超磁致伸缩材料的制备技术研究进展

指出超磁致伸缩材料的制备工艺、性能优化,磁 机耦合过程的理论分析与实验研究,是超磁致伸缩材料研究的两大主题.定向凝固技术是目前国内外广泛采用的超磁致伸缩材料的制备方法.较全面地评述了各种传统的定向凝固技术和新型定向凝固技术的原理和工艺技术特点及存在的问题,提出了一种新的改进型定向凝固技术.     

金属电磁加工工艺特点及应用

回顾了电磁加工工艺的发展过程,通过分析圆形、椭圆形等不同横截面形状的金属成型制品的电磁成形过程,从感应器结构、屏蔽罩插入深度、材料性状及抽拉速率等方面出发,详细论述了电磁加工定向凝固过程的技术特点,并阐述了电磁成形定向凝固技术的优缺点,指明了今后的发展方向。     

冶金法提纯太阳能级硅材料的研究进展

分析了国内外硅材料的供应及生产状况,对太阳能级硅材料冶金法提纯工艺中的湿法精炼技术、造渣提纯技术、电子束真空提纯技术、等离子体吹气技术、定向凝固技术等进行了综述,总结了有效去除金属及B、P杂质的提纯流程,指出冶金法可能是今后提纯多晶硅的研究方向.     

高纯铝定向凝固提纯技术应用研究

高纯铝是目前最主要的电子新材料,通过定向凝固工艺获得的高纯铝具有纯度高、成本低的优势,该法目前被产业界广泛采用。简单介绍了定向凝固技术的原理,重点分析了国内外高纯铝定向凝固技术的新工艺、新方法,最后对高纯铝定向凝固技术存在的问题及发展趋势进行了分析总结。     

纯镍板焊缝区胞状晶形成机制浅析

一般金属在定向凝固条件下会形成胞状晶或柱状晶,胞状晶的生长与宏观热流方向平行且与晶体学取向无关.文章对轧制纯镍板的焊缝区金相观察到了明显的胞状晶,显现出晶体学的择优取向,说明变形织构可能导致金属熔体在等轴凝固条件下也能形成胞状晶.     

金属凝固过程中的形核技术

在金属凝固过程中,对金属液施加各种物理场可以提高铸坯的等轴晶比例,细化凝固组织,从而提高铸坯的力学和物理性能.文章介绍了近年来一些机械法凝固技术的研究现状,并简要指出这些技术的优缺点所在.     

Re和Cr变化对定向高温合金凝固和偏析的影响

采用真空熔炼和定向凝固技术制备不同Re和Cr含量的定向试棒.利用差热分析(DSC)研究不同Re和Cr含量定向凝固高温合金的凝固行为,利用扫描电镜(SEM)和电子探针(EPMA)研究合金组织和元素分布特征.研究发现Re含量的增加对合金的固/液相线温度影响不大,Cr含量的增加降低了合金的固/液相线温度;随着Re含量增加,加...     

冶金法提纯太阳能级硅材料的研究进展

分析了国内外硅材料的供应及生产状况,对太阳能级硅材料冶金法提纯工艺中的湿法精炼技术、造渣提纯技术、电子束真空提纯技术、等离子体吹气技术、定向凝固技术等进行了综述,总结了有效去除金属及B、P杂质的提纯流程,指出冶金法可能是今后提纯多晶硅的研究方向。     

振动条件下金属凝固过程的研究现状与展望

介绍了振动被引入金属凝固过程的发展历程,重点归纳了机械振动技术、振动激发形核技术、超声振动技术和脉冲磁致振荡技术运用于金属凝固过程控制的振动方式、应用领域、冶金效果及优缺点,总结了四种振动产生的方式和机理,概述了振动对金属液凝固的影响及具体形式,总结了现有振动改善凝固组织的机理和振动技术在金属凝固过程中的研究现状,最后...     

