二元合金过冷液态的形核驱动力和非晶形成能力的热力学分析

利用CALPHAD(calculation of phase diagrams)技术和已有热力学数据,通过对比分析亚稳过冷液态合金中各结晶相的形核驱动力大小,寻找结晶能力弱而非晶形成能力强的成分范围.选择典型的非晶形成体系,以平衡相图中共晶深度明显不同的3个二元合金体系Cu-Zr,Ni-Nb和Pd-Si为研究对象,预测各体系非晶形成能力与成分的关系,获得非晶形成最优成分,并与共晶点成分及实验数据进行对比.预测结果与实验确定的块体非晶最优成分相符.     

First-principles prediction of the glass-forming ability in Zr–Ni binary metallic glasses

In the present study, the atomistic approach, developed previously by hybridizing both internal energies and atomic-scale defect structures, is extended to predict the trend of glass forming ability (GFA) from the Zr–Cu binary alloy system with good GFA to the Zr–Ni binary system with relatively poor GFA. The predicted composition dependence of the GFA in the Zr–Ni alloy system is consistent with those obtained from experimental results, indicating the validity of the proposed atomistic approach in both of the alloy systems. The different GFAs in the Zr–Cu and Zr–Ni systems have been puzzled by the metallic glass community for quite a long time, and our study provides the physical reasons for the different glass forming behaviors of the two alloy systems in terms of both atomic configurations and relative stability of their intermetallic phases.     

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.     

STRUCTURE AND GLASS FORMING ABILITY(GFA)OF AMORPHOUS ALLOYS

A new microstructure model is developed for amorphous alloys,so called Cluster medel,in which the amorphous phase is thought of composing of randomly distributed orderedclusters of different sizes.Thermodynamic calculation on this model deduces a parameterdescribing the glass forming ability of metallic alloys:α_c=(1-2.08/Φ_m)T_g/T_m,whereT_g is gass transition temperature,T_m is the melting temperature,and Φ_m is entralpychange of melting.It is believed that easy glass forming alloy systems have larger valuesof a_c.This new criterion of GFA not only provides the theoretical background for severalGFA criteria in the literature cited,but also can predict the GFA of many alloy systemsmore reasonably and accurately.     

Formation and properties of the Zr75−xAlxNi10Cu10Ti5 bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) exhibit interesting mechanical properties since they combine high fracture stress, elastic strain (up to 2%), significant fracture toughness and good corrosion resistance. Quaternary systems with general composition Zr–Ni–Cu–Ti show wide composition ranges in which BMG can be obtained. The addition of the another element to the quaternary alloys often increases the glass forming ability (GFA). The aim of this work was to study the influence of aluminium content on the GFA and on the mechanical properties of the Zr–Ni–Cu–Ti alloys. Multicomponent Zr_75−xAl_xNi₁₀Cu₁₀Ti₅ (x = 15, 20 at%) alloys were produced by melt spinning method obtaining ribbons, and by casting technique into a copper mould, manufacturing rod shape samples with maximum diameter of 2 mm. Supercooled liquid region depends on chemical composition and exceeds 45 °C. Vickers microhardness of studied alloys is comparable to the highest ones for other Zr-based BMG.     

Glass forming ability and crystallization behavior of Al–Ni–RE metallic glasses

Atomic size may change due to the interaction between different elements when pure metals are synthesized into alloys. In present paper, the effective atomic radii instead of the nominal radii were introduced in the cluster line method to predict the optimum glass forming compositions in Al-based Al–Ni–RE (RE = La, Y, Ce, Gd, Dy) systems. Wedge-shaped samples of the alloys were suction cast under well-controlled condition to experimentally determine the dependence of the glass forming ability (GFA) on the composition. It is found that such a modification to the method makes the prediction very close to the experimental results. When the effective atomic radii are used to calculate the topological instability parameter originally proposed by Egami and Waseda, λ′, the λ′ corresponding to the best GFA in each Al–Ni–RE system linearly changes with the radius of the RE element. Meantime, the onset temperature of crystallization and mixing enthalpy linearly increase with the λ′.     

Thermodynamic assessment of the glass-forming ability of Gd-Ni-Al alloy system

Gibbs free energy of amorphous alloys, solid solutions, and intermetallic compounds in the Gd-Ni-Al ternary system was calculated by a semi-empirical model based on the Miedema’s theory, to assess the predictive ability of a parameter γ′ on glass-forming ability (GFA) of amorphous alloys. It is found that the predicted GFA is consistent with experiments, in the region being far away from the eutectic point. However, they do not match well in the vicinity of the eutectic point, due to the effect of the eutectic point on GFA. It can be concluded that the parameter γ′ can be used to predict GFA for an alloy system, with the effect of the eutectic point on GFA being taken into account. One can select the composition with high γ′ value, or even the eutectic point with higher γ′ value, when the eutectic points are known, as a good start point in searching for the best glass former.     

