Recent progress in quantifying glass-forming ability of bulk metallic glasses

The γ parameter proposed by the authors has prompted a lot of new interests in quantifying glass-forming ability (GFA) of bulk metallic glasses (BMGs). As a result, many different GFA indicators/criteria have been suggested lately. Recent development in this area is summarized herein; it was found that all newly developed parameters can be grouped into three basic categories according to their definitions. Our statistical analysis, particularly the direct comparison with the σ parameter developed by Park et al., shows that the universal GFA indicator γ is still the best in terms of reliability and applicability. In addition, limitations of all the GFA parameters will be discussed, and future focuses in quantifying GFA of metallic systems will also be suggested.     

Misch metal based metallic glasses

In this paper, a glass-forming range of metallic glasses based on Ce-rich misch metal (Mm) was pinpointed in Mm-Al-Co composition map by melt spinning. The thermal analysis indicated that the wide supercooled liquid region (above 60 K) can be found out in a large composition range in Mm-Al-Co system. The investigation of the glass-forming ability (GFA) in this system indicated a glassy composition with a larger supercooled liquid region wouldn’t be the glassy former with higher GFA. The reduced glass transition temperature is a better indicator to explore metallic glasses with high GFA. Furthermore, the mechanical properties of Mm₆₅Al₁₀Co₂₅ bulk glassy samples were evaluated in a compressive measurement. The obvious advantages of the Mm-based BMGs with high GFA, good mechanical properties and low material cost make these BMGs hopeful to be applied in the future.     

一种预测非晶合金的非晶形成能力新判据

本文提出了一种非晶合金的非晶形成能力(GFA)新判据β',表达式为(Tg/Tx-Tg/T1/η),其中Tg,Tx,T1和η分别为合金的玻璃转变温度、起始晶化温度、液相线温度和常系数.新判据β'的理论基础是非晶形成能力的本质涵义,即GFA不仅表征合金熔体形成非晶的能力,也表征非晶合金在受热条件下的稳定性.采用文献报道的大...     

基于Tg复特征温度参数的玻璃形成能力及稳定性判定准则

本文从降温过程的玻璃形成能力(GFA)和升温过程的玻璃稳定性(GS)出发，构建出基于玻璃转变温度Tg衍生的复特征温度参数三角形，从而推导出判定GFA & GS的准则并从二温度参数和三温度参数对准则均衡贡献的角度，进一步对准则进行了修订：GTg=Tg/Tl+Tx/Tg+(Tx-Tg)/(Tl-Tg)和GTgm=Tg/Tl+(Tx/Tg)/2+((Tx-Tg)/(Tl-Tg))^0.3。通过大量金属玻璃、氧化物玻璃和有机化合物玻璃形成物从GFA和GS两方面验证了准则的可靠性，并与当前基于特征温度的判定准则进行了对比分析，结果表明新提出的准则在评判GFA & GS具有广泛应用性，尤其是修订后的准则在金属玻璃的GFA和GS判定方面表现最优，可以作为一个可靠的准则。     

Influence of the molten quenching temperature on the thermal physical behavior of quenched Zr-based metallic glasses

Thermo-physical behavior of some Zr-based metallic glasses prepared by different molten quenching temperatures was studied by Differential scanning calorimetry (DSC) measurements. The characteristic thermo-physical properties are normally used for evaluating the glass-forming ability (GFA) of metallic glasses. Our results show that the glass transition temperature, crystallization temperature and supercooled liquid region of these metallic glasses increased with increasing the molten quenching temperature. Their glass-forming abilities were discussed in terms of the GFA criterion γ and the reduced glass transition temperature, T_rg, using these thermo-physical properties.     

Role of addition in formation and properties of Zr-based bulk metallic glasses

A various multicomponent bulk metallic glasses (BMGs) were prepared at a low cooling rates of 1–100 K/s. The effects of various additions on the glass forming ability (GFA), properties and thermal stability of the alloy systems were investigated. The structural and properties changes of the BMGs upon addition were studies using X-ray diffraction, differential scanning calorimetry, density measurement, and acoustic measurement. It is found that the proper elemental addition can significantly improve the GFA and properties of the bulk glass-forming alloys. The addition is an effective way for improving GFA, and properties of the bulky glass-forming alloys. The roles of the additions in the glass formation, properties and crystallization are discussed.     

