深过冷Al72Ni12Co16合金熔体中的相选择

采用惰性形核涂层型壳和氩气保护下循环过热的方法，使Al72Ni12Co16合金获得200K的大过冷度，在此基础上从实验和理论两方面研究了深过冷Al72Ni12Co16合金熔体中的相选择规律。实验和理论计算表明：熔体过冷度是决定Al72Ni12Co16合金中准晶相与晶体相竞争形核的主要因素，且存在一临界过冷度，其值约为60K，当Al72Ni12Co16合金的初始过冷度大于临界过冷度时，十面体准晶相将作为初生相从熔体中析出；反之，当Al72Ni12Co16合金的初始过冷度小于临界过冷度时，熔体初生相为β晶体相。     

静电悬浮下铌异质形核及枝晶生长（英文）

采用无容器静电悬浮实验技术,对纯度99.7%和99.95%铌材料的过冷程度和形核凝固机制进行了系统研究。通过经典形核理论分析测量和计算得到材料样品在形核和凝固过程的热物理参数和热动力学参数。实验结果统计分析表明：铌样品的最大过冷度为455.7 K,临界过冷度约为739 K。系统分析并计算得到铌样品最大概率形核过冷度、指前系数、成核活化能、固液界面自由能和关键晶核尺寸。样品的枝晶生长速度与过冷度呈幂函数关系,在过冷度454 K时,枝晶生长速度达到42.1 m/s。考虑非等温条件下界面能的各向异性对自由枝晶生长的影响,理论预测结果与实验获得实验结果一致。     

Al-Cu-Fe系初生准晶相凝固过程的热力学分析

采用XRD,SEM和TEM等方法,研究了铸态 Al58.8Cu36.6Fe3.5Si1.1合金(973K保温2.5h后水淬)的显微组织及相组成.观察到铸态样品中存在4种不同的相,即初生准晶I相、Φ相、θ-Al2Cu相和η-AlCu相.对准晶I相及其晶体近似相R相,提出相应的自由能计算模型及算法,从理论上说明准晶(Al61.89Cu25.61Fe11.10)I相是高温稳定相,当温度低于938K时,将形成其晶体近似相R相.     

深过冷Cu-20%Pb亚偏晶合金的再辉与形核分析

采用熔融玻璃净化与循环过热相结合的方法研究Cu-20%Pb亚偏晶合金的再辉行为,利用经典形核理论与瞬态形核理论计算讨论偏晶合金的两相竞争形核规律.结果表明,在过冷度0～238K范围内,凝固过程出现两次再辉.一次再辉由a(Cu)相的形核和生长引起,二次再辉由偏晶反应引起.过冷亚偏晶Cu-20%Pb合金凝固过程中,相恒先形核,即匀晶转变先于偏晶反应发生.     

深过冷Al72Ni12Co16合金的组织演化及单相准晶的生成

采用惰性形核涂层型壳和氩气保护下循环过热的深过冷方法,系统研究了深过冷条件下Al72Ni12Co16合金的凝固组织演化过程及单相准晶的生成条件。结果表明:在0～200K的过冷度范围内,随过冷度的增大,Al72Ni12Co16合金发生小过冷树枝晶→柱状晶→等轴晶的组织转变,转变的两个临界过冷度分别为ΔT1=60K和ΔT2=120K;此外,当熔体过冷度大于60K时,准晶相在与晶体相的竞争形核中胜出,作为初始相从熔体中析出,并随过冷度的增大,凝固组织逐渐变为单相准晶。     

深过冷A172Ni12Co16合金的组织演化及单相准晶的生成

采用惰性形核涂层型壳和氩气保护下循环过热的深过冷方法，系统研究了深过冷条件下A172Ni12Co16合金的凝固组织演化过程及单相准晶的生成条件。结果表明：在0-200K的过冷度范围内，随过冷度的增大，A172Ni12Co16合金发生小过冷树枝晶→柱状晶→等轴晶的组织转变，转变的两个临界过冷度分别为ΔT1＝60K和ΔT2＝120K；此外，当熔体过冷度大于60K时，准晶相在与晶体相的竞争形核中胜出，作为初始相从熔体中析出，并随过冷度的增大，凝固组织逐渐变为单相准晶。     

过冷Cu-Pb偏晶合金的凝固热力学分析

采用熔融玻璃净化和循环过热相结合的方法实验研究了Cu-34.15%Pb偏晶合金在0~204K的宽过冷度区间的冷却曲线。实验结果表明,Cu-34.15%Pb偏晶合金在较小过冷时只有一次再辉,较大过冷时有两次再辉,偏晶反应中液相L2恒为初生相。根据经典形核理论和冷却曲线讨论了偏晶合金的两相竞争形核规律,并推断出Cu-Pb合金偏晶反应中液液相变焓ΔHL的取值范围为5×108~1.8375×109J.m-3。研究发现,ΔHL的大小对于偏晶反应中的α相和L2相的两相竞争形核起着至关重要的作用,需要精确地测定。     

