Crystallographic evolution of low-angle boundaries

Subgrain misorientation is a primary factor in the quality evaluation of directionally solidified, single-crystal alloy components. In this study of a Ni-base alloy, the crystallographic evolution of an array of dendrites was characterized using a combination of electron diffraction techniques. Electron backscatter diffraction (EBSD) was used to map localized orientation measurements and track changes in the subgrain orientation distribution. The orientation measurements were also used to characterize the subgrain boundary misorientation distribution. A misorientation axis figure (MAF) was designed to assess the misorientation distribution of a low-angle boundary array. The analysis quantitatively characterizes two combating trends toward divergence and convergence of a dendritic array during solidification.; Transmission electron microscopy (TEM) was also used to analyze subgrain boundaries in the directionally solidified alloy. Dark-field imaging at a particular diffraction condition was used to identify a boundary layer structure. This structure may indicate the presence of a wetted boundary layer after bulk solidification of the alloy. A novel semi-automatic technique was also developed to track the crystallographic orientation of the subgrain boundary. The methods and analyses resulting from this research have direct applications in the fields of casting, thermal spray processing, powder metallurgy, welding and other processes involving controlled solidification of crystalline materials.