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The microstructure of the Ni-based superalloy IN100 processed by a powder metallurgy route was evaluated to reveal the structures, volume fractions, distributions, and chemistries of the various phases present. These data were compared with those predicted by computational thermodynamics. It is shown that the microstructural parameters expected on the basis of global equilibrium conditions differ significantly from those measured experimentally. However, modification of these calculations by use of constrained and successive equilibria compensated for kinetic effects and led to accurate (or better) predictions of phase volume fractions and chemistries in this alloy. This demonstrated that such modified phase equilibria calculations could be powerful tools for modeling microstructures, even in complex multicomponent alloys processed under nonequilibrium conditions.
Metallic glasses can form in certain Al-Gd-Ni alloys. Devitrificaion occurs on subsequent heating to intermediate temperatures and although some phases form as expected the crystal structures of others are less certain. This paper presents a summary of transmission electron microscopy (TEM) data acquired from four devitrified Al-Gd-Ni(-Fe) alloys. It is shown that the alloys exhibit nanocrystalline microstructures consisting of face-centered-cubic α-Al, binary Al3Gd, and ternary phases. An Al-(Gd,Fe)-Ni phase forms as rods and exhibits the orthorhombic Al19Ni5Gd3 structure. Plates of the rhombohedral phase Al23(Ni,Fe)6Gd4 are also present. Complex faulting is observed in both ternary phases.
The results of a transmission electron microscopy study on the crystal structures and morphologies exhibited by each of the phases in a set of four Al-rich Al-Y-Ni alloys which contain 1.7–4.5 at. % Y and 3.5–10.1 at. % Ni are presented. It is shown that each alloy contains fcc-Al, a binary Al3Ni or Al3Y phase (depending on alloy composition), and a ternary phase. The same ternary phase was found in each alloy and this was found to correspond to a new phase Al19Ni5Y3 (Cmcm, a=0.4025 nm, b=0.799 nm and c= 2.689 nm, Al19Ni5Gd3 structure type). In many cases, the ternary particles also contain embedded slabs of the equilibrium Al23Ni6Y4 phase. This phase mixture did not decompose even after extended annealing.