     

Design of Bulk metallic glasses with high glass forming ability and enhancement of plasticity in metallic glass matrix composites: A review

To overcome some of the limits of existing metallic alloys, a new alloy design concept has been introduced recently in order to control the crystallinity, i.e. to utilize crystalline, quasicrystalline, and amorphous structures. In particular, bulk metallic glasses (BMGs) receive great attention because of their unique properties due to their different atomic configuration. Recently, significant progress in enhancing glass forming ability (GFA) has led to the fabrication of BMGs having potential for application as structural and functional materials. Moreover, successful design of BMG matrix composite microstructure suggests that the plasticity of BMGs can be controlled properly. In this review article, we introduce recent research results on the design of BMGs with high GFA and on the enhancement of plasticity in metallic glass matrix composites.     

The fracture toughness of bulk metallic glasses

Stiffness, strength, and toughness are the three primary attributes of a material, in terms of its mechanical properties. Bulk metallic glasses (BMGs) are known to exhibit elastic moduli at a fraction lower than crystalline alloys and have extraordinary strength. However, the reported values of fracture toughness of BMGs are highly variable; some BMGs such as the Zr-based ones have toughness values that are comparable to some high strength steels and titanium alloys, whereas there are also BMGs that are almost as brittle as silicate glasses. Invariably, monolithic BMGs exhibit no or low crack growth resistance and tend to become brittle upon structural relaxation. Despite its critical importance for the use of BMGs as structural materials, the fracture toughness of BMGs is relatively poorly understood. In this paper, we review the available literature to summarize the current understanding of the mechanics and micromechanisms of BMG toughness and highlight the needs for future research in this important area.     

Zr基多孔非晶合金的研究进展

Zr基多孔非晶合金因其具有轻质、良好的延展性以及生物相容性,许多科研工作者开展了这种极具优势材料的开发。综述了Zr基多孔非晶合金的发展、制备以及力学性能的研究进展。分析了Zr基多孔非晶合金当前需要解决的问题,并对未来发展方向及应用前景进行了展望。     

Influences of Ta, Nb, or Mo additions in Zr-based bulk metallic glasses on microstructure and thermal properties

The master-alloy ingots for casting bulk metallic glasses are routinely prepared by arc melting a mixture of pure elements. This paper addresses the difficulty in achieving complete and homogeneous melting of refractory component additions in Zr-based BMGs using the above procedure, and its influences on the microstructure and thermal behavior of alloys.     

Mechanical response of metallic glasses: Insights from in-situ high energy X-ray diffraction

The term “metallic glass” usually refers to a metallic alloy rapidly quenched in order to “freeze” its structure from the liquid state. A metallic glass is a metastable alloy, which lacks the symmetry typical for crystalline materials and at room temperature shows an amorphous liquid-like structure. Bulk metallic glasses (BMGs) represent a class of amorphous alloys. The most notable property of BMGs is their ultrahigh (near theoretical) strength and hardness. Because the known BMGs usually miss tensile plasticity and thus exhibit catastrophic failure upon tension it is important to understand deformation mechanisms involved and thus improve their performance. This aricle analyzes the use of synchrotron radiation for evaluating the elastic-plastic response of such materials.     

非晶合金的相变韧塑化

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,一直制约其大规模工程应用。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,其中利用“相变诱导塑性”概念制备块体非晶合金复合材料来韧塑化非晶合金成为卓有成效的方案之一,通过此方法成功地制备出同时具有拉伸塑性和加工硬化能力的非晶合金复合材料。然而,该类块体非晶合金复合材料要求的形成条件更严格,同时具有更复杂的多相协调变形过程和更独特的性能优化方案。从该类块体非晶合金复合材料的形成、性能特点、韧塑化机理及性能优化等方面进行综述,并对其未来发展进行了简要展望。     

Zr基和Ti基块体非晶合金的电化学腐蚀性能(英文)

用电化学方法研究Ti基和Zr基非晶合金及与非晶成分相同的Zr基晶态合金在1mol/LH2SO4和3.5%NaCl溶液中的腐蚀行为。极化曲线测试结果表明:在H2SO4溶液中,Zr基非晶和晶态合金自腐蚀电位比Ti基非晶合金的低;在NaCl溶液中,Zr基晶态合金的自腐蚀电位最低,而且在腐蚀过程中没有发生钝化,然而非晶合金都表现出钝化特性。交流阻抗测试结果表明:在NaCl溶液中非晶合金比晶态合金表现出更好的耐腐蚀性能,但是在H2SO4溶液中并没看到它们之间有明显的区别。表面形貌分析表明:在NaCl溶液中,这2种非晶合金都发生点蚀,而在H2SO4溶液中所有试验合金都表现出类似的特征,试样表面基本保持平整,只是在腐蚀表面的局部区域有一些裂纹出现。     

