過去幾十年當中，金屬玻璃（包括塊狀金屬玻璃）中非晶相分離的發生已經成為了一個具有爭議性的課題。一些報告報導在具有負混合熱的Pd-Ni-P合金體系中發生了非晶相分離。然而，有一些報告聲稱相分離不能在Pd-Ni-P非晶合金中被觀察到。文獻分析表明，困難在於缺乏直接的實驗證據。 / 為了解決這個難題，示差掃描量熱儀、高分辨電子顯微鏡、掃描透射模式下的高角環射暗場相、以及能量色散X射線光譜儀等檢測儀器在我們實驗當中被使用。同時為了清楚展示非晶相分離反應，在過冷Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅熔體被冷卻為固態非晶樣品之前引入了中間熱退火處理。 / 實驗研究了三種經由不同路徑製備的A、B、C型號樣品。結果表明在非晶/液態Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅合金中可能存在獨特的短程有序結構，它會導致相分離的發生。同时研究發現，在大約625 K，調幅分解的持續時間的下限大概是200 s。調幅分解的時間常數R在大約625 K 下為0.002 s⁻¹。三种类型样品在不同的溫度下被退火從而獲得部分的結晶。A型號和B型號具有相似的行為。在低溫下，圓形的核心首先形成，接著發生共晶反應。在高溫下，出現了一種形狀為立方體的析出相。在C型號的樣品當中，核心和立方的析出物同時被發現。但是核心的成分分佈與A和B型號中出現的不同。同時，隨著退火時間的加長形核的數量也具有獨特的行為表現。作為對比，Pd₄₀Ni₄₀P₂₀塊狀金屬玻璃的結晶行為也被展開了研究。同樣的，以形成核心開始，但是它的成分分佈異於A和B型號的樣品。 / Amorphous phase separation in metallic glass (including bulk metallic glass) has been a controversial issue in the past several decades. There are reports saying that amorphous phase separation occurs in Pd-Ni-P, which has a negative heat of mixing among its constituent elements. However, there are also as many reports claiming that phase separation is absent in amorphous Pd-Ni-P alloys. The lack of direct experimental evidence makes the issue to be difficult to be resolved. / To solve this problem, differential scanning calorimetry (DSC), high resolution transmission electron microscopy (HRTEM), high angle annular dark field (HAADF) in scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDX) have been employed. Intermediate thermal annealing is introduced before an undercooled Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ melt is cooled down to become a solid amorphous specimen. / A-type, B-type, and C-type specimens of composition, Pd₄₁.₂₅Ni₄₁.₂₅ P₁₇.₅, have been prepared via three different cooling paths. It was found that amorphous phase separation indeed occurs in C-type specimens. Results suggest that there may be unique short range orders in amorphous/liquid Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅, which are responsible for the phase separation. Experimental arrangements were made to study the occurrence of spinodal reaction in undercooled molten Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ alloys as a function of time. The lower bound of the duration of the spinodal decomposition at a temperature of {U+2248}625 K is about 200 s and the time constant R of the spinodal decomposition at a temperature of {U+2248}625 K is 0.002 s⁻¹. / A-type and B-type specimens have similar crystallization behavior. At low temperature, it starts with the formation of a spherical core and then eutectic crystallization takes over. At higher temperatures, an additional phase in the shape of a cube appears. In annealed C-type specimens, cores and cubic precipitates are also found. However, the composition profile of the cores is different and the number of nucleation events versus time has peculiar characteristics. The crystallization behavior of Pd₄₀Ni₄₀P₂₀ BMG was studied for comparison. It again starts out with the formation of a core, but with a composition profile different from those of A-type and B-type specimens. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lan, Si = 對於具有負混合熱的塊狀金屬玻璃非晶相分離的研究 / 蘭司. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstract also in Chinese. / Lan, Si = Dui yu ju you fu hun he re de kuai zhuang jin shu bo li fei jing xiang fen li de yan jiu / Lan Si. / Abstract of thesis --- p.i / Acknowledgements --- p.v / List of Tables --- p.x / List of Figures --- p.xi / Chapter Chapter 1 --- Introduction and literature review --- p.1 / Chapter 1.1 --- Introduction to metallic glasses --- p.1 / Chapter 1.1.1 --- Background of metallic glasses --- p.1 / Chapter 1.1.2 --- Glass transition --- p.2 / Chapter 1.1.3 --- The undercooling of liquids --- p.3 / Chapter 1.1.4 --- Crystal nucleation and growth in liquids --- p.3 / Chapter 1.1.4.1 --- Crystal Nucleation in liquids --- p.3 / Chapter 1.1.4.2 --- Crystal growth in liquids --- p.5 / Chapter 1.1.4.3 --- TTT diagram --- p.6 / Chapter 1.1.4.4 --- Crystallization in metallic glasses --- p.6 / Chapter 1.1.5 --- Glass formation methods and systems --- p.6 / Chapter 1.1.6 --- Glass forming ability and criteria --- p.8 / Chapter 1.1.7 --- Properties and applications --- p.9 / Chapter 1.2 --- The basic theory of phase separation in a binary system --- p.10 / Chapter 1.2.1 --- Thermodynamic background --- p.10 / Chapter 1.2.2 --- Solid state phase separation --- p.11 / Chapter 1.2.2.1 --- A miscibility gap of binary mixture --- p.11 / Chapter 1.2.2.2 --- Nucleation and growth mechanism --- p.12 / Chapter 1.2.2.3 --- Spinodal decomposition mechanism --- p.13 / Chapter 1.2.3 --- Liquid state miscibility gap in a binary system --- p.21 / Chapter 1.3 --- Literature review for phase separation in metallic glasses --- p.23 / Chapter 1.4 --- The aim of this thesis --- p.28 / Figures --- p.30 / References --- p.39 / Chapter Chapter 2 --- Experiments and characterization --- p.44 / Chapter 2.1 --- Introduction and the outline of the experiments --- p.44 / Chapter 2.2 --- Sample preparation --- p.45 / Chapter 2.2.1 --- Bulk metallic glasses preparation --- p.45 / Chapter 2.2.1.1 --- Preparation of clean fused silica tubes --- p.45 / Chapter 2.2.1.2 --- Weighing --- p.46 / Chapter 2.2.1.3 --- Alloying --- p.46 / Chapter 2.2.1.4 --- Fluxing --- p.47 / Chapter 2.2.2 --- Thermal annealing --- p.49 / Chapter 2.2.3 --- Specimens preparation for characterization --- p.50 / Chapter 2.2.3.1 --- Cutting, molding, grinding and polishing --- p.50 / Chapter 2.2.3.2 --- Etching --- p.51 / Chapter 2.2.3.3 --- Thinning for TEM foils --- p.51 / Chapter 2.3 --- Characterization --- p.55 / Chapter 2.3.1 --- Differential scanning calorimetry (DSC) --- p.55 / Chapter 2.3.2 --- Scanning electron microscopy (SEM) --- p.55 / Chapter 2.3.3 --- Transmission electron microscopy (CTEM and HRTEM) --- p.57 / Chapter 2.3.4 --- High angle annular dark field (HAADF) in Scanning transmission electron microscopy (STEM) --- p.58 / Chapter 2.3.5 --- Energy dispersive X-ray spectroscopy (EDX) --- p.59 / Figures --- p.62 / References --- p.69 / Chapter 3 --- p.70 / Chapter 3.1 --- Introduction --- p.70 / Chapter 3.2 --- Materials and Experimental --- p.73 / Chapter 3.3 --- Results --- p.75 / Chapter 3.3.1 --- Thermal behaviors of three types of specimens --- p.75 / Chapter 3.3.2 --- Microstructures of three types of specimens --- p.75 / Chapter 3.3.2.1 --- A-type specimens --- p.75 / Chapter 3.3.2.2 --- B-type specimens --- p.76 / Chapter 3.3.2.3 --- C-type specimens --- p.76 / Chapter 3.4 --- Discussion --- p.78 / Chapter 3.5 --- Conclusions --- p.79 / Chapter 3.6 --- Afterward --- p.79 / Figures --- p.80 / References --- p.89 / Chapter Chapter 4 --- The time constant of the spinodal decomposition in Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ bulk metallic glasses --- p.92 / Chapter 4.1 --- Introduction --- p.92 / Chapter 4.2 --- Materials and experimental --- p.92 / Chapter 4.3 --- Results --- p.94 / Chapter 4.3.1 --- Thermal behaviors --- p.94 / Chapter 4.3.2 --- Microstructures --- p.94 / Chapter 4.4 --- Discussion --- p.96 / Chapter 4.5 --- Conclusions --- p.98 / Figures --- p.100 / References --- p.123 / Chapter Chapter 5 --- Crystallization in homogeneous and phase-separated Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ bulk metallic glasses --- p.125 / Chapter 5.1 --- Introduction --- p.125 / Chapter 5.2 --- Experiments --- p.126 / Chapter 5.3 --- Results --- p.128 / Chapter 5.3.1 --- Low temperature thermal annealing at 613 K with 0≤t{U+2090} ≤ 8 h --- p.128 / Chapter 5.3.1.1 --- A-type and B-type specimens --- p.128 / Chapter 5.3.1.2 --- C-type specimens --- p.130 / Chapter 5.3.1.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.132 / Chapter 5.3.2 --- High temperature thermal annealing --- p.133 / Chapter 5.3.2.1 --- A-type and B-type specimens --- p.133 / Chapter 5.3.2.2 --- C-type specimens --- p.135 / Chapter 5.3.2.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.137 / Chapter 5.4 --- Discussion --- p.137 / Chapter 5.4.1 --- Formation of spherical cores --- p.138 / Chapter 5.4.1.1 --- A-type and B-type Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ specimens --- p.138 / Chapter 5.4.1.2 --- C-type Pd₄₁.₇₅Ni₄₁.₇₅P₁₇.₅ specimens --- p.139 / Chapter 5.4.1.3 --- Pd₄₀Ni₄₀P₂₀ BMG --- p.140 / Chapter 5.4.2 --- Formation of cubic precipitates --- p.141 / Tables --- p.142 / Figures --- p.144 / References --- p.188 / Chapter Chapter 6 --- Conclusions --- p.190 / Bibliography --- p.192
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_328394 |
| Date | January 2012 |
| Contributors | Lan, Si., Chinese University of Hong Kong Graduate School. Division of Materials Science and Engineering. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography |
| Format | electronic resource, electronic resource, remote, 1 online resource (xx, 192 leaves) : ill. (some col.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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