论文标题
球形颗粒的表面核转化的动力学和晶粒核核转化的新模型
Kinetics of the surface-nucleated transformation of spherical particles and new model for grain-boundary nucleated transformations
论文作者
论文摘要
球形粒子在其表面上具有成核的转换体积分数的方程，既不等温度和等温度，均在适合此问题的Kolmogorov方法的框架中得出。确定了控制转换动力学的特征参数；对后者进行了研究，并特别强调了Avrami指数的时间行为。结果表明，由于表面核的转化在特征参数的较大值下与散装 - 核核变化不同，这是由于新阶段的一维径向生长在过程的早期阶段完全转化后发生的新相位。这种效果也体现在被认为是尺寸分布的颗粒和晶界成核转换中的集合中。通过研磨获得的颗粒固有的对数正态分布用于数值计算，并显示出对相同粒子集合的时间延伸的体积分数和Avrami-Exponent依赖性。提供了一种新的模型，用于替代随机平面CAHN模型的晶核成核转换。它基于尺寸分布的球形颗粒的合奏，其可能会使核穿越晶界的可能性。该过程的动力学表明，与单个粒子一样，由相同的特征参数支配，并且与CAHN模型质量不同。特别是，在庞大的管理参数的较大值以实验曲线上观察到的特征性弯曲的末端，对数体积分数的绘制图是散装金属玻璃的结晶。这种特殊性以及整个图的形式直接表明了金属玻璃的晶粒（多簇）结构，并在群间边界处的成核。
Equations for the transformed volume fraction of a spherical particle with nucleation on its surface, both nonisothermal and isothermal, are derived in the framework of Kolmogorov method adapted for this problem. Characteristic parameters governing the transformation kinetics are determined; the latter is studied with particular emphasis on the Avrami exponent temporal behavior. It is shown that the surface-nucleated transformation qualitatively differs from the bulk-nucleated one at large values of the characteristic parameters due to the one-dimensional radial growth of the new phase occurring after the complete transformation of the surface itself at the early stage of the process. This effect also manifests itself in the considered ensemble of size-distributed particles and in the grain-boundary nucleated transformations. The logarithmic normal distribution inherent for the particles obtained by grinding is employed for numerical calculations and shown to stretch temporally the volume-fraction and Avrami-exponent dependences for the ensemble of identical particles. A new model for grain-boundary nucleated transformations alternative to the Cahn model of random planes is offered; it is based on the ensemble of size-distributed spherical particles with the possibility for a growing nucleus to cross grain boundaries. The kinetics of this process is shown to be governed by the same characteristic parameter, as for a single particle, and qualitatively differs from the Cahn-model one. In particular, the logarithmic volume-fraction plot at large values of the governing parameter ends by a characteristic bend observed on experimental curves for the crystallization of bulk metallic glasses. This peculiarity together with the form of the plot as a whole directly indicates to the grain (polycluster) structure of metallic glasses and nucleation at intercluster boundaries.
