High temperature cyclic oxidation behavior of magnetron sputtered Ni-Al thin films on Ni- and Fe-based superalloys

Ni-Al thin films were deposited on Ni- and Fe-based superalloys by RF magnetron sputtering in this work. The microstructures of the as-deposited films were characterized by XRD, AFM, and FE-SEM/EDS. The grain size of the Ni-Al thin films, using XRD results, was found to be 8.1 nm, 9.22 nm and 16.04 nm for Superni 76 (SN 76), Superni 750 (SN 750) and Superfer 800 (SF 800), respectively. The surface roughness of NiAl coated superalloys was calculated by using its AFM images and it showed a regular smooth surface. The Ni-Al thin films deposited superalloys were subjected to oxidation studies at 900 degrees C for 100 cycles. The kinetics of oxidation was determined from the weight change of the samples monitored under cyclic conditions. The oxide scales formed on the bare and Ni-Al deposited superalloys were characterized to elucidate the mechanisms of high temperature oxidation. The SF 800 superalloy has provided a better oxidation resistance in the given environment compared to SN 76 and SN 750 alloy. The weight gain was high in case of Ni-Al coated SN 750 but it was less on the coated SF 800 alloy, indicating a better protection among the coated superalloys. (C) 2008 Elsevier B.V. All rights reserved.