固溶钽原子与晶界偏析钽原子对纳米晶铜力学性能的影响

发布时间：2018-07-17 04:35

【摘要】：最近几十年,纳米晶材料受到了极大的关注,越来越多的人开始投入到纳米晶材料的研究中。这种尺寸的材料不仅拥有优异的机械性能,例如高的强度和高的应变速率敏感性,而且还有很好的物理特性,如磁性。这种优异的特性来源于它超小的晶粒尺寸,或者说是它拥有的高的晶界体积分数,即所谓的尺寸效应。但是这种高的晶界体积分数同时也带来了一些问题,内部不稳定是一个很大的问题。很多纳米晶材料,无论是用于基础研究,还是工程应用,现在被认为实质上是处于非平衡状态,即使在常温下也会自发的向粗晶转变。这种粗晶化趋势妨碍了其在室温下的应用,特别是当它作为需要使用很长时间的结构材料。纳米晶材料的粗晶化趋势主要是由晶界的内部活动(例如晶界滑移、迁移、翻转)所造成的,尽管这些晶界活动是提高塑性变形所必需的,但是,为了获得稳定的结构和纳米晶材料所具有的优异特性,我们仍然需要制止它。使用固态不溶的元素进行合金化是一种非常有效的方法,类比于在乳浊液中添加表面活性剂可以稳定表面区域,不溶的的元素会分布于晶界,从而会减小自由能,并且减缓晶粒生长,不溶的元素还能在晶界起着钉扎的作用。铜钽是一个非常适合的系统,这个系统的每个组元具有不同的晶体结构,在固态下具有非常小的互溶度。钽原子的原子半径远大于铜原子的,这会使得钽原子分布在铜的晶界处。在本次试验中,使用磁控溅射的方法在玻璃基体上制备出了厚度约为6微米的纳米晶铜和铜钽合金(钽5%)薄膜,两种薄膜是在同样的条件下得到的,将不溶性的纳米晶铜钽合金体系与纳米晶铜进行了对比。使用X射线衍射仪对纳米晶铜和纳米晶铜钽合金试样的微观结构进行了分析,使用透射电子显微镜对其表面形貌进行了观察,使用纳米压痕仪对其力学性能进行了测定,通过对比发现纳米晶铜和纳米晶铜钽合金试样具有相同的晶体结构和晶粒尺寸,纳米晶铜钽合金在室温下具有更高的硬度和抗蠕变性能,说明钽原子的固溶添加不会改变纳米晶铜的晶体结构,可以提高纳米晶铜的力学性能。将制备的纳米晶铜和纳米晶铜钽合金试样进行一定温度的回火处理,使用X射线衍射仪对纳米晶铜和纳米晶铜钽合金试样的微观结构进行了分析,使用透射电子显微镜对其表面形貌进行了观察,使用纳米压痕仪对其力学性能进行了测定,通过对比发现经过回火处理后,纳米晶铜钽合金中的钽原子向晶界偏析,纳米晶铜钽合金具有更高的硬度和抗蠕变性能,说明晶界偏析钽原子可以提高纳米晶铜的力学性能和热稳定性。
[Abstract]:In recent decades, nanocrystalline materials have received great attention, and more people begin to study nanocrystalline materials. The material of this size not only has excellent mechanical properties, such as high strength and high strain rate sensitivity, but also has good physical properties, such as magnetism. This excellent property comes from its ultra-small grain size, or its high grain boundary volume fraction, known as the size effect. But this kind of high grain boundary volume fraction also brings some problems, internal instability is a big problem. Many nanocrystalline materials, whether used in basic research or engineering applications, are now considered to be essentially in a non-equilibrium state, even at room temperature will spontaneously change to coarse crystal. This trend of coarse crystallization hinders its application at room temperature, especially when it is used as a structural material for a long time. The trend of coarse crystallization of nanocrystalline materials is mainly caused by the internal activities of grain boundaries (such as grain boundary slip, migration, turnover). Although these grain boundary activities are necessary to increase plastic deformation, however, In order to obtain stable structure and excellent properties of nanocrystalline materials, we still need to stop it. Alloying with solid insoluble elements is a very effective method, analogous to the fact that adding surfactants to the emulsion stabilizes the surface area, and the insoluble elements distribute at the grain boundaries, thus reducing the free energy. And slow down the grain growth, insoluble elements can also play the role of pinning at grain boundaries. Copper tantalum is a very suitable system. Each component of the system has a different crystal structure and a very small mutual solubility in solid state. The atomic radius of tantalum atom is much larger than that of copper atom, which causes the tantalum atom to distribute at the grain boundary of copper. In this experiment, nanocrystalline copper and copper tantalum alloy (5% tantalum) thin films with thickness of about 6 microns were prepared on glass substrates by magnetron sputtering. The insoluble nanocrystalline copper-tantalum alloy system was compared with nano-crystalline copper. The microstructure of nanocrystalline copper and nanocrystalline copper-tantalum alloy samples was analyzed by X-ray diffractometer. The surface morphology of nanocrystalline copper and tantalum alloy was observed by transmission electron microscope, and the mechanical properties were measured by nano-indentation instrument. It is found that nanocrystalline copper and nanocrystalline copper tantalum alloys have the same crystal structure and grain size, and nanocrystalline copper tantalum alloys have higher hardness and creep resistance at room temperature. The results show that the addition of tantalum in solid solution can not change the crystal structure of nanocrystalline copper and can improve the mechanical properties of nanocrystalline copper. The microstructure of nanocrystalline copper and nanocrystalline copper-tantalum alloy samples was analyzed by X-ray diffraction (XRD) after tempering the samples of nanocrystalline copper and nanocrystalline copper tantalum. The surface morphology of nanocrystalline copper tantalum alloy was observed by transmission electron microscope and its mechanical properties were measured by nano-indentation instrument. It was found that after tempering, tantalum atoms in nanocrystalline copper-tantalum alloy segregated to grain boundary. Nanocrystalline copper-tantalum alloy has higher hardness and creep resistance, indicating that grain boundary segregation of tantalum atoms can improve the mechanical properties and thermal stability of nanocrystalline copper.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O614.121;TB383.1

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