Three-dimensional analysis of secondary γ′ precipitates in Rene-88 DT and UMF-20 superalloys

Focused ion beam serial sectioning was used to study the three-dimensional morphology of secondary gamma' precipitates in two nickel-based superalloys: Rene-88 DT, a turbine disk alloy, and UMF-20, an experimental alloy. The precipitate morphology was reconstructed using a multi-step image-processing approach, including registration, intensity corrections, segmentation and segmentation cleanup. A total of 260 dendritic precipitates were obtained for the Rene-88 DT alloy, and 477 cuboidal precipitates in the UMF-20 alloy. The shapes of these precipitates were analyzed by means of moment invariants. The cuboidal precipitates in UMF-20 are well described by an analytical superellipsoid model. The morphological evolution of the dendritic precipitates in Rene-88 DT is analyzed by combining the affine moment invariant with the dimensionless shape quotient. This approach is promising as an objective tool for the description of complex precipitate shapes. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.