Amorphous-crystalline transition layers formation during quenching of Fe61Co7Zr10Mo5W2B15melt

New Fe-based multicomponent amorphous alloys have been developed recently based on empirical rules for large glass forming ability(GFA).In the present investigation,the master alloy ingot with the nominal composition of Fe61Co7Zr10Mo5W2B15(mole fraction,%)was prepared by arc-melting under Ti-gettered Ar atmosphere. The Fe-based uttons with different transverse cross sections were fabricated by arc-melting method,and the d2.5mm Fe-based rods were manufactured by injection technique.Characterization of the ingots and the parameters associated with the thermal stability were carried out by X-ray diffractometry(XRD)and high temperature differential scanning calorimeter(DSC),respectively.The interval of the supercooled liquid region is 39K for the Fe-based alloy.The GFA of Fe-based alloys is relatively lower,to the buttons obtained are all crystallized.The Fe-based rod exhibites a high Vickers hardness up to HV 1329.In addition,and amorphous-crystalline transition layers are observed in the rod.This transition zone is caused by unhomogeneous temperature distribution and relatively lower GFA for Fe-based alloys.     

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。     

Nd对Mg65Cu22Ni3Y10非晶形成能力及热稳定性的影响

利用楔形铜模铸造法成功制备了Mg65Cu22Ni3Y10-xNdx(x=0、2、4、5、6、8)块体非晶合金,采用XRD、DSC研究了Nd对该合金体系热稳定性和非晶形成能力(GFA)的影响。结果表明,当x=2、4时,Nd的添加可有效提高该合金的GFA和热稳定性;当Nd含量为2%(摩尔分数)时,合金具有最高的过冷液相区(ΔTx=61.5K)及最好的热稳定性;当x=5时,尽管过冷液相区(ΔTx=48.5K)最窄,但此时合金具有最强的非晶形成能力(Trg=Tg/Tl=0.568)和临界厚度(δmax=3.8mm);随着Nd的进一步增加(x>5),合金的玻璃形成能力降低。     

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.     

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.     

Continuous fabrication of bulk amorphous alloy sheets by twin-roll strip casting

Twin-roll strip casting was utilized to fabricate the sheet products of Zr- and Cu-base bulk amorphous alloys with quite different glass forming abilities (GFAs). Simulation of the solidification behavior of the these amorphous forming alloys during twin-roll strip casting shows that suitable cooling rate can be achieved by twin-roll strip casting to form amorphous structure through the thickness of sheet. Optimum twin-roll strip casting conditions have been suggested based on the simulation results. Actual twin-roll strip casting shows that both Zr-base alloy with high GFA and Cu-base alloy with much less GFA can be strip cast forming amorphous structure. The results indicate that the twin-roll strip casting is a viable process for continuous fabrication of sheets of bulk amorphous alloys with a wide range of critical cooling rates.     

Zr-Cu-Fe-Al合金的非晶形成能力、热稳定性及组织结构特征

采用铜模铸造法制备了Zr-Cu-Fe-Al非晶合金,利用X射线衍射仪、差热分析仪及高分辨透射电镜,系统研究了Al含量和Cu与Fe摩尔比对Zr59(Cu0.5Fe0.5)33Al8合金的非晶形成能力、热稳定性及组织结构的影响。结果表明,随着Al含量增加,Zr59(Cu0.5Fe0.5)41-xAlx和Zr67-x(Cu0.5Fe0.5)33Alx合金的非晶形成能力均呈现先增加后降低的趋势。对于Zr59(Cu1-xFex)33Al8合金,当Cu与Fe摩尔比在5∶5~8∶2之间时,合金非晶形成能力较好。γ参数及晶化温度研究表明,Zr59(Cu0.7Fe0.3)33Al8合金具有大的非晶形成能力及高的热稳定性。此外,Zr59(Cu0.5Fe0.5)33Al8合金的HRTEM结果表明,由于Cu与Fe混合焓为正,在快速冷却条件下,合金将会发生液-液相分离,形成富Fe和富Cu两液相,之后两液相分别发生玻璃转变,最终形成高数量密度的纳米富Fe非晶粒子分布在富Cu非晶基体上的组织结构。     

