Abstract
The precipitation of chromium-containing phases, in both the B2 type β-phase coating matrix (nominally NiAl) and the substrate of high-activity-pack-aluminized single crystals of a nickel-base superalloy, is considered in this paper. An ‘edge-on’ transmission electron microscopy (TEM) technique is employed to examine the precipitation of M23X6, σ, α-Cr and other phases after coating and diffusion treatment and subsequent post-coating treatment at 850 and 950 °C. Initial precipitation is dominated by the formation of M23X6 in both the coating and substrate, however, in the case of single-crystal substrates the formation of this carbon-rich phase is not sustained. M23X6 precipitation is superceded by the formation of coherent precipitates of the α-Cr phase which effectively retains the basis but removes the superlattice of the β-matrix. Extensive precipitation of α-Cr has the effect of changing the balance of chromium to molybdenum in solution in the β-phase and further precipitation is dominated by Σ-phase intermetallics and other Cr-Mo-containing phases.
Original language | English |
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Pages (from-to) | 4347-4354 |
Number of pages | 8 |
Journal | Journal of Materials Science |
Volume | 28 |
Issue number | 16 |
DOIs | |
Publication status | Published - 15 Aug 1993 |
Keywords
- aluminum alloys
- chromium
- coatings
- superalloys
- transmission electron microscopy
- beta phase coating matrix
- nickel aluminide
- nickel base superalloy single crystals
- phase precipitation
- age hardening