W-Cu纳米晶粉体的制备及表征

采用机械舍金化技术制备了W-20％Cu和W-50％Cu纳米晶粉体，通过XRD、SEM、TEM等手段对机械舍佥化过程中W-Cu纳米晶复合粉的组成、晶格常数、晶粒尺寸和形貌结构进行了表征与分析。结果表明，W-20％Cu混合粉经过高能球磨，Cu元素完全固溶进w晶格中，形成W（Cu）固溶体；W-50％Cu复合粉经过高能球磨，形成W（Cu）和Cu（W）两种固溶体。W、Cu的合金化主要是依靠高能球磨过程中产生的大量纳米晶界和高密度的缺陷（位错、层错等）促使W、Cu之间的固溶。W-Cu复合粉的晶格常数和晶粒尺寸随着球磨时间的延长而减小，球磨一定时间后，都趋于稳定。球磨20h后，W-20％Cu和W-50％Cu复合粉中W（Cu）的晶粒尺寸分别为6．6和8．0nm。     

大塑性变形工艺制备纳米晶过饱和固溶体的研究进展

合金在大塑性变形过程中能够形成纳米晶过饱和固溶体,呈现出不同于传统粗晶材料的微观结构和独特性能。近年来,纳米晶过饱和固溶体的形成机制及其热稳定性已成为国内外的一个研究热点。综述了大塑性变形工艺(如机械合金化法、高压扭转法等)制备纳米晶过饱和固溶体的研究概况,着重讨论分析了大塑性变形诱导纳米晶形成和固溶度扩展的几种机制及其局限性,简要介绍了纳米晶过饱和固溶体的热稳定性及其影响因素,最后对该领域今后的研究方向做出了分析和展望。     

机械合金化的机制

机械合金化是一种制备平衡态和亚稳态材料的新兴技术。机械合金化的热力学与动力学不同于常规的固态反应，而且相转变方式与合金系统及球磨条件密切相关。着重评述了机械合金化过程中非晶态，金属间化合物，过饱和固溶体及纳米晶形成的特点及机制。     

高能球磨制备Mo-3%Cu纳米晶复合粉末特性

利用机械合金化法制备出Mo-3%Cu(质量分数,以下同)超细复合粉末,采用X射线衍射、BET氮吸附法和DTA差热分析方法对球磨后的Mo-6%Cu纳米晶复合粉的组织结构变化、表面特性和热稳定性进行了系统的研究.结果表明,高能球磨可以制取纳米晶复合粉末,晶粒内部产生很大的晶格畸变,同时球磨产生的晶体缺陷使原子扩散加快,形成Mo-Cu超饱和固溶体和扩大Mo在粘结相中的溶解度,BET氮吸附结果证实了球磨使粉末产生大量微孔,且比表面、中孔表面和孔径降低.     

难互溶体系中合金的机械合金化合成

本文用x-ray衍射,电子探针和金相分析方法,系统地研究了因熔点和比重相差较大,难以用常规冶炼方法互溶的Ti-Pb和Ti-Al两个二元系.在球磨过程中的组织、结构变化。发现在普通熔炼条件下完全不互溶的Pb-Al二元系,在适当的条件下,能够形成固溶度很高的以Pb为溶剂的固溶体。而Ti-Pb二元系在球磨过程中则经过形成过饱和固溶体和非晶化2个阶段,最终形成相图上的PbTi_4金属间化合物。实现了在难互溶体系中,合金的机械合金化合成。     

W-35%Cu粉末形变强化复合材料组织及性能研究

为了提高W-Cu复合材料的致密度,采用机械球磨-冷压制坯-液相烧结-热静液挤压-热处理工艺,制备出微观组织弥散分布、性能优异的W-35%Cu复合材料.采用扫描电镜、电子探针等测试手段分别对烧结及挤压后材料的组织及性能进行了分析.实验结果表明,采用机械球磨技术制备的W-35%Cu复合粉,经液相活化烧结后,再经热静液挤压进一步形变和致密,材料的硬度以及导电性能都有较大提高.在800℃真空热处理2 h后,获得了硬度高于200HB,电导率高于40m/Ω·mm2的W-35%Cu形变复合材料.     

