【摘要】：在自然界、冶金技術(shù)以及材料制備過(guò)程中,凝固是一種非常普遍的物理現(xiàn)象。凝固廣泛存在于各個(gè)領(lǐng)域,物體從液體轉(zhuǎn)變?yōu)楣腆w都要經(jīng)歷凝固過(guò)程。凝固開(kāi)始于形核,形核又可以分為均質(zhì)形核和異質(zhì)形核。在實(shí)際生產(chǎn)中,大多數(shù)的形核過(guò)程都是異質(zhì)形核,因此研究固相粒子對(duì)熔體結(jié)構(gòu)以及凝固過(guò)程的影響有著非常重要的意義。本論文利用分子動(dòng)力學(xué)方法研究了楔形襯底以及受限空間對(duì)熔體的結(jié)構(gòu)以及凝固行為的影響,揭示了襯底與熔體結(jié)構(gòu)以及凝固組織之間的內(nèi)在關(guān)聯(lián)性。研究結(jié)果對(duì)于通過(guò)控制異質(zhì)形核從而改善材料的宏觀性能有著重要的意義。全文的主要內(nèi)容如下:(1)研究了楔形襯底如何將結(jié)構(gòu)信息傳遞給正在生長(zhǎng)的晶體,進(jìn)一步影響凝固過(guò)程。結(jié)果顯示,由于襯底的誘導(dǎo)作用靠近襯底的銅熔體在液固界面處分層形成一個(gè)"V"形結(jié)構(gòu),并且有形成孿晶的趨勢(shì)。但是隨著與襯底間距離的增加,襯底的誘導(dǎo)作用逐漸減弱致使銅熔體逐漸恢復(fù)其固有的結(jié)構(gòu)。當(dāng)楔形角為90°時(shí),由于銅原子內(nèi)部良好的晶格匹配,凝固組織是一個(gè)理想晶體。此外,冷卻速率以及襯底的原子排列方式對(duì)銅熔體的凝固組織也有很大的影響。這些研究結(jié)果有利于理解異質(zhì)凝固過(guò)程中,襯底與凝固組織之間的遺傳關(guān)系。(2)研究了鋁熔體在受限狹縫內(nèi)以及Fe襯底上的異質(zhì)形核過(guò)程。與孤立襯底相比,受限狹縫可以促進(jìn)鋁熔體的結(jié)晶,同時(shí)狹縫的尺寸對(duì)凝固組織有很大的影響。在對(duì)稱的受限狹縫內(nèi),Al原子可以根據(jù)襯底的堆垛模型進(jìn)行排列,而在非對(duì)稱的受限狹縫內(nèi),Al原子的堆垛模型取決于襯底的構(gòu)成。對(duì)于Fe(110)-Fe(111)這種狹縫來(lái)說(shuō),由Fe(110)襯底誘導(dǎo)的凝固區(qū)域要大于由Fe(111)襯底誘導(dǎo)的凝固區(qū)域。此外,對(duì)于鋁熔體在由銅鐵兩種襯底構(gòu)成的非對(duì)稱受限空間我們也進(jìn)行了研究。這些結(jié)果闡明了受限空間對(duì)熔體異質(zhì)凝固過(guò)程的影響。(3)探究了在不同壓強(qiáng)下以及不同距離的兩個(gè)石墨烯之間,受限水的結(jié)構(gòu)演變。結(jié)果顯示,受限狹縫的尺寸以及壓強(qiáng)都能夠引起受限水的結(jié)構(gòu)演變,具體表現(xiàn)為層數(shù)以及堆垛方式的變化。隨著壓強(qiáng)以及狹縫間距的增加,受限水的分層現(xiàn)象也越來(lái)越明顯。此外,隨著壓強(qiáng)的增加,在受限狹縫內(nèi),近鄰水分子首先形成鏈狀結(jié)構(gòu),之后演變成正方形結(jié)構(gòu),最后轉(zhuǎn)變?yōu)槿切谓Y(jié)構(gòu)。這些結(jié)果有助于了解受限空間內(nèi)水的結(jié)構(gòu)演變。
[Abstract]:Solidification is a very common physical phenomenon in nature, metallurgical technology and material preparation. Solidification exists widely in various fields, and the transformation of objects from liquid to solid has to go through the solidification process. Solidification begins with nucleation, which can be divided into homogeneous nucleation and heterogeneous nucleation. In practical production, most nucleation processes are heterogeneous nucleation, so it is very important to study the influence of solid particles on melt structure and solidification process. In this paper, the effects of wedge-shaped substrate and confined space on the structure and solidification behavior of melt were studied by molecular dynamics method, and the intrinsic relationship between substrate and melt structure and solidification structure was revealed. The results are of great significance for improving the macroscopic properties of materials by controlling heterogeneous nucleation. The main contents of the thesis are as follows: (1) the structure information of the wedge substrate is transferred to the growing crystal, which further influences the solidification process. The results show that due to the inducement of substrates, copper melts near the substrates form a "V" shaped structure at the liquid-solid interface and have a tendency to form twins. However, with the increase of the distance between the substrate and the substrate, the inductive effect of the substrate gradually weakened, and the copper melt gradually restored its inherent structure. When the wedge angle is 90 擄, the solidified structure is an ideal crystal due to the good lattice matching within the copper atom. In addition, the cooling rate and the atomic arrangement of the substrate also have a great influence on the solidification structure of copper melt. These results are helpful to understand the genetic relationship between substrate and solidification structure during heterogeneous solidification. (2) the heterogeneous nucleation process of aluminum melt in confined slit and on Fe substrate is studied. Compared with the isolated substrate, the confined slit can promote the crystallization of aluminum melt, and the size of the slit has a great influence on the solidification microstructure. In a symmetric confined slit, Al atoms can be arranged according to the stacking model of the substrate, while in the asymmetric confined slit, the stacking model of the Al atom depends on the composition of the substrate. For the slit of Fe (110)-Fe (111), the solidification region induced by Fe (110) substrate is larger than that induced by Fe (111) substrate. In addition, we also study the asymmetric confined space of aluminum melt in two kinds of substrates, copper and iron. These results illustrate the effect of confined space on the process of heterogeneous solidification of melt. (3) the evolution of confined water structure between two graphene at different pressures and distances is investigated. The results show that both the size and the pressure of the confined slit can cause the evolution of the confined water structure, which is manifested by the change of the number of layers and the way of stacking. With the increase of pressure and slit spacing, the stratification of confined water becomes more and more obvious. In addition, with the increase of pressure, in the confined slit, the near neighbor water molecules first form chain structure, then develop into square structure, and finally transform into triangular structure. These results help to understand the structural evolution of water in confined spaces.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG21

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