Production methods and properties of engineering glassy alloys and composites

Since the first synthesis of glassy alloys in 1960, a great large number of studies have been carried out in basic science and technological aspects. At present, glassy alloys and composites have been used as functional and structural materials. The production method for their practical materials was limited to a quenching type technique for many years before around 1990, but the finding of bulk glassy alloys caused a drastic change in production method of glassy alloys to a copper mold casting type technique which has enabled the production of glassy alloys in a three dimensional bulk form. Furthermore, glass alloy composites produced by semi-solid progressive solidification have been successfully developed recently, even using impure charge materials. The drastic changes in the production method and material form have also resulted in significant extension of application fields of glassy alloys. This paper aims to review the production methods and properties of glassy alloys and composites with useful critical sizes above 100 μm or below 4 μm in thickness for glassy powder in conjunction with the present situation of applications for their glassy alloys and composites which do not belong to materials with an ordinary thickness size range of 10–50 μm.     

Using Amorphous Phases in the Design of Structural Alloys

The recent discovery that amorphous alloy powders can be prepared by mechanically alloying a mixture of pure crystalline intermetallics is opening new windows to the synthesis of engineering materials. Amorphous powders synthesized by mechanical alloying may find application in the design of structural alloys, high thermal conductivity alloys, and metal-matrix composites.     

超高强钴基块体非晶合金的组成设计

块体非晶合金是一类具有高强度、高硬度和大弹性极限的无序金属材料,其优异的力学性能是目前先进金属材料领域研究热点之一,如何提高材料的强度是材料研究领域永恒的主题。系统地总结了已知具有超高强度的一类块体非晶合金材料——钴基块体非晶合金的成分、热学稳定性及力学性能;同时研究了不同非晶合金的断裂强度与其弹性常数、硬度和特征温度的关联。研究结果表明：在非晶合金体系中杨氏模量、维氏硬度、玻璃转变温度与断裂强度之间都存在较好的线性变化关系。基于以上结果,本课题组提出了超高强钴基块体非晶合金的组成设计方法,即选取具有强共价键特性的非金属元素和高模量、高熔点过渡金属元素与钴元素进行组合。     

不锈钢网增强锆基非晶复合材料的压铸制备及力学性能研究

全程真空压铸技术的快速发展为大块非晶合金的工业化应用提供了可能,受到了广泛关注。但是,非晶合金的室温脆性限制了压铸结构件在一些关键领域的应用。本论文利用压铸工艺高速充型及高压凝固的特性,通过在Vit1锆基非晶合金中引入304不锈钢网叠层焊接制造的骨架,成功制备出了不同体积分数晶态相增强的非晶复合材料,并系统研究了不锈钢网体积分数对力学性能的影响。研究结果表明,不锈钢网在非晶基体中均匀分布,与非晶合金存在冶金界面结合。力学性能测试显示,随着不锈钢编织网的引入,室温脆性的压铸Vit1块体金属玻璃的塑性得到了显著提升。随着不锈钢网目数增大(对应晶态相体积分数增大),非晶复合材料的塑性呈增大的趋势,但是,当目数超过200时,过细的孔洞会导致骨架局部区域无法填充,恶化性能。当晶态相的体积分数为53.7％时,断裂应变达到最大值,约为10％左右,其值高于传统不锈钢纤维增韧的Zr基非晶复合材料。韧化机制分析表明,压铸非晶合金出现脆-延性转变的根本原因是不锈钢网对剪切带扩展进行高效抑制,促进剪切带的增殖和萌生,减少宏观塑性变形的局域化。本研究为非晶复合材料的结构设计提供了新的思路,对于促进非晶合金的更广泛应用具有重要的工程价值。     

氧对Zr基非晶合金影响的研究进展

Zr基非晶合金作为新型结构材料得到广泛应用﹐然而其玻璃形成能力及ΔTx等指标对合金中氧的含量非常敏感。正确认识氧的作用机制及规律,控制Zr基金属玻璃在制备及应用过程中的稳定性非常重要。本文概述了氧对Zr基非晶合金热稳定性﹑晶化﹑氧化﹑微观结构与力学性能﹑腐蚀与疲劳等方面的影响,从不同角度理解合金中氧的作用机制及规律。     

