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.     

Tribological characterisation of Zr-based bulk metallic glass in simulated physiological media

Due to their excellent wear resistant properties and high strength, as well as a low Young's modulus, Zr-based bulk metallic glasses (BMGs) are potentially suitable biomaterials for low-friction arthroplasty. The wear characteristics of the Zr_60.14Cu_22.31Fe_4.85Al_9.7Ag₃ bulk amorphous alloy against ultra-high-molecular-weight polyethylene (UHMWPE) compared to a CoCrMo/UHMWPE combination were investigated in two different wear screening test devices, reciprocating and unidirectional. Hank's solution and sterile calf bovine serum were selected as the lubricant fluid media. It was found that different fluid media had insignificant effect on polyethylene wear against BMG counterfaces. The wear behaviour obtained on both test devices demonstrated that Zr-based BMG achieved UHMWPE counterface wear rates superior to conventional cast CoCrMo alloy, where the wear rate of UHMWPE is decreased by over 20 times. The tribological performance of these joints is superior to that of conventional metal-on-polymer designs. Contact angle measurements suggested that the advantage of BMG over a CoCrMo alloy counterface is attributed to its highly hydrophilic surfaces.     

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.     

Effect of energy density on defect evolution in 3D printed Zr-based metallic glasses by selective laser melting

In this study, the defects in 3D printed Zr-based bulk metallic glasses(BMGs) fabricated by selective laser melting(SLM) under different energy densities have been investigated via both experimental and simulation approaches. Different defects, including balling, interlayer pores, open pores and metallurgical pores, are detected in the 3D-printed Zr-based MGs depending on the energy inputs. Balling mainly occurs at a relatively low energy density(E<8.33 J/mm^3) due to the incomplete melting of particles, while interlayer pores and open pores are formed at modest energy densities(E=13.89-16.67 J/mm^3) because of incomplete welding and insufficient filling of molten liquid between layers. Fine metallurgical pores appear on the upper surface at relatively high energy densities(E=20.83-27.78 J/mm^3), which originate from gas escaping from molten pools during rapid solidification of the melt. Computational fluid dynamics(CFD) simulations are carried out to verify the experimental observations. The CFD simulations reveal that the various defects formed in the 3D-printed Zr-based BMG are related to the melt flow behaviours in the molten pools under different energy densities. The present work provides in-depth understandings of defect formation in the SLM process and provides methods for eliminating these defects in order to enhance the mechanical performance of 3D printed BMGs.     

Zr-based bulk metallic glass as a cylinder material for high pressure apparatuses

Zirconium-based bulk metallic glass (Zr-based BMG) has outstanding properties as a cylinder material for piston-cylinder high pressure apparatuses and is especially useful for neutron scattering. The piston-cylinder consisting of a Zr-based BMG cylinder with outer/inner diameters of 8.8/2.5?mm sustains pressures up to 1.81?GPa and ruptured at 2.0?GPa, with pressure values determined by the superconducting temperature of lead. The neutron attenuation of Zr-based BMG is similar to that of TiZr null-scattering alloy and more transparent than that of CuBe alloy. No contamination of sharp Bragg reflections is observed in the neutron diffraction pattern for Zr-based BMG. The magnetic susceptibility of Zr-based BMG is similar to that of CuBe alloy; this leads to a potential application for measurements of magnetic properties under pressure.     

Fracture mechanisms in bulk metallic glassy materials

We find that the failure of bulk metallic glassy (BMG) materials follows three modes, i.e., shear fracture with a fracture plane significantly deviating from 45 degrees to the loading direction, normal tensile fracture with a fracture plane perpendicular to the loading direction, or distensile fracture in a break or splitting mode with a fracture plane parallel to the loading direction. The actually occurring type of failure strongly depends on the applied loading mode and the microstructure of the material. Extensive evidence indicates that the Tresca fracture criterion is invalid, and for the first time, three fracture criteria are developed for isotropic materials with high strength, such as advanced BMGs or the newly developed bulk nanostructural materials.     

