块体金属玻璃本构关系及其多相结构的有限元分析

发布时间：2018-11-01 14:43

【摘要】：金属玻璃是通过快速冷却方法获得的非晶态合金,是一种区别于传统晶态金属合金的新型材料。金属玻璃在原子排列上呈现出长程无序,短程有序的结构特点。由于金属玻璃原子排列的特殊性,因此金属玻璃由于具有良好的物理、化学和力学性能,特别是在力学性能方面表现出高的压缩强度、高的断裂韧性、高的疲劳强度等。但其在室温单轴拉伸或压缩时,大多数单相块体金属玻璃表现为无宏观塑性变形的脆性断裂,这严重制约着金属玻璃作为高强度工程材料的应用。为了改善金属玻璃的室温塑性,人们参考晶体材料的塑性提高方法来提高金属玻璃的塑性。比如:表面处理(轧制,喷丸,激光烧蚀表面等),热处理以及生成复合材料等来提高非晶的塑性。由于晶体与非晶的结构不同,因此其微观变形机制也不同。由于两者的微观变形机制不同,因此适用晶体材料可以提高塑性的方法,不一定对金属玻璃有效。因此研究金属玻璃的变形机制和其对应的变形行为有非常重要的现实意义,对于提高金属玻璃的实验有着很重要的理论指导意义。现有最流行的微观变形机制是Spaepen提出的自由体积理论。自由体积理论将自由体积作为反映材料微观结构的微观变量。金属玻璃的力学性能与其微观结构有着非常紧密的联系,因此不同的初始应力状态或初始自由体积分布对金属玻璃的力学性能的影响。本文主要基于自由体积理论的微观变形机制建立金属玻璃的宏观本构关系并分析其多相结构变形行为。从材料设计的角度理解则是,建立基于自由体积理论的本构关系,以自由体积为材料结构参数,以提高金属玻璃塑性或力学性能为目的的材料设计和材料计算。研究金属玻璃本构关系及其多相结构变形行为,尤其是剪切带的形成和发展过程,对于提高金属玻璃及其多相复合材料的塑性有着非常重要的理论指导意义。本文的主要研究内容包括以下三个方面:第一:基于Spaepen的自由体积理论,结合宏观变形准则(Drucker-Prager屈服准则),建立大块金属玻璃的弹塑性本构关系。第二:基于单相大块金属玻璃的微观结构,本文首次提出初始自由体积呈现不同统计分布(自由体积的分布极限区间,自由体积的均值,自由体积分布的对称性和自由体积的分布方差)对金属玻璃的力学性能的影响。金属玻璃结构的非均匀性越大越有利于其塑性。第三:基于多相金属玻璃的微观结构对应的初始自由体积的空间非均匀分布,如:渐变式自由体积梯度分布,相分离(phase separation included Spinodal decomposition and Binodal decomposition)等,分析不同的自由体积空间非均匀分布对多相块体金属玻璃的力学性能的影响以及相应剪切带的形成过程(成核-扩展-发展-阻止-分叉-绕行等剪切带发展行为)。通过自由体积的渐变梯度分布可知，，对于多相金属玻璃的强化与剪切带的阻止有紧密联系,即自由体积梯度效应(free volume gradienteffect)。Spinodal相解析式的空间分布可知剪切带的形成不仅与最大剪切应力有关,更与自由体积的空间分布有关(微观结构)。分析了自由体积的统计分布作用,Spinodal形貌的角度作用以及内尺寸作用对Spinodal分解金属玻璃复合材料的力学性能影响。其中角度作用(orientation effect)有利于金属玻璃的塑性,而内禀尺寸效应(intrinsic size effect)遵循最小尺寸兼容原则(minimum size compatibility principle),即当相分离结构的尺寸大于最小剪切带变形尺寸,其相解析内禀尺寸效应不起作用。同时分析Binodal相解析的颗粒增强相的尺寸,体百分比和种类以及金属玻璃基体种类(matrix effect)对多相金属玻璃的力学性能影响。
[Abstract]:Metallic glass is an amorphous alloy obtained by rapid cooling method, which is a kind of new material which is different from traditional crystalline metal alloy. Metal glasses exhibit long-range disorder, short-range and orderly structure characteristics in atomic arrangement. Because of the particularity of metal glass atomic arrangement, the metal glass exhibits high compressive strength, high fracture toughness, high fatigue strength, etc. due to its good physical, chemical and mechanical properties. However, most of the single-phase bulk metallic glasses exhibit a brittle fracture without macroscopic plastic deformation at room temperature uniaxial tension or compression, which severely restricts the application of metal glass as high-strength engineering materials. In order to improve the room temperature plasticity of the metal glass, the plasticity of the metal glass is improved by the plastic improvement method of the crystal material. such as surface treatment (rolling, shot peening, laser ablation surface, etc.), heat treatment, and formation of composite materials, etc. Because the crystal is different from the amorphous structure, its micro-deformation mechanism is different. Because of the different micro-deformation mechanism, the application of the crystal material can improve the plasticity and not be effective for the metal glass. Therefore, it is very important to study the deformation mechanism of metal glass and its corresponding deformation behavior. The most popular micro-deformation mechanism is the free volume theory proposed by Spaepen. The free volume theory takes the free volume as a microscopic variable that reflects the microstructure of the material. The mechanical properties of the metal glass are closely related to their microstructure, so different initial stress states or initial free volume distributions affect the mechanical properties of the metal glass. In this paper, based on the micro-deformation mechanism of free volume theory, the macro-structure relation of metal glass is established and its multiphase structure deformation behavior is analyzed. It is understood from the viewpoint of material design that this structure is based on the free volume theory, and the free volume is the structural parameter of the material, so as to improve the plastic or mechanical properties of the metal. It is very important to study the structure of metal glass and its multiphase structure deformation behavior, especially the formation and development of shear zone. The main contents of this paper include the following three aspects: first, based on Spaepen's free volume theory, combining with the macro deformation criterion (Drucker-Prager yield criterion), the elastic-plastic constitutive relation of bulk metallic glass is established. Secondly, based on the microstructure of single-phase bulk metallic glass, the initial free volume presented in this paper presents the distribution limit of free volume and the mean value of free volume for the first time. The symmetry of free volume distribution and the distribution variance of free volume influence the mechanical properties of metal glass. The larger the non-uniformity of the metal glass structure is, the greater the plasticity thereof. Third, the spatial non-uniform distribution of the initial free volume corresponding to the microstructure of the multi-phase metal glass, such as gradient free volume gradient distribution, phase separation and the like, The effects of non-uniform distribution of free volume on the mechanical properties of multi-phase bulk metallic glass and the formation of corresponding shear bands (nucleation-expansion-development-prevention-bifurcation-detour, etc.) were analyzed. From the gradient distribution of free volume, it can be seen that the strengthening of multi-phase metal glass is closely related to the blocking of shear zone, i. e. free volume gradient effect. The spatial distribution of Spinodal phase analysis shows that the formation of shear zone not only relates to the maximum shear stress, but also relates to the spatial distribution of free volume (microstructure). The statistical distribution of free volume, the angle of Spinodal morphology and the effect of inner dimension on the mechanical properties of Spinodal decomposition metal glass composites were analyzed. The angle effect is beneficial to the plasticity of the metal glass, while the intrinsic size effect follows the minimum size compatibility principle, that is, when the size of the phase separation structure is larger than the minimum shear band deformation size, the intrinsic size effect in the phase analysis does not work. At the same time, the size, volume percentage and kind of particle reinforced phase resolved by Bindal phase and the influence of matrix effect on the mechanical properties of multiphase metal glass were analyzed.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG139.8

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