Structural investigation upon the high glass-forming ability in Fe-doped ZrCuAl multicomponent alloys

Understanding the underlying mechanism of microalloying affecting the glass formation in multicomponent alloys is scientifically required, while addressing this issue remains a challenge. In this work, the structural mechanisms of extraordinarily high glass-forming ability (GFA) caused by Fe doping in ZrCuAl bulk metallic glasses was investigated via synchrotron radiation techniques combined with simulations. It is revealed that when minor Fe (5 at.%) are doped, the local structures (clusters) have relatively high values of some structural parameters, in terms of fivefold symmetry, geometrical regularity, atomic packing, and chemical interaction between heterogeneous atoms. The combination of these structural factors leads to stabilized amorphous structure and enhanced GFA. This work may extend our understanding on the sensitive dependence of GFA on the concentration of doping atoms in multicomponent metallic glasses.     

Zr_(47)Cu_(44)Al_9大块非晶合金的制备及其力学性能

利用电弧炉制备一系列(Zr_(51.6)Cu_(48.4))_(100-x)Al_x(x=6.0～10.0, 摩尔分数,%)大块非晶合金,利用示差扫描量热仪、X射线衍射仪和金相显微镜研究Al的含量对其非晶形成能力的影响.结果表明:当铝的含量为9.0%时,合金具有最优的非晶形成能力.适量铝的加入不仅能够抑制初生相CuZr的析出,而且还能有效地抑制其长大.临界冷却速率的经验公式计算结果显示该合金的临界冷却速率为10 K/s,室温压缩力学性能显示其断裂强度为1.9 GPa,且有0.5%的塑性变形,式为韧性剪切断裂.     

Anomalous packing state in Ce-Ga-Cu bulk metallic glasses

Formation mechanism of bulk metallic glasses (BMGs) with high glass-forming ability (GFA) has been a long-standing subject in the field of solid state physics. To highlight the GFA-associated local atomic structure, element-specific positron annihilation spectroscopy was conducted for recently discovered ternary Ce₇₀Ga_xCu_30-x (x = 6–13; at.%) BMGs. We succeeded in identifying the packing structure under the condition of ambient pressure, in which Ce atoms are concentrated more than that in Ce crystal. This anomalous glassy state is most efficiently formed at the Ga concentration of ∼10%, where the best glass-forming ability (GFA) is experimentally observed. First-principles computer simulation results suggest that this anomalous packing structure is associated with Ce-4f electron delocalization in the Ce-Ga-Cu BMGs. The findings provide unambiguous evidence for the relationship between the packing-efficient local structure and the GFA.     

Effects of alloying elements on glass formation,mechanical and soft-magnetic properties of Fe-based metallic glasses

Effects of alloying additions on glass formation, mechanical and soft-magnetic properties of Fe-(Si,P,C,B)-based bulk metallic glasses (BMGs) were systemically studied in detail. It was found that the glass-forming ability (GFA) and the optimum doping content strongly depend on the electronegativity of the alloying elements, which are discussed in terms of liquid phase stability and crystallization resistance of the competing crystalline phases. These BMGs exhibit high fracture strength ranging from 2800 to 3800 MPa, which closely relates to the atomic size distribution in the alloys. Furthermore, appropriate additions of Co, Ga and Cu could improve not only the GFA but also the saturation magnetization due to different coupling mechanisms.     

Structural relaxation and related viscous flow of Zr–Cu–Al-based bulk glasses produced from the melts with different glass-forming ability

The relaxation ability of Zr₄₆(Cu_4/5Ag_1/5)₄₆Al₈ and Zr₄₆Cu₄₆Al₈ bulk glasses displaying different glass-forming ability (GFA) in the liquid state has been studied by measurements of the shear modulus, creep and stress relaxation. It has been found that the four-component alloy with higher GFA always displays higher relaxation ability in the glassy state. This fact does not seem to correlate with the amount of the frozen-in free volume as dependent on the GFA. It has been argued that the relaxation centers responsible for structural relaxation and related viscous flow are similar to dumbbell interstitials in simple metals. Such an approach precisely describes the kinetics of shear modulus relaxation and reasonably agrees with a phenomenological interpretation of structural relaxation-induced viscoelastic phenomena in metallic glasses.     

