Thermo-mechanical fatigue degradation of a nickel-aluminide coating on a single-crystal nickel-based alloy

Crack Progression during Sustained-Peak Low-Cycle Fatigue in Single-Crystal Ni-Base Superalloy René N5

“…Coating also affects SPLCF behavior. [9][10][11][12][13][14][15] Diffusionaluminide coating, which is based on b-NiAl, creates a composition gradient between the coating layer and the substrate alloy and forms an interdiffusion zone (IDZ), where c¢-Ni 3 Al is the matrix phase. When the surface is the crack initiation site, the easiness to initiate cracks on the surface layer and inward crack growth rate in each layer, i.e., b phase coating layer, c¢ phase in the IDZ, and c + c¢ substrate, is expected to affect the SPLCF life of the material.…”

Mechanisms Associated with Rumpling of Pt-Modified Beta-NiAl Coatings

“…The formation of even a small fraction of these cracks, in conjunction with repeated high-temperature thermal cycling, may have adverse effects on the longevity of a TBC system. Several papers have dealt with the effects of thermal mechanical fatigue (TMF) and low cycle fatigue (LCF) as failure mechanisms in aluminide coatings [51][52][53][54][55][56][57].…”

“…At higher temperatures (above 800°C) the formation of an oxide layer has been shown to be both beneficial and negative to the properties of the coating system [54]. Under externally imposed low strain conditions, the oxide layer has been shown to slow crack propagation by blunting the crack tip.…”

“…Under externally imposed low strain conditions, the oxide layer has been shown to slow crack propagation by blunting the crack tip. The formation of new cracks was able to occur and was initiated within internal micropores in the oxide [52,54]. Strain levels higher than 1.2% have resulted in growth of oxide within the crack, followed by oxide spallation.…”

“…New Al-rich oxide was then shown to reform, which resulted in Al depletion around the crack. Repeated oxidation and spallation of the scale resulted in the eventual formation of the ' phase and, in some cases, the -Ni phase [54]. The presence of these new phases in the system was said to create further stresses due to the inherent volume change associated with the transformation.…”