Formation and characterization of aluminide coatings on alloy 800 substrate

Fe-Ni-Cr based Alloy 800 substrates were pack aluminized at 1273 K for 8 hours in argon atmosphere. The cross-section of aluminized substrates indicated formation of multilayer of aluminides as revealed by microscopy, electron probe microanalysis and X-ray diffraction. The outermost layer (similar to 150 mu m) was found to consist of FeAl + Fe2Al5 type phases, while the adjoining layer (similar to 250 mu m) was composed of an FeAl type phase. The innermost layer (similar to 60 mu m), which was a solid solution zone, was found to consist of similar to 43 at.% Fe, 38 at.% Cr, 11 at.% Ni containing about 6 at.% Al. In microhardness test, a hardness variation of 213 to 1098 Knoop hardness number along the cross-section was obtained. Scratch test along the cross-section at load levels ranging from 0.9 to 10 N with a loading rate of 30 N/min showed a maximum penetration depth of 12 pm indicating a good adherence of aluminide coatings. (C) 2011 Elsevier B.V. All rights reserved.