Surface passivation of nanocrystalline silicon powder derived from cryomilling

The surface passivation mechanism of nanocrystalline silicon powder was studied. The liquid nitrogen/argon was used as the medium to prepare the nanocrystalline silicon powder, using a cryomilling technology. The X-ray diffraction, transmission electron microscopy, plasma emission spectroscopy and infrared spectrum were used to analyze the prepared samples, and density functional theory was used to investigate the cryomilling process. For nanocrystalline silicon powder cryomilled with liquid N2, the amorphous outer layer with N element is formed On the surface, and chemisorption caused by the formation of Si-N-Si bond leads to the surface passivation; although physisorpfion also he confirmed, the Si-N bond is steady after exploded in air for 30 days and no new bond is observed. For nanocrystalline silicon powder cryomilled with liquid At, no new chemical bond is Observed, Ar element absorbs on the surface of the prepared powder only through physisorption, and after exploded in air for 30 days, a Si-O bond can be observed obviously.     

Cu—Zr—Al大块非晶合金的制备及性能研究

采用铜模铸造的方法制备了Cu48Zr52-x Alx（x=6,7,8,9,10,at％）几种合金奠射线衍射（XRD）实验检验Cu48Zr44Al8,Cu48Zr43Al两种合金样品为完全非晶态．对样品进行差示扫描量热分析（DSC）考查三种大块非晶合金的非晶形成能力,以及灿的添加对非晶形成能力的影响．结果表明：当铝含量X=9时,合金的非晶形成能力及热稳定性最好．     

Molecular dynamics simulation of thermal stability of nanocrystalline vanadium

Currently, because of the thermal instability of nanocrystalline (NC) materials, there is little report on their thermal properties. Thus, for the NC, the study on their thermal sta- bility has been an urgent issue from the view of practical application and theoretical re- search. The difficulty for investigating the growth of NC material is to determine the crystal grain size precisely. Crystal grain size is generally determined by electronic mi- croscopes or X-ray diffraction[1]. Experime…     

激光能量对掺铒纳米Si晶薄膜形貌的影响

采用XeCl脉冲准分子激光器,保持激光脉冲比为1:2,分时烧蚀Er靶和高阻抗单晶Si靶。改变激光能量,在真空中沉积了掺Er非晶Si薄膜。在氮气保护下,分别在950℃,1010℃和1100℃温度下进行30min热退火处理,得到掺Er纳米晶Si薄膜。扫描电子显微镜的结果表明,高的退火温度或高的激光能量均会导致迷津结构的形成。     

原位合成TiC/Al基复合材料研究

用LEYBOLD-HERAEUS水冷铜坩埚真空电弧炉原位合成制备了TiC／Al基复合材料．X射线衍射谱表明，按20％TiC-Al配比，制得TiC-Al基复合材料中，TiC是唯一的增强相：在高温显微镜中在400℃、100MPa、真空度为0．00013Pa，压缩5h条件下，材料表现出良好的高温持久强度，TiC相未发生偏聚、差热分析(DTA)，显示该材料在900℃以下。TiC无相变发生．进一步证明原位。TiC／Al复合材料具有良好的热稳定性．光学金相、SEM和TEM观察显示，TiC颗粒与基体界面干净，压缩后位错呈半环状，绕TiC相堆积，说明即使在400℃高温下，加载后位错只能以Orowan机制绕过TiC相。     

SHS合成Ni3Al的粉碎及其微细化机制

通过机械粉碎获得了平均粒度为6．1μm的Ni3Al微细粉末，重点研究了Ni3Al的微细化机制。研究表明，在36ks的粉碎时间和球料比为3．5的工艺条件下，既能够避免引入过多的杂质，又具有很高的制粉效率和颗粒均匀化效果。Ni3Al的微细化是由Ni3Al板块颗粒和微晶集合体粒界的破坏而产生的，集合体内的微晶位置均化和粒界的磨蚀是导致有序度和表现晶粒尺寸下降的主要原因。     

