Jp. Gu et al., MOTION AND REMELTING OF DENDRITE FRAGMENTS DURING DIRECTIONAL SOLIDIFICATION OF A NICKEL-BASE SUPERALLOY, Metallurgical and materials transactions. A, Physical metallurgy andmaterials science, 28(7), 1997, pp. 1533-1542
The formation of spurious grains during the directional solidification
of a Ni-base superalloy is studied by modeling the movement and remel
ting of dendrite fragments originating in channels inside the mush. Su
ch channels exist because of thermosolutal convective instabilities du
ring solidification and persist as freckle chains in the solidified ma
terial. The fragment model is linked to a phase equilibrium subroutine
for multicomponent Ni-base superalloys, as well as to a previously de
veloped solidification and convection code. A parametric study is perf
ormed to investigate the effects of initial fragment location and size
on the fragment paths and survivability in the melt for one of the ch
annels predicted in a typical directional solidification simulation. I
t is found that only a small window of initial conditions exists which
leads to spurious grain formation. This window corresponds to medium-
sized fragments originating near the mouth of the channel. Other fragm
ents either remelt completely or sink into the channel. The need for a
n accurate fragment generation model is discussed.