發(fā)布時間：2018-05-19 22:31

  本文選題：熱力學特征 + 熔化熵��； 參考：《燕山大學》2016年博士論文

【摘要】：開發(fā)新的非晶合金體系、探究非晶化轉變的本質一直是非晶合金領域的主旋律,這兩個問題的解決都需要對非晶化轉變從熱力學和動力學兩方面系統(tǒng)研究。一直以來,相關研究主要集中在動力學方面,熱力學的研究相對較少。已有的熱力學研究主要關注合金熔體的混合焓(ΔH_(mix))、構型熵和穩(wěn)定晶相的熱力學驅動力(ΔG_(l-c))。相對于ΔG_(l-c)和ΔH_(mix),熵更能反映不同狀態(tài)結構的差異,因此應與非晶化轉變存在更根本的關聯(lián),但有關熵的研究很少報道。再則,亞穩(wěn)相在非晶化轉變中具有重要作用,認識亞穩(wěn)態(tài)的熱力學特征具有重要意義。本課題旨在探討非晶化轉變過程中熱力學因素的作用(尤其是亞穩(wěn)態(tài)的熱力學特征和非晶化轉變的關系)。首先以小分子樣品鄰甲基苯甲酸甲酯(MOT 99%)和對甲基苯甲酸甲酯(MPT99%)構成的二元體系為研究對象,分別探討動力學和熱力學因素與非晶形成能力的關聯(lián)性。為此采用差式量熱掃描儀(DSC)研究了不同組分體系的非晶轉變、晶化和熔化行為;研究了約化玻璃轉變溫度、過冷液區(qū)和組分的關系,確定了最佳非晶形成區(qū),并勾畫體系的相圖。采用寬頻介電譜儀研究了動力學行為和溫度、組分的關系。討論了動力學、熱力學因素對非晶組分的影響;發(fā)現(xiàn)動力學因素使最佳非晶組分趨于共晶點,熱力學因素使最佳組分偏離共晶點�；�于五種不同類型簡單共晶體系的分析,發(fā)現(xiàn)最佳非晶組分在共晶組分和共晶線等分點之間�；�于相圖計算方法(CALPHAD)得到的自由能數(shù)據(jù),研究確定了四種不同類型二元共晶合金的無溶質分配固溶體相的熱力學特征量。結合穩(wěn)定晶相的熔化焓和熔化熵,發(fā)現(xiàn)兩相的熔化熵之差和非晶形成能力、組元間相互作用、混合焓強相關。兩晶相的熔化熵之差越小,體系的非晶形成能力越高,組元間的相互作用越強,混合焓越負�；�于過冷液體、非晶合金和二十面體準晶相似的局域結構特征,對準晶形成體系Zr_(40)Ti_(40)Ni_(20)摻雜金屬Co和Be,制備了系列非晶合金,確定了體系的最佳非晶組分。研究了非晶樣品的晶化行為,發(fā)現(xiàn)具有特殊熱力學特征的準晶相作為初晶相可以提高體系的非晶形成能力。采用分子動力學模擬方法研究了體系結構隨組分的變化。模擬結果表明Be的添加提高并且扭曲了熔體中的二十面體和類二十面體短程序,這既確保了準晶的首要競爭相地位,同時又使準晶的析出變得困難,從而導致體系的非晶和準晶形成能力可以同步提高。本工作還發(fā)現(xiàn)(Zr_(40)Ti_(40)Ni_(20))_(100-x)Be_x合金體系的非晶和準晶形成能力在很寬成分范圍內(nèi)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.
【學位授予單位】：燕山大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG139.8
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本文編號：1911984