Characterization of sputter-deposited hydrophobic chromium doped nickel alumnide coatings for mechanical and high-temperature oxidation-resistant applications

Ni₃Al and Cr-Ni₃Al films were deposited on Inconel-718 using the DC magnetron sputtering at a substrate temperature of 400 °C. The evolution of phase, microstructure, surface topography, and mechanical properties of the deposited films have been characterized using XRD, FESEM, AFM, and nanoindentation, respectively. The results of nanoindentation showed that the hardness, modulus, and adhesive strength of the coatings increased with increase in Cr concentration in the host Ni₃Al matrix. The maximum hardness and modulus of 10.62 and 150.42 GPa respectively are shown by 5.7 at% of Cr-Ni₃Al films. The cyclic oxidation tests were performed at elevated temperatures of 900 °C, 1000 °C, and 1100 °C in the open-air environment to study the actual oxidation attack. The results of the test showed that the rate of oxidation in Ni₃Al and Cr-Ni₃Al films was low as compared to the uncoated substrate. Ni₃Al film doped with 5.7 at% of Cr-Ni₃Al has resulted in providing better protection to the substrate against oxidation attacks. The surface morphology and elemental composition of the oxidized samples were investigated using FESEM and EDS to elucidate the surface scale analysis and mechanism of oxidation due to the formation of different oxide layers.