Gamma -> Epsilon Martensite Transformation and Twinning Deformation in fcc Cobalt During Surface Mechanical Attrition Treatment

The deformation microstructure of face-centered cubic cobalt subjected to surface mechanical attrition treatment was studied as a function of strain levels. Strain-induced gamma --> epsilon transformation and twinning deformation were evidenced by transmission electron microscopy and were found to progress continuously in ultrafine and nanocrystalline grains as the strain increased.

Strain-Induced Grain Refinement of Cobalt During Surface Mechanical Attrition Treatment

The microstructural evolution during surface mechanical attrition treatment of cobalt (a mixture of hexagonal close packed (hep) and face-centered cubic (fcc) phases) was investigated. In order to reveal the mechanism of grain refinement and strain accommodation. The microstructure was systematically characterized by both cross-sectional and planar-view transmission electron microscopy. In the hcp phase, the process of grain refinement. Accompanied by an increase in strain imposed in the surface layer. Involved: (1) the onset of 110 111 deformation twinning, (2) the operation of (1 120) 110 1 0} prismatic and (1 120) (000 1) basal slip, leading to the formation of low-angle dislocation boundaries, and (3) the successive subdivision of grains to a finer and finer scale. Ressulting in the formation of highly misoriented nanocrystalline grains. Moreover. The formation of nanocrystalliies at the grain boundary and triple junction was also observed to occur concurrently with straining. By contrast. The fec phase accommodated strain in a sequence as follows: (1) slip of dislocations by forming intersecting planar arrays of dislocations, (2) {1 1 1} deformation twinning, and (3) the gamma(fcc) --> epsilon(hcp) martensitic phase transformation. The mechanism of grain refinement was interpreted in terms of the structural subdivision of grains together with dynamic recrystallization occurring in the hep phase and the gamma --> E: martensitic transformation in the fcc phase as well.

Nanocrystalline Formation During Mechanical Attrition of Cobalt

The nanocrystalline (nc) formation was studied in cobalt (a mixture of c (hexagonal close packed) and gamma (face-centered cubic) phases) subjected to surface mechanical attrition treatment. Electron microscopy revealed the operation of {10(1) over bar 0}< 11(2) over bar 0 > prismatic and {0001}< 11(2) over bar 0 > basal slip in the E phase, leading to the successive subdivision of grains to nanoscale. In particular, the dislocation splitting into the stacking faults was observed to occur in ultrafine and nc grains. By contrast, the planar dislocation arrays, twins and martensites were evidenced in the gamma phase. The strain-induced gamma ->epsilon martensitic transformation was found to progress continuously in ultrafine and nc grains as the strain increased. The nc formation in the gamma phase was interpreted in terms of the martensitic transformation and twinning.

Explosive consolidation of amorphous cobalt-based alloys

This paper addresses the explosive consolidation of amorphous cobalt-based alloys. Using the experimental setup introduced in the present paper, specimens with high compact density, excellent magnetic properties and great wearability have been made. In comparison with permalloy and ferrite, the present specimens exhibit superior magnetic properties. Therefore, the compact is deemed as being a promising material for magnetic recording heads.

Microstructural evolution and formation of nanocrystalline intermetallic compound during surface mechanical attrition treatment of cobalt

Nanocrystalline intermetallic Co3Fe7 was produced on the surface of cobalt via surface mechanical attrition (SMA). Deformationinduced diffusion entailed the formation of a series of solid solutions. Phase transitions occurred depending on the atomic fraction of Fe in the surface solid solutions: from hexagonal close-packed (<4% Fe) to face-centered cubic (fcc) (4-11% Fe), and from fcc to body-centered cubic (>11% Fe). Nanoscale compositional probing suggested significantly higher Fe contents at grain boundaries and triple junctions than grain interiors. Short-circuit diffusion along grain boundaries and triple junctions dominate in the nanocrystalline intermetallic compound. Stacking faults contribute significantly to diffusion. Diffusion enhancement due to high-rate deformation in SMA was analyzed by regarding dislocations as solute-pumping channels, and the creation of excess vacancies. Non-equilibrium, atomic level alloying can then be ascribed to deformation-induced intermixing of constituent species. The formation mechanism of nanocrystalline intermetallic grains on the SMA surface can be thought of as a consequence of numerous nucleation events and limited growth. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

第57届国际宇航大会会议介绍

1概况 第57届国际宇航大会于2006年10月2—6日在西班牙瓦兰西亚召开，10月1日还召开了国际宇航科学院院士会和国际宇航学会各委员会会议．会议参加人数超过2000人，开幕式大礼堂座无虚席．这次会议的主题是“开创更贴近人民的空间事业（bringing space closer to people）”．大会在瓦兰西亚的大展览馆召开，群众与代表交混．除大会会场外，所有分会会场都是用木板临时安装的，会场条件简单．

