非晶态合金晶化过程中晶体长大速率的数学表达式

根据前文提出的晶化微观机制,导出了非晶态合金晶化过程中晶体长大速率的数学表达式。用此表达式圆满地解释了Nunogaki、Heimendahl以及我们的实验结果,并能模拟原位加热时非晶态Ni-P合金薄膜晶化过程中的晶体长大过程及晶体长大尺寸与时间的关系。根据此表达式,讨论了影响晶体长大速率的因素,如温度、时间及非晶态合金的微观结构等。     

STUDIES ON PRIMARY CRYSTALLIZATION OF RAPIDLY QUENCHED Al-Ni-Cu-Nd METALLIC GLASS BY USING HIGH RESOLUTION TRASMISSION ELECTRON MICROSCOPY

Rapidly solidified Al87Ni7Cu3Nd3 metallic glasses, prepared by using melt spinning, were treated under both isothermal and non-isothermal regime. The amorphous ribbon and the annealed samples were closely examined by means of differential scanning calorimetric, conventional X-ray diffraction and high resolution transmission electron microscopy with selected-area electron diffraction, with special interest in primary crystallization into α-Al nanocrystalline particles, in order to understand structural characteristics of Al-based amorphous/nanocrystalline alloys, and nucleation and grain growth mechanism on the nanometer scale during primary crystallization. The results show that, the as-prepared ribbons are fully amorphous and homogeneous in the micron scale, but contain high density of quenched-in clusters or crystallite embryos. Primary crystallization mainly leads to formation of two-phase mixture of a-Al crystal and residual amorphous phase. The annealed ribbons exposed isother-mally at HOP C for 5     

INFLECTION OF COERCIVITY DURING LOCAL CRYSTALLIZATION OF Fe-Si-B AMORPHOUS ALLOYS

An inflection hehaviour was revealed during isothermal annealing under the observation oftransition of the coercivity of Fe-Si-B amorphous alloys during local crystallization.It maybe interpreted by the transition of α-Fe grain precipitated from single to multiple domain,Thus,the theoretical expression of H_0-t_a may be derived.The plot of expression H_0-t_a calcu-lated well represents the feature of the experimental curve.     

HRTEM study of crystallization of Zr–Cu–Ni metallic glass

Employing differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM), the micromechanism for crystallization of Zr₇₀Cu₂₀Ni₁₀ metallic glass under isothermal annealing conditions has been investigated. It is found that the relationship between the annealing temperature and the peak position, incubation time and ending time in the isothermal annealing DSC traces of Zr₇₀Cu₂₀Ni₁₀ metallic glass obeys a first-order exponential function. However, the time–temperature transformation curves of Zr₇₀Cu₂₀Ni₁₀ metallic glass at different crystallized volume fractions can be well fitted by a second-order exponential function. It is observed that at the initial crystallization stage some ordered atomic clusters precipitate first, acting as nucleation sites and facilitating the subsequent crystallization process, and the crystal growth process mainly proceeds through the atomic depositing on the previously formed crystals. This behavior confirms that the new micromechanism for crystallization of amorphous alloys proposed by Lu and Wang can also be applied to the new series of zirconium based amorphous alloys.     

Effects of Zr on crystallization kinetics of Pr—Fe—B amorphous alloys

The effects of Zr on crystallization kinetics of Pr-Fe-B amorphous alloys have been investigated by DTA and XRD methods.It was found that for Pr8Fe86-xZrxB6(x=0,1,2)amorphous alloys,the final crystallized mixture is α-Fe and Pr2Fe14B,and the metastable Pr2Fe23B3 phase occurs during crystallization of Pr8Fe86B6 amorphous alloy,not during crystallization of Pr8Fe86-xZrxB6(x=1,2)amorphous alloys,By analyzing the activation energy of crystallization,the formation of an α-Fe/Pr2Fe14B composite microstructure with a coarse grain size in annealed Pr8Fe86B6 alloy,is attributed to a difficult nucleation and an easy growth for both the α-Fe and Pr2Fe14B in the alloy.The addition of Zr can be used to change the crystallization behavior of the α-Fe phase in Pr-Fe-B amorphous alloy,which is helpful to reduce the grain size for the α-Fe phase.     

