高纯难熔金属及其合金单晶的发展

介绍了难熔金属及其合金单晶的制备技术,对电子束悬浮区域熔炼技术和等离子弧熔炼技术进行了比较。电子束悬浮区域熔炼法温度梯度易于控制、材料不受坩埚材料污染,但熔体表面张力对活性杂质和温度梯度敏感性高,所能制备的高纯难熔金属及其单晶材料尺寸规格受到很大限制,且材料内部位错密度较高。等离子弧熔炼法加热源能量密度高,原料规格形式多样,可制备单晶棒材、板材、管材及其他特定形状的单晶铸件,可最大程度地去除杂质元素(尤其是C元素),但设备系统复杂,单晶材料位错密度大。讨论了单晶材料发展现状,通过固溶强化可进一步提高材料的高温性能及其稳定性。单晶管材的制备也是一个发展方向。此外还对单晶材料制备技术和发展前景提出了一些建议。     

难熔金属材料先进制备技术

介绍了现代烧结技术(微波烧结、放电等离子烧结、选择性激光烧结)、先进高纯材料制备技术(电子束精炼、区域熔炼、等离子弧熔炼)、近净成形技术(3D打印、金属注射成形、高能喷涂成形)和抗氧化技术(涂层、复合材料等)4类先进制备技术。阐述了基本原理、技术优势、国内外研究现状及其在难熔金属材料制备方面的初步应用,并指出难熔金属材料的制备正在向着更高纯度、更高抗氧化性能及近终成形方向发展。最后提出了采用先进技术制备高性能难熔金属材料亟待解决的一些突出问题:从实验室走向实际应用还需要大量的的试验和基础研究数据;需要进一步提高难熔金属单晶纯度、扩大单晶品种和规格;近净成形件完全代替传统锻件要先解决内部组织和缺陷的控制、综合力学性能的调控等;高温抗氧化时长需进一步提高。     

真空电子束悬浮区熔炉的研制

介绍了真空电子束区熔炉技术性能、区熔原理、设备结构及特点。该设备是国内第一台国产化的电子束区熔炉,能够对最大尺寸为φ30mm×1000mm的难熔金属及其合金棒料进行悬浮区域熔炼提纯,而且可以进行难熔金属及其合金单晶的制备工艺。该设备的研制成功,对我国难熔金属区域熔炼提纯及单晶制备技术的研究和生产具有重要的现实意义。     

电子束真空精炼直接定向凝固制备高纯铜的研究

以电子束真空熔炼直接定向凝固技术制备5N高纯铜大铸锭为研究目标,利用电子束熔炼原材料,熔体直接定向凝固后得到高纯铜铸锭.采用GDMS-VG9000辉光放电质谱仪和TCH600氧氢分析仪研究了金属杂质及氧氢元素的去除效果,通过EPMA-1600电子探针研究了提纯后元素的分布情况.结果表明:真空电子束熔炼直接定向凝固技术可将原料为4N(99.9988711％)的电解阴极铜板,制备出纯度5N(99.9997235％)、Φ59 mm大尺寸高纯铜铸锭,杂质元素总量降低了75.506％,中间凝固组织为单晶;五种含量较高的元素Ag、Cu、O、P和S均匀分布,没有出现杂质的偏聚现象;与原材料相比,0、H元素分别降低了86.47％,85.00％.研究表明真空电子束精炼直接定向凝固技术能够制备氧氢含量较低的5N大尺寸高纯铜铸锭.     

难熔金属单晶的电子束悬浮区熔定向凝固

难熔金属及合金以其优异的性能在航空航天、电子信息、能源、化工、冶金和核工业等国防及民用领域有着不可替代的作用,其发展日益受到高度重视.本文综述了难熔金属及合金的应用和发展,以钼、钨及其合金单晶的发展历程为例,概述了难熔金属单晶的电子束悬浮区熔定向凝固制备技术的发展,简要介绍了难熔金属钼的电子束悬浮区熔定向凝固生长工艺与组织的研究.     

冶金法制备太阳能级多晶硅的耦合除杂研究

以工业硅为原料,利用介质熔炼、定向凝固和电子束熔炼三种熔体处理技术对工业硅中的B、P和金属杂质进行了去除,制备出了99.9999%级多晶硅材料,其中,杂质B和P的含量分别低于0.20 ppmw（parts per million (weight),百万分之一质量）,金属杂质总含量（TM）低于0.23 ppmw。研究发现,介质熔炼去除杂质B的过程中,熔体中发生氧化还原反应可以有效去除大部分的杂质Al和Ca;电子束熔炼过程中,利用饱和蒸气压原理可以有效去除挥发性杂质P、Al、Ca,同时降束诱导多晶硅定向凝固,可将其他金属杂质进一步去除。本研究通过各技术间的耦合除杂,减少了冶金法提纯多晶硅的工序,为连续化、规模化生产提供了技术支撑。     