新型Pr基大块非晶及其特性研究

用铜模吸铸法获得了直径为5mm的一种新的Pr基大块非晶.与以往其他稀土-过渡金属(RE-TM)大块非晶不同的是，这种新的Pr基大块非晶具有明显的玻璃转变和稳定的过冷液相区，且其玻璃转变温度在目前已知的大块非晶中是最低的，T_g=409K.研究了该大块非晶的玻璃转变动力学，并给出了Kauzmann温度T_k、Vogel-Fulcher温度T⁰_g及脆性参数m等重要参数. 关键词： 大块非晶 玻璃转变 脆性参数m     

Physical aging in Zr46.75Ti8.25Cu7.5Ni10Be27.5 typical bulk metallic glass manifested as enthalpy relaxation

Enthalpy recovery is not only an important characteristic of physical aging of glass, but also a good tool to investigate the physical aging. Using differential scanning calorimeter (DSC), the enthalpy recovery of Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 bulk metallic glass (BMG) was studied. The typical characteristics of enthalpy recovery of glass including the sub-T _g peak and ‘overshot’ were found in BMG. The evolution of the sub-T _g peak and ‘overshot’ were described by the free volume theory and Hodge’s model, respectively. It was found that the former failed to describe the enthalpy recovery in the BMG, while the latter could give a qualitative explanation. In combination with the dynamics in the BMG, the origin of the enthalpy recovery in the BMG was discussed. The results show that BMGs are an ideal material to investigate the physical aging. The further understanding of physical aging of BMGs is useful to clarify the nature of glass and improve the application and device of new types of BMGs. Supported by the National Natural Science Foundation of China (Grant No. 50671118)     

冲击加载下Zr51Ti5Ni10Cu25Al9金属玻璃的塑性行为

进行了10—27 GPa应力范围内Zr₅₁Ti₅Ni₁₀Cu₂₅Al₉金属玻璃的平面冲击实验以研究其高压-高应变率加载下的塑性行为.由样品自由面粒子速度剖面的分析获得了冲击加载过程的轴向应力,并通过轴向应力与静水压线的比较获得剪应力.实验结果表明,尽管存在明显的松弛效应,但Zr基金属玻璃的Hugoniot弹性极限随着冲击应力的增加而增加.然而,塑性波阵面上的剪应力则显示先硬化而后软化现象,而且软化的幅度随冲击应力的增加而增加.冲击加载下Zr基金属玻璃的上述剪应力变化特征与分子动力学模拟结果比较一致,但与压剪实验结果和一维应力冲击实验结果明显不同.     

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     

Dynamic strength behavior of a Zr-based bulk metallic glass under shock loading

Dynamic strength behavior of Zr51Ti5Ni10Cu25Al9 bulk metallic glass(BMG) up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments.Particle velocity profiles measured at the sample/Li F window interface were used to estimate the shear stress,shear modulus,and yield stress in shocked BMG.Beyond confirming the previously reported strain-softening of shear stress during the shock loading process for BMGs,it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state,and both the shear modulus and the yield stress appear as strain-hardening behaviors.The work provides a much clearer picture of the strength behavior of BMGs under shock loading,which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.     

Static and cyclic mechanical behaviours and fracture mechanisms of Zr-based metallic glass at elevated temperatures

To comprehensively understand the quantitative mechanical–thermal properties and fracture mechanisms of Zr-based bulk metallic glass (BMG), by using self-made miniature tensile/compressive device and motor-piezoelectric coupling driven fatigue device, a series of static and dynamic mechanical tests at elevated temperatures of bulk Zr₅₅Cu₃₀Al₁₀Ni₅ BMG with glass transition temperature T_g of 411°C were carried out. Uniaxial tensile and compressive behaviours at temperatures with range from RT to 400°C were experimentally obtained by means of digital speckle correlation analysis, the estimation of Young’s modulus and fracture strengths as a function of the applied temperatures were investigated. The static and cyclic fracture morphologies at various temperatures were obtained to describe the mechanical–thermal fracture mechanisms in detail. The coupling effect of loading types, stress-induced temperature rise and applied temperature on the evolution of cleavage features, dimples, vein patterns and shear softening behaviours were investigated.     

Recent Advancements in Bulk Metallic Glasses and Their Applications: A Review

Bulk metallic glasses (BMGs), that display extraordinary properties of high strength, corrosion resistance, polymer-like formability, and excellent magnetic properties, are emerging as modern quintessential engineering materials. BMGs have garnered significant research enthusiasm owing to their tremendous technological and scientific standing. In this article, the recent advancements in the field of BMGs and their applications are put in a nutshell. Novel state-of-the-art production routes and nano/microimprinting strategies with salient features capable of circumventing the processing related complexities as well as accelerating modern developments, are briefly summarized. Heterogeneous BMG composite systems that lead to incredible combination of otherwise conflicting properties are highlighted. Biocorrosion studies and recent developments in the field of magnetic BMGs are presented owing to their significance for prospective biomedical and magnetic applications, respectively. In the last section, the current status of BMGs applications in the field of catalysis, biomedical materials, structural materials, functional materials, microelectromechanical systems (MEMS), and micro/macro devices are summed up.     

