Al及其合金异质形核过冷度与形核界面的相关性

发布时间：2018-01-16 08:30

本文关键词：Al及其合金异质形核过冷度与形核界面的相关性　出处：《上海交通大学》2015年博士论文　论文类型：学位论文

【摘要】：形核问题一直在金属凝固过程研究中占有重要地位,而界面行为是影响形核的主要因素。本文主要研究Al熔体形核过程中的界面特征及其影响因素,用气悬浮技术测得了纯Al及其添加了合金元素(Ti、Ce、Sb)的合金的本征过冷度,并选用不同取向的氧化物单晶(六种取向的Al_2O_3和三种取向的MgO)作为基底,测定了高真空环境下异质相基底触发金属熔体形核的过冷度及熔体与异质相基底之间的润湿角,运用SEM(Scanning Electronic Microscopy),EDS(Energy Dispersive Spectrometer),XRD(X-Ray Diffraction),TEM(Transmission Electron Microscopy),HRTEM(High Resolution Transmission Electron Microscopy)等方式考察了界面微观结构和生成相,并基于Bramfitt的二维晶格匹配模型,异质相外延形核等模型探讨了形核相与异质相间的晶格匹配度与异质相触发形核的过冷度、形核机制、熔体/异质相间润湿性的关系以及合金元素对形核过程的影响。获得了如下主要结果:1.在界面晶格错配度较小(f14%)的情况下,过冷度和晶格错配度的平方成正比:与形核相晶格匹配度越好的异质相,其触发形核所需的过冷度越小,随着晶格错配度的增加,所需形核过冷度逐渐增大。而当f14%时,上述基体触发熔体形核的过冷度随着错配度的增加而减小。2.通过TEM的观察,在f14%时,Al/Al_2O_3的界面是平直的,新相Al直接在Al_2O_3的表面形核生长,未出现中间应变层;在f14%时,形核界面处发现一层几十到几百纳米厚度的存在应变的Al中间层,这层应变层充满微孪晶缺陷。3.新相和基底存在错配时最先生成的应变层可以通过原子的晶格畸变、引入位错或孪晶等晶体缺陷来释放新相与基底之间的界面能。当晶格错配度f3.1%时,界面能可以通过新相晶格的弹性畸变能和错配能完全释放,即Etotal=Eε+Em。当晶格错配度在3.1%f5.8%范围内,界面能通过晶格的弹性应变能和引入刃型位错的位错能释放,即Etotal=Es+Eed。当晶格错配度在5.8%f14%范围内,界面能通过晶格的弹性应变能和引入螺型位错的位错能释放,即Etotal=Es+Esd。当晶格错配度f14%时,界面能通过晶格的弹性应变能和引入孪晶的孪晶能释放,即Etotal=Es+ET。4.Al/Mg O异质形核体系其形核过冷度不受基体MgO的晶格取向影响,其原因在于界面处生成MgAl2O4层。该层MgAl2O4覆盖了整个Al/MgO界面,成为新的形核基底。因此即使采用不同的MgO基底,其得到Al熔体形核的过冷度趋于一致。5.合金元素的添加可以通过生成新的金属间化合物影响形核过程,从而改变熔体形核的过冷度及晶粒取向。6.对润湿角的测量发现Al熔体对不同取向的单晶氧化物的润湿性存在差异。比较连续的中间Al层对于润湿性有很大的改善,不存在中间层时,润湿性随着错配度的增加而变差。
[Abstract]:The nucleation problem has played an important role in the study of metal solidification process, and the behavior of the interface is the main factor affecting the nucleation. The interface characteristics and influence factors of this paper studies the Al nucleation in the melt in the process of gas suspension technology obtained pure Al and adding alloy elements (Ti, Ce, Sb) of the alloy. The degree of supercooling, and different oxide single crystal orientation (six orientations of Al_2O_3 and three oriented MgO) as the substrate, were measured under high vacuum environment of heterogeneous nucleation in the melt phase substrate metal trigger the wettability between cold and melt and the heterogeneity of basal angle, using SEM (Scanning Electronic Microscopy EDS (Energy), Dispersive Spectrometer), XRD (X-Ray Diffraction), TEM (Transmission Electron Microscopy), HRTEM (High Resolution Transmission Electron Microscopy) and investigated the interface microstructure and phase formation, Based on Bramfitt, and two-dimensional lattice model, nucleation model of heterogeneous phase epitaxial nucleation and heterogeneous phase of lattice mismatch and heterogeneous phase nucleation undercooling, nucleation mechanism, effects of melt / heterogeneity between the wettability and alloying elements on the nucleation process. The main results are given are as follows: 1. in the interface lattice mismatch is smaller (f14%) under the condition of undercooling and lattice mismatch is proportional to the square of the nucleation phase and heterogeneous lattice matching degree and better phase, the nucleation undercooling required is small, with the lattice mismatch increases, the for the nucleation undercooling increases gradually. And when f14%, the substrate triggered the nucleation in the melt undercooling increases with misfit decreases.2. observed by TEM, f14%, Al/Al_2O_3 interface is flat, the new phase Al directly on the surface of Al_2O_3 nucleation and growth, no intermediate The strain in f14% layer; when the nucleation at the interface to find the Al middle layer strain of a layer of tens to hundreds of nanometers in thickness of the strained layer this layer of strained layer full of microtwin defects in.3. new phase and base mismatch can be generated by the first atomic lattice distortion, the dislocation or twin crystal defects to release between the new phase and substrate interface. When the lattice mismatch of f3.1% interface, can be through the new phase elastic distortion energy and lattice mismatch can be fully released, namely Etotal=E e +Em. when the lattice mismatch in the range of 3.1%f5.8%, the interface can release through the elastic strain energy and lattice dislocation introduced edge dislocation that is, when the Etotal=Es+Eed. lattice mismatch in the range of 5.8%f14%, the interface energy release through dislocation elastic strain energy and the lattice dislocation, that is Etotal=Es+Esd. when the lattice mismatch between f14% interface, can pass through a lattice The elastic strain energy and energy release into the twin twin, namely Etotal=Es+ET.4.Al/Mg O heterogeneous nucleation system the nucleation undercooling is not affected by the crystal orientation effect of matrix MgO, the reason is that the MgAl2O4 layer formed at the interface. The MgAl2O4 layer covering the entire Al/MgO interface, a new nucleation. Therefore, even with the MgO substrate different from Al, the nucleation in the melt undercooling consistent.5. alloy elements added can generate new intermetallic compounds affect the nucleation process, thus changing the nucleation in the melt undercooling and grain orientation of.6. revealed the presence of Al melt wettability on single crystal oxide with different orientation difference on the measurement of wetting angle. The middle Al layer for Continuous Wetting have greatly improved, there is no intermediate layer, wettability with increasing misfit and worse.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.21

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