大型钢锭定向凝固技术的发展

介绍了定向凝固技术的原理，定向凝固钢锭的制造方法和在实际生产中的应用，以及该技术对特厚钢板综合性能的影响，因而为产生高质量各向同性特厚钢板指明了工艺方向。     

Preparation,Properties, and Applications of Lamellar Ni3Si

Metallurgical and Materials Transactions A - Lamellar Ni3Si was electrochemically prepared. Its structure and microhardness were controlled by the directional solidification growth rate and...     

Liquidus Projection of the Ternary Bi-Sb-Te Thermoelectric Material System

The ternary Bi-Sb-Te system is important for thermoelectric applications. Its liquidus projection is determined, except for the Bi-rich corner with various unconfirmed binary Bi-Te compounds. Fifty Bi-Sb-Te ternary alloys are prepared. Primary solidification phases are identified using metallographic observations and X-ray diffraction techniques. Phase transformation temperatures are determined using differential thermal analysis. No ternary compound is found. (Bi,Sb)₂Te₃ and (Bi,Sb) are continuous solid solutions. The Bi₂Te₃ and Sb₂Te₃ phases form a pseudo-binary section. Alloys of the primary solidification phases of Te, (Bi,Sb)₂Te₃, γ, δ, and (Bi,Sb) are determined and the boundaries of various primary solidification phases are delineated. The Bi-Sb-Te liquidus projection is also calculated with the CALPHAD method using preliminary thermodynamic models, and the calculated results are qualitatively in agreement with the experimental determinations.     

Fe-5Mn-2Al-0.15C中锰钢连铸凝固偏析及粒子析出行为

为研究Fe-Mn-Al-C系中锰钢连铸凝固偏析及粒子析出特性,采用光学显微镜观察Fe-5Mn-2Al-0.15C中锰钢的显微组织,并通过Thermo-Calc热力学软件研究了其凝固模式、溶质元素偏析及粒子析出行为。结果表明,该中锰钢铸锭的显微组织主要为板条状马氏体,且含有少量铁素体;其凝固模式为L→L+δ→L+δ+γ→δ+γ→γ;Al元素的平衡分配系数大于1,发生负偏析,偏聚到δ-铁素体枝晶内部;而Mn、Nb、V、S等溶质元素发生正偏析,均偏聚到枝晶间。AlN主要在枝晶内析出,其析出温度为1 448 ℃;MnS、Nb和V的富集物主要在枝晶间析出,且MnS和Nb的富集物均在1 400 ℃以上开始析出,而V的富集物的析出温度为760 ℃。     

振动激发金属液形核过程的传热研究

为了提高铸坯凝固组织的均匀性,减轻宏观偏析,提出了振动激发金属液形核技术,其传热机理是为了促进形核,需要确保晶核发射器棒体表面温度控制在金属液的固、液相线之间,为此开展了传热计算及模拟试验研究。通过试验可知,在气冷条件下,棒体表面因冷却强度不够而无法产生大量的细小晶粒;而在水冷条件下,棒体表面因与钢液间的过冷度太大而迅速结壳,达不到向钢液连续弹射晶粒的目的。通过气雾冷却条件下的传热研究,在气流量为65 m3/h,水雾加湿量为3 kg/h的气雾冷却条件下,与棒体表面接触的钢液能够获得26℃以上的过冷度,因此棒体表面迅速形成大量的晶核而且不会结壳,进而可使晶粒被连续不断地弹射至金属液中,成为凝固过程中等轴晶的形核核心,促进铸坯凝固组织的均匀化。     

Niobium-Alloyed high speed steel by powder metallurgy

A philosophy for the use of strong carbide formers like niobium in high speed steels is described. It follows the concept of independently optimizing the compositions of the matrix (for maximum secondary hardening potential) and the volume fraction of the blocky carbides (for protection against abrasive wear). Normally, the two are interdependent through the action of the solidification equilibria, but separate control becomes possible when the blocky carbides are formed by a strong carbide former such as niobium. During normal ingot solidification, such strong carbide formers would produce very large primary carbides. This can be avoided by atomization and powder metallurgical processing. In this way, a steel has been produced whose matrix composition is similar to that of AISI M2, and whose primary carbides are all of NbC type. Its composition is 1.3C, 2W, 3Mo, 1.6V, 3.2Nb (wt pct). Because of its high stability, NbC is a much more effective obstacle to grain growth than the normal high speed steel carbides, and this allows substantially higher austenitization temperatures to be used. Despite its leaner composition, the Nb-alloyed steel matches the cutting performance of AISI M2, and its secondary hardening seems to be more persistent at high temperatures.     

