本文關(guān)鍵詞：Al及其合金異質(zhì)形核過冷度與形核界面的相關(guān)性　出處：《上海交通大學》2015年博士論文　論文類型：學位論文

  更多相關(guān)文章： 異質(zhì)形核 晶體取向 過冷度 晶格錯配度 潤濕

【摘要】：形核問題一直在金屬凝固過程研究中占有重要地位,而界面行為是影響形核的主要因素。本文主要研究Al熔體形核過程中的界面特征及其影響因素,用氣懸浮技術(shù)測得了純Al及其添加了合金元素(Ti、Ce、Sb)的合金的本征過冷度,并選用不同取向的氧化物單晶(六種取向的Al_2O_3和三種取向的MgO)作為基底,測定了高真空環(huán)境下異質(zhì)相基底觸發(fā)金屬熔體形核的過冷度及熔體與異質(zhì)相基底之間的潤濕角,運用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觀結(jié)構(gòu)和生成相,并基于Bramfitt的二維晶格匹配模型,異質(zhì)相外延形核等模型探討了形核相與異質(zhì)相間的晶格匹配度與異質(zhì)相觸發(fā)形核的過冷度、形核機制、熔體/異質(zhì)相間潤濕性的關(guān)系以及合金元素對形核過程的影響。獲得了如下主要結(jié)果:1.在界面晶格錯配度較小(f14%)的情況下,過冷度和晶格錯配度的平方成正比:與形核相晶格匹配度越好的異質(zhì)相,其觸發(fā)形核所需的過冷度越小,隨著晶格錯配度的增加,所需形核過冷度逐漸增大。而當f14%時,上述基體觸發(fā)熔體形核的過冷度隨著錯配度的增加而減小。2.通過TEM的觀察,在f14%時,Al/Al_2O_3的界面是平直的,新相Al直接在Al_2O_3的表面形核生長,未出現(xiàn)中間應(yīng)變層;在f14%時,形核界面處發(fā)現(xiàn)一層幾十到幾百納米厚度的存在應(yīng)變的Al中間層,這層應(yīng)變層充滿微孿晶缺陷。3.新相和基底存在錯配時最先生成的應(yīng)變層可以通過原子的晶格畸變、引入位錯或?qū)\晶等晶體缺陷來釋放新相與基底之間的界面能。當晶格錯配度f3.1%時,界面能可以通過新相晶格的彈性畸變能和錯配能完全釋放,即Etotal=Eε+Em。當晶格錯配度在3.1%f5.8%范圍內(nèi),界面能通過晶格的彈性應(yīng)變能和引入刃型位錯的位錯能釋放,即Etotal=Es+Eed。當晶格錯配度在5.8%f14%范圍內(nèi),界面能通過晶格的彈性應(yīng)變能和引入螺型位錯的位錯能釋放,即Etotal=Es+Esd。當晶格錯配度f14%時,界面能通過晶格的彈性應(yīng)變能和引入孿晶的孿晶能釋放,即Etotal=Es+ET。4.Al/Mg O異質(zhì)形核體系其形核過冷度不受基體MgO的晶格取向影響,其原因在于界面處生成MgAl2O4層。該層MgAl2O4覆蓋了整個Al/MgO界面,成為新的形核基底。因此即使采用不同的MgO基底,其得到Al熔體形核的過冷度趨于一致。5.合金元素的添加可以通過生成新的金屬間化合物影響形核過程,從而改變?nèi)垠w形核的過冷度及晶粒取向。6.對潤濕角的測量發(fā)現(xiàn)Al熔體對不同取向的單晶氧化物的潤濕性存在差異。比較連續(xù)的中間Al層對于潤濕性有很大的改善,不存在中間層時,潤濕性隨著錯配度的增加而變差。
[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.

【學位授予單位】：上海交通大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG146.21

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