深过冷Co-B合金外源触发形核行为及组织研究

合金的形核机制及其控制方法是凝固理论的重要研究领域之一。触发形核方式可自主控制形核过冷度,对研究形核理论及组织演变具有极大帮助。但熔体具有亚稳性,在实际处理时,外源性杂质引入熔体后将作为触发形核异质点,改变过冷度ΔT和再辉度ΔT_R,显著影响后续凝固行为,该种现象更为普遍。本文通过玻璃包覆结合循环过热过冷方式,获得两类不同形核模式凝固的Co80B20合金。自发形核模式下,ΔT及ΔT_R分别为280和199 K,组织组成为Co/Co₃B细小规则共晶。外源性触发形核模式下,ΔT和ΔT_R降至122和21 K。组织转变为初生Co枝晶及晶间的Co₂₃B₆基体相。外源性杂质将降低f(θ),减小临界形核半径,降低ΔT,使得组织更加不均匀,在实际的熔体处理过程中应予以控制。     

连续冷却多阶段快速凝固过程起始形核温度的计算

基于快速凝固的瞬态形核理论和对连续冷却条件下整个温度区间的瞬态形核数和晶核体积积分 ,导出了连续冷却多阶段快速凝固条件下过冷熔体中各析出相起始形核温度的计算方法。假定界面传热处于牛顿冷却方式 ,对Ni Al合金平面流铸条带形成过程中析出的化合物相起始形核温度做了计算     

深过冷Ni-21.4%Si共晶合金的凝固特性研究

对熔融玻璃净化后深过冷Ni-21.4%Si（原子分数,下同）共晶合金的凝固特性进行了实验研究,并对其均质形核过冷度进行了理论预测.结果发现,采用熔融玻璃净化可使Ni-21.4%Si共晶合金获得318 K的过冷度.理论计算表明,此过冷度达到了Ni-21.4%Si共晶合金的均质形核过冷度.Ni-21.4%Si共晶合金凝固特性与过冷度△T有关:当过冷度小于250 K时,冷却曲线有2个再辉峰,其中当过冷度小于206 K时,凝固组织由Ni3Si相和规则共晶组成,当过冷度在206 K到250 K之间时,凝固组织由α-Ni相和规则共晶组成;过冷度大于250 K后,冷却曲线只有1个再辉峰,凝固组织为反常共晶.过冷度会影响初生相Ni3Si的生长方式.随着过冷度的增大,初生相Ni₃Si的生长会由小平面生长方式转为非小平面生长方式.     

Microstructure Formation and Mechanical Property Involving Icosahedral Quasicrystal Phase of Y Rich Mg-Zn-Y Quasicrystal Alloy

The microstructure formation and mechanical property involving icosahedral quasicrystal (I-phase) in the Y-rich Mg-Zn-Y alloy have been studied. The equilibrium formation of I-phase from the Y-rich Mg-Zn-Y melt is through a peritectic reaction between the Y-rich melt and the primary W-phase, which is discussed in detail. The independent nucleation and coupling growth mechanism between the W-phase and the I-phase, from the melt, are revealed, which is significant for understanding the peritectic reaction process involving icosahedral quasicrystal in the Mg-Zn-Y alloy. The mechanism of the quasicrystal phase strengthened magnesium alloys is also discussed here.     

Al-Mg-Zn二十面体准晶合金中的Frank-Kasper相

Frank-Kasper相Mg32(Al,Zn)49是与其准晶相相对应的1/1近似相,它具有二十面体壳层密堆结构。研究了在常规凝固条件下化学成分为AlxMg40Zn60-x(x=20~45,摩尔分数)合金中Frank-Kasper相的组织形貌。利用光学显微镜、X射线衍射仪及扫描电镜,确定了Frank-Kasper相的组织及成分。结果表明:AlxMg40Zn60-x(x=20~45)合金中均为单相的Frank-Kasper相;随铝含量的增加,其形貌由花瓣状逐渐向“十字架”状组织转变。     

Crystal–quasicrystal transition depending on cooling rates in directionally solidified Al–3Mn–7Be (at.%) alloy

The transition of primary phases from the crystalline approximant phase to icosahedral quasicrystal phase (I-phase) is observed in the directional solidified Al–3Mn–7Be (at.%) alloy. The structures of I-phase and approximant phases are characterized by SEM, TEM and HRTEM. The addition of Be significantly enhances the formation ability of I-phase, combining with the directional solidification method where the growth rates and temperature gradients can be separately controlled, giving rise to a promising way to prepare quasicrystal-reinforced Al-matrix composite.     

