Formation of stray grain in cross section area for Ni-based superalloy during directional solidification

Abstract

Stray grains which may appear during production of single-crystal blades, can severely deprave the performance of turbine blades. This investigation primarily explores the conditions of stray grains formed in DZ417G superalloy by using samples with varying cross sections. The effect of withdrawal velocities on the microstructure of DZ417G superalloy in directional solidification is investigated. It is observed that the growth direction of dendrites did not change, and no stray grain appears in the re-entrant corner at low withdrawal velocity. Nevertheless, the stray grains grow up when the withdrawal velocity is higher than 150μm/s. The temperature profiles in the region of the cross section change at different velocities are examined. The increase of undercooling in the corner of the cross section change leads to the formation of stray grains.