Nanostructure controlling in Zr-based metallic glasses using icosahedral local structure

Glass-nano(quasi)crystal composite materials based on Zr–Al–Ni–Cu metallic glasses have been synthesized by controlling the nucleation and growth rates of the precipitated phase correlated with a unique icosahedral local structure. It is well known that the Zr₆₅Al_7.5Ni₁₀Cu_17.5 metallic glass has a high glass-forming ability (GFA), which enables us to produce the glassy sample with a bulky shape. Controlling a substitution of QC-forming elements such as noble metals with Cu and annealing condition, the nanoscale icosahedral quasicrystalline phase (I-phase) with various grain sizes and nucleus densities can be formed. Moreover, we have succeeded to control the nano-QC phase nucleation by changing the atmosphere pressure during casting, which results in the formation of new bulk metallic glasses (BMGs). These nanoscale structure and nucleation controlling techniques in BMGs bring a significant improvement of mechanical properties such as high strength and good ductility.     

Effect of addition of Be on glass-forming ability,plasticity and structural change in Cu–Zr bulk metallic glasses

The present study reports the effect of the addition of Be in Cu–Zr bulk metallic glass (BMG) on glass-forming ability (GFA), plasticity and structural change. Although Be has a negative enthalpy of mixing with all the constituent elements of these glasses, Cu_47.5Zr₄₀Be_12.5 alloy exhibits apparent double glass transitions (T_g) and enhanced plasticity as well as improved GFA. Intensive structural analysis using extended X-ray absorption fine structure suggests that a large difference in the enthalpy of mixing between atom pairs in multi-component BMGs can cause atomic scale structural inhomogeneity and/or locally favored structures in the amorphous matrix, resulting in enhanced compressive strains, although the enthalpies of mixing for atom pairs are all negative. This concept may shed light on the development of BMGs with large plasticity as well as high GFA.     

A new glass-forming ability criterion for bulk metallic glasses

A new indicator of glass-forming ability (GFA) for bulk metallic glasses (BMGs) is proposed based on crystallization processes during cooling and reheating of the supercooled liquid. The interrelationship between this new parameter and the critical cooling rate or critical section thickness is elaborated and discussed in comparison with two other representatives, i.e. reduced glass transition temperature T_rg (=T_g/T_l, where T_g and T_l are the glass transition temperature and liquidus temperature, respectively) and supercooled liquid range ΔT_xg (=T_x−T_g, where T_x is the onset crystallization temperature and T_g the glass transition temperature). Our results have shown that ΔT_xg alone cannot infer relative GFA for BMGs while the new parameter γ, defined as T_x/(T_g+T_l), has a much better interrelationship with GFA than T_rg. An approximation of the critical cooling rate and critical section thickness for glass formation in bulk metallic glasses is also formulated and evaluated.     

Structural mechanisms of the microalloying-induced high glass-forming abilities in metallic glasses

The issue, doping-induced high glass-forming abilities (GFAs) in metallic glasses (MGs), has been investigated by systematic experimental measurements coupled with theoretical calculations in the ZrCuAgAl quaternary alloys. It is found that minor Ag addition leads to a high fraction of Ag-centered icosahedral like local structures, as well as enhanced atomic-packing efficiency and structural regularity in Zr- and Cu-centered major clusters. This can stabilize the amorphous structure and the GFA is accordingly enhanced. However, these structural factors have smaller values when excessive Ag atoms are added, leading to a deteriorated GFA. The present work provides an understanding of GFAs in multicomponent alloys and will shed light on the development of more MGs with high GFAs.     

