罗乐
,
胡素辉
金属学报
采用Nb管富Sn固-液相扩散法,研究了Nb_6Sn_5向Nb_3Sn转化过程中Sn的扩散方式及微组织结构.实验结果表明:Nb_3Sn层生长受Nb_6Sn_5分解时Sn的短程扩散和长程扩散两种机制的控制,分别形成晶粒较粗的内层和晶粒较细的外层;粗细晶粒的差别和热处理温度有关.根据此机制得出的扩散方程解与Nb_3Sn生长曲线符合得很好.
关键词:
扩散
,
growth
,
microstructure
,
Nb_3Sn
,
Nb_6Sn_5
刘庆冬彭剑超刘文庆周邦新
金属学报
Nb-V微合金钢在1200 ℃固溶0.5 h后淬火, 在450-650 ℃回火不同时间, 用显微
硬度和TEM测试并观察析出强化和组织软化现象, 用三维原子探针(3DAP)对产生二次硬化
的合金碳化物的成分进行定量分析, 研究其析出长大规律. 结果显示, 二次硬化主要是合金
碳化物析出强化的作用. 随着回火温度的升高或回火时间的延长, 合金碳化物的成分动态变
化, 即强碳化物形成元素取代或部分取代较弱的碳化物形成元素. 首先, V和Nb取代Mo,
然后Nb部分取代V, 最后形成具有一定原子比的合金碳化物. 相对回火温度, 回火时
间对碳化物内合金元素的相对含量影响不大. 在合金碳化物长大过程中, 薄片状碳化物优先
沿径向方向生长, 然后沿厚度方向长大并开始粗化.
关键词:
三维原子探针(3DAP)
,
tempering martensite
,
alloy carbide
,
growth
Y.Y. Zhu
金属学报(英文版)
A modified two-sphere model of sintering neck has been proposed, wherein three diffusion mechanisms including surface diffusion, grain-boundary diffusion and coupled surface and grain-boundary diffusion are assumed. Sintering neck is appropriately simulated using the modified model. The dynamic change of sintering neck is presented using the simulation. The variational shape of sintering neck in surface diffusion mechanism is continuous, whereas in grain-boundary diffusion mechanism, besides the variational shape of sintering neck being continuous, the center distance between the particles is also assumed to contract. However, the variational shape of sintering neck in coupling diffusion mechanism is integrated using the two diffusion mechanisms mentioned above.
关键词:
sintering simulation
,
simulation
,
neck
,
growth
,
Visual
Applied Physics Letters
Rope-like bundles of single-walled carbon nanotubes (SWNTs) similar to those obtained by laser vaporization and electric-are techniques were synthesized on a relatively large scale and at low cost by the catalytic decomposition of hydrocarbons at a temperature of about 1200 degrees C using an improved floating catalyst method. The SWNTs thus obtained have larger diameters and are self-organized into ropes. The addition of thiophene was found to be effective in promoting the growth of SWNTs and in increasing the yield of either SWNTs or multiwalled carbon nanotubes under different growth conditions. (C) 1998 American Institute of Physics. [S0003-6951(98)01125-5].
关键词:
growth
Journal of Crystal Growth
Superconducting fibrous crystals which were long enough for the measurements of many physical properties have been prepared by heating an amorphous plate in a steady stream of oxygen. The fibrous crystals have remarkably oriented structures, and their crystal structures are (2212) single phase, and their compositions approach Bi2Sr1Ca1Cu2Ox. The influence of a partially crystallized substrate without Pb doping on the growth of fibrous crystals has also been discussed briefly.
关键词:
growth
H.J.FAN
,
M.Zacharias
材料科学技术（英文）
Vapor-phase growth of ZnO nanowires based on gold catalyst is usually accompanied with lateral crawling growth on the substrate surface. We present results from our systematic experiments where the growth temperature and catalyst size are controlled. The data corroborate that it is possible to obtain clean vertical nanowire arrays while avoiding the crawling growth. On the other hand, crawling growth can be manipulated to obtain root-interconnected nanowire arrays, which could be useful for certain applications. Our results also imply that the previously suggested growth mechanism for the wire-on-wall hybridstructure might be incorrect. Finally, we show the formation of sub-millimeter long, straight ZnO nanowalls by combining a gold-catalyzed epitaxial growth of vertical nanowires and their mergence due to a confined crawling growth. These unconventional nanostructures might have unique electric or optical transport properties.
关键词:
Nanowire
,
nanowall
,
ZnO
,
crawling
,
growth
Materials Science
The rates of growth of short fatigue cracks initiated from a notch are much greater than the rates of growth of long fatigue cracks for the same values of Delta K. A decrease in the strength of materials caused by aging affects the behavior of long cracks. The geometric form of the notch strongly affects the behavior of short cracks. The growth rate of a short crack initiated from a sharp notch decreases and attains a minimum value at a length of 0.45 mm, which is far beyond the region of its influence. However, short cracks initiated from blunt notches exhibit slower growth in the region of stress concentration than outside this region. Strain fields induced by deformation of the tip of the notch are not the only factor inhibiting the propagation of short cracks from notches. To explain the behavior of a short crack initiated at a notch, one must take into account some other factors, in particular, crack closure.
关键词:
growth
张修睦
,
李依依
金属学报
本文使用光学和电子显微镜低温台对Fe-Mn-C合金中ε马氏体的形成过程和Fe-Ni-C合金中蝶状、透镜状、薄片状和复片状马氏体的形成过程进行了原位观察。本文实验结果指出;ε马氏体由4—5个层错重叠形成,证实了Olson和Cohen提出的层错化模型;薄片状马氏体优先在晶界和三角晶界处形核,初始长大形态(表面浮突)为细针状;观察到透镜状马氏体由薄片状向两侧加厚而形成,提出了相变孪晶长大受阻时,半共格孪晶界面位错可经位错分解反应发射出a/2[111]b=a_0/2[101]_f全位错,提供薄片状马氏体由孪生切变向滑移切变转换所需的位错源。
关键词:
马氏体形核、长大
,
nucleation
,
growth
ZHANG Xiumu LI Yiyi Institute of Metal Research
,
Academia Sinica
,
Shenyang 110015
,
China
金属学报(英文版)
In situ observations of the nucleation and growth of ferrous martensites,including ε-, lenticular,butterfly,thin-plate and composite-plate ones at low temperature stage on optical or transmission electron microscope were carried out.The results confirmed the faulting model for the formation of ε-martensite proposed by Olso and Cohen.The grain boundaries and tri- ple points are the favourable nucleation sites for the thin plates,and their surface relief grown initially like a small needle.The lenticular martensite was observed as two stages of formation.According to the dislocation resolving reaction. (a/6)[111]_b→(a/3)[]_b+(a/2)[111]_b,the emission dislocation(=(a/2)[111]_b)acting as the dislocation source for the transition of lattice invariant shear from twinning to slip was proposed.
关键词:
martensite
,
null
,
null
,
null
,
null
