Plastic strain-induced rafting of gamma prime precipitates in Ni superalloys: Elasticity analysis
Résumé
Rafting in Ni-based superalloys is investigated by examining the dependence of elastic energy on the shape and orientation of gamma prime particles.
The precipitation misfit strain and the plastic strain occurring in the matrix are taken into account. The elastic energies associated
with spherical or disc-shaped particles with different orientations are evaluated for some combinations of transformation strain and
matrix plastic strain. The anisotropy in elastic constants as well as the difference in elastic constant between the particles and matrix
are taken into account. It is found that the elastic energy becomes minimum when gamma prime particles adopt a certain shape and direction with
respect to the elongation axis [001]. These results are in agreement with the rafted morphologies observed in crept superalloys. The onset
of the shearing of rafted gamma prime particles, leading to accelerated creep of the alloy, is also discussed by examining the stress state of rafted gamma prime particles
particles.