Niyama判据对铸件缩孔缩松预测的适用性

应用ProCAST有限元模拟软件包的Niyama判据对TiAl合金十字板状铸件中肉眼可见的宏观缩孔缩松进行了预测,并通过实验进行了验证.结果表明:对于Ti-47Al-2Cr-2Nb合金十字板状铸件,判据值主要受到铸件壁厚(冷速)的影响,判据值随铸件壁厚的增加而增大,宏观缩孔缩松最严重的区域不是判据值最小的区域,而判据值最小的区域只有显微缩松而没有宏观缩孔缩松,所以无法根据判据值大小来确定宏观缩孔和宏观缩松产生的位置及大小.分析表明,Niyama判据是一种基于枝晶间显微缩松的预测判据,其判据值适用于评定显微缩松产生的倾向性,可以较准确地预测出显微缩松产生的位置.由于宏观缩孔和宏观缩松形成机理与显微缩松不同,所以不宜用于壁厚悬殊的复杂铸件宏观缩孔缩松的预测.

Applicability of shrinkage porosity prediction for casting with Niyama criterion

The macroscopic shrinkage cavity and porosity of the TiAl alloy crisscross and clintheriform casting was predicted by the finite element casting simulation software ProCAST with Niyama criterion. The prediction results were tested by experiment. The results show that for the Ti-47Al-2Cr-2Nb alloy crisscross and clintheriform casting, the Niyama criterion values are mainly affected by the casting section thickness (cooling rate). The criterion values increase with the augment of the casting section thickness. The region that the most serious of the macro shrinkage and porosity is not the region that the minimum of the criterion value. While the region that the minimum of the criterion value has only the microporosity but no macro shrinkage and porosity, so it cannot confirm the location and bulk of the macro shrinkage and porosity on the basis of the criterion values. Analyzing makes clear that Niyama criterion is founded on interdendritic microporosity, and its function values are well applied to assessing the tendentiousness of microporosity. It can well predict the microporosity. Because the formation mechanism of macro shrinkage and porosity is different from microporosity, it isn't suitable for predicting the macro shrinkage and porosity of complex castings with great disparity in casting section thickness.