IMECH-IR  > 非线性力学国家重点实验室
非晶合金塑性流动的玻色峰解释
英文题名Boson Peak Interpretation of Plastic Flow in Metallic Glasses
杨杰
导师蒋敏强
2018-05-19
学位授予单位中国科学院大学
学位授予地点北京
学位类别硕士
学位专业固体力学
关键词非晶合金 塑性流动 剪切转变 玻色峰 方向序
英文摘要

    相比于晶体塑性的位错机制,拓扑无序非晶合金的塑性流动是否具有明确的结构起源一直存在很大的争议。非晶合金作为玻璃家族的新成员,其振动态密度在低频THz范围也表现出偏离经典德拜模型的过剩行为,即所谓的“玻色峰”现象。玻色峰有望从原子振动角度,为探究非晶塑性的结构起源打开一扇窗口。本文以此为研究内容,结合原子尺度模拟和理论分析,取得如下主要进展:

1、通过分析不同局域环境的原子振动,提出一个结构参量-方向序,表征组成玻色峰的低频振动的最可能方向。方向序的模长可定量预测玻色峰的强度,而其空间分布符合玻色峰的准局域振动图像。

2、通过对角化非晶合金系统的海森矩阵,解耦原子集体运动方程,发现原子集体位移主要由组成玻色峰的低频振动控制。基于此,实现了对Tg附近的非晶合金应力松弛的定量描述。

3、以玻色峰为线索,在时域空间实现了对非晶合金塑性流动基本事件“剪切转变”的捕捉。同时,基于单原子的玻色峰参与度,预测了“剪切转变”事件的空间位置。

;

    Not like the dislocation-mediated plasticity of crystals, there is much controversy on the plastic flow of amorphous alloys with long-range disorder, since its structural origin is not clear. Amorphous alloys as a new member of glasses display an excess of low-frequency vibrational density of states over the Debye level, i.e., the so-called "boson peak". From a viewpoint of atomic vibrations, the boson peak opens an window into the structural origin of amorphous plasticity. To this end, this study performs both atomistic simulations and theoretical analyses, and some results are obtained as follows.

1. Through analyzing the atomic vibrations in different local environments, an structural parameter, termed orientation order, is proposed to characterize the most probable direction of low-frequency modes contributing to the boson peak. It is interesting to find that the intensity of boson peak has a linear dependence with the length of orientation order. Spatially, the orientation order shows an inhomogeneous distribution, which is consistent with the picture of the quasi-localized modes.

2. The motion equations of atoms in amorphous alloys are decoupled via diagonalizing Hessian Matrix. It is revealed that the large displacements of atoms in amorphous alloys are controlled by those low-frequency modes belonging to boson peak. Based on this, the stress relaxation around Tg, a typical plastic behavior, can be quantitatively described.

3. The shear transformation events is captured in time domain, by using the sudden increasing of boson peak as an indicator. The spatial location of shear transformation is predicted by atomic participation ratio within the boson peak frequencies.

语种中文
文献类型学位论文
条目标识符http://dspace.imech.ac.cn/handle/311007/73134
专题非线性力学国家重点实验室
作者单位中国科学院力学研究所
推荐引用方式
GB/T 7714
杨杰. 非晶合金塑性流动的玻色峰解释[D]. 北京. 中国科学院大学,2018.
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非晶合金塑性流动的玻色峰解释.pdf(5161KB)学位论文 开放获取CC BY-NC-SA
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