一种电子束熔炼用供料、熔铸拖锭装置研制

电子束熔炼具有高真空、高能量密度、可精准控制等特点,被广泛应用于难熔金属行业。本文依托核工业理化工程研究院电子枪技术和LT102真空装置,设计研制了一套难熔金属电子束熔炼用供料、熔铸拖锭装置。主要阐述了供料、熔铸拖锭装置的设计技术要求,针对难熔金属进行了熔炼功率计算,并对结构设计功能进行了详细介绍。所研制的供料装置具有多工位、换料功能,拖锭装置具备水冷、下拉、旋转功能。最终装配测试的供料、熔铸拖锭装置性能满足设计要求,整体熔炼实验中设备运行良好。     

冶金法提纯工业硅的研究

以冶金级硅为原料进行了制备高纯多晶硅锭的研究,自行设计了真空感应熔炼与定向凝固设备、电子束熔炼设备.通过酸洗、真空感应熔炼与第一次定向凝固、电子束熔炼、真空感应熔炼与第二次定向凝固等组合步骤对工业硅进行提纯.利用电感耦合等离子体发射光谱仪(ICP-AES)进行成分分析,实验结果表明,定向凝固有效去除了金属杂质,电子束对蒸汽压高的元素,尤其是磷元素的去除作用明显.Al的浓度降低到了0.4×10~(-6),Fe、Ca、Ti、Mn、Cu、Zn等金属杂质的浓度降到了0.1×10~(-6)以下,P含量降低到1.5×10~(-6).     

电子束熔炼制备太阳能级多晶硅的研究现状与发展趋势

电子束熔炼具有高能量密度、高真空度等优点, 能够有效地去除硅中的挥发性杂质, 使其在制备太阳能级多晶硅材料方面具有巨大的优势和广阔的应用前景, 目前已经实现了产业化应用, 成为冶金法制备太阳能级硅材料的关键环节之一。本文在阐述挥发性杂质去除的热力学原理的基础上, 对其去除效果和去除机制进行了总结。同时, 针对电子束熔炼技术目前存在的问题, 结合作者在这些方面的探索, 从数值模拟、节能型熔炼方式以及与定向凝固技术的耦合等角度对现阶段的研究重点进行了综述, 并对其未来的发展趋势进行了展望。     

真空冶金装置(二)——第二讲 真空电子束炉

电子束熔炼的设想于1907年提出,直到1954年才显出它的重要性。它既能使液态金属在真空下充分脱气,又没有坩埚材料的污染。其优点主要有:熔炼速度可在大范围内调节,功率密度高且易控制,熔池表面温度高,因而可熔炼难熔金属,适用于任何形状的原料(如棒、块、屑、板等),易于精确控制熔料的化学组分,得到一定性能要求的稀有难熔和高纯金属材料。电子束对熔料的扫描还有搅拌作用,有利于合金化与去除杂质。     

杂质元素对镁合金组织与性能的影响及其对应措施

镁及镁合金中杂质元素的含量及作用已受到广泛关注.介绍了镁合金中Fe、Cu、Ni、Si等杂质的存在形式,综述了杂质元素对镁合金显微组织、腐蚀性能、力学性能的影响规律及机制,并叙述了几种提高镁合金纯度常见的方法,包括选用高纯原料、优化熔炼工艺、镁合金熔体纯净化,指出有效降低杂质含量将是未来高性能镁合金材料研究的重要方向.     

LASER AND ELECTRON BEAM PROCESSING OF AMORPHOUS SURFACE ALLOYS ON CONVENTIONAL CRYSTALLINE METALS

During last fifteen years various superior surface characteristics including extremely high corrosion resistance and unique electrocatalytic activity have been found for novel melt-spun ribbon-shaped amorphous alloys. Preparation of those amorphous alloys as surface alloys covering bulk conventional crystalline metals has been eagerly awaited for the purpose of utilizing their superior surface characteristics. This is a review of efforts devoted to developing methods for processing amorphous surface alloys by instantaneous melting of a very restricted volume of the surface by irradiation with a CO₂ laser or electron beam and subsequent self quenching by the cold bulk substrates. Processing of a wide area by these high energy density beams requires heating the previously amorphized phase, which is easily crystallized by heating. Consequently, high energy density beam processing is most difficult among various methods for preparation of thermodynamically metastable amorphous alloys. Nevertheless, various amorphous surface alloys have been successfully prepared. The materials consisting of the amorphous surface alloys and bulk crystalline metals are quite suitable for corrosion resistant materials and electrodes for electrolysis of aqueous solutions. A comparison of CO₂ laser and electron beam processing showed the superiority of the latter to the former because of a significantly shorter processing time.     

Containerless Automated Processing of High-Purity Intermetallic Compounds and Composites

An automated containerless processing system to directionally solidify high temperature reactive materials has been previously described (1). The software used for control has: been simplified and improved over that previously reported. Temperature has been eliminated as a necessary control variable for the directional solidification process. All proportional and integral (PI) control is based upon image processing using parallel processing software. Control actions can occur several times a second using a DEC 11/23+ computer assisted by two PC's. The system has since been used to produce high-purity bulk metallurgical samples of high melting intermetallic compounds, single crystals grown from oriented seeds, and new polyphase intermetallic/metallic in-situ composites. New characteristics of the process are described; and properties of recently produced materials reviewed and related to current high temperature materials.     

