Annealing Embrittlement in Fe-Mo-Si-B Amorphous Alloy

Annealing at Ta=200℃ or so, the enhancement in the average tensile fracture strength of as-quenched (Fe0.99Mo0.01)78Si9B13 metallic glass increases about 7～8%. The origin of the annealing embrittlement at 244℃ in the metallic glass (Fe0.99 Mo0.01)78Si9B13 was revealed that due to the formation of nanoscale granular with bcc structure resulting in the stress localization.The temperature of annealing embrittlement was in agreement with the calculated value from Tbcc=0.637Tc (Tc is the crystallized temperature), based on micromechanism of crystallization of metallic glass.     

基于第一性原理的α-Fe(001)/Mo2FeB2(001)界面性能的研究

采用第一性原理方法,研究了α-Fe(001)/Mo_2FeB_2(001)界面性能。建立了4种不同的原子堆垛方式界面模型,计算了其界面粘附功、界面结合能和断裂功。结果表明,以空心位置堆垛的Fe终端界面性能最稳定,而顶部位置的Fe+B终端界面性能最不稳定,两者的裂纹断裂均趋向于发生在基体相或硬质相内。在此基础上,进一步分析了空心位置Fe终端界面模型和顶部位置Fe+B终端界面模型的电子结构,电荷差分密度图显示在空心位置的Fe终端界面系统中,界面处Fe原子与Fe原子间形成金属键,界面处Fe原子与Mo原子间形成金属键。在顶部位置的Fe+B终端界面系统中,界面处的Fe原子与B原子间形成共价键,但界面强度比空心位置的Fe终端界面系统低。分态密度显示界面处原子间重新排列,发生杂化,形成共价键,揭示了界面成键特性。     

Microstructure of nanostructured Fe40Ni38Mo4B18 alloy

Nanostructured Fe40Ni38Mo4B18 specimens with a wide range of different nanostructures can be produced by annealing the amorphous alloy in the temperature range from 700 K to 1060 K. The nanostructured Fe40Ni38Mo4B18 specimens prepared between 700 K and 760 K have a microstructure of the 4–9 nm fcc (Fe, Ni) solid solution crystallites embedded in the amorphous matrix. The nanostructured Fe40Ni38Mo4B18 specimens obtained between 780 K and 910 K show a polycrystalline microstructure of the major cubic (Fe, Ni, Mo)23B6 phase with grain sizes from 20 nm to 40 nm and the minor fcc (Fe, Ni) solid solution crystallites of about 10 nm. The nanostructured Fe40Ni38Mo4B18 specimens produced between 930 K and 1060 K represent a polycrystalline microstructure of the 12–25 nm fcc (Fe, Ni) solid solution crystallites and the 45–240 nm cubic (Fe, Ni, Mo)23B6 crystallites.     

Ag晶体的力学稳定性和理论强度

把MAEAM与Milstein改进的Born力学稳定性判据相结合,讨论了fcc晶体Ag在单轴裁荷下的力学稳定性和理论强度.结果表明,在压缩过程中,晶体结构首先转变为无应力不稳定的bcc相,随后通过消耗内能自发地转变为另一个无应力的bct亚稳相.计算的bcc和fcc相的结构能量差与实验值很符合,其力学稳定性范围为-2.076～4.390GPa,相应的应变范围为-7.972%～8.672%.     

Kinetics of crystallization of a Fe-based multicomponent amorphous alloy

The Fe-based multicomponent amorphous alloys (also referred to as metallic glasses) are known to exhibit soft magnetic properties and, it makes them important for many technological applications. However, metallic glasses are in a thermodynamically metastable state and in case of high temperature operating conditions, the thermally activated crystallization would be detrimental to their magnetic properties. The study of crystallization kinetics of metallic glasses gives useful insight about its thermal stability. In the present work, crystallization study of Fe₆₇Co₁₈B₁₄Si₁ (2605CO) metallic glass has been carried out using differential scanning calorimetry (DSC) technique. Mössbauer study has also been undertaken to know the phases formed during the crystallization process. The alloy shows two-stage crystallization. The activation energy has been derived using the Kissinger method. It is found to be equal to 220 kJ/mol and 349 kJ/mol for the first and second crystallization peaks, respectively. The Mössbauer study indicates the formation of α-(Fe, Co) and (Fe, Co)₃B phases in the alloy.     

