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应用双模PFC模型,计算二维PFC相图,模拟二维六角晶格向正方晶格的结构转变过程,观察新相(二维正方相)的形核、长大特点,以及相结构转变的动力学特征.结果表明:六角结构相向正方结构相的转变,正方相最易在六角相晶界处,尤其是在三晶粒的交汇处首先生成正方相的晶核,之后是正方相逐渐通过吞噬六角相的边缘,向六角相内部推进,并不断长大.对于结构转变生成的正方相晶粒,其晶粒取向几乎是随机的,与原先六角相晶粒取向角没有明显的关系.正方相转变的面积分数随时间变化的动力学曲线呈现典型的“S”形.由Avrami曲线可将相变曲线看成由两阶段组成.计算模拟得到的Avrami曲线的第二阶段直线斜率K的范围在2.0和3.0之间,与JMAK理论的指数n相符合.
The dual-mode PFC model was used to calculate the two-dimensional PFC phase diagram and simulate the structural transition from two-dimensional hexagonal lattice to square lattice. The nucleation and growth characteristics of the new phase (two-dimensional square phase) The results show that the transformation of the hexagonal phase to the square structure phase is the most easy to happen. The orthorhombic facies is the first to form the nucleus of the tetragonal phase at the hexagonal phase boundary, especially at the intersection of the three crystal grains, Swallowed the edge of the hexagonal phase, to the hexagonal phase internal advance, and continue to grow.For the structural transformation of the square phase grains, the grain orientation is almost random, and the original hexagonal grain orientation angle is not obvious. The kinetic curve of the area fraction of phase transition with time is typical “S” shape.The phase transition curve can be regarded as two phases by the Avrami curve.Calculating the second-stage straight line slope of the simulated Avrami curve K In the range of 2.0 and 3.0, consistent with the index n of the JMAK theory.