Numerical and experimental study on the fragmentation of dendrites in the mushy zone of binary metal alloys

枝晶的破碎是发生在凝固熔体的糊状区中的技术上重要的现象，主要发生在凝固的后期阶段。破碎对不同铸件的晶粒结构有着至关重要的影响，这反过来又决定了凝固材料的性能。拟议的研究项目的目标是数值和实验研究复杂的相互作用的参数（温度场，浓度场和界面能）在枝晶破碎，并量化破碎的详细建模的第一次。本文将二维枝晶生长的CA稳定扩散模型推广到三维。通过分析浓度场和毛细作用的相互作用，探讨了破碎的条件和机理。多尺度的2D和3D相场模拟不同的工艺条件下，流体流动的影响下的枝晶破碎过程将进行验证和比较与CA计算。此外，实验研究也将进行比较，并验证数值模型。在梯度炉中用Al-Cu合金制备了枝晶破碎的等轴组织。将建立在扩散条件下导致碎裂的参数组合的“数据库”。

Fragmentation of dendrites is a technologically important phenomenon occurring in the mushy zone of a solidifying melt, mainly during late stages of solidification. Fragmentation has a crucial impact on the grain structure of different cast parts, which in turn determines the properties of the solidified material. The goal of the proposed research project is to numerically and experimentally investigate the complex interaction of the parameters (temperature field, concentration field and interfacial energy) involved in the dendrite fragmentation, and to quantify fragmentation by detailed modelling for the first time. A fast 2-dimensional “CA stabilised diffusion model” for dendritic growth will be extended to 3 dimensions. The interaction of concentration field and capillarity will be analysed to investigate the conditions and mechanisms of fragmentation. Multiscale 2D and 3D phase-field simulations of dendritic fragmentation processes for different process conditions and under the influence of fluid flow will be performed for validation and comparison with the CA computations. In addition, experimental investigations will also be carried out for comparison and to validate the numerical model. Equiaxed microstructures with fragmented dendrites will be generated in a gradient furnace using Al-Cu alloys. A ”data base” of combinations of parameters that lead to fragmentation under diffusive conditions will be established.