Electron Microscopy Study of the Precipitation of Rhenium in the B₂ Nickel Aluminide
Precipitation of rhenium in β-NiAl was studied by analytical and high resolution electron microscopy. Extended solid solutions were created by solidification processing, and the precipitation and hardening behavior were studied. Evidence suggests that rhenium is initially precipitated as disks parallel to 100 of β-NiAl. Subsequent growth produces either a rod morphology or a pair of twin-related rods that form the shape of a butterfly. The twin plane of the butterfly is 1̄011 and this plane is nearly parallel to 11̄0 of β-NiAl. A twinning transformation given by K1 = 1̄011, K2 = 1̄ 013, η1 = 〈1̄012̄〉, and η2 = 〈3̄032̄〉 was determined for the butterfly-shaped particles. All of the precipitates exhibited an orientation relationship consisting of parallel close-packed planes and directions, i.e., (101)∥(0001) and [111̄]∥[12̄10]. Performing the twinning transformation on a rhenium precipitate produces a variant rather than a new orientation relationship. After elevated temperature aging, a rod morphology was observed with the rod axes aligned parallel with either 〈12̄1̄〉 or 〈131̄〉 of the β-NiAl matrix. A total of 24 different variants are possible based upon the observed orientation relationship and the two observed growth directions.
D. C. Van Aken et al., "Electron Microscopy Study of the Precipitation of Rhenium in the B₂ Nickel Aluminide," Journal of Materials Research, Materials Research Society, Jan 1993.
The definitive version is available at https://doi.org/10.1557/JMR.1993.2524
Materials Science and Engineering
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© 1993 Materials Research Society, All rights reserved.