本文選題：晶體相場方法　切入點：應(yīng)變　出處：《廣西大學》2015年碩士論文

【摘要】：納米金屬材料微觀結(jié)構(gòu)決定了材料的性能,掌握納米金屬材料的晶體結(jié)構(gòu)和缺陷(空位、位錯)、晶界以及晶粒大小對探究納米金屬材料的塑性變形的機制是具有重要的指導(dǎo)意義。對納米金屬材料,位錯可作為其塑性變形機制的主導(dǎo)作用,但當晶粒尺寸很小只有幾納米時,空位也將是其塑性變形機制中不可或缺的一種變形機制。由于納米金屬材料晶粒尺寸非常小,在實驗室實驗中時時觀察材料塑性變形的過程是具有一定難度,但計算機模擬實驗可以彌補實驗室實驗中的不足。晶體相場模型作為一種全新的計算機模擬實驗的模型,憑借其自身的優(yōu)越性已被廣泛的應(yīng)用到研究晶粒結(jié)構(gòu)領(lǐng)域中,利用該模型將空位和位錯同時作為研究納米材料的塑性變形機制是十分有意義的。因此,本文應(yīng)用空位晶體相場方程,首次研究了空位晶體相場方程在不同的晶體相中所表述的二維周期性形貌圖,并從溫度和壓應(yīng)力兩個外界因素分別討論了對單晶和多晶空位濃度的影響,本文所做的創(chuàng)新工作和取得主要成果如下：1、通過選取位于不同相的平均原子密度數(shù)值,呈現(xiàn)的是不同形貌的二維周期性晶體結(jié)構(gòu)的形貌圖,主要有六角“疙瘩”相、條狀相和六角“凹坑”相。當體系的平均原子密度數(shù)值足夠小時,體系中將有空位的出現(xiàn)；當平均原子密度數(shù)值為某些數(shù)值時,制備的為幾種相共存的形貌圖。這些不同相形貌圖可以用于解釋實驗室實驗中制備納米薄膜形貌圖。2、無論是單晶體系還是多晶體系,溫度對晶體中的空位濃度影響很大,并且體系呈現(xiàn)的形貌圖也是有差別的。當所處環(huán)境的溫度越高時,體系達到穩(wěn)定狀態(tài)時空位飽和濃度也就越高,但空位濃度的數(shù)量級仍保持在10-3～10-4數(shù)量級。當體系所處的環(huán)境溫度越高時,體系有空位出現(xiàn)所需的時間也越短,即體系中空位的形成速率大。說明空位濃度受溫度的影響較大。3、在相同的生長環(huán)境下,單晶中空位飽和濃度比多晶中空位飽和濃度要小,由于含有晶界的多晶更有利于空位的形成,并且空位會優(yōu)先選擇在晶界位錯處生長。在單晶中,晶粒達到穩(wěn)定狀態(tài)后只有空位的存在,而多晶體系,當晶體達到穩(wěn)定狀態(tài)會有空位和空位團的出現(xiàn)。4、無論是單晶還是多晶,晶體在壓應(yīng)力作用后晶體繼續(xù)產(chǎn)生大量空位,并且空位的數(shù)量遠大于受溫度影響產(chǎn)生的空位數(shù)量。多晶體系在壓應(yīng)力的作用下產(chǎn)生新空位,所需的應(yīng)力值要小于單晶體系。以上研究思路與結(jié)論,以期有助于利用晶體相場模型揭示空位在納米金屬材料的塑性變形過程中演變行為,進而探討其作用規(guī)律并對該模型今后應(yīng)用到具體材料中具有重要的指導(dǎo)意義。
[Abstract]:The microstructure of nanometallic materials determines the properties of materials, and the crystal structure and defects of nanometallic materials are mastered.Dislocation, grain boundary and grain size are of great significance in exploring the mechanism of plastic deformation of nanometallic materials.For nanometallic materials, dislocation can play a leading role in the plastic deformation mechanism, but when the grain size is very small and only a few nanometers, the vacancy will also be an indispensable deformation mechanism in the plastic deformation mechanism.Because the grain size of nanometallic materials is very small, it is difficult to observe the process of plastic deformation in laboratory experiments, but computer simulation experiments can make up for the deficiency in laboratory experiments.As a new computer simulation model, the crystal phase field model has been widely used in the research of grain structure by virtue of its own superiority.It is very meaningful to study the plastic deformation mechanism of nanomaterials by using the model to study both vacancies and dislocations.Therefore, in this paper, the two-dimensional periodic morphologies of the vacancy crystal phase field equations in different crystal phases are studied for the first time by using the vacancy crystal phase field equation.The effects of temperature and compressive stress on the concentration of single crystal and polycrystalline vacancy are discussed respectively. The main results of this paper are as follows: 1. The average atomic density in different phases is selected.There are hexagonal "pimples", stripe and hexagonal "pit" phases.When the average atomic density of the system is small enough, there will be vacancies in the system, and when the average atomic density is some values, the morphologies of several coexisting phases will be prepared.These morphologies can be used to explain the morphologies of nanocrystalline films prepared in laboratory experiments. Whether in single crystal system or polycrystalline system, the temperature has a great influence on the vacancy concentration in the crystal, and the morphologies of the system are also different.The higher the temperature of the system is, the higher the vacancy saturation concentration is when the system reaches the stable state, but the order of vacancy concentration is still in the order of 10 ~ (-3) ~ (-3) ~ (-4) ~ 10 ~ (-4).The higher the ambient temperature of the system is, the shorter it takes for the vacancies to appear in the system, that is, the higher the rate of the formation of vacancies in the system.Under the same growth environment, the vacancy saturation concentration in single crystal is smaller than that in polycrystalline, because the polycrystal with grain boundary is more favorable for the formation of vacancy.And the vacancy will be preferred to grow at the grain boundary dislocation.In a single crystal, there is only a vacancy when the crystal reaches a stable state, while in a polycrystalline system, when the crystal reaches a stable state, there will be vacancies and vacancy groups.A large number of vacancies continue to be produced after compressive stress, and the number of vacancies is much larger than that caused by temperature.A new vacancy is produced in polycrystalline system under compressive stress, and the required stress value is smaller than that of single crystal system.The above research ideas and conclusions are helpful to reveal the evolution of vacancies in the plastic deformation of nanometallic materials by using the crystal phase field model.Furthermore, it is of great significance for the application of the model to the concrete materials in the future.
【學位授予單位】：廣西大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB383.1

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本文編號：1704964