The process analysis of seeding-grain selection and its effect on stray grain and orientation control

A combined technique denoted as seeding-grain selection (SGS) was designed for fabricating single crystal turbine blades. The microstructural evaluation during SGS process was metallographically analyzed in both starter section and spiral section of this technique. Four zones with distinct dendritic morphologies were identified in seed melt back region. After epitaxial propagating from melted seed and branching through the spiral passage, the lined-up dendritic pattern was observed at the outlet of the passage. The effectiveness of the technique on stray grain and orientation control was also assessed by Electron Back-Scattering Diffraction (EDSD) technique. The results indicated that the technique can control stray grain with no detrimental effect on crystal orientation.