镍在WC合成中加速效应的机理

本文以钨-碳体系为研究出发点，高能球磨钨、活性炭和镍的混合粉末，应用XRD、SEM、化学分析等手段，对反应产物进行分析。结果发现当镍含量为5％，球料比为50：1（体积比）时，球磨50h即可合成WC，或者当镍含量为5％，球料比为30：1（体积比）时，球磨100h也可合成WC，而没有镍参与的情况下，当球料比为30：1（体积比），球磨50h后，仍有大量未反应的钨和碳存在，这说明在机械合金化合成WC的过程中，镍能有效的缩短反应时间，提高反应速率，原因是在镍的周围形成了以镍为中心的微聚团，增大了钨和碳的接触几率和接触面积，缩短了扩散距离，从而缩短了反应时间。     

氢化燃烧合成镁基储氢合金的电化学性能的研究

研究了氢化燃烧合成Mg2NiH4产物的电化学性能，并探索了机械球磨处理对产物电化学性能的影响。电化学测试表明，HCS产物不经任何处理，最大放电容量仅为45.13mAh／g；产物球磨后最大放电容量和高倍率放电能力得到提高，如产物经球磨1h后，最大放电容量增至259．24mAh／g，产物添加3％（质量分数）的石墨球磨5h，最大放电容量增加了10倍以上，达到481．50mAh/g。     

WC/TiO_2纳米复合材料的微结构及性能研究

以纳米TiO2为载体,偏钨酸铵为钨源,经机械球磨后制备成WC/TiO2前驱体,将前驱体在900℃,甲烷/氢气气氛下碳化还原,获得了系列WC/TiO2纳米复合材料.采用XRD、SEM、HRTEM、STEM-Z衬度像、EDS-Mapping方法对样品的晶相、微观结构、化学成份及空间分布进行了系统表征;采用三电极体系粉末微电极方法测试了样品在碱性溶液中的电化学催化活性,结果表明:随着碳化还原时间的延长,样品中钨的物相由WO3→WO2→W→W2C、WC发生变化;碳化钨晶粒在20 nm以下且分布于载体TiO2表面;还原碳化6h样品电化学性能最佳,此时活性相以WC和W2C为主,晶粒最细且均匀分布于稳定的金红石载体表面.     

Co—Al金属粉末机械合金化X—射线分析

本文研究了不同成份的Co-Al混合金属粉末经不同时间强力球磨后的x-射线衍射谱,并研究了退火对经50h球磨的Co_(70)Al_(30)粉的x-射线衍射谱的影响。结果表明,Co-Al混合粉经10h球磨后可形成CoAl化合物;Co含量在50～70(at)%的Co-Al混合粉经40～70h球磨可形成非晶结构.     

高能球磨时间和退火温度对制备TiNi合金粉的影响

为获得高能球磨时间和退火温度对TiNi机械合金粉特性的影响机制,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、差示扫描量热法(DSC)等分析方法对TiNi合金粉进行了研究。结果表明,机械合金的相成分随着在氩气保护气氛中的球磨时间和退火温度的不同而发生变化。球磨22h的产物是非晶态TiNi合金、Ti的固溶体、Ni的固溶体,球磨27h的产物是非晶态TiNi合金粉和Ni固溶体相,球磨30h发生了明显的固相反应,生成了TiNi、Ni3Ti、Ti3Ni4等物相;在650℃/5h和1000℃/5h下的退火产物都是Ni3Ti、Ti2Ni、TiNi2、TiNi和TiC,但在上述2个退火温度下TiNi并不是主要物相,其中在650℃退火时TiNi的含量明显更低。     

反应球磨钛与尿素制备氮化钛的反应机理研究

将Ti粉与尿素在室温下进行反应球磨制备了TiN粉末,对球磨不同时间后的粉末进行XRD分析,采用TG-FTIR技术分析了尿素的分解温度与产物,利用TEM及EELS观察和分析了球磨70h粉末的微观形貌、结构及成分. 结果发现,球磨70h合成了纳米TiN粉末,晶粒度为6~7nm,Ti/N原子比约为1.0∶0.6. 经800℃,5h真空退火处理后粉末的XRD谱图表明粉末组成为单相TiN. 在反应球磨过程中,Ti与尿素的分解产物NH₃与HNCO发生反应形成TiN,随球磨时间延长,Ti的缺陷能增大、活性增加,N在Ti中的扩散激活能减小,在球磨作用下N的扩散距离变短,TiN的含量逐渐增加形成晶核并逐渐长大形成纳米晶.     

