  A mesoscale study of a single crystal nickel-base superalloy subjected to an
industrially relevant process simulation has revealed the complex interplay
between microstructural development and the micromechanical behaviour. As
sample gauge volumes were smaller than the length scale of the highly cored
structure of the parent material from which they were produced, their subtle
composition differences gave rise to differing work hardening rates, influenced
by varying secondary dendrite arm spacings, gamma-prime phase solvus
temperatures and a topologically inverted gamma/gamma-prime microstructure. The
gamma-prime precipitates possessed a characteristic `X' morphology, resulting
from the simultaneously active solute transport mechanisms of thermally
favoured octodendritic growth and N-type rafting, indicating creep-type
mechanisms were prevalent. High resolution-electron backscatter diffraction
(HR-EBSD) characterisation reveals deformation patterning that follows the
gamma/gamma-prime microstructure, with high geometrically necessary dislocation
density fields localised to the gamma/gamma-prime interfaces; Orowan looping is
evidently the mechanism that mediated plasticity. Examination of the residual
elastic stresses indicated the `X' gamma-prime precipitate morphology had
significantly enhanced the deformation heterogeneity, resulting in stress
states within the gamma channels that favour slip, and that encourage further
growth of gamma-prime precipitate protrusions. The combination of such
localised plasticity and residual stresses are considered to be critical in the
formation of the recrystallisation defect in subsequent post-casting
homogenisation heat treatments.