Elastic moduli inheritance and the weakest link in bulk metallic glasses

We show that a variety of bulk metallic glasses (BMGs) inherit their Young's modulus and shear modulus from the solvent components. This is attributed to preferential straining of locally solvent-rich configurations among tightly bonded atomic clusters, which constitute the weakest link in an amorphous structure. This aspect of inhomogeneous deformation, also revealed by our in situ neutron diffraction studies of an elastically deformed BMG, suggests a rubberlike viscoelastic behavior due to a hierarchy of atomic bonds in BMGs.     

Monte Carlo simulation of dual magnetic phase behavior in bulk metallic glasses

Taking magnetic clusters as magnetic units, the Monte Carlo simulation method was employed to investigate the behavior of dual magnetic phase in bulk metallic glasses (BMGs). The hysteresis loops of a BMG system containing two kinds of magnetic clusters at different temperatures were simulated. The results showed that at high temperatures, only one kind of magnetic cluster is active, however, at low temperatures, both clusters responded to the applied field, which was evidenced by a step observed in the hysteresis loop of a BMG system. The simulated magnetic behavior of the two-cluster BMG system is consistent with the experimental findings of a Nd-based bulk metallic glass with dual magnetic phases.     

高温高压下冲击波淬火的锆基大块金属玻璃的相演化过程研究

 采用同步辐射能散X射线衍射技术,研究了高温高压下利用冲击波淬火技术制备的Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5大块金属玻璃的相演化过程。研究结果发现：在实验压力范围内,在不同压力下试样具有相同的初始析出相Zr₂Be₁₇,但是随后的相演化过程是不同的,根据应用压力的不同,试样的相演化过程可以分为3个不同的区域;另外,试样的晶化温度随着压力的增大而升高,但是在6.0 GPa存在一个突然的下降,在此压力点试样具有不同于其它压力点的相演化过程。相演化过程的不同和晶化温度的突然下降,可能归因于在不同压力下试样具有不同的原子构型。     

焊后热处理对聚变堆用奥氏体不锈钢MAG焊焊缝金属冲击韧性的影响

After heat treatment of metal active gas arc welding (MAG weld) joints of 316LN austenitic stainless steel for fusion reactor at different temperatures, Charpy impact test at liquid nitrogen temperature was carried out. The effects of heat treatment temperature on microstructure, fracture morphology and precipitates were studied with optical microscope, SEM and EDS analysis. Results indicated that the impact toughness of weld metal could be significantly improved by 873K heat treatment. However, with the rising of heat treatment temperature, the precipitates were generated gradually along the grain boundary and a gradual decrease of toughness occurred as well. All fracture was ductile. The dimple became shallow and less with the increase of temperature. Spherical and irregular precipitates were found at the bottom of the dimple. The spherical precipitates generated during welding were free from the influence of the heat treatment, and the irregular precipitates increased with the rising of temperature. High content of Mo in filler materials led to a great segregation of Mo at the grain boundary, which would promote the precipitation of σ phase. Impact toughness of weld metal decreased significantly when continuous distribution of σ phase formed at grain boundary.     

Long-Term Thermal Stability of Binary Cu50.3Zr49.7 Bulk Metallic Glass

We investigate the kinetics and thermal stability of a simple Cu50.3Zr49.7 binary bulk metallic glass （BMG）. The long-term thermal stability of CU50.3Zr49.7 BMG is evaluated by a newly developed method from an extension of Vogel- Fulcher-Tammann analysis. The method has been proven to be valid in CU50.3Zr49.7 or even other BMGs.     

Mechanism,condition and characteristics for the formation of the network structure in Zr-Al-Ni-Cu bulk metallic glasses

Mechanism,condition and characteristics for the formation of the network structure in a group of Zr-Al-Ni-Cu bulk metallic glasses(BMGs) were investigated.The results show that the constituent segregation and/or the symplastic growth would be the mechanisms for the formation of the cell structure in the present Zr-Al-Ni-Cu BMGs.The cell structure can be easily obtained for the glass forming alloys whose compositions locate nearby the eutectic point.The shorter the distance is from the eutectic point,the larger the cell and the thicker the cell wall of the network structure will be.The present investigation would provide useful information for the development of the BMG with the network structure.