激光熔覆大厚度Fe_(57)Co_8Ni_8Zr_(10)Si_4B_(13)非晶表层及其微结构研究

利用激光熔覆制备出1.2mm厚的Fe_(57)Co_8Ni_8Zr_(10)Si_4B_(13)大厚度非晶表层。用XRD,ES,TEM,DSC及硬度对获得的非晶表层进行了多种分析，研究了非晶合金表层的微结构与非晶形成能力。初步探讨了大厚度非晶表层的形式机制。

Nanocrystalline Formation during Mechanical Attrition of Cobalt

The nanocrystalline (nc) formation was studied in cobalt (a mixture of c (hexagonal close packed) and gamma (face-centered cubic) phases) subjected to surface mechanical attrition treatment. Electron microscopy revealed the operation of {10(1) over bar 0}< 11(2) over bar 0 > prismatic and {0001}< 11(2) over bar 0 > basal slip in the E phase, leading to the successive subdivision of grains to nanoscale. In particular, the dislocation splitting into the stacking faults was observed to occur in ultrafine and nc grains. By contrast, the planar dislocation arrays, twins and martensites were evidenced in the gamma phase. The strain-induced gamma ->epsilon martensitic transformation was found to progress continuously in ultrafine and nc grains as the strain increased. The nc formation in the gamma phase was interpreted in terms of the martensitic transformation and twinning.

联合固氮菌Enteroabcter gergoviae 57-7氮代谢相关基因的克隆和泌氨工程菌的构建

从构建具有稳定泌氨能力的联合固氮工程菌的目的出发，首先构建Enterobacter gergoviae57-7 (E57-7)基因文库并与所筛选的泌氨突变株进行遗传互补实验，得到可互补 泌氨特性的克隆，经Southern杂交后推测其中包含与glnA、amtB基因无关的另一类与泌 氨相关的基因。同时根据铵载体基因amtB的已知序列设计两对简并性引物，经PCR从 E57-7 DNA中扩增得到约340bp的片段，序列分析和Blast序列同源性比较后确定为amtB 基因片段，申报并获得序列号AJ132232，最终从基因库中筛选到两个包含E57-7 amtB 基因的克隆。 用K. pneumoniae的glnA基因片段为探针，通过Southern杂交从E57-7基因库中筛选到包含有glnAntrBC基因的克隆，经亚克隆后对包含有这个操纵元的4316bp片段进行了全序列分析，申报GenBank获得序列号AF072440。在体外实验中构建了Km-cassette 插入glnA的重组质粒pA，将此质粒转入E57-7野生型菌株后经筛选同源重组子获得glnA 突变的具有稳定泌氨能力的菌株15、I9。并进行了盆栽玉米接种实验，确定在灭菌上壤实验体系下I5对玉米幼苗有显著促生效应。 利用绿色荧光蛋白(GFP-S65T，V68L，S72A)基因建立分子生物学研究手段，构建了新 型克隆载体pGreenLD，建立了绿白斑筛选重组质粒的的技术。构建组成型表达gfp的质粒载体研究了E57-7在玉米根际的定殖模式;构建nifH-gfp表达载体，确定在与植物联合生活时其固氮酶结构基因nifHDK的表达与碳源物质供应密切相关。利用不同抗性基因和gfp基因片段构建出在E57-7中组成型表达抗性和GFP的质粒载体，建立了监测接种菌在土壤中释放的双标记系统。 最后克隆了E57-7 glg cluster并测定部分glgCA和glgP基因序列，申报后获得序列号AJ132233和AJ132234，这是首例从联合固氮菌中克隆得到glg cluster的报道。

Interface as the origin of ferromagnetism in cobalt doped ZnO film grown on silicon substrate

We have investigated the magnetic properties of Co-doped zinc oxide (ZnO) film deposited on silicon substrate by magnetron sputtering. Co ions have a valence of 2+ and substitute for Zn sites in the lattice. By using a chemical etching method, an extrinsic ferromagnetism was demonstrated. The observed ferromagnetism is neither associated with magnetic precipitates nor with contamination, but originates from the silicon/silicon oxide interface. This interface ferromagnetism is characterized by being temperature independent and by having a parallel magnetic anisotropy. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2989128]

Magnetic properties of ZnO-doped cobalt ferrite

The cobalt ferrites with chemical composition Co1+xZnxFe2-2xO4 (r=0.0, 0.1, 0.2, 0.4) were obtained with conventional solid reaction. The ZnO-doped samples have lower lattice constant than CoFe2O4 by adjusting Co ions to the octahedral sites. The results show that doping ZnO could extremely improve the magnetic properties. In comparison with pure CoFe2O4, the little ZnO-doped sample has higher permeability and much lower coercivity at the condition of a little decrease of magnetization saturation. Sample with x=0.1 shows evident magnetostrictive effect at the magnetic field of 30-60 mT while pure cobalt ferrite sample does not, though the saturation magnetostriction decreases. These indicate that ZnO-doping improves the magnetostrictive sensitivity of the cobalt ferrites and have potential applications in magnetoelectric devices and magnetic detector.