声空化作用下金属熔体中的原子团簇在诱发形核中的作用及声空化诱发形核机理研究

Cavitation induced nucleation is a key of solidification structures refining of metals through melt ultrasonic treatment, and a deep understanding of the mechanisms of cavitation induced nucleation in metallic melts is quite important for scientific research and engineering practice. The present proposal is aimed to experimentally and theoretically study role of atomic clusters in the nucleation process and then thoroughly revel the nucleation mechanisms at a nanoscale via synchrotron radiation X-ray involved real-time detection combined with molecular dynamic calculation, by starting with a melt structure analysis, and finally quantify the nucleation. Synchrotron radiation SAXS (small angle X-ray scattering) & WAXS (wide angle X-ray scattering) are used to analyze melt structures and the influence by cavitation, of metals with different alloy elements and the contents, and metals modified by nano-sized of impurity and refiner particles. Moreover, the technologies are applied to identify nucleation events induced by cavitation in the different melts. On the basis of that, cluster evolutions during cavitation, relationships between the clusters and the induced nucleation are accessed to clarify the role of clusters in the nucleation, by combing with the corresponding molecular dynamic calculations. Furthermore, mechanisms of the cavitation induced nucleation in metallic melts are reveled at a nano-level, through an additionally contrastive analysis of the impurities and the refiners exerted effects on the induced nucleation. After that, numerical modelling is built to quantify the nucleation. Through the above work, a further theoretical progress on mechanisms of cavitation induced nucleation during melt ultrasonic treatment is expected, and a guideline is provided for the technique to practically use.

声空化诱发形核是熔体超声处理细化金属凝固组织的关键，深入研究该形核机理具有重要的科学与工程意义。本项目提出从金属熔体结构入手，利用同步辐射X射线实时检测与分子动力学计算，实验结合理论研究熔体中原子团簇在声空化诱发形核中的作用，并从纳米尺度深入揭示声空化诱发形核机理并量化形核。通过同步辐射SAXS&WAXS检测不同合金元素及含量，杂质及细化剂纳米颗粒存在时的熔体结构及受声空化作用的影响，检测不同熔体条件下的声空化诱发形核，结合分子动力学计算，研究不同熔体时原子团簇在声空化过程中的演变规律，原子团簇与诱发形核的关系，从而研究原子团簇在诱发形核中的作用，并对比分析杂质及细化剂纳米颗粒对诱发形核的影响，进而在纳米尺度上揭示金属熔体中的声空化诱发机理。在此基础上，通过数值建模以量化形核。通过本研究，以期在金属熔体中的声空化诱发形核机理方面取得理论突破，并为熔体超声处理的工业化应用提供指导。

超声是金属凝固组织细化一种简单、高效手段，超声处理过程中的声空化诱发形核是超声细化作用关键。然而，长期以来有关金属熔体中声空化诱发形核机理并不清楚，致使对金属的超声细化作用认识不明，阻碍超声细化方法在金属中的运用。鉴此，本项目通过基于同步辐射X射线的原位研究技术，结合分子动力学计算、多物理场模拟及数值建模，研究了以铝合金为代表的金属熔体中的声空化行为，熔体结构及原子团簇在声空化下的演变，原子团簇、以Al2O3为代表的外加第二相杂质颗粒及TiB2为代表的细化剂颗粒存在时对声空化诱发形核的影响，以深入揭示金属熔体中的声空化诱发形核机理。在此基础上，构建不同机制时声空化诱发形核数值模型，及描述超声工艺与凝固组织细化间关系的数值模型，以量化形核与组织细化，深化超声细化理论，并为超声细化的工业应用提供指导。分子动力学研究发现，AlCu合金熔体由不同温度时的平衡团簇构成，声空化作用下团簇结构发生改变，随声空化强度的增加促进低温稳定团簇的形成与形核，Cu含量的增加不仅促进了二十面体团簇的产生，且减小了体系的自扩散系数，易于形成大过冷熔体；通过同步辐射X射线超快成像直接观察到了AlCu合金熔体中一个周期内的声空化过程，这进一步证实了金属熔体中的声空化现象；通过同步辐射WAXS&SAXS对有无Al2O3或TiB2存在时超声作用下微过热熔体中出现了铝质相，这直接证实了金属熔体中的声空化诱发形核；通过对不同形核机制的声空化诱发形核建模，以及超声工艺对凝固组织细化的量化建模研究表明，声空化诱发形核与组织细化存在一效力最优区间，输入声强超过这一区间上限并不能对声空化诱发形核与细化程度进一步有效提升，这一发现可直接指导超声细化的具体实践。在本项目资助下共发表SCI论文5篇，中文核心1篇，获授权发明专利3项，完成了既定研究内容，并达到预期目标。