IMECH-IR  > 非线性力学国家重点实验室
无序合金的变形与剪切带行为研究
Alternative TitleDeformation and shear banding behaviours of disordered alloys
刘兴发
Thesis Advisor戴兰宏 ; 陈艳
2019-05-29
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline固体力学
Keyword无序合金 非晶合金 高熵合金 剪切带
Abstract

近年来,通过调控材料的“序”实现金属材料的强韧化获得了国内外研究人员的广泛关注。在这一指导思想下,不断涌现出具有优异的力学性能的拓扑无序结构非晶合金和化学无序高熵合金,展现了在国防、航天等领域的应用前景。目前对这两类无序合金的变形尤其是塑性流动不稳定引起的剪切带行为同它们微观结构关联的认识还不全面,需要进一步开展相关工作。为此,本文针对拓扑无序非晶合金与化学无序高熵合金两类无序合金的变形与剪切带行为开展了系列的研究工作

(1) 基于单脉冲霍普金森扭杆装置探究非晶合金由宏观弹性变形至剪切带涌现的过程。通过宏观弹性区间的循环简单剪切加载,发现了动态储存能达到某一临界值时会形成剪切带;基于STZ演化动力学与有效无序温度理论建立非晶合金在循环载荷下的运动方程,揭示剪切带的形成是由有效无序温度软化主控与热温度软化辅助的失稳过程;结合扰动分析,给出剪切失稳的判据,说明了循环加载过程中储存能将降低剪切带形核时间。

(2) 通过成分调节获得具有不同枝晶体积分数的内生枝晶非晶合金复合材料,通过变形冻结实验,捕捉到复合材料中剪切带萌生、扩展和演化的图像;研究了不同枝晶体积分数对复合材料力学性能以及剪切带行为的影响,复合材料的屈服强度随体积分数的增加而线性下降,存在临界体积分数使复合材料发生脆-塑转变,并揭示了这一转变过程是剪切带逾渗的结果。

(3) 通过DIC方法并结合有限元模拟给出了球状晶体增强非晶合金复合材料内部变形的演化过程,分析了两相在变形过程中的作用。从实验上观察到复合材料内部在微米尺度非均匀分布的应变场。两相界面处是变形集中区域;随着应变的增加,材料内部形成变形局部化的带状区;揭示了复合材料的塑性变形主要通过众多剪切带的滑移实现,晶体相促进了多重剪切带的形成;非晶基体相是载荷的主要承担者。

(4) 基于化学无序高熵合金的合金设计理念开发了具有新型多相钨高熵合金WMoFeNi。该高熵合金微观组织由枝晶状BCC相、连续的FCC基体相以及弥散的微尺度金属间化合物 构成。通过静动态压缩实验发现该合金具有良好的强度与塑性的匹配特征,结合纳米压痕实验与微结构分析,这一匹配源于BCC与金属间化合物提供足够的强化效应以及FCC良好的塑性变形能力。

Other Abstract

In recent years, strengthening and toughening of metallic materials by tuning the "order" of materials has attracted extensive attentions. Under this guiding ideology, topological disordered amorphous alloys and chemically disordered high-entropy alloys with excellent mechanical properties have been developed and fabricated, which show potential application in the fields of national defence and aerospace. At present, the correlation between the microstructures of these two kinds of disordered alloys and their deformation, especially the shear banding behaviour, is far from being totally understood, and further work is needed. Therefore, this dissertation carried out a series of research work on the deformation and shear band behaviour of amorphous alloy and high-entropy alloy.

(1) Based on a single-pulse Hopkinson torsional bar, the process of an amorphous alloy from macroscopically elastic deformation to the emergence of shear bands is explored. By performing cyclic simple shear loading of samples in the macroscopically elastic limit, it is found that the shear band is formed when the dynamic stored energy reaches a critical value. The deformation equation under cyclic loading is established based on the STZ kinetics and the effective disordered temperature theory. It is revealed that the formation of the shear band is an instability dominated by effective disordered temperature softening and assited by thermal temperature softening. Combined with the perturbation analysis, the criterion of shear instability is given, and it is indicated that the stored energy will reduce the nucleation time of the shear band.

(2) In-situ dendrites reinforced amorphous alloy composites with different dendritic volume fraction were obtained by tuning compositions. The interrupted technique was used to capture the images of shear band initiation, propagation and evolution in the composites. The effects of volume fraction on the mechanical properties and shear banding behaviours were investigated, and the results shows that the yield strength of the composite decreases linearly with the increase of the volume fraction, and the composite undergoes a brittle-plastic transition when the volume fraction reaches a critical value. It is revealed that the transformation process is a result from the percolation of shear bands.

(3) The evolution of the internal deformation field of a spherical crystal reinforced amorphous alloy composites was studied by DIC method combined with finite element simulation, and the role of crystals and the amorphous matrix in the deformation process was analysed. The strain field of the composite is unevenly distributed at the microscale. There exists strain concentrations at the interface between the two phases, and strain localization will be formed with the increase of external straining. It is found that the plastic deformation of the composite is mainly mediated by the slip along multiply shear bands, and the crystal promotes the formation of multiple shear bands. It is revealed that the amorphous matrix phase is the main bearer of the load.

(4) A new multi-phase tungsten high-entropy alloy WMoFeNi has been developed based on the alloy design concept of chemically disordered high-entropy alloy. This alloy consists of a BCC dendrite phase and an intermetallic precipitation phase embedded in the continuous FCC matrix. The quasi-static and dynamic compression tests show that the alloy has good combination of strength and plasticity. By performing nanoindentation experiments and microstructure analysis, this match is derived from sufficient strengthening effect of BCC and intermetallic compounds, and the good plastic deformation ability of FCC.

Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/79124
Collection非线性力学国家重点实验室
Recommended Citation
GB/T 7714
刘兴发. 无序合金的变形与剪切带行为研究[D]. 北京. 中国科学院大学,2019.
Files in This Item:
File Name/Size DocType Version Access License
刘兴发-博士论文-20190603-终版(9086KB)学位论文 开放获取CC BY-NC-SAApplication Full Text
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Google Scholar
Similar articles in Google Scholar
[刘兴发]'s Articles
Baidu academic
Similar articles in Baidu academic
[刘兴发]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[刘兴发]'s Articles
Terms of Use
No data!
Social Bookmark/Share
All comments (0)
No comment.
 

Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.