Crystallization of Zr-Ni metallic glasses

The crystallization of Zr-Ni metallic glasses of composition between 55 and 70 at % Zr has been investigated using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The samples were prepared by splat quenching in an arc-hammer device. Transformation temperatures, effective activation energies, and enthalpy changes are reported as a function of composition. Results of XRD patterns obtained as a function of annealing temperature in the DSC are presented. A high temperature exothermic DSC peak and XRD patterns indicate the presence of a metastable phase which occurs between 57 and 63.5 at % Zr. The results tend to support suggestions of a connection between the short range structure of the glass and the crystalline phase to which it transforms. It was found that the metastable phase, whose presence is strongest at 57 to 59 at % Zr, and the process of phase separation around the eutectic composition (63.5 at % Zr) play important roles in the crystallization process.     

Effects of supercooling and cooling rate on the microstructure of Cu–Co–Fe alloys

The effects of supercooling and cooling rate on the microstructure of ternary Cu–Fe–Co alloys were investigated. Electromagnetic levitation was used to supercool the liquids down by 180 K. Alloys with 11 at.% Cu and less than 19 at.% Fe contained fcc (Fe, Co) and fcc Cu phases; those with 19 to 23 at.% Fe contained bcc (Fe, Co), fcc (Fe, Co) and fcc Cu; those with more than 23 at.% Fe contained bcc (Fe, Co) and fcc Cu. The primary dendrites contained 10 to 20 at.% Cu, with Fe and Co contents depending on the alloy composition. Supercooling the melt below a certain temperature resulted in metastable separation of the melt into two liquids, one (Co + Fe)-rich, the other Cu-rich. The metastable phase separation temperatures and the two liquid compositions were determined experimentaly, and compared with calculated ones. Isothermal cross-sections at various temperatures were constructed for stable and metastable cases based on thermodynamic and experimental data of the Cu–Co, Cu–Fe, and Co–Fe systems. A peritectic reaction for the ternary alloys was found at approximately 1100°C.     

Impurity-driven nanocrystallization of Zr-based bulk amorphous alloys

The effect of oxygen content and Ti addition on the glass forming ability (GFA) and crystallization kinetic of Zr-based bulk glass forming alloys have been studied by means of thermal analysis and X-ray diffraction techniques. Presence of oxygen triggers the formation of a nanocrystalline metastable f.c.c. Zr2 Ni-type phase which can act as heterogenous nucleation sites for the formation of dendrites during solidification. An increase in oxygen content changes the crystallization behaviour from a single- to a double-step process and triggers the crystallization of stable Zr2(Cu,Al) besides metastable Zr2 Ni-type phase. Oxygen-triggered nucleation of a nanocrystalline metastable Zr2 Ni-type phase is found to be the initial step of crystallization. The important parameters of GFA such as glass transition temperatures, Tg, the crystallization temperatures, Tx, and crystallization enthalpies, deltaH, were determined by using DSC. It was observed that the presence of oxygen, even in a very small amount, and Ti addition cause a drastic reduction of the supercooled liquid region, deltaTx, accompanied by a change of the crystallization kinetic. This leads to the decrease in stability of the supercooled liquid, consequently results in a deterioration of the glass forming ability of the alloy.     

电镀Ni-Mo非晶态合金的晶化与强化

用透射电镜研究了电镀 Ni-Mo 非晶态合金晶化过程中形貌和相结构的变化。发现晶化初期除了在非晶基体上析出 Ni 的固溶体外,还先后出现两个亚稳相,一个为面心立方的,a=1.11nm;另一个为六角相,a=0.30,c=0.47nm。最后稳定相是 Ni 和 Ni_3Mo。两相有固定取向关系和良好共格关系。这样,可以从固溶,弥散和析出相几种强化机制上来理解电镀 Ni-Mo 非晶态合金加热过程中的强化现象。     

Crystallization Behavior of C-containing FINEMET Amorphous Alloy Melt-spun Ribbon

The crystallization kinetics of amorphous Fe68.5Si13.5B9Cu1Nb3C5 (at. Pct) melt-spun ribbons were studied by the DSC method in the mode of continuous heating. The apparent activation energy Ep1 and Ep2 (373.07±7.92 and 518.75±21.35 k J/mol, respectively) derived from the Kissinger plots were calculated by the peak temperatures Tp1,Tp2, which display a strong dependence on the heating rates. The crystallization behavior during isothermal annealing at 823 K for 1, 5, 10 h and 973 K for 5 h were investigated using XRD and TEM. The results show that crystallization behavior becomes completely different from that of FINEMET. It is not bcc α-Fe (Si) but metastable fcc γ-Fe (Si)that participates in the first crystallization step combining the appearance of Fe23B6 and Nb2B. Therefore, the addition of C promotes the combination of Fe and B. Fe3.5B is participated in the second step together with the disappearing of Fe23B6, which indicates that transition Fe23B6→Fe3.5B Fe2B presumably happens. Γ-Fe (Si) with peculiar stability cannot transform into nano-sized α-Fe (Si) crystals until the amorphous ribbons were annealed for 5 h at 973 K.     

