Crystallographic investigation of grain selection during initial solidification

4th International Conference on Advances in Solidification Processes

材料科学;物理学

Esaka, H.^1 ; Kataoka, Y.^2 ; Shinozuka, K.^1

National Defense Academy, Dept. of MSE, Yokosuka, Japan^1

National Defense Academy, Graduated Stud., Yokosuka, Japan^2

关键词: Columnar grain;    Crystallographic orientations;    Grain selection;    Growth directions;    Initial solidification;    Preferred growth;    Solidified shell;    Solidified structures;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/117/1/012030/pdf
DOI  :  10.1088/1757-899X/117/1/012030

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

Normally, macroscopic solidified structure consists of chill, columnar and equiaxed zones. In a chill zone, many fine grains nucleate on the mold surface and grow their own preferred growth direction. Only a few of them continue to grow because of grain selection. In order to understand the grain selection process, crystallographic investigation has been carried out in the zone of initial solidification in this study. 10 g of Al-6 wt%Si alloy was melted at 850 °C and poured on the thick copper plate. Longitudinal cross section of the solidified shell was observed by a SEM and analyzed by EBSD. The result of EBSD mapping reveals that crystallographic orientation was random in the range of initial solidification. Further, some grains are elongated along theirdirection. Columnar grains, whose growth directions are almost parallel to the heat flow direction, develop via grain selection. Here, a dendrite whose growth direction is close to the heat flow direction overgrows the other dendrite whose growth direction is far from the heat flow direction. However, sometimes we observed that dendrite, whose zenith angle is large, overgrew the other dendrite. It can be deduced that the time of nucleation on the mold surface is not constant.