Conseil national de recherches du Canada. Aérospatiale
ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, GT 2014, 16 June 2014 through 20 June 2014
Aluminum; Cathodes; Deposition; Electrodes; Energy dispersive spectroscopy; Heat treatment; Microstructure; Nickel; Porosity; Scale (deposits); Scanning electron microscopy; Single crystals; Sintering; Spark plasma sintering; X ray diffraction; Cathodic arc deposition; Coating microstructures; Duplex microstructures; Heat-treated coatings; Ni-base single crystal superalloy; Postdeposition heat treatment; Two-step heat treatment; X-ray diffraction techniques; Aluminum coatings
NiCrAlY overlay coatings were applied on Ni-base single-crystal superalloy CMSX-4 substrates by cathodic arc deposition. The coated specimens were subjected to one- and two-step heat treatments performed under 870°C/20h/AC (AC stands for air cooling) and 1140°C/6h/AC+870°C/20h/AC conditions, respectively. The microstructure of the original NiCrAlY cathodes fabricated by spark plasma sintering and the as-deposited as well as heat-treated coatings were characterized using the scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction techniques. It was observed that the cathodes contained multiple phases uniformly distributed across the cathode volume. The as-deposited coatings exhibited a duplex microstructure consisting of splats and inter-splat regions with the latter showing internal porosity and a significantly lower Al concentration compared to that of the cathodes. The post-deposition heat treatments eliminated the porosity but further reduced the Al content, resulting in a coating microstructure dominated by the solid solution γ-Ni phase. The total thickness of the coating including the interdiffusion zone increased significantly during the two-step heat treatment. The oxide scale formed on the coating surface during heat treatment consisted primarily of α-Al2O3, with Y2O3 pegs underpinning the scale to the coating. The oxide scale was continuous on the smooth sections of the coating surface, but became fragmented at the protruding macroparticles present on the coating surface.
Date de publication
Proceedings of the ASME Turbo Expo6 (16 juin 2014).