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Formation and time-evolution of three-dimensional long-range ordered domains from short-range ordered states

短程有序态三维长程有序域的形成和时间演化

基本信息

批准号：
15360336
负责人：
MATSUMURA Syo
金额：
$ 9.86万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-15360336/
关键词：
ordered domain structure ordered precipitate electron tomography transmission electron microscopy nickel based alloys Monte Carlo simulation 国際研究者交流:ドイツ

项目摘要

This project aimed to analyze three-dimensional (3D) morphologies of crystalline ordered domains in alloys at nanometer scale. To this end, we developed a new experimental technique taking advantage of the computed tomography procedure for transmission electron microscopy (TEM), namely electron tomography. So far, the application of electron tomography has been mostly limited to biological or non-crystalline materials, since the image intensity should satisfy a simple projection relation given as a monotonous function of mass density and thickness of imaged objects. Currently, incoherent imaging by high angle scattering in scanning TEM is sometimes employed for crystalline materials to suppress the dynamical diffraction effects which violate the projection requirement on the imaging. However, the latter technique also cannot be adopted for imaging crystalline nanostructures, such as morphologies of crystal grains and ordered domains, which are identified by diffraction contrast images. … More In this study, we examined the feasibility of dark-field imaging for 3D tomography and proved it to be a practical method to reveal 3D nonostructures of ordered domains in alloys. In the proposed procedure, a specimen is placed on the specimen holder so that a systematic row containing superlattice reflections becomes parallel to the tilt axis of the holder. A tilt series of dark-field TEM images are taken with a superlattice reflection which is excited all the while. We applied this procedure to visualize 3D morophologies of ordered domains of D1a-type in Ni-Mo as well as of L12-type in Ni-Al-Ti. The results obtained are summarized as follows.1.Tilt series observations of ordered domains are achieved by not only precise setting of the tilt axis of a specimen but fine adjustment of diffraction conditions with the tilt function of electron beam.2.Ordered precipitates of D1a are formed in the matrix of disordered fcc phase in a characteristic rugby ball like shape, the main axis of which is parallel to [001] direction in a hypo stoichiometeric Ni4Mo alloy.3.Ordered domains of D1a have a tendency to grow with habit planes in a single phase state of Ni4Mo..4.Platelets of disordered phase is formed facing to a {100} plane within L12 ordered precipitates in Ni-Al-Ti. Less

本计画旨在分析奈米尺度下合金中结晶有序区域的三维形貌。为此，我们开发了一种新的实验技术，利用透射电子显微镜（TEM）的计算机断层扫描程序，即电子断层扫描。到目前为止，电子层析成像的应用主要局限于生物或非晶体材料，因为图像强度应满足作为成像对象的质量密度和厚度的单调函数给出的简单投影关系。目前，在扫描TEM中通过大角度散射的非相干成像有时被用于晶体材料以抑制违反对成像的投影要求的动态衍射效应。然而，后一种技术也不能用于成像晶体纳米结构，例如通过衍射对比图像识别的晶粒和有序域的形态。 ...更多信息在这项研究中，我们研究了暗场成像的三维层析成像的可行性，并证明它是一个实用的方法来揭示三维有序畴的合金。在所提出的程序中，试样放置在试样保持器上，使得包含超晶格反射的系统行变得平行于保持器的倾斜轴。在超晶格反射的情况下，拍摄了一系列倾斜的暗场TEM图像。我们应用这个程序来可视化三维形态学的有序域的D1 a型的Ni-Mo以及L12型的Ni-Al-Ti。结果表明：1.通过精确地设置样品的倾斜轴，并利用电子束的倾斜功能，对衍射条件进行微调，可以实现有序畴的连续观察; 2.在无序fcc相的基体中形成了具有特征性橄榄球形状的D1 a有序沉淀物，在亚化学计量比的Ni_4Mo合金中，D_1a的有序畴的主轴平行于[001]方向。4.在Ni-Al-Ti合金中，L12有序析出相内形成了面向{100}面的无序相片状结构。少