U-2Nb合金凝固过程的计算机模拟

Modeling of Solidification of U-2Nb Alloy

用ViewCast软件对U 2Nb合金管形铸件的凝固过程进行了计算机模拟,初步分析了夹杂、疏松缺陷形成的原因。采用具有一定温度梯度的铸型温度初始条件以及经最小二乘法拟合的热物性参数。充型过程的速度矢量图表明,顶注式使金属液呈现紊流特征,造成夹杂物在铸件内随机分布;温度场的变化表明,铸件自下而上顺序凝固,计算温度值与实测温度值符合较好;由于U Nb合金具有较宽凝固温度区间,在凝固过程中因枝晶阻碍液体金属的流动而不能有效地补缩,容易产生疏松缺陷,模拟预测的疏松缺陷定性地与实际铸件经过γ射线无损探伤结果一致。

Solidification of tube-shaped U-Nb alloy was simulated by ViewCast software and the causes of inclusion and shrinkage defects were analyzed. Initial condition of mould temperature with a given gradient and least squares fitted thermophysical properties were adopted. The calculated velocities of mould-filling indicates the turbulence of liquid metal caused by top-filling, which results in the stochastic distribution of inclusion in casting. Variety in temperature fields indicates a progressive solidification from the top to down and a good agreement of calculated results compared with tested results. With a wider range of solidifying temperature, flowing liquid metal is blocked by dendrite and can't effectively compensate the shrinkage. Thus the shrinkage defects can easily come into being. The simulated forecast of shrinkage defects shows a good agreement with that of tested casting by qualitative comparison with γ-ray non-destructive test.