二元互不溶体系中纳米晶过饱和固溶体机械合金化的研究进展

互不溶体系合金在机械合金化的非平衡过程中能够形成纳米晶过饱和固溶体,并显示出与其微米尺度结构合金所不同的独特性能。纳米晶过饱和固溶体不仅是互不溶体系中重要的一种亚稳态结构,也是一种重要的纳米材料体系。综述了近年来二元互不溶体系中纳米晶过饱和固溶体机械合金化的研究进展,着重介绍了纳米晶过饱和固溶体的形成机制,以及纳米晶过饱和固溶体的热稳定性、力学和物理性能。     

机械合金化制备Cu-Fe过饱和固溶体及其时效分解

采用机械合金化工艺制备Cu-xFe(x=1,2,4,质量分数/%)过饱和固溶体,研究时效对其硬度和导电性能的影响.X-ray衍射分析结果表明:机械合金化显著提高了Fe在Cu中的固溶度,Cu-4Fe复合粉末经32h球磨.Fe完全固溶于Cu基体中,此时Cu晶粒尺寸为20nm,点阵常数降低到0.3621nm.硬度和导电率测试结果表明:时效处理能促进过饱和固溶体发生分解,Cu-4Fe过饱和固溶体冷压成型压坯在400℃保温8h后显微硬度HV由时效前的175降低到96,电导率由35%IACS(国际退火铜标准)提高到60%IACS.     

不同晶粒尺寸的三元Cu40Ni40Cr20合金的制备及其显微组织研究

采用电弧熔炼和机械合金化,随后在750℃,58MPa下热压制备了晶粒尺寸差别较大的Cu40Ni40Cr20合金,用X射线衍射仪、扫描电镜等分析手段对比研究了显微组织结构.结果表明:电弧熔炼制备的晶粒尺寸较大的Cu40Ni40Cr20合金为二相,组织极其不均匀;采用机械合金化,通过控制热压条件制备的纳米晶Cu40Ni40Cr20合金仍为双相,但显微组织均匀,稳定.随着球磨时间的延长,由于晶粒细化和应变的结果,衍射峰偏移并有明显的宽化产生,Cu在Cr或Cr在Cu中的固溶度明显增加,当球磨60h后,合金已由双相变成亚稳态的单相.由于机械合金化的粉末处于非平衡态,其超固溶度溶质随热压和真空退火过程的进行会慢慢脱溶分解出来,合金已由单相变为两相,两相颗粒均成倍长大,但仍然保持纳米级尺度;机械合金化、热压和退火后样品中Cu,Ni和Cr的晶格均未发生崎变;讨论了晶粒细化对合金显微组织的影响.     

Mo-Cu高能球磨过程实验研究及固溶度数值模拟

采用高能球磨方法对Mo-3%(质量分数)Cu、Mo-10%(质量分数)Cu复合粉末进行机械合金化加工,球磨时间为0～50h。通过扫描电镜及X射线衍射等对复合粉末的形貌、X射线衍射特征进行了分析,并对Cu在Mo中的固溶度用热力学方法进行了研究。结果表明,通过机械合金化方法可以得到超细小且均匀的纳米晶复合粉末,平均晶粒尺寸在60nm左右;从热力学平衡角度出发,通过细化晶粒来提高Cu在Mo中的固溶度极限可以用数值模拟来表达。     

Solid solubility extension of copper‐tin immiscible system during mechanical alloying

In this paper, copper‐5 wt.%‐tin (Cu‐5wt%Sn) powder mixture was mechanically alloyed in order to study the solid solubility extension during the alloying process. Nanocrystalline supersaturated solid solution has been prepared in this system by high energy ball milling. Based on the thermodynamic model, the Gibbs free energy change in this alloy system during the formation of solid solution is calculated to be positive, which means that there is no driving force to form solid solution in copper‐tin (Cu?Sn) immiscible system. It has been found that a large fraction of grain boundaries and a high density of dislocations play a significant role in the solid solubility extension of immiscible copper and tin.     

