【作者】 许泉；

【导师】 杨根仓；

【作者基本信息】 西北工业大学 ， 计算材料学， 2007， 硕士

【摘要】 晶粒长大是纯金属、合金、陶瓷等多晶材料中最普遍的晶粒生长现象，对材料性能有重要影响，系统研究多晶材料晶粒长大过程及其动力学具有重要的理论和工程意义。随着计算材料科学的发展，计算机模拟已逐渐成为材料微观组织设计及微观组织演化研究的重要手段。本文采用多序参量唯象晶粒长大相场模型，系统研究了单相系统中正常晶粒长大、晶界能各向异性的晶粒长大、两相多晶材料的晶粒长大以及有第二相颗粒存在条件下的晶粒长大过程，全面分析了多晶材料中晶粒组织演变、动力学以及拓扑学演化规律，主要结论如下： 1．相场模型可真实再现多种条件下的多晶材料晶粒演化过程及其拓扑学变化，模拟结果与实验结果吻合良好。 2．在单相晶界能各向同性晶粒演化过程中，晶界夹角趋于120°，晶粒平均表面积或截面积和演化时间成线性关系，当晶粒生长趋于稳定后，晶粒归一化半径分布不随演化时间而变化；晶粒生长速率和梯度能系数k^0.5成正比，与耦合参数r^1.5成反比。 3．晶界能各向异性系统中低能晶界比较稳定，高能晶界迅速合并，晶粒大小分布不均匀。各向异性系统中，晶粒尺寸和边数的分布较各向同性系统宽，平均晶粒面积在两个不同系统中呈现出不同的分布形式。随着晶界能各向异性的增强，晶粒生长变缓，组织均匀化程度降低。 4．两相组织晶粒长大过程中，不同体积分数相晶粒归一化半径分布峰值随着演化时间的增加都逐渐趋近于1，相体积分数越大，其归一化晶粒半径峰值趋于1的速度越快。随着相体积分数的增大，晶粒组织达到稳定的时间越短。两相体积分数相差较大时，其生长指数小于3，而两相体积分数比较接近时，两相晶粒生长指数大于3。 5．第二相颗粒的存在对晶界有钉扎作用，颗粒体积分数越大，对晶界的钉扎作用越强，晶粒演化过程减缓，且在一定体积分数下，系统会发生晶粒异常长大现象；颗粒尺寸越大，对晶界的钉扎作用也越强。通过对Zener公式的验证表明，模拟的拟合指数与Monte Carlo法模拟结果一致，且较Zener和Hillert的理论模型更符合实测结果。更多还原

【Abstract】 Grain growth, which is widely observed in metals, alloys, ceramics and other polycrystalline materials , has significant effect on the material’s properties. Investigation on the process and the kinetics of the grain growth is of both theoretical and practical significance. In recent years, computer simulation has become an effective means in the field of materials design and microstructure evolution with the development of computational materials science. Thus, in present thesis, the grain growth process under the conditions of normal single phase, anisotropic in grain boundary energy, two phase and the second-phase particles pinning are simulated by means of the phase-field method. The microstructural evolution, the kinetics of the grain growth and the topological evolution in polycrystalline are also systematically analyzed in detail. The main conclusions are as follows:1. The microstructural evolution and the topological evolution in polycrystalline under different conditions can be really reappeared by the phase field method. The simulated results are in greatly accordance with experimental results.2. In the case of the normal grain growth, the simulated results indicate the angle between two adjacent grains tends to 120°, the average area of grain is linear with the evolution time, and the distribution of normalized grain size is time independent. The grain growth velocity is in direct proportion to the coefficient of the grain boundary energy k^0.5 and inverse proportion to the parameter r^1.5.3. In the anisotropic system, the low energy boundary is stable, while the high energy boundary is unstable and grows faster. Moreover, the distribution of the grain size is non-uniform. The scales of the grain size and the distributions of edges were broadened than that of the isotropic system. And the distributions of the average grain area are different in these two systems. With the increasing of the grain boundary energy anisotropy, the grain grows slowly and the uniformity of the grain structure decreases.更多还原