Coarsening of γ' in Ni-Al alloys aged under uniaxial compression:: III.: Characterization of the morphology

The morphological evolution of gamma' precipitates during coarsening at 640 degreesC under applied compressive stress in the range 0-150 MPa was investigated in a monocrystalline Ni-Al alloy containing nominally 13.36 at. % Al. The strain was primarily elastic. The microstructures were examined by transmission electron microscopy, primarily in the section (100) perpendicular to the applied stress. The aspect ratio of a gamma' precipitate, as well as a shape parameter which provides a measure of how cuboidal it is, were used to characterize the gamma' morphology. As the stress increases precipitates of a given size generally tend to become more non-equiaxed and their interfaces are more planar, though this depends on the gamma' volume fraction. The applied compressive stress also promotes the coalescence of gamma' precipitates. This tendency is more pronounced the higher the gamma' volume fraction and appears to be its main influence on directional coarsening during elastic deformation. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.