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根据合金凝固理论和体积平均多相模型,对NH4Cl-70%H2O凝固过程进行了数值模拟和实验验证.虽然研究者已研究过NH4Cl-70%H2O凝固过程,但是只针对单个现象进行分析,比如通道偏析的形成、对流形式以及晶粒的形成.在前人研究的基础上,本文首次通过数值模拟和实验对比两种手段相结合的方式全面地研究了氯化铵水溶液凝固整个计算域的全部现象,尤其再现了等轴晶在铸锭中的下落漂移现象以及由此引起的对流,并且更深入地探究了偏析的形成原因.通过计算发现等轴晶从型壁处沉降并逐渐向铸型底部积聚,直到体积分数达到一临界值后,柱状晶停止生长,完成柱状晶向等轴晶转化过程.由于溶质再分配,底部晶粒集中的区域形成了负偏析,在尚未凝固的上部区域形成较大范围的正偏析.通过实验验证发现,等轴晶在铸锭中的下落漂移现象和对流形式的预测值与实验值较为一致,从而全面揭示出凝固过程中固相的移动和对流是产生宏观偏析的关键因素.
The solidification process of NH4Cl-70% H2O has been numerically simulated and experimentally verified according to the solidification theory of alloy and volume-averaged heterogeneous model.Although the researchers have studied the solidification process of NH4Cl-70% H2O, it only analyzes single phenomena, such as The formation of channel segregation, the form of convection and the formation of grains.On the basis of previous studies, this paper first comprehensively studied the whole calculation domain of ammonium chloride aqueous solution solidification by means of a combination of numerical simulation and experimental comparison. Phenomenon, in particular, the reproduction of the equiaxed grains in the ingot drop drift phenomenon and the resulting convection, and more in-depth study of the formation of segregation was found by the calculation of equiaxed grains settlement from the wall and gradually to the mold At the bottom, after the volume fraction reaches a critical value, the columnar crystal ceases to grow, and the columnar crystal equiaxed crystal transformation is completed. Due to the solute redistribution, the region where the bottom crystal is concentrated forms a negative segregation and forms in the upper region that has not solidified A large range of positive segregation.Experimental verification found that the drop of equiaxed grains in the ingot drift phenomenon and the convection form of the predictive value and the experimental value Consistent, so that the solidification process so fully reveal the mobile solid phase and convection are key factors macrosegregation.