Methodology of Single Crystal Growth and Microstructure Analysis of CoTi(Zr) Intermetallic Compounds

1. IntroductionThe strong bonding between different atoms in inter-metallic compounds often results in attractive properties,such as strength retention at high temperature. A posi-tive temperature dependence of yield stress in some com-pounds such like Ni3Al, CuZr, FeCo and Fe3Al was dis-covered at an early stage. Now many other compoundshave been found to show this peculiar mechanical be-haviour, which can be useful in high temperature struc-ture applications.Ordered B2-type intermetallic…     

Analysis of strengthening mechanisms in a severely-plastically-deformed Al–Mg–Si alloy with submicron grain size

Methods of severe plastic deformation of ductile metals and alloys offer the possibility of processing engineering materials to very high strength with good ductility. After typical amounts of processing strain, a submicrocrystalline material is obtained, with boundaries of rather low misorientation angles and grains containing a high density of dislocations. In the present study, an Al–Mg–Si alloy was severely plastically deformed by equal channel angular pressing (ECAP) to produce such a material. The material was subsequently annealed for dislocation recovery and grain growth. The strength of materials in various deformed and annealed states is examined and the respective contributions of loosely-arranged dislocations, many grain boundaries, as well as dispersed particles are deduced. It is shown that dislocation strengthening is significant in as-deformed, as well as lightly annealed materials, with grain boundary strengthening providing the major contribution thereafter.     

大尺寸6H-SiC半导体单晶材料的生长

报道了生长SiC单晶的PVT法生长工艺,研究了晶体生长温度、温度梯度、生长室压力、杂质等因素对晶体生长和晶体质量的影响,确定出合理的工艺条件,生长出φ45mmSiC单晶.X射线衍射表明,生长的单晶为6H多型结构,通过腐蚀法得到晶体中微管道密度约为10³cm^-2,位错密度约为10⁴～10⁵cm^-2.测试了SiC单晶的半导体特性,结果表明:晶体为n型,电阻率约300Ω·cm,迁移率90cm2V^-1S^-1,载流子浓度在10¹⁴cm^-3量级.     

Photoacoustic microscopy of the effect of mechanical processing on the martensite structure of near-surface layers in Cu-Al-Ni alloy single crystals

The near-surface layers in single crystals of copper-based alloys possessing shape memory and superelasticity have been studied using the photoacoustic microscopy (PAM) techniques. It is established that the PAM is advantageous to optical microscopy in studying the martensite structure, in particular, because this structure can be revealed without preliminary polishing of the sample surface. This circumstance allowed the effect of mechanical processing and related stresses on the twin structure in Cu-Al-Ni alloy single crystals to be studied. The sensitivity of PAM is sufficient to observe the structural transformations in samples at the early stages of martensite phase formation.     

ZnSe多晶料的提纯与化学比的控制

采用区域升华法对由两单质直接合成的ZnSe多晶原料进行了处理.电感耦合等离子体质谱仪(ICP-MS)分析结果表明,区域升华法对高纯原料中杂质的去除率仅为10%左右.X射线衍射(XRD)和能谱分析(EDS)结果表明提纯后原料的化学比得到了有效调节,其多晶化学比与单晶的化学比非常接近,适于单晶生长使用.采用区域升华法处理高纯多晶原料的主要目的应该放在去除过量元素和调节原料化学比上.     

Fundamental factors on formation mechanism of dislocation arrangements in cyclically deformed fcc single crystals

This paper systematically summarizes the cyclic deformation behaviors of different kinds of face-centered cubic (fcc) single crystals, including copper, nickel, silver, as well as copper-aluminium, copper-zinc alloys in attempt to provide a historical perspective of the developments over the last several decades. Combined with plenty of previous research results, the influencing factors on cyclic deformation behaviors can be listed as follows: orientations, stacking fault energy (SFE), short-range order (SRO) and friction stress, or more generally, the ease of cross slip. Among them, the effect of orientations mainly reflects in the formation of the complex dislocation patterns, which depends on the activating secondary slip system. According to the effect of slip mode, the materials can be divided into two types: pure metals and alloys. For pure fcc metals, the effect of SFE is decisive. Due to the easy cross slip of screw dislocations, regular dislocation arrangements, e.g. veins, persistent slip bands (PSBs), labyrinth and cell patterns, are always to form. With increase in alloying element, antiphase boundary energy gradually replaces SFE to become a new decisive factor affecting the cyclic deformation behaviors of fcc alloy single crystals. The corresponding dislocation arrangements consist of dipole array and stacking faults (SFs) under the influence of planar slip. The relationship among several factors is well explained, which will help us better understand the nature of the fatigue damage of metallic materials and then improve the performance of the related materials.