Formation of Secondary Reaction Zones in Diffusion Aluminide-Coated Ni-Base Single-Crystal Superalloys Containing Ruthenium

Abstract

The formation of secondary reaction zones (SRZs) beneath aluminide coatings in several Ru-bearing single-crystal Ni-base superalloys has been investigated. The presence of significant amounts of Ru in the superalloys did not prevent the formation of the secondary reaction zone. However, the Ru content of the alloys affected the type of refractory element-rich phase formed during the transformation. As the Ru content increased, the phase involved in the transformation shifted from the orthorhombic P to the b-RuAl phase. A differential tendency to SRZ formation was observed between the dendritic and interdendritic regions of the alloys. Significant growth of the SRZ was also observed during the high-temperature oxidation exposure of the coated alloys. The effects of the alloying elements on SRZ formation are discussed.

A magnetron sputtered microcrystalline β-NiAl coating for SC superalloys. Part I. Characterization and comparison of isothermal oxidation behavior at 1100°C with a NiCrAlY coating

“…Similar results were found in a MCrAlY coated Co-based superalloy [47]. Das et al [42] pointed out that no SRZ formed in the SC superalloys coated by Pt-Hf modified ␥-␥ coatings. In this work, however, SRZ in the NiCrAlY coated specimens was observed too.…”

“…2d). It is well known that the solidsolubility of refractory elements such as Cr, W, Mo and Re in ␥-Ni are much higher than that in ␤-NiAl and ␥ -Ni 3 Al [42]. So, when the ␥-Ni phases transform into ␤-NiAl as a result of inward diffusion of Al, the refractory elements will precipitate out and aggregate into particles.…”

“…7). The formation of SRZ in Re-bearing nickel-based SC superalloys with coatings has been extensively studied [42,43]. The inward diffusion of Al from the coatings into the substrates leads to the phase transformation from ␥ to ␤ or ␥ to ␥ in the substrate.…”

Effect of Surface Treatment and Crystal Orientation on Microstructural Changes in Aluminized Ni-Based Single-Crystal Superalloy

“…Since the SRZ formation can destroy the and 0 coherent two-phase microstructure, which accordingly leads to a deterioration of mechanical properties of the substrate, understanding of formation kinetics of SRZ is important. [5][6][7][8] On the other hand, microstructural anisotropy of Ni-based superalloys which were fabricated by the directionally solidified method can cause anisotropic microstructural differences. There is another important report which revealed that surface re-crystallization formed during service at elevated temperatures was promoted by the residual stress that had been applied to the components during machining.…”

Microstructural stability in multi-alloy systems: Nanostructured two-phase, dual alloy multilayers

“…In a similar fashion, enhanced microstructural coarsening will take place when a coarse microstructure is in contact with a fine one. Typical examples include the development of precipitate-free zones and secondary reaction zones, as well as the formation of new phases [16][17][18][19][20]. Of scientific interest and technical importance is the fact that the new microstructures formed in the interdiffusion or reaction zones are significantly different from the starting microstructures of the individual alloys.…”