本文關(guān)鍵詞：表面張力各向異性對(duì)深胞晶生長的影響　出處：《北京科技大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 定向凝固 深胞晶 各向異性 固液界面 形態(tài)穩(wěn)定性

【摘要】：本文系統(tǒng)的介紹了深胞晶生長理論的發(fā)展過程,這是材料科學(xué)中的重大理論課題之一,研究了材料科學(xué)和加工過程中的固-液界面微結(jié)構(gòu)斑圖這一問題。利用匹配漸近展開法和多變量展開法,得到了在定向凝固過程中,當(dāng)表面張力和界面動(dòng)力學(xué)同為各向異性時(shí),深胞晶生長的一致有效的漸近解,揭示了各向異性對(duì)定向凝固中深胞晶生長界面的影響。論文包括深胞晶生長的全局性理論和全局穩(wěn)定性理論兩部分工作:(1)深胞晶生長的全局性理論:在考慮表面張力和界面動(dòng)力學(xué)同為各向異性的情況下,研究了它們的共同作用對(duì)定向凝固中深胞晶生長的影響,得到問題的解析解以及該解所對(duì)應(yīng)的界面形狀。研究表明,各向異性界面動(dòng)力學(xué)與各向異性表面張力的優(yōu)選方向不一定相同,假設(shè)它們之間相差的角度θ0。當(dāng)兩種各向異性優(yōu)選方向相同,即θ0為0時(shí),隨著各向異性系數(shù)的增大,深胞晶的指狀界面全長增大,根部底端的曲率半徑會(huì)減小,即根部底端的曲率增大,且各向異性表面張力系數(shù)對(duì)深胞晶生長界面形狀的影響更為顯著。當(dāng)0≤θ0≤π/4時(shí),隨著θ0增大,深胞晶的指狀界面全長減小,根部底端的曲率半徑會(huì)減小,即根部底端的曲率增大;當(dāng)π/4≤θ0≤π/2時(shí),隨著θ0增大,深胞晶的指狀界面全長增大,根部底端的曲率半徑會(huì)增大,即根部底端的曲率減少。(2)深胞晶生長的全局穩(wěn)定性理論:通過對(duì)表面張力為各向異性的定常深胞晶生長的整體穩(wěn)定性的研究發(fā)現(xiàn),與表面張力為各向同性的定向凝固系統(tǒng)中深胞晶界面形態(tài)穩(wěn)定性比較,表面張力各向異性的定向凝固中深胞晶生長界面形態(tài)也有兩種整體不穩(wěn)定性機(jī)制:整體波動(dòng)不穩(wěn)定性(GTW)和低頻不穩(wěn)定性(IF)。隨著表面張力各向異性的增加,中性模式產(chǎn)生強(qiáng)振蕩的枝晶結(jié)構(gòu)的整體波動(dòng)不穩(wěn)定性的不穩(wěn)定區(qū)域減小,而中性模式產(chǎn)生弱振蕩的胞晶結(jié)構(gòu)的低頻不穩(wěn)定性的不穩(wěn)定區(qū)域增加。
[Abstract]:This paper introduces the development process of deep cellular crystal growth theory, which is one of the major problems in material science, material science and research in the process of solid-liquid interface micro structure pattern of this problem. By using the matched asymptotic expansion method and multi variable expansion method, obtained during directional solidification and when the surface tension and interface dynamics with anisotropic, deep cellular crystal growth of the uniformly valid asymptotic solution, to reveal the effect of anisotropy on the growth interface in directional solidification of deep cellular crystal. The thesis consists of two parts of the global theory of deep cellular growth and global stability theory: (1) deep cellular crystal the growth of the global Theory: in consideration of surface tension and interface dynamics with anisotropic, studied their common effects on the growth of directional solidification of deep cellular crystal, obtained the analytical solution of the problem and its solution The corresponding interface shape. The research results show that the preferred orientation of anisotropic interface dynamics and anisotropic surface tension is not necessarily the same, the difference between them is that the angle of 0. when the two kinds of anisotropic preferably the same direction, namely is 0 to 0, with the increase of anisotropy, deep cellular crystal finger length increase interface the radius of curvature, the root ends will decrease, which is at the bottom of the root curvature increases, and the effect of anisotropic surface tension coefficient of deep cellular crystal growth interface shape is more significant. When less than 0 and less than 0 theta PI /4, with about 0 increase of deep cellular crystal finger interface length decreases, the radius of curvature the root of the bottom will decrease, which is at the bottom of the root curvature increases; when /4 = 0 = Pi Pi theta theta /2, with 0 increase of deep cellular crystal finger interface length increases, the radius of curvature of the root of the bottom will increase, which is at the bottom of the root curvature decreases. (2) deep cellular crystal the growth of global Stability theory: through the research on the overall stability of surface tension anisotropy constant deep cellular crystal growth was found, compared with the surface tension of the stability of directional solidification system deep cellular crystal interface shape is isotropic, the directional solidification of deep cellular crystal surface tension anisotropy growth interface morphology also has two kinds: overall instability mechanism the overall fluctuation (GTW) and low frequency instability (IF). With the increase of surface tension anisotropy, the unstable region overall volatility model produces strong oscillations of neutral dendrite structure instability decreases, the unstable region of low frequency and mode of neutral cellular crystal structure and weak oscillation instability increases.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB30

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