Mg17Al12相电子结构计算与键络分析

基于EET理论，计算了Mg-Al系合金中主要的强化相γ-Mg17Al12的价电子结构，分析了其键络空间分布。Mg17Al12空间键络由Al-Al原子集团主键络、Al-MgⅢ次键络和Al-MgⅡ、Al-MgⅠ弱键络及MgⅡ-MgⅢ层状键络组成，其中Al-MgⅢ原于形成的弱键G是整个键络的薄弱环节。Mg17Al12晶内、晶界弥散析出，钉扎位错运动，阻碍品界滑移传递的强化作用主要依靠Al-Al原子集团主键络。通过合金化增强Mg17Al12弱键G是改善其热稳定性，提高Mg-Al基合金工作温度的有效途径。     

Synthesis of nanocrystalline NiCrC alloy feedstock powders for thermal spraying by cryogenic ball milling

Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized us-ing the cryogenic ball milling (cryomilling) method.The morphology,microstructure,size distribution,and phase transformation of the powders were characterized by scanning electron microscopy (SEM),laser scattering for particle size analysis,X-ray diffraction (XRD),and transmission electron microscopy (TEM).After cryomilling for 20 h,the average grain size of the as-milled powders ap-proached a constant value of 30 nm by XRD measurement.The average particle size slightly increased from 17.5 to 20.3 μm during the 20-h milling.About 90vo1% of the powders satisfied the requirement for thermal spraying with the particle dimension of 10-50 grn,and most of the powders exhibited spherical morphology,which were expected to have good fluidity during thermal spraying.The Cr2O3 phase formed during the cryomilling process as revealed in the XRD spectra,which was expected to enhance the thermal stability of the as-milled powders during the followed thermal spraying or other heat treatment.     

Structural evolution and stability of mechanically alloyed Fe-Ni nanocrystalline

The structural evolution and stability of Fe100-xNix(x=10, 20, 35, 50) alloys prepared by mechanical alloying were investigated through X-ray diffraction analysis and transmission electron microscopy. The intrinsic conditions of preparation determining phase stability in nanocrystalline were clarified. After being milled for 120 h, the powders of Fe90Ni10 and Fe80Ni20 consist of a single α(bcc) phase, Fe30Ni30 powders are a single γ(fcc), and for Fe65Ni35 powders there is co-existence of α and γ phases. The as-milled Fe80Ni20 powders annealed at 680 ℃ exhibits the stability of high-temperature γ phase at room temperature, which is consistent with the theoretical prediction.     

Enhancement of magnetic properties and thermal stability of nanocrystalline （NdDyTb）12.3（FeZrNbCu）81.7B6.0 alloy with Co substitution

The major drawbacks of Nd-Fe-B magnets are relatively low Curie temperature and poor thermal stability. Ribbons with the near stoichiometric 2:14:1 composition of Nd_(10.8)Dy_(0.75)Tb_(0.75)Fe_(79.7-x)Co_xZr_(0.8)Nb_(0.8)Cu_(0.4)B_(6.0)(x=0, 3, 6, 9, 12, 15) were prepared by rapid quenching and subsequent heat treatment. The effect of Co element on the magnetic properties, thermal stability, and microstructure of the ribbons was systematically studied by vibrating sample magnetometer(VSM), thermal magnetic analysis, atomic force microscopy (AFM), and transmission electron microscopy (TEM).It was found that Co substitution was significantly effective in improving the magnetic properties and the thermal stability of nanocrystalline ribbons. Although the intrinsic coercivity decreased from 1308.7 kA/m for x=0 to 817.4 kA/m for x=15, the remanence polarization and maximum energy product increased from 0.839 T and 116.5 kJ/m~3 for the Co-free samples to 1.041 T and 155.1 kJ/m~3 for the 12at% Co-substituted samples,respectively.About 10 K increase in Curie temperature was observed for the 2:14:1 phase with lat% Co substitution. The absolute values of temperature coefficients of induction and coercivity were significantly decreased with Co substitution, which may be attractive for high operational temperature applications. The microstructure of nanocrystalline ribbons was slightly refined with Co substitution.     

