發(fā)布時間：2018-06-17 09:49

  本文選題：鈦鋁層合復合材料 + 分子模擬��； 參考：《哈爾濱工業(yè)大學》2015年碩士論文

【摘要】：本文主要研究了鈦鋁層合復合材料的單軸拉伸力學性能。通過采用分子動力學模擬的方法分析了鈦鋁各單獨材料及其層合材料在單軸拉伸過程中內部位錯的演化情況。分析了由于兩邊添加保護相鋁后,鈦內部位錯演化的改變;以及當保護相鋁晶粒尺寸減小時,對鈦內部位錯演化所造成的影響。為此,本文首先建立了9晶粒的多晶鈦模型,以及4晶粒和9晶粒的多晶鋁模型。借助Voronoi原理,使模擬盒子被劃分為幾個不同的晶粒部分,然后再將初始建立好的足夠大單晶模板按照一定旋轉角投影到各晶粒部分中,逐一完成各晶粒的建模過程。所完成多晶模型形狀均為密排方向平行于軋制面的柱狀晶,且滿足各晶粒在平面方向不聯(lián)通的條件。對多晶模型進行單軸拉伸模擬,發(fā)現(xiàn)拉伸曲線可以很好的表現(xiàn)出材料的塑性階段,且4晶粒的多晶鋁與9晶粒的多晶鋁拉伸曲線形狀大致相似,表示本文所建立的多晶模型合理。為能夠合理分析鈦鋁單獨材料及其層合材料在拉伸過程中位錯的演化情況,本文采用了一種參數化方法,先根據模型在拉伸過程每一步中各個晶粒內所有原子所處位置偏離完整晶體時對應原子所應處在位置的距離,得出一個g參數,再通過分析g參數的變化曲線得出總的結構位錯在每一步的演化程度。其中對單晶而言,只需對整個模型計算一個g參數;而對多晶而言,需要對每個晶粒分別計算一個g參數。利用g參數分析兩種邊界條件下單晶鋁單軸拉伸的模擬情況,可以發(fā)現(xiàn)g參數在結構處于彈性段時基本保持接近零的直線,而當拉伸曲線達到最高點結構失效時則突然發(fā)生階躍,表示此時結構內部有大量位錯萌生運動并直接導致結構塑性失穩(wěn)。利用g參數分析單獨4晶粒和9晶粒鋁的拉伸破壞情況。發(fā)現(xiàn)應變直到15%時,g曲線都基本成平緩上升趨勢,沒有較大階躍,這表示鋁結構雖然發(fā)生塑性變形,但位錯并未大量演化,結構仍能繼續(xù)承載。利用g參數分析單獨9晶粒鈦的拉伸破壞情況,發(fā)現(xiàn)g曲線上升陡峭,且基本在應變達到7%時所有晶粒全部失效,表明鈦的塑性性能遠差于鋁。利用g參數分析當兩邊層合4晶粒鋁后9晶粒鈦的拉伸破壞情況,相比鈦單獨拉伸而言,g曲線有明顯變平緩趨勢,整體結構的破壞應變推遲到11.3%,表明與保護相鋁的層合作用可以顯著提升鈦的拉伸塑形性能。利用g參數分析當兩邊層合9晶粒鋁后9晶粒鈦的拉伸破壞情況,相比之前兩邊4晶粒鋁層合時,鈦的拉伸塑形又有一定提高,破壞應變達到13.4%,表明層合結構中保護相為細晶鋁時更能提高承載相鈦的拉伸塑形性能。
[Abstract]:The uniaxial tensile mechanical properties of Ti-Al laminated composites were studied in this paper. The evolution of internal dislocations in the uniaxial tensile process of individual titanium and aluminum materials and their laminated materials was analyzed by molecular dynamics simulation. The changes of dislocation evolution in titanium due to the addition of aluminum on both sides of the protective phase and the effect on the evolution of dislocation in titanium are analyzed when the grain size of aluminum in the protective phase is reduced. For this reason, the polycrystalline titanium model of 9 grain and the polycrystalline aluminum model of 4 grain and 9 grain are established in this paper. With the help of Voronoi principle, the simulation box is divided into several different grain parts, and then the initial large enough single crystal template is projected to each grain part according to a certain rotation angle, and the modeling process of each grain is completed one by one. The completed polycrystalline models are all columnar crystals with dense rows parallel to the rolling surface and satisfy the condition that the grains are not connected in the plane direction. The uniaxial tensile simulation of the polycrystalline model shows that the tensile curve can well show the plastic stage of the material, and the shape of the tensile curve of the 4 grain polycrystalline aluminum is similar to that of the 9 grain polycrystalline aluminum. It is shown that the polycrystalline model established in this paper is reasonable. In order to reasonably analyze the evolution of dislocations in the tensile process of titanium-aluminum single material and its laminates, a parameterized method is used in this paper. Firstly, a g parameter is obtained according to the distance of the position of all atoms in each grain deviating from the complete crystal when the model is located in each step of the tensile process. The evolution degree of the total structural dislocation in each step is obtained by analyzing the variation curve of the g parameter. For single crystals, only one g parameter is needed for the whole model, while for polycrystals, one g parameter is needed for each grain. By using g parameter to analyze the simulation of uniaxial tension of single crystal aluminum under two boundary conditions, it can be found that g parameter basically keeps a straight line close to zero when the structure is in the elastic region. When the tensile curve reaches the highest point, the structural failure occurs step by step, indicating that there is a large number of dislocation initiation motion in the structure, which directly leads to the plastic instability of the structure. The tensile failure of single 4 grain and 9 grain aluminum was analyzed by g parameter. It is found that the strain and g curves have a gentle upward trend until 15, which indicates that although plastic deformation occurs in the aluminum structure, the dislocation does not evolve in large quantities and the structure can continue to carry the load. By using g parameter to analyze the tensile failure of single 9 grain titanium, it is found that the g curve rises steeply and almost all the grains fail when the strain reaches 7, which indicates that the plastic property of titanium is much worse than that of aluminum. By using g parameter to analyze the tensile failure of titanium with 9 grain after laminated with 4 grain aluminum on both sides, the g curve has an obvious tendency of flattening compared with that of titanium alone. The failure strain of the whole structure was delayed to 11. 3, which indicates that the tensile plastic properties of titanium can be significantly improved by the cooperation of the protective aluminum layer. The tensile failure of titanium was analyzed by using g parameter when both sides were laminated with 9 grain aluminum. Compared with the former four grain aluminum layers, the tensile shape of titanium was improved to a certain extent. The failure strain reached 13.4, which indicates that the tensile molding properties of titanium bearing phase can be improved more when the protective phase in the laminated structure is fine crystalline aluminum.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB331

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本文編號：2030608