Improvement of corrosion resistance in NaOH solution and glass forming ability of as-cast Mg-based bulk metallic glasses by microalloying

The influences of the addition of Ag on the glass forming ability (GFA) and corrosion behavior were investigated in the Mg-Ni-based alloy system by X-ray diffraction (XRD) and electrochemical polarization in 0.1 mol/L NaOH solution.Results shows that the GFA of the Mg-Ni-based BMGs can be improved dramatically by the addition of an appropriate amount of Ag;and the addition element Ag can improve the corrosion resistance of Mg-Ni-based bulk metallic glass.The large difference in atomic size and large negative mixing enthalpy in alloy system can contribute to the high GFA.The addition element Ag improves the forming speed and the stability of the passive film,which is helpful to decrease the passivation current density and to improve the corrosion resistance of Mg-Ni-based bulk metallic glass.     

Effect of Si, Pd and La additions on glass forming ability and thermal stability of Zr-Ni-based amorphous alloys

In the present paper, the influence of minor additions of Si, Pd and La with representative atomic sizes on glass forming ability (GFA) and thermal stability of Zr-Ni-based amorphous alloys has been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The results show that minor additions of La, Pd and Si can improve GFA of Zr-Ni-based alloys and La exhibits the optimum effect on enhancing GFA. The efficient cluster packing model can well explain the correlation between atomic sizes of additional elements and GFA of amorphous alloys. In addition, the relationship of the atomic size between the additional element and Zr has a more important effect on GFA than that between the additional element and Ni. The activation energy for crystallization of the Zr-Ni-based amorphous alloys with Si, Pd and La additions is obviously higher than that of the Zr_66.7Ni_33.3 amorphous alloy, and increases with decreasing distance between neighboring atoms. The thermal stability has a relation with topological short-range ordering of amorphous alloys. The proper addition of small atoms is preferential to enhance thermal stability of amorphous alloys due to stronger short-range ordering. Moreover, the small or intermediate atom addition can produce even better effect on thermal stability than the large atom addition.     

激光熔覆Ni60Zr20Nb15Al5非晶合金涂层组织及性能研究

依照非晶形成能力的三判据原则及非晶成分团簇线定律法则,选取在常规非晶合金制备过程中呈现较强非晶形成能力的Ni60Zr20Nb15Al5合金成分,研究其在不同激光功率条件下在45#钢表面得到的熔覆层的微观组织和力学及腐蚀性能.结果表明:熔覆涂层由熔覆层、结合区和热影响区组成,物相包括非晶相及Al3Zr5、Al3Nb11N...     

Glass formation in Fe-Cr-Zr-B-Mo alloys by tuning Nb addition

Fe-based bulk metallic glasses (BMGs) with high boron content have potential application as a coating material used in the framework for storing spent nuclear fuels to support their safe long-term disposal. The high glass forming ability (GFA) and large supercooled liquid region are therefore required for such Fe-based BMGs in either the glassy powder fabrication or the subsequent coating spraying. In order to meet these requirements, the influence of Nb content on the GFA of Fe₅₇Cr₁₀Zr₈B₁₈Mo_7−xNb_x (x=1–5, at.%) alloys was investigated, as Nb has positive roles in GFA and thermal stability of BMGs. The results indicate that a fully amorphous phase in the as-cast samples with 3 mm in diameter is obtained for both the Fe₅₇Cr₁₀Zr₈B₁₈Mo₅Nb₂ and Fe₅₇Cr₁₀Zr₈B₁₈Mo₄Nb₃ alloys. The corresponding supercooled liquid regions of the two BMGs are 78 K and 71 K, respectively. The mechanism for improving their GFA was analyzed based on the principle of metal solidification, the parameters for glass formation and thermal properties of the alloys. The compression strength and Vicker’s hardness of the two BMGs are 1,950 MPa and 1,310 HV, 2,062 MPa and 1,180 HV, respectively. The developed BMGs with high B content, good GFA, and very high hardness can be used as coating materials to the framework for spent nuclear fuels.

     

Formation of Bulk Metallic Glasses from Cu-Zr Based Alloys with Yttrium Addition

采用工业级的低纯Zr,通过稀土Y的微合金化作用,制备Cu46Zr46Al8非晶合金。结果表明:Y能有效提升Cu46Zr46Al8合金的玻璃形成能力,主要原因是Y能吸附液态合金中溶解的氧,起到晶化合金的作用。当Y的添加量为2at%,3at%时,效果最为明显。经过Y微合金化后的非晶合金的抗压缩断裂强度超过2GPa,高于用高纯原料制备的非晶,但是塑性明显下降。