大方坯凝固过程鼓肚应变及内裂纹形成的研究

通过建立大方坯凝固过程的传热模型,获得大方坯冷却传热过程的主要凝固参数,在此基础上建立了凝固前沿坯壳所承受的应变模型,讨论了大方坯凝固过程的主要应变及其主要影响因素,并针对实际铸机的设备和工艺状况,计算大方坯凝固过程的鼓肚应变,讨论了具体钢种产生裂纹的可能性.     

The development of a pseudoeutectic nickel-based composite alloy

This paper gives a detailed account of the development of a Ni-Cr-Be composite alloy. Its cast structure is that of a duplex eutectic with hard nickel beryllide fibers embedded in a softer Ni-Cr solid solution matrix. A partial liquidus projection of the Ni-Cr-Be system was determined in order to define the solidification conditions and optimum composition range for the alloy. Alloying with aluminum, tungsten, and molybdenum was used to enhance the mechanical properties of the material. Heat treatment conditions, mechanical properties, and oxidation behavior are presented. Formerly with P. R. Mallory & Co., Inc., is with A. D. Little, Inc., Cambridge, Mass.     

亚快速凝固技术的研究进展

介绍了实现亚快速凝固的两种方法：激冷法和深过冷法,并概述了亚快速凝固理论的最新研究进展.亚快速凝固的冷却速度介于快速凝固和近平衡凝固之间,为10^0～10^3 K/s,其凝固过程比较复杂,兼有快速凝固和近平衡凝固的优点.与传统工艺生产的材料相比,亚快速凝固材料的组织和性能更加优异.尽管亚快速凝固的理论研究还刚刚起步,但随着薄带连铸技术的快速发展,该技术在工业生产中的应用前景十分广阔.     

Dendrite coarsening and microsegregation in Al-Cu alloys

Solute redistribution and the amount of eutectic are predicted in the solidification structure of a dendritic Al-Cu alloy. The effect of dendrite coarsening on microsegregation during solidification is formulated. Local solidification time and alloy composition are found to change the type of operating dendrite coarsening. While one type of dendrite coarsening operates for a shorter local solidification time and/or lower alloy composition, at longer solidification times and/or higher alloy composition a different type of dendrite coarsening prevails. Local solidification time and alloy composition are the parameters which determine the homogenization and solution treatment, and the structural heterogeneity of the solidified ingot. METIN BASARAN, formerly Associate Professor, Department of Mechanical Engineering, Technical University of Istanbul, Turkey     

New Composition Based Technique for Solidification Cracking Resistance Evaluation

Predicting the occurrence of solidification cracking during the solidification of metallic alloys by numerical simulation is a crucial move for avoiding such defects. Several models are widely available, however, the application of such are impacted due to the specific and not accessible parameters required. A simple, composition-based approach to rank solidification cracking susceptibility is presented. The procedure links computational thermodynamic and computational fluid dynamics (CFD) to provide an evaluation tool for solidification cracking. The method is related to the liquid filling phenomena in dendritic arms during solidification, which plays a critical role in solidification cracking phenomena. The dendritic profiles were constructed using the fraction of solid calculated by commercial thermodynamic software packages. The calculated results were compared with experimental solidification cracking data and showed satisfactory accuracy. The method capability to rank the solidification cracking propensity of similar alloys based on composition provides an important new operative tool to aid alloy development in welding and additive manufacturing related areas.