Development Of Aluminide Coatings On Ni-Cr-Fe Based Superalloy 690 Substrates For High Temperature Applications Using Atmospheric Plasma Spraying Technique

Ni-Cr-Fe based superalloy 690 substrates were subjected to atmospheric plasma spraying using aluminium powder. SEM-EDXS analysis of as-sprayed sample indicated mainly aluminium layer on the topmost surface and similar to 25 mu m thick adjoining layer rich in Al and Ni, while analysis of heat-treated (1273 K) substrate revealed formation of multilayer (similar to 50 mu m) next to the aluminium layer comprising Cr-aluminide + ( Ni, Cr) Al, NiAl, ( Ni, Cr) 3Al and Cr-rich layers. Scratch test indicated good adherence of the multilayer. The friction coefficient for the substrate and the layers was recorded as similar to 0.2 and 0.1, while the penetration depth was 1.3 mu m and 0.9 mu m respectively.