Transformations accompanying shape-instability govern the morphological configuration and distribution of the phases in a microstructure. Owing to the influence of the microstructure on the properties of a material, the stability of three-dimensional rods in a representative polycrystalline system is extensively analysed. A multiphase-field model, which recovers the physical laws and sharp-interface relations, and includes grain boundary diffusion, is adopted to investigate the morphological evolution of the precipitate. Moreover, the efficiency of the numerical approach is ensured by establishing the volume-preserving chemical equilibrium through the incorporation TCFe8 (CALPHAD) data and solving phase-field evolution in the Allen-Cahn framework. The morphological evolution of the rod in the multiphase system exhibits a unique transformation mechanism which is significantly different from the evolution of an isolated finite-structure. It is realised that, in a polycrystalline arrangement, irrespective of the initial rod-size , the shape-change begins with the energy-minimising events at the triple junctions. This early transformation renders a characteristic morphology at the longitudinal ends of the structure, which introduces sufficient driving-force through the curvature-difference for the subsequent morphological changes. The continued mass transfer to the terminations, ultimately, breaks-off the rod into separate entities that are entangled in the grain boundary. With increasing aspect ratio of the rod, it is identified that the source of mass transfer, which turns into the ovulation site, shifts from the centre. This increases the number of fragmentation events and introduces satellite particle. A comprehensive understanding of the transformation kinetics and mechanism governing the morphological evolution of the rods in a polycrystalline system is rendered in this work.

中文翻译：

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多晶体系中三维渗碳体棒的形态稳定性：相场分析

伴随形状不稳定性的转变控制着微观结构中相的形态配置和分布。由于微观结构对材料性能的影响，对代表性多晶系统中三维棒的稳定性进行了广泛的分析。采用恢复物理规律和锐界面关系并包括晶界扩散的多相场模型来研究沉淀物的形态演变。此外，通过掺入 TCFe8 (CALPHAD) 数据建立体积保持化学平衡并解决 Allen-Cahn 框架中的相场演化，确保了数值方法的效率。多相系统中棒的形态演化表现出一种独特的转化机制，与孤立的有限结构的演化有着显着的不同。人们认识到，在多晶排列中，无论初始棒尺寸如何，形状变化都始于三重结处的能量最小化事件。这种早期的转变在结构的纵向端呈现出特征形态，通过曲率差异为随后的形态变化引入足够的驱动力。到终端的持续质量转移最终将棒折断成单独的实体，这些实体纠缠在晶界中。随着棒纵横比的增加，确定了传质源，变成排卵位点，从中心偏移。这增加了碎片事件的数量并引入了卫星粒子。这项工作全面了解了控制多晶系统中棒形貌演变的转化动力学和机制。