Spark Effect on the Densification of SiCp/Al Composites by SPS

1 IntroductionSiCp/Al composites have aroused considerable inter-ests in manyfields of industry due to their tailorable me-chanical and thermophysical properties .SiCp/Al compos-ites have been developed mainly as structural materials inapplicationfor automobile industries and aerospace indus-tries . However ,thermal management applicationsin elec-tronic packaging,such as substrates ,heat slugs and heatspreads have been focused on. Electronic componentsused in thermal management applications …     

温度控制Fe基合金带纳米微晶生长技术的研究

研究了Fe73.0CuNb1.5V2Si13.5B9非晶带经不同温度（480℃、510℃、540℃、570℃）退火而长成的纳米微晶薄带的软磁特性,发现540℃是其最佳退火温度,经该温度退火可获得最高的巨磁阻抗效应。     

微波CVD法低温制备纳米金刚石薄膜

利用甲醇和氢气的混合气体，用微波等离子体CVD方法在480℃下成功地在硅片表面制备出纳米金刚石薄膜，本文研究了甲醇浓度和沉积温度对金刚石膜形貌的影响．通过Raman光谱、原子力显微镜及扫描隧道显微镜对样品的晶粒尺寸及质量进行了表征．研究结果表明：通过提高甲醇浓度和降低沉积温度可以在直径为50mm的硅片表面沉积高质量的纳米金刚石薄膜，晶粒尺寸大约为10～20nm，并对低温下沉积高质量的纳米金刚石薄膜的机理进行了讨论．     

纳米锌锡氧化物的制备与表征

以四氯化锡和氯化锌(摩尔比4:1)为起始原料,在配制的一定浓度的水溶液体系中滴加氨水,于一定的焙烧温度下处理,获得了晶粒完整、粒度在20 nm左右的四方相锌锡氧化物晶体;借助热重差热分析(TG—DTA),X-射线衍射(XRD),对锌锡氧化物超细粉末的晶相组成、大小、烧结过程进行了分析.试验结果表明:pH值的调节、锌锡比是影响溶胶稳定的关键因素.XRD衍射表明,锌锡氧化物保持了SnO2原有的四方晶体结构.Zn2 的掺杂引起了晶格畸变.在400℃烧结时,Zn2 是进入O2-形成的间隙位置,形成间隙固溶体.在600℃烧结时,Zn2 进入Sn4 的晶格位子形成置换固溶体.     

Mechanical model for yield strength of nanocrystalline materials under high strain rate loading

To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mechanism of nanocrystalline materials under high strain rate loading was developed.As a first step of the research,the yield behavior of the nanocrystalline materials under high strain rate loading was mainly concerned in the model and uniform deformation was assumed for simplification.Nanocrystalline materials were treated as composites consisting of grain interior phase and grain boundary phase,and grain interior and grain boundary deformation mechanisms under high strain rate loading were analyzed,then Voigt model was applied to coupling grain boundary constitutive relation with mechanical model for grain interior phase to describe the overall yield mechanical behavior of nanocrystalline materials.The predictions by the developed model on the yield strength of nanocrysatlline materials at high strain rates show good agreements with various experimental data.Further discussion was presented for calculation results and relative experimental observations.     

Influence of mechanical alloying time on the properties of Fe_3Al intermetallics prepared by spark plasma sintering

The Fe3Al-based intermetallics were prepared by mechanical alloying and spark plasma sintering (SPS), and the influence of milling time on the properties of materials was investigated. The phase identification was investigated by X-ray, and the surface morphology and fractography were observed by scanning electron microscope (SEM). The mechanical properties such as bending strength, strain, and microhardness were tested. The results show that Fe reacts with Al completely to form Fe3Al during short SPS processing time. The relative densities of the sintered samples were nearly 100/. The mechanical properties of the sintered samples can be improved along with the milling time. The representative values are the bend strength of 1327 MPa and the microhardness of 434.     

