|Alternative Title||Deformation and shear banding behaviours of disordered alloys|
|Thesis Advisor||戴兰宏 ; 陈艳|
|Place of Conferral||北京|
|Keyword||无序合金 非晶合金 高熵合金 剪切带|
(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。
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.
|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.|
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