脉冲电沉积纳米晶Co-Ni合金相变及纳米孪晶形成机制研究

发布时间：2018-01-21 00:58

本文关键词： 纳米晶Co-Ni合金脉冲电沉积晶粒长大相变纳米孪晶　出处：《上海交通大学》2015年博士论文　论文类型：学位论文

【摘要】：材料的晶粒尺度在纳米级别时会在力学、热学、电磁学、光学以及化学催化等各个方面显示出优越的性能。然而,要保持纳米晶材料的性能要求其晶粒尺寸及相结构稳定。通常,在加热的过程中纳米晶材料都会发生晶粒长大的过程,金属材料在温度变化或是形变过程中往往还会发生相结构变化,这些都会对纳米晶材料的性能造成影响。因此,研究纳米晶材料的晶粒长大和相变以及其相互间的影响有重要作用。纳米材料中纳米孪晶等亚结构的引入可以对其各方面的综合性能进行进一步优化。近些年来的研究对纳米孪晶金属的一些基本力学性能、物理性能已有初步的认识。但有关纳米孪晶强化机理和纳米孪晶金属的发展还面临许多挑战,包括发展纳米孪晶金属的制备方法及工艺等。本文通过脉冲电沉积方法制备了成分可控的纳米晶Co-Ni合金,经过退火和拉伸后观察到了纳米孪晶结构。研究的内容主要为三个部分:1.纳米晶Co-Ni合金的脉冲电沉积制备;2.纳米晶Co-Ni合金的晶粒长大与相变;3.纳米孪晶的形成及性能。利用DSC、XRD和TEM等手段研究了脉冲电沉积方法制备的纳米晶Co-Ni合金在升温及拉伸过程中的结构变化,包括晶粒长大和相变。结果显示纳米晶粒对Co-Ni合金中的HCP→FCC相变具有抑制作用,而晶粒长大过程和该相变则相互促进。因此,纳米晶Co-Ni合金中晶粒长大与HCP→FCC相变总是同时发生,这一耦合过程可以被温度或形变所触发,触发的条件为足够高的温度或足够大的应变量。纳米晶Co-Ni合金经过晶粒长大与HCP→FCC相变后形成了纳米孪晶结构,其晶粒直径为几百纳米而孪晶片层厚度为40nm左右,晶粒内部的纳米孪晶具有很高的密度以及不同的取向。对纳米孪晶的形成机制及性能的研究显示该纳米孪晶结构在晶粒长大与相变共同作用下形成,两种结构变化缺一不可。这一通过晶粒长大与相变的耦合过程获得纳米孪晶结构的方法如果可以推广到其他的体系中,将为制备高质量纳米孪晶材料提供了新的思路和方法。同时,具有纳米孪晶结构的Co-Ni合金在4.2K至1000K超宽温度范围内显示出结构的稳定性,纳米孪晶结构本身是其具有超高稳定性的主要原因。
[Abstract]:The grain size of materials in mechanical, thermal, electromagnetism at the nanometer level, various optical and chemical catalysis showed excellent performance. However, to maintain the properties of nanocrystalline materials for its grain size and phase structure stability. Usually, process of nanocrystalline materials in the heating process will occur grain growth the metal material changes in temperature or deformation process often happens phase structure changes, which will have an impact on the performance of nanocrystalline materials. Therefore, the grain of nanocrystalline materials and the growth of the mutual influence and transformation plays an important role. The introduction of nano twinned nano materials such as sub structure can be integrated the performance of all aspects of further optimization. Some basic mechanical properties research in recent years on the physical properties of nano twinned metal, has an initial understanding. But the nano twin Grain strengthening mechanism and the development of nano twinned metal still faces many challenges, including the development of nano twinned metal preparation method and process. The nanocrystalline Co-Ni alloy composition controllable pulse electrodeposition method to prepare, after annealing and stretching was observed. The content of nano twinned structure includes three parts 1.: the pulse of nanocrystalline Co-Ni alloy electrodeposition; grain 2. nanocrystalline Co-Ni alloy growth and transformation; the formation and properties of 3. nano twinned. Using DSC, XRD and TEM were used to investigate the structural changes of pulse electrodeposition method for preparation of nanocrystalline Co-Ni alloy during heating and stretching process, including the grain growth and phase transformation. The results showed that nano grain has inhibitory effect on HCP and FCC transformation in Co-Ni alloy, and the grain growth process and the phase change is mutual promotion. Therefore, nanocrystalline Co-Ni alloy grain grow At the same time, FCC and HCP have always phase transition, the coupling process can be triggered by temperature or deformation, the trigger conditions for a sufficiently high temperature or large enough strain. The nanocrystalline Co-Ni alloy through grain growth and HCP to FCC transformation after the formation of the nano twinned structure, the grain diameter of several hundred nanometers and the twin film thickness is about 40nm and the nano twinned grains with high density and different orientation. To study the forming mechanism and properties of nano twin crystal showed that the nano twinned grain growth in the formation and interaction of transformation, two kinds of structural changes are indispensable. The grain growth and phase transition process by coupling the obtained if the method of nano twinned structure can be extended to other systems, will provide new ideas and methods for the preparation of high quality nano twinned materials. At the same time, with nano twinned structure The structure stability is shown in the ultra wide temperature range from 4.2K to 1000K, and the nanostructure itself is the main reason for its super high stability in the Co-Ni alloy.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.16;TB383.1

【相似文献】