Modification of nano-TiO2 by Al2O3 in-situ coating

A novel technology of in-situ coating Al2O3 on the surface of H4TiO4 was developed to prevent the aggregation of nano-TiO2 powders and improve the dispersibility and thermal stability in the way of forming a uniform coating layer. The heterogeneous nucleation was conducted to prepare the precursor of nano-TiO2 and then Al2O3 was coated on the surface of precursor. The effects of Al2O3 in-situ coating on the properties of nano-TiO2 were investigated. The results show that H4 TiO4 can be dispersed well under alkaline condition （pH 8. 5） and the heterogeneous nucleation can be controlled easily. The optimized uniform coating layer is obtained by adding 5 % （mass fraction ） and 10% of Al2O3 and the aggregation of nano-TiO2 powders is effectively inhibited and the dispersibility is obviously improved. The crystal sizes of TiO2 powders are 12.3, 11.4 and 8. 7 nm after coating 0, 5% and 10% of Al2O3 respectively. Al2O3 on the surface of particulates in amorphous phase could increase the thermal stability of nano-partieles after calcined at 550℃.     

高分子固化剂加固土质边坡的稳定性分析

分析高分子固化剂的加固机理,并利用室内试验测得的抗剪强度参数,采用Slide软件进行数值建模,主要研究在不同边坡坡比工况下,固化剂的浓度和加固厚度对边坡稳定性的影响。研究结果表明:高分子固化剂的护坡机理主要为高分子固结成膜加固,植被根系的锚固和加筋作用。高分子固化剂对于不同坡比工况下的边坡稳定性的提高均具有积极的作用。在同一坡比工况下,加固深度对于稳定性的影响受其他因素相关性小,而固化剂浓度对于稳定性的影响受本身稳定性系数影响,与其他因素相关性较大。当边坡坡比越小时,即原坡面稳定性系数越小时,加固后稳定性系数增加的比例越小。高分子固化剂应用到工程边坡上,促进边坡坡面的植被生长与恢复,根被根系的加固作用将更有利于提高边坡的稳定性。     

梯度(Ti,Al)N涂层的微观结构与机械性能研究

利用电弧离子镀技术在航空发动机压气机用1Cr11Ni2W2MoV在不锈钢上沉积了（Ti,Al）N梯度涂层,X射线衍射的结果表明涂层为B1型（Nacl）单相结构,具有（220）择优取向．扫描电镜观察表明,涂层均匀致密,与基体结合良好．电子探针元素线分析和截面面分布表明,所制备的涂层是内层富TiN、外层富（Ti,Al）N的梯度涂层,试验结果表明,（Ti,Al）N梯度涂层具有良好的耐磨性等机械性能．     

原位合成Al_2O_3/FeAl复合材料的组织与性能

利用Fe-Al-Fe2O3体系的放热反应,原位热压合成了Al2O3/FeAl复合材料.借助XRD和SEM等研究了复合材料的物相组成和显微结构,以及Al2O3生成量对复合材料显微结构和力学性能的影响.结果表明:经1 250℃保温1.5h热压烧结的块体材料主要由FeAl及少量Al2O3相构成,FeAl基体为片层结构,增强相Al2O3分散在基体和晶界处.随着Al2O3含量的增加,基体晶粒尺寸明显减小,同时对材料起增强增韧作用.在Al2O3含量为1.2wt%时,试样的抗弯强度达到最大值1 329.22MPa;在Al2O3含量为0.8wt%时,试样的断裂韧性达到最大值29.95MPa·m1/2.此值正好处于金属与陶瓷材料性能链的断缺处.因此,本研究结果对于完善材料性能体系具有重要意义.