The different wall thickness of form effect samples is designed according to section and wall thickness of complex DD6 single crystal superalloy blade. The solidified microstructure of form effect sample of DD6 alloy is investigated. The results show that with the increasing of the wall thickness, the primary and secondary dendrite arm spacing increase, the extent of elements segregation is slightly increase, the size of gamma' phase particles of dendritic core and interdendritic increases, the volume fraction of gamma-gamma' eutectic increases. When the section of sample gradually increases, the single crystal enlarges to grow by outside dendrite branching. When the section of sample abruptly increases, the dendrite grows along cross direction because there is biggish temperature gradient in that orientation. The regions with different color have different direction, so low angle boundary or the high angle boundary is formed.