Mechanical milling to foster the solid solution formation and densification in Cr-W-Si for hot-pressing of PVD target materials

Based on the significantly different melting points and high oxygen affinities, the fabrication of chromium-based tungsten silicides is restricted to powder metallurgical production routes. To foster particle contacts and diffusion processes between chromium and tungsten, which are known to necessitate long sintering times, mechanical alloying or milling processes prior to sintering are established. Nonetheless, due to spinodal decomposition of Cr and W, the solid solution formation is complex and yet little understood. For this reason, the influence of the mechanical milling time (0–24 h) on the crystal structure and the microstructural properties of hot-pressed 60Cr30W10Si (wt.–%) is examined. In this context, two different powders containing a different tungsten particle size (0.8 and 3 µm) were mechanically alloyed to analyze the impact on the phase formation and the particle distribution in the microstructure. It was shown that mechanical milling supported the mechanical clamping between the particles. However, the increased milling times significantly decreased the crystallite sizes of the particles and fostered the tungsten solubility in the Cr-rich (Cr, W) solid solution formed during sintering, thus supporting the densification.     

Thermodynamic analysis of nanocrystalline solid solutions formation in copper-lead-tin ternary immiscible system during mechanical alloying

In this paper, copper-15 wt.%-lead-1 wt.%-tin (Cu-15wt %Pb-1wt %Sn), copper-15 wt.%-lead-2 wt.%-tin (Cu-15wt %Pb-2wt %Sn) and copper-15 wt.%-lead-3 wt.%-tin (Cu-15wt %Pb-3wt %Sn) powder mixtures were mechanically alloyed in order to study the solid solubility extension during the alloying process. Nanocrystalline supersaturated solid solutions have been prepared in copper-lead-tin (Cu−Pb−Sn) ternary immiscible system by mechanical alloying (MA). Based on the thermodynamic model, the Gibbs free energy changes in these alloys during the formation of solid solutions are calculated to be positive, which means that there are no driving force to form solid solutions in copper-lead-tin ternary immiscible system. It was found that a large fraction of grain boundaries and a high density of dislocations play a significant role in the solid solubility extension in copper-lead-tin ternary immiscible system.     

Direct evidence of nanocrystal enhanced complete mutual solubility in mechanically alloyed CoCu powders

A continuous series of Co_xCu_(100−x) solid solutions have been fabricated by mechanical alloying. Transmission electron microscopy observations found that there are three kinds of particle morphology with lamellar, irregular and spherical shapes and their corresponding energy dispersion X-ray spectroscopic analyses (EDAX) values are quite different; the larger the crystallite size, the lower the content of cobalt. The greatly enhanced mutual solubility in Co and Cu powders during mechanical alloying may be caused by Co atoms substituting Cu atoms in the grain boundaries and vice versa, and by the large increase in the diffusion coefficient between Co and Cu atoms induced by the structural defects and local stresses in the nanocrystals.     

Investigation on preparation and diffusion barrier properties of W-Ti thin films

An W-10 wt.%Ti alloy target was prepared by the W-Ti ball-milled powders, and W-Ti thin ?lms were deposited by dc magnetron sputtering on Si substrates. Then Cu/W-Ti/Si structures were prepared after Cu films were deposited on the W-Ti/Si structures. The results show that W-Ti alloy has a single phase structure with fine grain size. The structures of W-Ti thin films evolved from an amorphous film to a dual phase structure with bcc W and hcp Ti, followed by W-Ti solid solution with increasing sputtering powers. W-Ti thin ?lms can effectively block against Cu diffusion and maintain good adhesion strength with Cu ?lms at 600 °C. The failure mechanism of the crystal W-Ti films is related to the grain boundary which provides fast diffusion paths for Cu and Si atoms, while the amorphous W-Ti diffusion barrier layer is directly related to the thermal stress and interface reaction.     