在酸性条件下采用高能球磨法制备 Cu2O纳米粉末

采用行星球磨机在pH=2的稀盐酸溶液中对Cu粉进行球磨，球磨机简体和磨球材质均为纯Cu，球料比为20：1，球磨机转速为300r／min，通过X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）等对球磨产物进行了表征．XRD结果表明，球磨3h后，所加入的纯Cu粉末基本转化为Cu20粉末．球磨70h后得到纯的Cu20粉末，粉末粒度为50-100nm．并对Cu20纳米粉末的生成机制及球磨工艺参数对Cu20形成的影响进行了讨论．     

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。     

微波烧结制备WC-TiC-Co硬质合金的组织和性能研究

以WC粉为基体,Co为粘结相,TiC颗粒为抑制剂,通过球磨、压制成型,微波烧结制备WC-TiC-Co硬质合金.结果表明,在1360℃微波烧结为液相烧结,Co与WC会发生反应生成η相(Co3W3C).随TiC含量升高,合金的晶粒逐渐变得均匀细小,合金的相对密度、硬度和抗弯强度均先升高后下降,硬度在0.5％TiC时达到最高值,相对密度和抗弯强度在1.0％TiC时达到最高值.     

激光熔覆(WC+W2C)p/Ni基合金复合涂层的微观结构特征

运用XRD、SEM及显微硬度试验等手段研究了激光熔覆Co包铸造（WC W2C）p增强Ni基合金复合涂层的微观组织特征，分析了Co包铸态（WC W2C）p 在激光熔覆过程中的冶金行为，研究结果表明：在激光熔覆过程中，（WC W2C)p的Co包覆层完全熔化，（WC W2C）p本身也发生部分熔解，其稳定性随W2C/WC比增大而降低；当熔池凝固时，（WC W2C）p在涂层中的分布主要受激光熔池中存在的强烈对流和颗粒/凝固前沿相互作用所控制；依赖于局部成分，涂层中形成变成分的η1-M6C（M=Co、W、Ni)型碳化物，优先分布（WC W2C）p表面；涂层基体的典型组织由分布在γ-Ni M23C6为主加硼化物Ni4B3、Ni3B和碳化物M7C3的伪多元共晶中的η1-W6C组成。     

Synthesis and structural evolution of tungsten carbide prepared by ball milling

Tungsten carbide has been synthesized directly by ball-milling tungsten powder and activated carbon in vacuum. The structural development of the WC phase with milling times up to 310 h has been followed using X-ray, neutron diffraction and scanning electron microscopy. Subsequent annealing (at 1000 °C for 1 and 20 h) of material milled for 90 h or longer, results in samples comprising almost entirely crystalline WC. The production of WC itself during milling results in enhanced iron contamination from the steel mill and balls on extended milling which were monitored by energy-dispersive X-ray and Mossbauer spectroscopies. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of milling time,MWCNT content,and annealing temperature on microstructure and hardness of Fe/MWCNT nanocomposites synthesized by high-energy ball milling

Nanocrystalline pure Fe and Fe/MWCNT nanocomposites powders with 0.25, 0.5, 1, and 10 wt% MWCNT contents were synthesized by high-energy ball milling (HEBM). The as-milled powders were cold-compacted and annealed at 400 °C and 600 °C for 1 h in Ar atmosphere. The effect of ball milling on pristine MWCNT and Fe/MWCNT composite powders was also investigated as a function of milling time up to 20 h. The physical properties of MWCNT were imaged by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) before and after HEBM. The structural damage of MWCNT as a function of milling time and MWCNT content was studied using Raman spectroscopy. The structural characterization of MWCNT and Fe/MWCNT composites was conducted by X-ray diffraction (XRD) as a function of milling time, MWCNT content, and annealing temperature. The chemical properties of the synthesized composite powders were investigated using X-ray photoelectron spectroscopy (XPS). The microhardness test was performed to assess the effect of milling time, annealing temperature, and MWCNT content on the mechanical properties. The results indicated that after the ball milling process, the structure of MWCNT was destroyed, and the formation of the amorphous carbon phase was observed, which was confirmed by XRD and TEM analyses. In addition, decreased defect and carbon intensity ratios (I_D/I_G) were calculated from the Raman results with longer ball milling processes, which is attributed to the destruction of carbon bonds. The XPS results confirmed the presence of FeC bonds as a result of the formation of carbide phases. A fine dispersion of precipitated carbides determined by TEM is found to promote the grain size stability below 100 nm in the nanocrystalline Fe matrix. The results from the micro-hardness tests showed that Orowan particle strengthening resulting from the carbide formation, as well as grain size hardening, is an important contributor to strengthening in Fe/MWCNT composites.     

高能球磨制备立方AlN及其高温相变

研究了高能球磨过程中Al₂O₃的相变, 随着球磨时间的延长, 粉末中发生了γ -Al₂O₃向α -Al₂O₃3的转变. 高能球磨20h, Al₂O₃部分非晶化, 同时, 有立方AlN生成. 增加球磨强度, 立方AlN生成量增加, 650r/min高能球磨40h, AlN生成量达到72%. 随后的氮气气氛退火实验发现, 在500℃以上, 立方氮化铝与氧化铝反应, 生成AlON相. AlON相的生成, 有效地降低了碳热还原氮化反应激活能.     