Ce对非晶态Fe76B15Si9合金脆化及晶化的影响

在非晶态Ｆｅ７６Ｂ１５Ｓｉ９合金中加入Ｃｅ可明显改变合金的退火脆化倾向，Ｃｅ与杂质元素化合生成高熔点的化合物，在晶化过程中成为晶体形成的核心，加快了非均匀成核速率，降低了开始发生晶化的温度，但对其晶化反应进行顺序及晶化产物不产生影响。     

Microstructure formation and electrical resistivity behavior of rapidly solidified Cu-Fe-Zr immiscible alloys

The immiscible Cu-Fe alloy was characterized by a metastable miscibility gap. With the addition element Zr, the miscibility gap can be extended into the Cu-Fe-Zr ternary system. The effect of the atomic ratio of Cu to Fe and Zr content on the behavior of liquid-liquid phase separation was studied. The results show that liquid-liquid phase separation into Cu-rich and Fe-rich liquids took place in the as-quenched Cu-Fe-Zr alloy. A glassy structure with nanoscale phase separation was obtained in the as-quenched(Cu_(0.5) Fe_(0.5))40Zr_(60) alloy sample, exhibiting a homogeneous distribution of glassy Cu-rich nanoparticles in glassy Fe-rich matrix. The microstructural evolution and the competitive mechanism of phase formation in the rapidly solidified Cu-Fe-Zr system were discussed in detail. Moreover, the electrical property of the as-quenched Cu-Fe-Zr alloy samples was examined. It displays an abnormal change of electrical resistivity upon temperature in the nanoscale-phase-separation metallic glass. The crystallization behavior of such metallic glass has been discussed.     

Preparation and crystallization of Ti53Cu27Ni12Zr3Al7Si3B1 bulk metallic glass with wide supercooled liquid region

Ti-based bulk metallic glass (BMG) alloy with the composition of Ti₅₃Cu₂₇Ni₁₂Zr₃Al₇Si₃B₁ was prepared by copper molder casting method and ribbon sample was prepared by melt spinning to compare. The thermal instability of this glass phase was examined by using differential scanning calorimetry (DSC) and differential thermal analysis (DTA). The results revealed that the supercooled liquid region (ΔT_x), glass transition temperature (T_g) and reduced glass transition temperature (T_g/T_m) of the glassy alloy are detected to be 69, 685 and 0.62 K, respectively. The crystallization behavior of the Ti-based glass phase was also investigated by annealing the glass phase at series temperatures above T_g. The annealed microstructures were examined by means of X-ray diffraction experiments. The crystallization process of the BMG can be characterized by metastable crystalline phases at the first crystallization step and further transition to stable crystalline phases at high temperature through metastable crystalline phase.     

Effects of Nb Alloying on Nano-Crystallization Kinetics of Fe55-x Cr18Mo7B16C4Nbx(x=0, 3) Bulk Amorphous Alloys

Crystallization kinetics of Fe55-xCr18Mo7B16C4Nbx(x= 0, 3) bulk amorphous alloys were analyzed using X-ray diffraction and differential scanning calorimetric (DSC) tests. In practice, crystallization and growth mechanism were evaluated using DSC tests at four different heating rates (10, 20, 30, and 40 K/min) and kinetic models. Two-step crystallization behavior was observed when Fe55Cr18Mo7B16C4 and Fe52Cr18Mo7B16C4Nb3 bulk amorphous alloys were annealed, where Fe36Cr12Mo10 phase was crystallized in the first step of crystallization. Results show that Fe36Cr12Mo10 and Fe3C phases were crystallized in the structures of the alloys after further annealing process. Activation energy for the crystallization of Fe36Cr12Mo10 phase was measured to be 543 kJ/mol in Fe52Cr18Mo7B16C4Nb3 alloy and 375 kJ/mol for Fe55Cr18Mo7B16C4 alloy according to Kissinger-Starink model. Moreover, a two-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in Fe52Cr18Mo7B16C4Nb3 alloy whereas a three-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in crystallization of Fe36Cr12Mo10 phase dur- ing annealing of Fe55Cr18Mo7B16C4 alloy. TEM (transmission electron microscopy) observations reveal that crystalline Fe36Cr12Mo10 phase nucleated in the structures of the alloys in an average size of 10 nm with completely mottled morphology.     

