体积深过冷熔体非平衡凝固组织中的再结晶研究

Recrystallization transformation is widely used in industrial production, and it can be used to control the grain size and texture of the microstructure of the alloy to obtain the required performance. At present, most theories and techniques of recrystallization are based on the recrystallization of the annealed solid metal or alloy after the processing of plastic deformation. It is very urgent to explore and design new recrystallization processing technologies. In the past, the theoretical and experimental research on non-equilibrium solidification and recrystallization are independent of each other, the non-equilibrium effects in the processing of extreme non-equilibrium solidification are not considered. The study of these two closely related physical processes has been lacked. This project is based on the undercooling rapid solidification technology and the study of the two simple single phase solution alloy, , the effect of non-equilibrium effect on solid state recrystallization during solidification are to be studied, the two simple single phase solution alloy, the interface morphology and migration rate of recrystallized grains and the evolution rule of the recrystallization kinetic energy barrier with undercooling are to be studied, and the related physical model will be established. Applying the quenching technology to quench the undercooled melt before rapid solidification, incombination with cold deformation, we study the characteristics of crystal defects and the mechanism of recovery and recrystallization under the annealing condition and solid-state recrystallization, then expanding the theory and technology of the intrinsic link between the non-equilibrium solidification and solid-state recrystallization transformation.

再结晶转变在工业生产中的应用十分广泛，其主要被用于调控金属材料微观组织的晶粒度和织构等, 从而获取所需性能。目前，传统的再结晶理论和技术大多是基于固态金属或者合金在塑性变形后退火过程中的再结晶，探索和设计新的再结晶加工工艺方法的需求十分迫切。以往非平衡凝固和再结晶的理论和实验研究相互独立，未考虑极端非平衡凝固过程中非平衡效应的物理作用，致使关于非平衡凝固与固态再结晶这两个密切关联的物理过程的研究长期进展缓慢。本项目立足于深过冷快速凝固等技术，研究快速凝固过程中非平衡效应对固态再结晶的影响，以及非平衡凝固组织中再结晶晶粒界面形貌、迁移速率和再结晶动力学能垒随过冷度的演化规律, 并建立相关物理模型。在大过冷度熔体快速凝固前，采用快淬技术对过冷熔体快淬，结合冷变形，揭示极端非平衡凝固组织中晶体缺陷特征及其回复和再结晶机制，从而拓展关于非平衡凝固与固态再结晶间内在联系的理论与技术。

本项目立足于深过冷快速凝固等技术，研究Ni-Cu合金快速凝固组织细化机制。在大过冷度熔体快速凝固前，采用快速冷却技术对过冷熔体快速冷却，揭示极端非平衡凝固组织中晶体缺陷特征。使用高速摄影技术测量出了深过冷Ni-Cu合金的凝固速率与合金熔体过冷度之间的关系。实验研究发现合金凝固速率随熔体过冷度增加而不断增大，并且在临界过冷度处出现不连续，即凝固速率突然增加。这种在临界过冷度处的凝固速率不连续行为可归因于树枝晶尖端处液相的有限溶质扩散。微观组织都呈现出四种组织特征区。例如对于Ni95Cu5合金：当过冷度ΔT<50K，微观组织主要由树枝晶主干占据；当过冷度50K<ΔT<110K，微观组织由树枝晶组织改变为等轴晶组织, 此外, 大量弯曲晶界说明晶粒粗化大量发生。当过冷度110K<ΔT<180K，树枝晶又大量出现，但是相比小过冷度区间的树枝晶组织，大量细密的二次树枝晶臂出现。当过冷度ΔT>180K，微观组织主要由等轴晶组成且包含大量孪晶，这说明在再辉之后发生了很高程度的再结晶。以上成果在Journal of Alloys and Compounds等期刊发表SCI论文15篇，其中TOP期刊4篇，申报国家发明专利4项。研究成果不仅对非平衡凝固过程控制及晶粒细化机制研究有指导作用，还推动了二元单相合金非平衡凝固理论的发展。