W-Cu薄膜沉积初期亚稳态固溶体形成机制

采用直流双靶磁控溅射共沉积的方法制备了W含量为75%(原子分数)的W-Cu薄膜,并通过EDS、XRD、SEM、TEM等对W-Cu薄膜沉积初期的微观形貌及组织结构进行了表征和分析。结果表明,沉积初期,随着沉积时间延长,W-Cu薄膜有逐渐晶化的趋势,并形成了W(Cu)基亚稳态固溶体,且Cu在W中的固溶度逐渐增加。沉积10s时薄膜呈长程无序、短程有序的非晶态,局部有由于靶材粒子扩散不充分而形成的小于5nm的W、Cu纳米晶;20s时局部纳米晶消失但晶化程度升高;30s时晶化显著。沉积初期W-Cu薄膜随沉积时间延长逐渐晶化的原因是沉积过程中高能量的原子或原子团与已沉积的原子碰撞,传递能量,促进原子进一步扩散,克服了薄膜的晶化形成能,从而形成了亚稳态的W(Cu)固溶体。     

Mechanically Driving Solid Solution in an Immiscible W-Cu System

In order to improve the homogeneity of the pseudo-alloy W-Cu used in a certain ordnance component. the formation of solid solution of W-Cu system with a positive heat of mixing by mechanical alloying (MA) has been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM).transmission electron microscopy (TEM ) and differential thermal analysis (DTA). It was found that the supersaturated solid solution phase formed in the whole investigated composition range from W90Cu10 to W60Cu40 (at.-%). although the systern W-Cu exhibits a total immiscibility in both solid and liquid states, A systematic investigation on W70Cu30 showed that a solid solubility of Cu in W increased with the milling time. The Iattice parameters of phase W decreased with the increasing of the milling time and solute content of Cu. The thermal stability of the solid solution was studied by DTA. It was found that the decomposition of solid solution. the recovery and the growth of the grain occurred over 2 50℃. The driving force of the solid solution W-Cu system by MA mainly comes from high density of defects bV ball milling, which would enhance the free energy of the system. The solution process is diffusion-controlled     

Modeling of metastable phase formation diagrams for sputtered thin films

A method to model the metastable phase formation in the Cu–W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu–W and Cu–V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering.     

Fabrication of the supersaturated solid solution of carbon in copper by mechanical alloying

Mechanical alloying of powder mixtures of copper and graphite was performed in a high energy ball mill. The as-milled powder was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, respectively. These investigations indicated that high energy ball milling could largely extend the solid solubility of carbon in copper and the 4 wt.% C was dissolved in Cu. It was ascribed to the decrease of the grain size and the increase of the lattice strain. Nanostructures, amorphous carbon and lamellar graphite were observed in the as-milled powder after milling for 24 h.     

Nanocrystalline formation in immiscible Cu-Mo system subjected to mechanical alloying

The mechanical alloying process has been studied on the Cu-Mo system, the atomic pair of which is characterized by a positive heat of mixing of +19 kJ/mol. The EXAFS and X-ray diffraction measurements have been employed to analyze the structural changes taking place during milling. Two phases mixture of nanocrystalline fcc-Cu and bcc-Mo with a grain size of 10 nm has been formed by MA of Cu30Mo70 powders for 200 hours. The structural analysis based on the EXAFS spectra revealed that bcc and fcc crystal structure clearly do not change around Mo and Cu atoms up to 200 h of milling, respectively. Studies of the thermodynamical considerations by DSC analyses confirmed that the alloying does not occur even after 200 hours of MA in Cu-Mo system.