金属玻璃近表面区域力学行为及动力学研究

发布时间：2018-04-19 08:52

本文选题：金属玻璃 + 尺度效应　；参考：《中国科学院大学(中国科学院物理研究所)》2017年博士论文

【摘要】：作为一种亚稳态的非晶合金材料,金属玻璃由于其特殊的结构特征(原子排列短程有序而长程无序),而表现出优异的力学、物理和化学性能,并且具备在过冷液相区超塑性成型的能力,因此被认为是制备微纳米尺度器件的一种新的结构材料。但是,随着金属玻璃尺寸的减小,其力学行为会与块体有显著的差异,出现明显的尺寸效应。在微纳米尺度,比表面积的急剧增大使表面成为主导金属玻璃力学行为的主要因素,因此金属玻璃表面的力学行为一直是金属玻璃研究领域的热点和难点。阐明金属玻璃表面微纳米尺度力学行为不仅能够加深我们对金属玻璃基础研究的认知,并且能够推进现在单纯的以晶体材料为主的微纳米器件制造技术。在这篇论文中,我们首先采用动态纳米压痕的方法仔细地研究了金属玻璃近表面微纳米尺度的塑性变形与样品尺度的关系。实验结果说明在不同金属玻璃体系中,当塑性变形超过一定临界尺度时,剪切带都会经历一个从离散分布(表面或近表层)到局域分布(内部)的变化过程。在低于临界尺度时,也就是在离散分布区,塑性变形以多重剪切带为主,并且剪切带的剪切位移很小。但是在大于临界尺度时,也就是局域分布区,塑性变形局域于几个剪切带内,并且剪切带的剪切位移很大。这种塑性变形方式的转变导致了金属玻璃中硬度的尺度效应,随着压入深度增加,硬度逐渐减小直至接近体材料硬度数值。通过实验和理论分析,我们发现这种塑性转变与金属玻璃的弹性模量和脆性相关,并且定性的给出了三者之间的关联。将观察区域进一步缩小至金属玻璃表面,我们发现金属玻璃表面动力学行为与块体有明显不同。首先,我们发现动态原子力显微镜技术第一次实现了金属玻璃塑性变形过程中纳米尺度结构演化的实验观测。实验结果说明对于块体金属玻璃塑性变形,随着外界应力的增加,结构中软区所占的比例会不断增加,呈现聚集长大的特征,导致结构向更高的能态演化。但金属玻璃表面的结构演化则与块体的完全不同,即随着外界应力的增大,表面结构演化依次经历了四个阶段:从最开始的随机结构演化变为结构弛豫,中间经历一个动态平衡的过程最后到达不断向高能态演化的阶段。表面这种偏离块体结构演化的特殊的变形特征与软玻璃体系的非线性流变学非常相似,这就说明在实验观察尺度上金属玻璃表面并不是像内部一样处于固态,而是一种更接近液体的状态。最后我们采用纳米压痕仪的划痕功能研究了金属玻璃表面类液体属性对摩擦行为的影响。实验结果说明金属玻璃表面的类液体层可以起到自润滑的效果,能有效地降低表面的摩擦系数,其最小值仅为块体内部摩擦系数的1/3。这种自润滑效果源于类液体层的均匀塑性变形,与块体材料局域剪切带的变形方式完全不同。同时,实验结果还量化了金属玻璃表面自润滑的深度范围,并且揭示了自润滑深度范围与玻璃转变温度的负相关关系。本论文对金属玻璃近表面区域微纳米尺度力学行为的初步研究所获得的结果不仅揭示了金属玻璃在小尺度范围内形变和近表面结构演化动力学行为的一些现象和基本规律,为完善和发展金属玻璃形变和相关的科学理论提供了实验依据,同时对于设计具有新功能特性的微纳米器件,比如自修复,自润滑等,指明了方向。
[Abstract]:As a kind of amorphous alloy material metastable metallic glass, because of its special structure (the atomic arrangement of short-range order and long Cheng Wuxu), and exhibits excellent mechanical, physical and chemical properties, and have the ability in the supercooled liquid region superplastic forming, so it is considered as a kind of new structural material the preparation of micro nano scale devices. However, with the decrease of the size of the metallic glass, its mechanical behavior have significant difference with the block, appear obvious size effect. In the micro nano scale, the specific surface area increases rapidly to become the dominant factor of glass surface mechanical behavior of metal, so the mechanical behavior of metallic glass surface has been a hot and difficult field of metal glass research. Clarify the metal glass surface micro nano scale mechanical behavior can not only deepen our cognition of the basic research of metallic glass, and can promote Now to the crystal material based micro nano device manufacturing technology only. In this thesis, we first proposed a dynamic nanoindentation carefully studied metal glass near the surface of the micro nano scale plastic deformation and the sample scale. The experimental results show that in different metallic glass system, when more than a certain critical scale plastic deformation, shear zone will experience a discrete distribution (from the surface or near surface) to local distribution (internal) change process. Below the critical scale, is also in the discrete distribution area of plastic deformation of the multiple shear bands, and the shear displacement of shear band is very small but. In is greater than the critical length, which is the local distribution area of plastic deformation in several local shear zones and shear displacement of shear band. The change of plastic deformation mode leads to the hardness of metallic glass ruler The degree of effect, with the increase of indentation depth, the hardness decreases gradually until close to the material hardness. Through numerical experiments and theoretical analysis, we found that the plastic and glass transition metal elastic modulus and brittleness, and given qualitative correlation between the three. The observation area was further reduced to the metal surface of the glass, we found the metal surface of the glass block and dynamic behavior are significantly different. First, we found that dynamic atomic force microscopy for the first time in the process of plastic deformation of metallic glass evolution of nano structure experimental observation. Experimental results show that the bulk metallic glass and plastic deformation, with the increase of external stress, for soft structure the proportion will continue to increase, showing the characteristics of agglomeration, leading to a higher energy state structure evolution. But the structure evolution of metal glass surface and the end block All different, with the increase of external stress, surface structure evolution successively experienced four stages: to structural relaxation from the beginning of the stochastic structural evolution process through a dynamic equilibrium and finally to evolve toward high-energy stage. The nonlinear rheological deformation characteristics of the surface from special evolution block the structure and soft glass system very similar to that in the experimental observation on the scale of the metallic glass surface is not like inside the same in solid, but a more close to the liquid state. Finally we use nano indentation scratches function effect of metal glass surface liquid properties on the friction behavior. The experimental results this kind of liquid metal on the surface of the glass layer can play the role of self lubricating effect, can effectively reduce the friction coefficient of the surface, the minimum value is only block internal friction coefficient 1/3 . the self lubrication effect from liquid layer uniform plastic deformation, deformation is completely different from the bulk materials of local shear zone. At the same time, the experimental results also quantify the depth of metal glass surface self lubrication, and reveal the self lubrication depth and glass transition temperature. The negative correlation between the preliminary study in this paper, the metallic glass near surface micro nano scale mechanical behavior of the obtained results not only reveal dynamics evolution of deformation of metallic glass in a small scale and near surface structure and basic laws provide an experimental basis for the perfection and development of the metal deformation of glass and related scientific theory, micro nano devices at the same time with new features for the design, such as self repairing, self lubrication, pointed out the direction.

【学位授予单位】：中国科学院大学(中国科学院物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG139.8

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