杭州大剧院——当前中国建筑用钛的典范——杭州大剧院：我国利用钛作为建筑外墙装饰材料的里程碑

快淬双相纳米复合稀土永磁材料非晶晶化过程决定了材料的微观组织和磁性能。从形核规律出发，提出了持续形核长大和“爆炸式形核长大”的非晶晶化模型。讨论了快淬速度、添加合金元素、退火工艺以及外加磁场等对非晶晶化过程的影响，重点分析了合金元素在非晶晶化过程中的重新分布。在此基础上，提出了利用中间相的分解细化晶粒等获得理想材料的不同方法。     

Primary crystallization process of rapidly solidified Al-Ni-Cu-Nd metallic glasses under continuous heating regime

1　INTRODUCTIONManyAl basedamorphous/nanocrystallinealloyscontainingtransitionmetal (TM =Fe ,Co ,Ni,Cu ,etc)andrareearth (RE =La ,Y ,Ce ,Nd ,etc)ele mentshaveanattractivecombinationofmechanicalproperties[13] .InthelasttenyearsawideinterestwasspurredtoresearchprimarycrystallizationofAl richmetallicglasses[4 9] .ThenanophasecompositesofAl TM REsystemcanbeobtainedbyasuitableprocessingcombinationofrapidsolidificationandheattreatment[10 16 ] .Asanimportantwell controlledmethod ,annealin…     

The effect of Si addition on crystallization behavior of amorphous Al-Y-Ni alloy

This article reports the effect of silicon (Si) addition upon the crystallization behavior and mechanical properties of an amorphous AlYNi alloy. An amount of 1 at.% Si was added to a base alloy of Al₈₅Y₅Ni₁₀ either by substitution for yttrium (Y) to form Al₈₅Y₄Ni₁₀Si₁, or by substitution for nickel (Ni) to form Al₈₅Y₅Ni₉Si₁. Differential scanning calorimetry (DSC) of all three alloys showed three exothermic peaks. Comparing the peak temperature for the first exothermic peak, a significant shift occurs toward the lower temperature. This indicates that 1 at.% substitutions of Y or Ni by Si decreases the stability of the amorphous phase. DSC study of these amorphous alloys during isothermal annealing at temperatures about 5–15 K lower than their first crystallization peaks showed that the formation of α-Al nanocrystals via primary crystallization occurred without an incubation period. The Avrami time exponent (n) of the primary crystallization from the amorphous structure was determined to be 1.00–1.16 using the Johnson-Mehl-Avrami (JMA) analysis. This suggested a diffusion-controlled growth without nucleation. However, a DSC study of these amorphous alloys during isothermal annealing at higher temperatures between 585 and 605 K showed a clear incubation period during the formation of the Al₃Ni and Al₃Y intermetallic phases. An n value of 3.00–3.45 was determined using JMA analysis. This suggested that the transformation reaction involved a decreasing nucleation rate and interface-controlled growth behavior. The tensile strength σ_f and Vickers hardness for these amorphous alloys are in the range 1050–1250 MPa and 380–398 diamond pyramid hardness number (1 diamond pyramid hardness number=1 kg/mm²=9.8 MPa), respectively.     

PREPARATION OF AMORPHOUS Ti-Pd ALLOYS AND THEIR PHYSICAL PROPERTIES

The amorphous Ti_(l_x)Pd_x alloys within a wider composition range of 0.25相似文献   

Crystallization of amorphous Zr70Cu30—xNix alloys

X－ray diffraction (XRD)and differential scanning calorimetry(DSC) were employed to investigate the influence of Ni content on the crystallization of amorphous Zr70Cu30-xNix(atom fration in%) alloys,Experimental results show that with the Ni content increasing the activation energies for crystallization of amorphous Zr70Cu30-xNix alloys increase correspondingly,indicating that the thermal stability is greatly improved.All the DSC traces of amorphous Zr70Cu30-xNix alloys exhibit two exothermic peaks,suggesting that the crystallization process via a double-stage ticles,while the second one corresponds to the precipitaion of nano-scale Zr2Ni phase and crystallization of residual amporphous phase,The mechanism on the crystallization of amorphous Zr70Cu30-xNix alloys was discussed.     

