CuZr非晶合金玻璃形成能力、塑性变形单元及晶化问题的原子尺度理论研究

发布时间：2018-05-07 22:21

本文选题：非晶合金 + 玻璃形成能力　；参考：《上海大学》2015年博士论文

【摘要】：非晶合金具有优异的物理、化学、磁学性能,这使得非晶合金具有巨大的潜在应用前景,但尺寸问题及塑性变形问题制约着它们的实际应用。为了给寻找尺寸更大、塑性变形能力更好的非晶合金提供理论指导,本论文在原子尺度研究了非晶合金的玻璃形成能力、塑性变形单元及晶化问题:(1)玻璃形成能力的研究。借助分解的Morse势,本论文首次把合金的混合焓分解为三部分,!Enn、!Estrain和!Ennn。!Enn反映不同元素间的化学作用;!Estrain反映局部有序结构的结构匹配特性(物理作用);!Ennn反映次近邻以外原子间相互作用。根据“化学作用”、“物理作用”在玻璃形成能力中所占决定性作用的不同,本论文把非晶合金分为“化学作用主导”型和“应变能主导”型。本论文提出!Enn和(!Enn/2+!Estrain)能量判据,它可预测合金体系在A50B50成分点处的玻璃形成能力强弱。(2)塑性变形单元的研究。本论文揭示了非晶处于亚稳态的本质原因:局部化学成分和局部结构的不均匀性;原子间的相互作用势呈现出非线性和非谐性特征。体系通过Voronoi cell划分成不同类型多面体。通过对不同类型的多面的键长进行统计分布,结果表明越不稳定的多面体其严重压缩键越多(导致其对外界刺激更敏感),且其长键数目也越多(导致其具有大的体积和小的变形能垒)。因此,本论文提出相对更不稳定的多面体是非晶变形单元(deformation units)的结构起源。Cu50Zr50体系压缩模拟结果表明塑性变形集中区域趋向于在这些不稳定的区域形成,进一步验证了此结论。(3)过冷液态合金晶化机理的研究。本论文通过模拟方法具体研究了Ni50Al50、Cu15Zr85和Cu50Zr50三个体系的晶化过程。Ni50Al50体系晶化是由于强的Ni-Al化学成键作用;无Zr-Cu强化学键作用的Cu15Zr85体系晶化是由体系应变能降低作为驱动力。本论文以Q6、CSRO为反应坐标并通过metadynamics方法模拟了Cu50Zr50非晶体系的晶化过程。通过模拟过程中添加高斯偏势方法,本论文得到了Cu50Zr50非晶体系的晶化能垒和自由能势能面。基于metadynamics方法获得的合金熔点Tm和!Sf并结合热力学积分公式!Sf与Toc的关系,本论文得到了Cu50Zr50体系理想玻璃转变温度Toc。
[Abstract]:Amorphous alloys have excellent physical, chemical and magnetic properties, which make amorphous alloys have great potential applications, but their practical applications are restricted by size problems and plastic deformation problems. In order to provide theoretical guidance for finding amorphous alloys with larger size and better plastic deformation capacity, the glass forming capacity, plastic deformation unit and crystallization problem of glass forming capacity of amorphous alloys have been studied in this paper at atomic scale. With the help of the decomposed Morse potential, In this paper, the mixing enthalpy of the alloy is first decomposed into three parts: Ennn strain and Ennn. Enn reflect the chemical action among different elements. The Estrain reflects the structural matching characteristics of the local ordered structure. (the physical action of Enn reflects the interaction between atoms outside the next nearest neighbor. According to the difference of "chemical action" and "physical action" in glass forming ability, the amorphous alloys are divided into two types: "chemical action leading" type and "strain energy leading" type. In this paper, the energy criterion of Enn and Enn / 2 / Estrain is proposed, which can predict the glass-forming ability of alloy system at the point of A50B50 composition. In this paper, the essential reasons for the metastable state of amorphous crystals are revealed: the inhomogeneity of local chemical composition and local structure, and the nonlinear and anharmonic characteristics of the interaction potential between atoms. The system is divided into different types of polyhedron by Voronoi cell. By statistical distribution of different types of multiplanar bond lengths, The results show that the more unstable polyhedron has more serious compression bonds (which leads to its more sensitive to external stimuli, and the more the number of long bonds), which leads to its large volume and small deformable energy barrier. Therefore, in this thesis, it is suggested that the relatively unstable polyhedron is the structural origin of the amorphous deformation unit deformations. The results of compression simulation of the Cu50Zr50 system indicate that the concentrated plastic deformation regions tend to form in these unstable regions. The crystallization mechanism of the supercooled liquid alloy was further verified. In this paper, the crystallization process of Ni50Al50 / Cu15Zr85 and Cu50Zr50 systems is studied by simulation. The crystallization of Ni50Al50 system is due to strong chemical bonding of Ni-Al, and the crystallization of Cu15Zr85 system without strong Zr-Cu chemical bond is driven by the decrease of system strain energy. In this thesis, the crystallization process of Cu50Zr50 amorphous system was simulated by metadynamics method, using Q6 CSRO as the reaction coordinate. In this paper, the crystallization energy barrier and free energy potential surface of Cu50Zr50 amorphous system are obtained by adding Gao Si bias method in the simulation process. Based on the melting point TM and Sf obtained by metadynamics method and the relation between SF and Toc, the ideal glass transition temperature (Toct) of Cu50Zr50 system has been obtained in this paper.
【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG139.8

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