钛铝层合材料拉伸破坏的分子模拟研究

发布时间：2018-06-17 09:49

本文选题：钛铝层合复合材料 + 分子模拟　；参考：《哈尔滨工业大学》2015年硕士论文

【摘要】：本文主要研究了钛铝层合复合材料的单轴拉伸力学性能。通过采用分子动力学模拟的方法分析了钛铝各单独材料及其层合材料在单轴拉伸过程中内部位错的演化情况。分析了由于两边添加保护相铝后,钛内部位错演化的改变;以及当保护相铝晶粒尺寸减小时,对钛内部位错演化所造成的影响。为此,本文首先建立了9晶粒的多晶钛模型,以及4晶粒和9晶粒的多晶铝模型。借助Voronoi原理,使模拟盒子被划分为几个不同的晶粒部分,然后再将初始建立好的足够大单晶模板按照一定旋转角投影到各晶粒部分中,逐一完成各晶粒的建模过程。所完成多晶模型形状均为密排方向平行于轧制面的柱状晶,且满足各晶粒在平面方向不联通的条件。对多晶模型进行单轴拉伸模拟,发现拉伸曲线可以很好的表现出材料的塑性阶段,且4晶粒的多晶铝与9晶粒的多晶铝拉伸曲线形状大致相似,表示本文所建立的多晶模型合理。为能够合理分析钛铝单独材料及其层合材料在拉伸过程中位错的演化情况,本文采用了一种参数化方法,先根据模型在拉伸过程每一步中各个晶粒内所有原子所处位置偏离完整晶体时对应原子所应处在位置的距离,得出一个g参数,再通过分析g参数的变化曲线得出总的结构位错在每一步的演化程度。其中对单晶而言,只需对整个模型计算一个g参数;而对多晶而言,需要对每个晶粒分别计算一个g参数。利用g参数分析两种边界条件下单晶铝单轴拉伸的模拟情况,可以发现g参数在结构处于弹性段时基本保持接近零的直线,而当拉伸曲线达到最高点结构失效时则突然发生阶跃,表示此时结构内部有大量位错萌生运动并直接导致结构塑性失稳。利用g参数分析单独4晶粒和9晶粒铝的拉伸破坏情况。发现应变直到15%时,g曲线都基本成平缓上升趋势,没有较大阶跃,这表示铝结构虽然发生塑性变形,但位错并未大量演化,结构仍能继续承载。利用g参数分析单独9晶粒钛的拉伸破坏情况,发现g曲线上升陡峭,且基本在应变达到7%时所有晶粒全部失效,表明钛的塑性性能远差于铝。利用g参数分析当两边层合4晶粒铝后9晶粒钛的拉伸破坏情况,相比钛单独拉伸而言,g曲线有明显变平缓趋势,整体结构的破坏应变推迟到11.3%,表明与保护相铝的层合作用可以显著提升钛的拉伸塑形性能。利用g参数分析当两边层合9晶粒铝后9晶粒钛的拉伸破坏情况,相比之前两边4晶粒铝层合时,钛的拉伸塑形又有一定提高,破坏应变达到13.4%,表明层合结构中保护相为细晶铝时更能提高承载相钛的拉伸塑形性能。
[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.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB331

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