EFFECT OF PRE-ANNEALING ON CRYSTALLIZATION KINETICS OF AMORPHOUS Ni-P ALLOYS

The effect of pre-annealing treatment on the crystallization kinetics parameters of amorphous Ni-P alloys has been investigated.Experimental results showed that the crystallization tem- perature,T_p and T_x,the apparent activation energy,E_c,as well as the Avrami exponent for isothermal crystallization,n,decrease significantly,while ΔT_(px)=T_p-T_x increases with the elongation of pre-annealing time at 570 K.     

SELECTIVE OXIDATION AND THERMAL STABILITY OF Ni-Zr AMORPHOUS ALLOYS

用精密电阻测量、DSC和X射线衍射分析,研究了非晶态Ni-Zr合金在低于T_c的保温过程中的氧化和晶化.其氧化表现为Zr的选择氧化,它降低Ni_(65)Zr_(35)表面层的热稳定性、提高Ni_(37)Zr_(63)表面层的热稳定性.对这种现象发生的原因进行了讨论.     

Nanocrystallization of Zr61Al7.5Cu17.5Ni10Si4 metallic glass

The primary nanocrystallization behavior and microstructural evolution of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During continuous heating of the 4Si and the base (contains no Si) amorphous alloys at a heating rate of 10 K/min, the saturation point of nucleation for the 4Si amorphous alloy occurs at a crystallization fraction of 78%, which is significantly higher than 65% for the base alloy, implying that these metalloid atoms would extend the nucleation stage and refine crystalline particles. The sequence of crystallization phase from the amorphous matrix for the isothermally annealed 4Si amorphous alloy at 703 K is observed to be Zr₂Cu and Zr₂Ni at the early stage, Zr₃Al at an intermediate stage, and Zr₂Si at the final stage. Moreover, enrichment of Si atoms at the interface between Zr₂Cu crystal and the amorphous matrix is detected. This may result in increasing the thermal stability of the remaining amorphous phase and retardation of the crystal growth of Zr₂Cu particles.     

Multi-phase nanocrystallization induced fast degradation of methyl orange by annealing Fe-based amorphous ribbons

Different from the common understanding that crystallization deteriorates the degradation capability of amorphous alloys, we show here that the Fe-based multi-phase nanocrystalline ribbons (Fe-MNRs) exhibit 3 and 17 times higher degradation rate than its amorphous counterpart and the conventional zero valent iron powders, respectively. The formation of multi-phase nanocrystals and nanoporous structure resulted from selective corrosion during degradation is responsible for the high degradation capability of Fe-MNRs. The present results suggest that suitable nano-crystallization annealing treatment could be a novel approach to enhance the degradation capability of Fe-based amorphous alloys.     

Stability of amorphous Al90TMxCe10—x（TM=Fe or Ni） alloys

X-ray diffraction(XRD) and differential scanning calorimetry(DSC) were used to investigate the crystallization process of amorphous Al90TMxCe10-x (atom fraction in%;TM=Fe or Ni;x=3,5)alloys,Aging effects were examined by X-ray diffraction,The structure corresponding to the prepeak for the amorphous Al90Fe5Ce5 alloy is more stble than the amorphous matrix,but it is not stable for amorphous Al90Ni5Ce5 alloy during the first crystallization stage and even decomposes at room temperature,Although both Al-Ni and Al-Fe have strong chemical bonding,the cyrstallization onset temperature of amorphous Al-Fe-Ce alloys is much higher than that of amorphous Al-Ni-Ce alloys,which is likely caused by the different stability of the structure corresponding to the prepeak.The crystallization onset temperature increases as Ce/Ni ratio increases in amporphous Al90NixCe10-x alloys,whereas it decreases as Ce/Fe ratio increases in amorphous Al90FexCe10-x alloys.A better atomic packing produces as Ce content increases because of the size mismatch in Al-Ni-Ce systems and as Fe content increases because of the increasing Fe central structural units.     