液淬条件对非晶态合金制备脆化和晶化的影响

研究了用单辊法制备非晶态合金条带时，冷却辊表面线速、熔体射流压力、喷射距离等参数对非晶态Ｆｅ３０Ｂ１１．４Ｓｉ３．５合金条带的形成、条带结构、性能及其退火脆化和晶化的影响。液淬工艺参数的合理配合下获得的足够高的液淬速率是得到非晶结构的关键，也是制备质量条带的决定因素。液淬速率愈高，条带厚度愈小，其脆化敏感性愈低。因此，高液淬速率下薄带的制备，有益于提高非晶态合金脆化抗力。非晶合金的晶化与液淬条件之间不存在直接的联系。     

金属玻璃Pd_(77.5)Ni_(6.0)Si_(16.5)的晶化过程

本文报道了三元金属玻璃Pd_(77·5)Ni_(5·)Si_(·5)经不同温度退火后的透射电子显微镜观察结果。初步确定了Pd_(77·5)Ni_(6·)Si_(16·s)的晶化过程和亚稳相的结构。由于Ni元素的加入,使其晶化过程相对于二元金属玻璃Pd_(su)Si_(2u)变得更加复杂。     

Crystallization of amorphous CoSiB alloys: Effect of Fe additions

The results of transmission electron microscopy and X-ray diffraction studies of the crystallization behavior of different CoSiB alloys with and without Fe additions are reported. It is shown that a metastable bcc phase is formed by crystallization in all of the alloys with Fe additions. The bcc phase is not observed in the alloys without Fe additions.     

Studies of crystallization kinetics of Fe40Ni40P14B6 and Fe80B20 metallic glasses under non-isothermal conditions

A model for the glass crystallization at constant rate heating is presented. Based on the model a technique for determination of the constants involved in the classical equations for the rates of homogeneous nucleation and linear crystal growth is derived. The effect of the heating rate (in the wide range from 2×10-2 to 16 K s-1) on the temperature of crystallization as well as on the average grain size in fully crystallized specimens of Fe40Ni40P14B6 and Fe80B20 metallic glasses has been studied. The values of the interface diffusion coefficient, the rates of nucleation and growth and the volume density of quenched-in nuclei deduced in the present study are in good agreement with those derived from direct observations. It has been confirmed that crystallization of Fe80B20 occurs mainly by the three-dimensional growth of the pre-existing crystallites while the Avrami exponent for the Fe40Ni40P14B6 glass exceeds 4 implying non-steady-state nucleation. It has been demonstrated that the proposed model allows one to generalize the isothermal and non-isothermal kinetic crystallization curves. This revised version was published online in November 2006 with corrections to the Cover Date.     

Analytic EAM Model for the Thermodynamic Properties of the Disordered Solid Solution and Ordered Intermetallic Alloys of Iron Aluminides

1.IntroductionInthepastfewyearsthemeth0dsf0rempiricalandsemiempiricalcalculations0fpropertiesformet-alsandalloyshaveevolvedrapidly.Oneofthem0stsuccessfulmethodsistheembeddedatommethod(EAM)originallypresentedbyDawandBaskes[1J,butitsembeddedenergyandpairpotentialaregivenintheform0fsplinefunctions,suchanunanalyticalf0rmmakesthismodelverydifficulttobeappliedtoal1oys[2].J0hnsonhasdevelopedana1yticalEAMmode1sforfcc,bccandhcpmetal,[3~6j.Moreover,usingthefccanalyticalEAMmodel,J0hnsonhasca1culate…     

Crystallization behaviour of Metglas 2826 MB (Fe40Ni38Mo4B18)

Differential scanning calorimetry, x-ray diffraction and transmission electron microscopy have been employed to determine the thermal stability and identify the crystalline phases on devitrification of Metglas 2826 MB. The glass crystallizes intoγ-FeNiMo and fcc (FeNi)₂₃B₆ with activation energies of 270 and 375 kJ mol⁻¹ respectively. The reactions are primary and polymorphic in nature. The influence of Mo towards crystallization of Fe₄₀Ni₄₀B₂₀ has been to enhance the formation of the fcc (FeNi)₂₃B₆ phase in preference to orthorhombic (FeNi)₃B phase and to raise the thermal stability of the amorphous state.