非晶组分设计和非晶形成能力的热力学研究

发布时间：2018-05-19 22:31

  本文选题：热力学特征 + 熔化熵　； 参考：《燕山大学》2016年博士论文

【摘要】：开发新的非晶合金体系、探究非晶化转变的本质一直是非晶合金领域的主旋律,这两个问题的解决都需要对非晶化转变从热力学和动力学两方面系统研究。一直以来,相关研究主要集中在动力学方面,热力学的研究相对较少。已有的热力学研究主要关注合金熔体的混合焓(ΔH_(mix))、构型熵和稳定晶相的热力学驱动力(ΔG_(l-c))。相对于ΔG_(l-c)和ΔH_(mix),熵更能反映不同状态结构的差异,因此应与非晶化转变存在更根本的关联,但有关熵的研究很少报道。再则,亚稳相在非晶化转变中具有重要作用,认识亚稳态的热力学特征具有重要意义。本课题旨在探讨非晶化转变过程中热力学因素的作用(尤其是亚稳态的热力学特征和非晶化转变的关系)。首先以小分子样品邻甲基苯甲酸甲酯(MOT 99%)和对甲基苯甲酸甲酯(MPT99%)构成的二元体系为研究对象,分别探讨动力学和热力学因素与非晶形成能力的关联性。为此采用差式量热扫描仪(DSC)研究了不同组分体系的非晶转变、晶化和熔化行为;研究了约化玻璃转变温度、过冷液区和组分的关系,确定了最佳非晶形成区,并勾画体系的相图。采用宽频介电谱仪研究了动力学行为和温度、组分的关系。讨论了动力学、热力学因素对非晶组分的影响;发现动力学因素使最佳非晶组分趋于共晶点,热力学因素使最佳组分偏离共晶点。基于五种不同类型简单共晶体系的分析,发现最佳非晶组分在共晶组分和共晶线等分点之间。基于相图计算方法(CALPHAD)得到的自由能数据,研究确定了四种不同类型二元共晶合金的无溶质分配固溶体相的热力学特征量。结合稳定晶相的熔化焓和熔化熵,发现两相的熔化熵之差和非晶形成能力、组元间相互作用、混合焓强相关。两晶相的熔化熵之差越小,体系的非晶形成能力越高,组元间的相互作用越强,混合焓越负。基于过冷液体、非晶合金和二十面体准晶相似的局域结构特征,对准晶形成体系Zr_(40)Ti_(40)Ni_(20)掺杂金属Co和Be,制备了系列非晶合金,确定了体系的最佳非晶组分。研究了非晶样品的晶化行为,发现具有特殊热力学特征的准晶相作为初晶相可以提高体系的非晶形成能力。采用分子动力学模拟方法研究了体系结构随组分的变化。模拟结果表明Be的添加提高并且扭曲了熔体中的二十面体和类二十面体短程序,这既确保了准晶的首要竞争相地位,同时又使准晶的析出变得困难,从而导致体系的非晶和准晶形成能力可以同步提高。本工作还发现(Zr_(40)Ti_(40)Ni_(20))_(100-x)Be_x合金体系的非晶和准晶形成能力在很宽成分范围内同步提高。
[Abstract]:The development of new amorphous alloy systems and the exploration of the nature of the amorphous transition are the main themes in the field of amorphous alloys. The solution of these two problems requires a systematic study on the thermodynamics and kinetics of the amorphous transition. All along, the related research mainly concentrates on the dynamics, the thermodynamics research is relatively few. The existing thermodynamic studies mainly focus on the mixture enthalpy (螖 H / C) of the alloy melt, the configuration entropy and the thermodynamic driving force of the stable crystalline phase (螖 G / T). Compared with 螖 G / C) and 螖 H / C / C, entropy can better reflect the difference of different state structures, so there should be a more fundamental relationship between entropy and amorphous transition, but there are few reports on entropy. Furthermore, metastable phase plays an important role in the amorphous transition, and it is of great significance to understand the thermodynamic characteristics of metastable state. The purpose of this paper is to investigate the role of thermodynamic factors in the process of amorphous transition (especially the relationship between the thermodynamic characteristics of metastable state and the amorphous transition). Firstly, the binary system consisting of a small molecular sample of methyl o-methylbenzoate (MOT99) and a binary system consisting of methyl p-methylbenzoate (MPT99) was used to study the relationship between kinetic and thermodynamic factors and the ability of amorphous formation. For this reason, the amorphous transformation, crystallization and melting behavior of different component systems were studied by differential calorimeter (DSCS), and the transformation temperature of reduced glass, the relationship between supercooled liquid region and composition were studied, and the optimum amorphous formation zone was determined. And draw the phase diagram of the system. The relationship between kinetic behavior, temperature and composition was studied by broadband dielectric spectrometer. The effects of kinetic and thermodynamic factors on the amorphous components are discussed, and it is found that the kinetic factors make the optimum amorphous components tend to eutectic points, and the thermodynamic factors make the optimum components deviate from the eutectic points. Based on the analysis of five kinds of simple eutectic systems, it is found that the optimum amorphous components are between eutectic components and eutectic lines. Based on the free energy data obtained by the method of phase diagram calculation, the thermodynamic characteristics of four different types of binary eutectic alloys without solute partitioning solid solution phase were studied. In combination with the melting enthalpy and melting entropy of the stable crystalline phase, it is found that the difference of the melting entropy of the two phases and the ability of amorphous formation, the interaction between components, and the strong correlation of the mixing enthalpy are found. The smaller the difference of melting entropy between the two phases is, the higher the amorphous formation ability of the system is, the stronger the interaction between the components is, and the negative the mixing enthalpy is. Based on the local structural characteristics of supercooled liquid, amorphous alloy and icosahedron quasicrystal, a series of amorphous alloys were prepared by doping Co and Bein with Zr40TiS40 / NiS20). The optimum amorphous components of the system were determined. The crystallization behavior of amorphous samples was studied. It was found that quasicrystalline phase with special thermodynamic characteristics as primary phase could improve the amorphous formation ability of the system. Molecular dynamics simulation method was used to study the change of system structure with composition. The simulation results show that the addition of be increases and distorts the icosahedron and icosahedron short programs in the melt, which ensures the primary competitive phase position of quasicrystals and makes the precipitation of quasicrystals difficult. As a result, the amorphous and quasicrystalline formation ability of the system can be improved simultaneously. It has also been found that the amorphous and quasicrystalline formation ability of the ZR / ZR _ (40) T _ (40) TiP _ (40) / Nis / T _ (20) / T _ (100) B _ (x) B _ (x) alloy system increases synchronously in a wide range of compositions.
【学位授予单位】：燕山大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG139.8
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本文编号：1911984