Development of High Performance Functional Materials by Controlling Grain Boundary Character Distribution and Grain Boundary Geometrical Configuration

“高性能多晶材料开发的晶界设计与控制”这一概念由作者首次提出，最近被称为“晶界工程”，作为实现结构材料性能增强的有力工具，已被广泛接受。因此，本项目的目的是将晶界工程应用于高性能功能材料的开发。得到的主要结果如下：(1)磁场对纳米晶镍晶粒生长的影响：发现磁场可以通过抑制纳米晶镍的异常晶粒生长而产生均匀的晶粒结构。此外，均匀晶粒结构的磁退火样品的热稳定性优于普通退火样品，因为在磁场作用下形成均匀晶粒结构后很少观察到进一步的晶粒长大。(2)晶界特征/结构对多晶硅电学性能的影响：采用电子束感应电流（EBIC）技术和开尔文探针显微镜（KFM）研究了多晶硅中单个晶界的电学性能。晶界电活动随有效面间距的增大而减小。KFM测量显示，在随机边界处势垒的高度比在特殊边界处高两倍。(3)晶界几何构型对多晶硅整体电学性能的影响：引入新的显微组织参数“定向晶粒尺寸（定向晶界密度）和定向晶界特征分布”，定量评价不同晶界几何构型的晶界显微组织。研究发现，多晶硅的电导率随晶界密度和晶界特征分布的增加而降低。(4)非晶磁晶化控制铁基合金晶界组织：通过对非晶铁基合金（Fe_<78>Si_9B_<13>）进行磁晶化，更精确地控制晶界组织。结果表明，磁晶化可使材料产生尖锐的{110}织构，从而提高了材料的软磁性能。少

The concept of "grain boundary design and control for development of high performance polycrystalline materials", which was first proposed by the present author and was recently called "Grain Boundary Engineering", has been extensively accepted as a powerful tool for achieving enhanced properties of structural materials. The aim of this project was therefore to apply the grain boundary engineering to develop high performance functional materials. The chief results obtained were as follows:(1) Effect of Magnetic Field on Grain Growth in Nanocrystalline Nickel : It has been found that a magnetic field can produce a uniform grain structure by suppressing abnormal grain growth in nanocrystalline nickel. In addition, the thermal stability of magnetically annealed sample with uniform grain structure was found to be superior to ordinarily annealed one because further grain growth rarely observed after development of a uniform grain structure by application of the magnetic field.(2)Effect of G … More rain Boundary Character/Structure on Electrical Properties of Polycrystalline Silicon : The electron beam induce current (EBIC) technique and Kelvin probe microscopy (KFM) were applied to study electrical properties of individual grain boundaries in polycrystalline silicon whose character was determined by OIM. It was found that electrical activity of grain boundaries decreased with increasing effective interplanar spacing. KFM measurements revealed that the height of potential barrier was twice higher at random boundaries than at special boundaries.(3)Effect of Grain Boundary Geometrical Configuration on Bulk Electrical Property of Polycrystalline Silicon : We introduced a new microstructural parameters "directional grain size (directional grain boundary density) and directional grain boundary character distribution" to quantitatively evaluate grain boundary microstructures with different grain boundary geometrical configuration. We found that the electrical conductivity of polycrystalline silicon decreased with increasing directional grain boundary density and directional grain boundary character distribution.(4)Control of Grain Boundary Microstructure in Iron Based Alloy by Magnetic Crystallization of Amorphous : Magnetic crystallization of amorphous iron based alloy (Fe_<78>Si_9B_<13>) was carried out to more precisely control gain boundary microstructure. It was found that a sharp {110} texture could be introduced by magnetic crystallization, which resulted in enhanced soft-magnetic properties. Less