Ag42In42Ca16二十面体准晶与2/1立方近似相Ag42In45Ca13的稳定性研究

Ag3In3Ca中的主要合金相是简单立方Ag42In45Ca13(空间群为Pa3↑-，α=2．496nm)，它是Ag42In42Ca16二十面体稳定准晶的2／1立方近似相．选区电子衍射(SAED)实验表明，2／1立方近似相与二十面体准晶有相似的局部结构．X射线能谱(EDS)、电子能量损失谱(EELS)和X射线粉晶衍射分析表明，Ag3In3Ca合金中的立方相Ag42In45Ca13不稳定．薄膜电镜样品在空气中易发生化学反应，产物中主要是Ca和O，还有少量C．块状合金在空气中放置14d后，其中的立方相Ag42In45Ca13分解，二元合金相AgIn2和In4Ag9的含量明显增加．在550℃保温55h后，立方近似相Ag42In45Ca13的含量显著减少．在相同条件下，二十面体准晶Ag42In42Ca16保持不变，具有高的结构和化学稳定性。     

Quasicrystalline phases and their approximants in AlMnZn alloys

Two AlMnZn alloys in melt-spun condition have been studied by transmission electron microscopy. The Al₂₄Mn₅Zn alloy was found to be fully icosahedral, while the Al₁₂Mn_2.9Zn alloy gave rise to decagonal quasicrystal. The decagonal phase grew in clusters with an orientation relationship between the grains suggesting nucleation on an icosahedral seed. On annealing at 500–600°C, the quasicrystalline phase transformed to a body centered orthorhombic phase L (a = 1.24, b = 1.26 andc = 3.05nm) with a high density of planar defects. This phase transforms to an ordered and defect free monoclinic phase M, a superlattice structure of L (a = c = 1.77, b = 3.05nm and β = 89.1°). The L phase is shown to be a rational approximant of the icosahedral phase. The interrelationship among quasicrystalline phases and their rational approximants in AlMnZn system are highlighted.     

Magnetic properties of the 1/1 approximant Ag42In42Gd16 to the icosahedral quasicrystal Ag-In-Gd

The structural, magnetic, and ¹⁵⁵Gd Mössbauer spectral properties of the 1/1 approximant Ag₄₂In₄₂Gd₁₆ to an icosahedral quasicrystal Ag-In-Gd are reported. Based on dc magnetic susceptibility measurements, it is shown that the studied compound develops no long-range magnetic order in the temperature range 1.8-300 K. The dc zero-field-cooled and field-cooled susceptibility data indicate that the 1/1 approximant Ag₄₂In₄₂Gd₁₆ is a spin glasss with freezing temperature T_f = 3.6(1) K. This is further confirmed by the analysis of the frequency dependence of T_f using the Vogel-Fulcher law and the dynamic scaling behavior near T_f. It is argued that the spin freezing process is a true equilibrium phase transition rather than a nonequilibrium phenomenon. The large frustration parameter of the studied compound indicates that it belongs to a category of strongly geometrically frustrated magnets. The ¹⁵⁵Gd Mössbauer spectra of the 1/1 approximant Ag₄₂In₄₂Gd₁₆ confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The Debye temperature of the 1/1 approximant Ag₄₂In₄₂Gd₁₆ is 200(1) K.     

六方Al14.2(Fe,V)3.0Si1.3准晶近似晶体相的电子衍射分析

利用选区电子衍射和会聚束衍射研究了喷射沉积Ａｌ－Ｆｅ－Ｖ－Ｓｉ合金中一种六方相的晶体结构,其点阵常数为：ａ＝２．５２ｎｍ,ｃ＝１．２６ｎｍ,空间群为Ｐ６／ｍｍｍ。该六方相与立方相具有固定取向关系,且ＥＤＳ分析表明,两相成分相近。系统对比分析ＳＡＥＤ花样发现,六方相的某些带轴衍射谱具有立方相的二十面本结构基元表现出的衍射特征。表明六方相也是一种准晶近似晶体相,其结构构架可能由（Ｆｅ＋Ｖ）和（Ａｌ＋Ｓ     

Mg-Zn-Y三元合金中二十面体准晶相生长形貌及其演化

采用常规凝固方法在Mg-Zn-Y三元合金系中获得了大体积分数的二十面体准晶。二十面体准晶相有2种典型形貌特征：一种为花瓣状，另一种为多边形形状。这是准晶在生长过程中形貌演化的结果。合金的成分和冷却速率是影响准晶形貌的主要岗素。准晶合金中生成的低温相越多，冷却速率越慢，准晶相生长的时间和空间条件越好，准晶相越容易由花瓣状演化成多边形状。准晶的形成有包晶反应参与，包晶反应是一种由初生固态相扩散控制的反应，因此，准晶在生长初期和最终形态其元素含量有明显差别，分析表明，准晶生长初期Mg元素含量偏低，Zn和Y元素含量偏高。     

3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al-Mn Alloy

Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al-18 Mn alloy(in wt%).Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons.3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching.A model has been proposed to describe the formation process of the icosahedral phase and α-Al during the rapid solidification.The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles,and subsequently engulfed by the α-Al which propagates in a planar morphology.     

Ti40Zr40Ni20块体铸态准晶的相变研究

用吸铸法制备出单相块体Ti40Zr40Ni20。其准点阵参数为aR=0．523nm。通过差示扫描量热法(DSC)和X射线衍射等手段研究了该铸态准晶合金在加热过程中的相变行为。结果表明,Ti40Zr40Ni20铸态准晶在964K温度以下稳定;在964K附近温度,准晶发生分解,形成由β-Zr(Ti)固溶体与C14相组成的两相混合组织;在1107K,该混合物发生熔化。