Mechanical alloying and sintering of nanostructured tungsten carbide-reinforced copper composite and its characterization

Elemental powders of copper (Cu), tungsten (W) and graphite (C) were mechanically alloyed in a planetary ball mill with different milling durations (0–60 h), compacted and sintered in order to precipitate hard tungsten carbide particles into a copper matrix. Both powder and sintered composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and assessed for hardness and electrical conductivity to investigate the effects of milling time on formation of nanostructured Cu–WC composite and its properties. No carbide peak was detected in the powder mixtures after milling. Carbide WC and W₂C phases were precipitated only in the sintered composite. The formation of WC began with longer milling times, after W₂C formation. Prolonged milling time decreased the crystallite size as well as the internal strain of Cu. Hardness of the composite was enhanced but electrical conductivity reduced with increasing milling time.     

Formation of a FCC Al_(54)Ti_(23)C_(23) Metastable Phase by Ball Milling

The powder mixture of Al, Ti and graphite has been mechanically alloyed in a planetary ball mill.The structural evolution of as-milled powder sample has been characterized by XRD, DTA. The results show that the amorphous phase is formed first at an early milling stage, then crystallization occurs during further milling, leading to formation of a nanocrystalline fcc metastable phase. In contrast, during annealing the amorphous phase is crystallized to the equilibrium phase instead of the fcc phase. This indicates that crystallization during ball milling is different from that induced by annealing     

Effect of starting composition on formation of MoSi2–SiC nanocomposite powder via ball milling

MoSi₂?CSiC nanocomposite powders were successfully synthesized by ball milling Mo, Si and graphite elemental powders. Effects of milling time and annealing temperature were also investigated. The composite formation and phase transformation were monitored by X-ray diffraction. The microstructure of milled powders was studied by SEM, TEM and XRD peak profile analysis. Formation of this composite was completed after 10 and 20?h of milling for 25%SiC and 50%SiC, respectively. High temperature polymorph (HTP) of MoSi₂ was obtained at the end of milling (20?h). On the other hand, annealing led to transformation of HTP to low temperature polymorph (LTP) of MoSi₂. Mo₅Si₃ was formed during annealing as a product of a reaction between MoSi₂ and excess graphite. Mean grain size <50?nm was obtained for 20?h milled sample on the basis of peak profile analysis and TEM images.     

Anisotropic mullitization in CuO-doped oxide mixture activated by high-energy ball milling

Mullite phase formation and grain growth, in a CuO-doped Al₂O₃ and silica mixture, has been investigated. The oxide mixture was activated with both stainless steel and tungsten carbide milling media. The milled powders demonstrated a much lower mullite formation temperature when compared to the conventional solid-state reaction process. Anisotropic grain growth was observed in the powders milled with stainless steel media, while well-shaped mullite whiskers were produced in the WC milled samples. The lowered mullitization temperature together with the anisotropic grain growth behavior was attributed to the refined microstructure of the powders as a result of the high-energy ball milling process.     

Production of nanocrystalline powders by high-energy ball milling: model and experiment

A model of high-energy ball milling of powders has been proposed. It is demonstrated that part of the energy is consumed for initiation of microstrains ε during milling and, hence, the process of the powder grinding is decelerated. An analytical expression has been deduced describing the size of nanocrystalline powder particles as a function of the milling time. The model and the experiment have been compared, using a powder of tungsten carbide (WC). The average size of the particles and the value of the microstrains in the ball-milled powder were determined by an x-ray method from broadening of diffraction reflections. The size of the particles was also evaluated using scanning electron microscopy and the sedimentation method.     

Synthesis and characterization of V8C7 nanocrystalline powder by heating milled mixture of V2O5, C and Ca via mechanochemical activation

In this study, nano-crystalline vanadium carbide was synthesized through reduction of V₂O₅ by carbon and Ca using high energy ball milling and subsequent heat treatment. Vanadium pentoxide, calcium and carbon black were placed in a planetary ball mill and sampled after different milling times. The activated powders were synthesized by microwave heating at temperatures 800 °C. XRD and FESEM were used for characterization of synthesized powder. On the basis of obtained results, the synthesized V₈C₇ crystallites were in the scale of nanometers and the lattice parameter had some deviation from the standard value. Furthermore, investigations showed that at higher milling time, the amorphization degree of V₄C₃ phase increased, while the degree of crystallite decreased.     

Mechanically activated synthesis of nanocrystalline ternary carbide Fe3Mo3C

In this investigation, Fe₃Mo₃C ternary carbide was synthesized from the elemental powders of 3Mo/3Fe/C by mechanical milling and subsequent heat treatment. Structural and morphological evolutions of powders were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that no phase transformation occurs during milling. A nanostructure Mo (Fe) solid solution obtained after 30 h of milling. With increasing milling time to 70 h no change takes place except grain size reduction to 9 nm and strain enhancement to 0.86%. Milled powders have spheroid shape and very narrow size distribution about 2 μm at the end of milling. Fe₃Mo₃C was synthesized during annealing of 70 h milled sample at 700 °C. Undesired phases of MoOC and Fe₂C form at 1100 °C. No transformation takes place during annealing of 10 h milled sample at 700 °C. Mean grain size and strain get to 69 nm and 0.23% respectively with annealing of 70 h milled sample at 1100 °C.