Zr–(Cu,Ag)–Al bulk metallic glasses

In this paper, we report the formation of a series Zr–(Cu,Ag)–Al bulk metallic glasses (BMGs) with diameters at least 20 mm and demonstrate the formation of about 25 g amorphous metallic ingots in a wide Zr–(Cu,Ag)–Al composition range using a conventional arc-melting machine. The origin of high glass-forming ability (GFA) of the Zr–(Cu,Ag)–Al alloy system has been investigated from the structural, thermodynamic and kinetic points of view. The high GFA of the Zr–(Cu,Ag)–Al system is attributed to denser local atomic packing and the smaller difference in Gibbs free energy between amorphous and crystalline phases. The thermal, mechanical and corrosion properties, as well as elastic constants for the newly developed Zr–(Cu,Ag)–Al BMGs, are also presented. These newly developed Ni-free Zr–(Cu,Ag)–Al BMGs exhibit excellent combined properties: strong GFA, high strength, high compressive plasticity, cheap and non-toxic raw materials and biocompatible property, as compared with other BMGs, leading to their potential industrial applications.     

Zr,Nb对Fe—B合金非晶形成能力的影响

根据获得高玻璃形成能力（ＧＦＡ）非晶合金的多元化理论,研究了Ｚｒ,Ｎｂ对二元Ｆｅ－Ｂ非晶合金ＧＦＡ的影响,结果表明,高Ｂ含量Ｆｅ－Ｂ非晶合金中加入适量Ｚｒ能够促进玻璃态转变,三元Ｆｅ－Ｂ－Ｚｒ非晶合金中加入少量Ｎｂ能够有效地提高其ＧＦＡ,多元化是促进非晶合金玻璃态转变和提高其ＧＦＡ的有效方法。     

微合金化对U-Co金属玻璃形成能力的影响

U-Co系具有较宽非晶成分区间,但其玻璃形成能力(GFA)较差。针对该体系的U_(69.2)Co_(30.8)合金,选择不同类型的元素M(M=Sn,Si,Be,Cu,Pd,Y,Zr)进行微合金化,采用铜辊甩带方法制备U_(69)Co_(30)M_1非晶合金条带样品,结合X射线衍射与差示扫描量热技术研究了微合金化对合金GFA的影响。结果表明,Sn添加对U-Co合金的GFA具有明显改善作用,Si次之,Be、Cu影响不大,Pd、Y、Zr起到恶化效果。结合合金熔化行为的改变和GFA与M元素的熔点、电负性、原子尺寸及M-C混合焓等参数的关联性分析,初步揭示出微合金化对U-Co合金GFA的影响机制,其本质应该与改变合金液体稳定性和晶化驱动力有关。     

微量Cr对Cu基块体非晶合金的形成能力及耐蚀性能的影响

XRD,DSC和DTA分析测试表明,微量Cr有利于提高块体非晶合金(Cu47Zr11Ti34Ni8)100-xCrx(x=0,0．5,1)非晶形成能力．室温动电位极化法对该合金在1mol／LHCI溶液、3％Nacl溶液和6mol／L KOH溶液中的电化学测试表明,非晶合金存在自钝化现象,随Cr含量增加,非晶合金的钝化区宽度显著增大,维钝电流密度降低,耐蚀性能增强,含微量Cr的Cu基块体非晶合金比不含Cr的具有更好的抗腐蚀性能,且远远优于不锈钢1Cr18Ni9Ti的抗腐蚀性能．     

Effects of atomic size difference and heat of mixing parameters on the local structure of a model metallic glass system

Atomic size differences between constituting elements and the heat of mixing are key factors in designing a metallic glass system. In this study, the effects of atomic size differences and the heat of mixing on the glass-forming ability and the local structure of metallic glasses were studied via molecular dynamic simulations of an ideal system known as the Lennard-Jones embedded-atom method model. The atomic size difference and the heat of mixing of the system were varied by means of the Lennard-Jones parameters. The glass transition behavior was characterized based on the chemical short-range order and by a Voronoi analysis. Our simulations lead to optimized windows of atomic size differences and heat of mixing parameters for metallic glass-forming of the model system. Both a greater negative heat of mixing and a larger atomic size difference are necessary for the enhancement of the glass-forming ability.