Impurity levels and fatigue lives of pseudoelastic NiTi shape memory alloys

In the present work we show how different oxygen (O) and carbon (C) levels affect fatigue lives of pseudoelastic NiTi shape memory alloys. We compare three alloys, one with an ultrahigh purity and two which contain the maximum accepted levels of C and O. We use bending rotation fatigue (up to cycle numbers >10⁸) and scanning electron microscopy (for investigating microstructural details of crack initiation and growth) to study fatigue behavior. High cycle fatigue (HCF) life is governed by the number of cycles required for crack initiation. In the low cycle fatigue (LCF) regime, the high-purity alloy outperforms the materials with higher number densities of carbides and oxides. In the HCF regime, on the other hand, the high-purity and C-containing alloys show higher fatigue lives than the alloy with oxide particles. There is high experimental scatter in the HCF regime where fatigue cracks preferentially nucleate at particle/void assemblies (PVAs) which form during processing. Cyclic crack growth follows the Paris law and does not depend on impurity levels. The results presented in the present work contribute to a better understanding of structural fatigue of pseudoelastic NiTi shape memory alloys.     

Unconventional elastic properties, deformation behavior and fracture characteristics of newly developed rare earth bulk metallic glasses

Significant differences in the thermal, elastic and mechanical behavior of bulk metallic glasses (BMGs) based on rare earth (RE) elements (i.e., Pr-based, Ce-based and Nd-based) have been found when comparing them with archetypical Zr-based and Ti-based amorphous metallic alloys. Our results show that RE-BMG exhibits a large supercooled liquid region, low elastic constants and concomitant elastic softening, low hardness, complete lack of macroscopic plasticity and compressive fracture angles, ψ_C,F, larger than 45° (as opposed to polycrystalline materials, where ψ_C,F = 45°, and conventional BMGs, where ψ_C,F ≤ 45°). Most of these features stem from the rather low glass transition temperature displayed by these alloys, which is relatively close to room temperature. However, contrary to some previous studies, our observations reveal that the lack of plasticity of these materials cannot be simply rationalized in terms of their Poisson’s ratio but is also due to some tensile features (i.e., dilatational effects) accompanying compressive fracture behavior.     

Ordered intermetallic alloys,part I: Nickel and iron aluminides

This article summarizes recent progress in research and development on nickel and iron aluminide intermetallic alloys. Ordered intermetallics possess attractive properties for structural applications at elevated temperatures in hostile environments; however, brittle failure and poor fracture resistance limit their use as engineering materials. In recent years, efforts to understand this brittle fracture behavior have identified both intrinsic and extrinsic factors governing brittle fracture. Parallel work on alloy design using physical metallurgy principles has led to the development of aluminide alloys with improved mechanical and metallurgical properties for structural use.     

Application of advanced materials for ship construction – Experiences and problems

Within the paper a short overview is given regarding the application of advanced materials in the shipbuilding world. The trends for application of high‐strength structural steel, aluminium alloys and composites as well as their limits and restrictions are mentioned. Specific attention is paid to material and corrosion problems observed in shipbuilding and ships in service. As main topics the application of high‐tensile strength structural steel for ship structural members, for ballast water tanks and the involved corrosion problems, the fatigue resistance and “undermatch” situation of welded aluminium alloys compared to steel as well as the corrosion of composites, i.e. osmosis, are mentioned. New developments of ships, e.g. high‐speed crafts and wigs, are pointed out. Conclusions for further research and development in the material field are drawn. The importance of the inter‐relationships amongst the improved material properties, design and calculation aspects as well as the fabrication technologies are stated.     

Zr基块体金属玻璃的形成和性能

研究了一系列具有很强非晶形成能力（ＧＦＡ）和优异性能的块体金属玻璃（ＢＭＧ）及含有纳米晶的ＢＭＧ的制备过程,结果表明,对掺碳的Ｚｒ／Ｔｉ基ＢＭＧ,当碳含量（原子分数,％,下同）,在１－２时,合金具有很宽的过冷液相区（ＳＬＲ,晶化开始温度Ｔｘ和玻璃转变温度Ｔｇ之间的温区）和较高的约化玻璃转变温度Ｔｒｇ（Ｔｒｇ＝Ｔｇ／Ｔｍ）;当碳含量增至３－８时,合金为含有纳米晶ＺｒＣ的ＢＭＧ基复合材料。加Ｆｅ的Ｚｒ     

Corrosion and degradation behavior of Zr-based AB2 alloy electrodes during electrochemical cycling

Zr-based AB₂ Laves phase alloys are promising materials for the negative electrodes in Ni–MH batteries. In this work, their cyclic durability and corrosion behavior in the electrolyte were systematically investigated using instrumental analyses such as ICPS, XRD, SEM, EPMA, XPS as well as PCT and specific surface area measurement.