Aluminide formation on Alloy 800 by plasma spraying and heat treatment

Abstract

ABSTRACTSpecimens of Fe–Ni–Cr based Alloy 800 were subjected to atmospheric plasma spraying using aluminum powder. Quantitative microscopic analysis of as-sprayed specimen revealed formation of aluminum-rich oxygen-containing layer (∼100 µm) on the uppermost surface, while adjoining layer (∼25 µm) comprising oxygen-rich Fe–Ni–Cr–Al-containing phase. Microscopy with quantitative analysis of as-sprayed + heat-treated (at 1273 K) substrate revealed formation of FeAl type layer (∼80 µm) on the uppermost surface with an Al-rich intermediate layer (∼25 µm) adjacent to substrate. Knoop hardness number was obtained as 764 (±20), 477 (±10), and 210 (±10) for FeAl layer, Al-rich intermediate layer, and substrate, respectively. During scratch tests at 2, 4, and 6 N loads, friction coefficient for the aluminides was recorded in the range of ∼0.05–0.15, while that was ∼0.18 for the substrate. Scratched surfaces at 2 and 4 N load tests revealed neither cracking nor peeling off at aluminides or interfaces indicating good adherence, whereas cracking occurred at aluminides during 6 N load test. Penetration depths for the aluminides were recorded as lower than that of the substrate during the scratch tests. X-ray photoelectron spectroscopy on thermally oxidized FeAl layer revealed formation of Al2O3 type oxide on the surface.