【作者】 白锐；

【导师】 周志敏；

【作者基本信息】 东北大学 ， 材料物理与化学， 2006， 硕士

【摘要】 半固态成型合金浆料制备新工艺—液相线铸造法可获得均匀、细小的非枝晶组织，二次加热后能完全转变为均匀、细小的等轴晶，是适于触变成型的理想半固态组织。液相线铸造法中在浇铸前熔体先降至液相线温度进行保温一段时间，通过等温分解的相场模拟显示，在近双相区将会发生成分与相的分解过程，这种分解作用促进新相胚芽产生，有助于大量均匀形核。对凝固过程中晶粒长大的相场动力学模拟的结果表明，晶粒长大速率随过冷度增大而显著增加，其枝晶形成趋向随过冷度增大而明显增强。说明液相线铸造是在较小过冷度范围实现了结晶凝固，这种情况下具有很小的长大速率和枝晶形成趋向，得到细小的非枝晶组织，从而在随后的浇注熔体中获得大量均匀、细小非枝晶组织；二次加热至双相区，引起部分熔化和重新分解晶化，同样情况会使组织进一步得到改善。 结合形核理论模型与晶粒长大相场模型，对液相线铸造条件下的凝固动力学过程及所得到的半固态合金浆料组织进行了计算机模拟，模拟结果显示出液相线铸造条件下形核与长大的动力学过程及其铸造组织形貌。更多还原

【Abstract】 Liquidus Casting, a new semi-solid metal slurry making technology, was used to get uniform, fine non-dendritic structures that can further be turned into uniform and fine equiaxed grains by reheating process. The simulation of isothermal decomposition of composition and phase in double phase area shows that a lot of uniform solid nuclei should be promoted to form during holding of the casting melts at liquidus temperature. As a result, the fine and uniform non-dendritic structures are obtained. It is shown by phase-field simulation of solidification that the forming tendency of dendrite and its growing rate are remarkably increased with enlarging undercooling. Under liquidus casting the solidification is performed in such a range of temperature that dendrite is hardly formed and growing rate is slow. Therefore, the fine non-dendritic structures can be obtained by Liquidus Casting. Similarly, reheating at double phase area will result in the improvement of the structure through partly remelting and resolidification.Joining the theoretical model of nucleation and the phase field model of grain growth, the computer simulation has been performed of the solidification dynamic process and the structure of the semi-solid metal slurry made by the Liquidus Casting. The dynamic process of nucleation and grain growth under liquidus casting condition and the morphology of resulted solidification structure have been shown.更多还原