High Resolution Electron Microscope Study on Formation and Growth Processes of Atomic Medium Range Order in Amorphous Alloys

本研究是1990-1991年为期两年的项目研究，目的是研究非晶态合金中原子中程有序的结构和形态，特别是它的形成和生长过程。作为非晶态合金系统，我们选择了Pd-Si系统。因为该系统一直以拥有大量的X射线和中子衍射数据而闻名。本文以快淬法制备的共晶Pd_&lt；82&gt；18&gt；合金薄带和Ar束溅射法制备的Pd_&lt；82&gt；Si_&lt；18&gt；薄膜为研究对象。用高分辨电子显微镜(HREM)和分析电子显微镜对样品的结构进行了观察。对于带状样品的减薄，使用了本研究项目资助的离子研磨设备。得到的结果如下：(1)在带状和溅射样品中都观察到了MRO结构。基于fcc-mro结构模型计算的高分辨电子显微镜图像与…一致。(2)快速淬火或气相沉积的冷却速度决定了MRO磁畴的大小和分布。(3)在573K以下的温度下，观察到了MRO磁畴的生长。在573K时，MRO结构域长大到大约5 nm的尺寸，使得第二个晕衍射环在选定的区域衍射中分裂成两个扩散环。通过纳米束衍射，得到了清晰的面心立方衍射图。在573K退火时，MRO磁区中的Si原子向外扩散到母体区。(4)在623K退火时，选区的衍射区开始出现清晰的面心立方衍射图。在此温度下，α-Pd开始析出，尺寸约为8 nm。在相同的温度范围内，观察到了相同形貌的带状和薄膜样品中的MRO结构及其在相同温度范围内的生长。非晶态合金在退火时的“结构弛豫”可以理解为自由体积的减少主要是由于MRO的生长，而基体中原子的化学有序化是由局部成分的变化引起的。较少

This study has been made as a two years project study from 1990 to 1991 in order to investigate structure and morphologies of atomic medium range order (MRO) in amorphous alloys, especially to investigate its formation and growth processes. As an amorphous alloy system we chose Pd-Si system. since the system has been well known as having a lot of X-ray and neutron diffraction data. In this study, eutectic Pd_<82>Si_<18> alloy ribbons made by rapid-quenching and Pd_<82>Si_<18> thin films prepared by Ar-beam sputtering were used as specimens. Structure observations of as-formed and annealed specimens were made by high resolution electron microscopy (HREM) and analytical electron microscopy. For thinning ribbon specimens, an ion-milling equipment was used which was funded by this research project. Obtained results are as follows:(1)MRO structures were observed in both of the ribbon and sputtered specimens. Calculated HREM images based on a fcc-MRO structure model were consistent with thos … More e observed.(2)Size and distribution of MRO domains were dependent of the cooling rate in rapid-quenching or in the vapor deposition.(3)On Annealing up to 573K, a MRO domain growth was observed. At 573K the MRO domain grows to a size of about 5nm, giving a splitting of the second halo diffraction ring into two diffuse rings in the selected area diffraction. Clear fcc diffraction patterns are obtained from the domains by the nano-beam diffraction. Si atoms in the MRO domains diffuse out to the matrix region on annealing at 573K.(4)On annealing at 623K clear fcc diffraction patterns start to appear in the selected area diffraction. The precipitation of alpha-Pd with a size of about 8nm starts at this temperature.The MRO structure and its growth on annealing are observed in both ribbon and thin film specimens in the same morphology in the same temperature ranges. The "structural relaxation" in an amorphous alloy on annealing can be understood as a phenomenon in which a free-volume reduction occurs mainly by the growth of MRO and a chemical ordering of atoms in the matrix proceeds by the local compositional variation on annealing. Less