On the evolution of cast microstructures during processing of single crystal Ni-base superalloys using a Bridgman seed technique
On the evolution of cast microstructures during processing of single crystal Ni-base superalloys using a Bridgman seed technique
复制标题
DOI：
10.1016/j.matdes.2017.05.001
复制
发表时间：
2017-08-15
影响因子：
8.4
通讯作者：
Frenzel, J.
中科院分区：
文献类型：
--
作者：
Hallensleben, P.;Schaar, H.;Frenzel, J.
本研究采用改进的Bridgman工艺（Bridgman seed technology， BST）生产直径/长度为12/ 120mm的实验室镍基单晶（SX）高温合金圆柱体。这种类型的试样需要进行廉价的参数研究，以开发新的SX，并了解SX铸造过程中微观组织的演变。在融化过程中，种子部分融化。基本偏析过程引起某种类型的本构加热/冷却。竞争增长最终建立了一个恒定的平均枝晶间距。在目前的工作中，记录了这种枝晶间距如何在一个圆柱形铸锭中变化，以及当生产一系列SX铸锭时它是如何分散的。这类信息是稀缺的。计算得到的固液界面温度梯度（FEM计算）与Kurz-Fisher方程的预测非常吻合，该方程根据实验提取速率和微观结构决定的平均枝晶间距得到枝晶间距。在垂直于凝固方向的截面上存在的小角度晶界可以通过与单个初生枝晶理想生长方向的小偏差来加以合理化。
The present work takes a new look at a modified Bridgman process (Bridgman seed technique, BST) for the production of laboratory Ni-base single crystal (SX) superalloy cylinders of 12/120 mm diameter/length. This type of specimen is needed to perform inexpensive parametric studies for the development of new SX and for understanding the evolution of microstructures during SX casting. During melting, the seed partially melts back. The elementary segregation processes cause a certain type of constitutional heating/cooling. Competitive growth eventually establishes a constant average dendrite spacing. In the present work it is documented how this dendrite spacing varies in one cylindrical ingot, and how it scatters when a series of SX ingots is produced. This type of information is scarce. The calculated temperature gradient across the solid/liquid interface (calculated by FEM) is in excellent agreement with predictions from the Kurz-Fisher equation which yields a dendrite spacing based on the experimental withdrawal rate and the microstructurally determined average dendrite spacing. The presence of small angle grain boundaries on cross sections which were taken perpendicular to the solidification direction can be rationalized on the basis of small deviations from the ideal growth directions of individual primary dendrites.