几种单晶高温合金的形核过冷度测量及相应凝固组织研究

Investigation on the undercoolability and solidification structure of some single crystal superalloys

摘要:

采用悬垂小球法在工业条件下对DD5、DD6以及 WZ30三种镍基高温合金进行熔体过冷试验，测得这三种合金的临界形核过冷度△TN分别是33、36和42K。合金DD5和DD6试样凝固时由于过冷度相对较小，形成细枝状单晶组织。合金WZ30的临界形核过冷度相对较大，试样凝固时主要形成由晶向一致的树枝状单晶基体框架和晶向散乱的碎粒状杂晶组成的的混合体组织，其中大部分碎粒状杂晶的形态和尺寸特征像是从液体中直接形核长大的等轴晶粒团簇，而不是来源于枝晶臂的熔断。

Abstract:

The undercooling behavior of 3 single crystal（SC）superalloys DD5, DD6 and WZ30 was investigated under the industrial process condition. During isothermal heating and cooling processes the liquidus temperature TL and the critical nucleation temperature TN of the alloys were measured. As the undercoolability the average critical nucleation undercooling ?TN = TL-TN was respectively determined to be 33, 36 and 42K for the 3 alloys. In the samples of alloy DD5 and DD6 with relatively low ?TN value, very fine dendritic microstructure was formed during isothermal cooling processes. In the sample of alloy WZ30 with relatively high nucleation undercooling, the solidification structure became a mixture of SC dendrite frame and grain clusters with random orientations. It appears that, the most random oriented grains were equiaxed crystal formed directly from the interdendritic residual melt, instead of dendrite arm fragment owing to remelting.