Effects of quenching conditions on crystallization behavior of amorphous Al90Ni5Ce5 alloys

X-ray diffraction and DSC were used to investigate the crystallization behavior of amorphous Al90Ni5Ce5 alloys at different quenching temperatures.All the amorphous Al90Ni5Ce5 alloys quenched at different temperatures crystallize by two stages.The first stage corresponds to FCC Al phase precipitating from the amorphous matrix.The crystallization onset temperature increases with increasing quenching temperature.The quenching temperature also influences the isothermal behaviors.At low quenching temperatures,the FCC Al precipitation is only through grain growth.At high quenching temperatures,the FCC Al precipitation is through growth of quenched-in Al unclei and nucleation and growth of new crystallites.The reason that the crystallization onset temperature varies with quenching temperature is likely as that the quenched-in Al nuclei decreases with increasing temperature.     

Cu_(46)Zr_(47-x)Al_7Ti_x(x=0,1.5)非晶合金晶化动力学研究

采用铜模吸铸法制备Cu46Zr47-xA l7Tix(x=0,1.5)大块非晶合金。用X射线衍射仪(XRD)确定合金的结构,采用差示扫描量热仪(DSC)对非晶合金的晶化动力学进行了研究。结果显示,随着升温速率的加快,这两种非晶合金的玻璃转变温度Tg,晶化开始温度Tx和晶化峰值温度Tp均向高温区移动,且过冷液相区逐渐加宽,表明非晶合金的玻璃化转变和晶化均具有动力学效应。利用K issinger方程计算合金的晶化激活能。通过晶化动力学研究了热稳定性和晶化反应速率常数之间的关系,以及Ti元素添加对Cu-Zr-A l大块非晶合金热稳定性的影响。     

Electric-field-enhanced crystallization of amorphous Fe86Zr7B6Cu1 alloy

The effect of external electric field on the crystallization of amorphous Fe₈₆Zr₇B₆Cu₁ alloy was studied. It is shown that its crystallization process is markedly enhanced by external electric field. The crystallization time at 600 °C decreases from 1 to 0.5 h on application of a modest (10⁴ V/m) external electric field. The volume fraction of crystalline -Fe increases from 65.2 to 68.6%, while the grain size decreases from 13.2 to 11.9 nm. The electric-field-enhanced crystallization may result from the fact that the external electric field results in the increases of the crystal nucleation rate and the crystal growth rate. The complex permeability shows an apparent improvement in soft magnetic properties induced by electric field, thereby demonstrating the practical utility of electric-field-enhanced crystallization technique.     

非晶态合金晶化过程的一种新微观机制SCIEI

根据对非晶态合金微观结构的分析和原位加热TEM观察非晶态Ni-P合金薄膜动态晶化过程的实验结果,本文提出了一个新的晶化微观机制,即非晶态合金的晶化过程由两个不同过程组成;(1)单原子由非晶态问晶胚(或晶体)表面的扩散过程;(2)有序原子团的长大及切变合并或切变沉积过程。部分晶化非晶态Ni-P合金的TEM观察结果为新晶化微观机制的适用性提供了证据。并用此机制解释了晶化过程中的初生晶体结构形态等实验结果。     

FINEMET非晶合金激波晶化中Cu和Nb作用的失效

应用ＸＲＤ,ＤＳＣ及ＴＥＭ等技术,将ＦＩＮＥＭＥＴ非晶合金的激波晶化与退火晶化及不含Ｃｕ,Ｎｂ的Ｆｅ－Ｂ－Ｓｉ和Ｆｅ－Ｍｏ－Ｂ－Ｓｉ合金的激波晶化作了对比研究。结果表明：该合金的激波晶化除了具有极高的转变速率和转变速率相当完全的晶化度外,合金元素Ｃｕ和Ｎｂ在退火晶化时具有的细化晶粒,阻止晶粒长大和稳定非晶态的三个作用均失效了,采用激波作用下非晶固体转变成流体状态的模型可以定性地解释这一现象。