Scholz Felicitas, Cevik Mustafa, Hallensleben Philipp, Thome Pascal, Eggeler Gunther, Frenzel Jan
Institute for Materials (IFM), Ruhr University Bochum, Universitätsstraße 150, 44801 Bochum, Germany.
Materials (Basel). 2021 Aug 28;14(17):4904. doi: 10.3390/ma14174904.
Ni-based single crystal superalloys contain microstructural regions that are separated by low-angle grain boundaries. This gives rise to the phenomenon of mosaicity. In the literature, this type of defect has been associated with the deformation of dendrites during Bridgman solidification. The present study introduces a novel serial sectioning method that allows to rationalize mosaicity on the basis of spatial dendrite growth. Optical wide-field micrographs were taken from a series of cross sections and evaluated using quantitative image analysis. This allowed to explore the growth directions of close to 2500 dendrites in a large specimen volume of approximately 450 mm. The application of tomography in combination with the rotation vector base-line electron back-scatter diffraction method allowed to analyze how small angular differences evolve in the early stages of solidification. It was found that the microstructure consists of dendrites with individual growth directions that deviate up to ≈4° from the average growth direction of all dendrites. Generally, individual dendrite growth directions coincide with crystallographic <001> directions. The quantitative evaluation of the rich data sets obtained with the present method aims at contributing to a better understanding of elementary processes that govern competitive dendrite growth and crystal mosaicity.
镍基单晶高温合金包含由低角度晶界分隔的微观结构区域。这就产生了镶嵌现象。在文献中，这类缺陷与布里奇曼凝固过程中枝晶的变形有关。本研究引入了一种新颖的连续切片方法，该方法能够基于枝晶的空间生长来合理解释镶嵌现象。从一系列横截面获取光学宽视场显微照片，并使用定量图像分析进行评估。这使得能够在约450立方毫米的大样本体积中探究近2500个枝晶的生长方向。断层扫描与旋转矢量基线电子背散射衍射方法相结合的应用，使得能够分析凝固早期微小角度差异是如何演变的。研究发现，微观结构由具有各自生长方向的枝晶组成，这些生长方向与所有枝晶的平均生长方向偏差高达约4°。一般来说，单个枝晶的生长方向与晶体学<001>方向一致。用本方法获得的丰富数据集的定量评估旨在有助于更好地理解控制竞争性枝晶生长和晶体镶嵌的基本过程。
