Improving the oxidation resistance of Inconel 718 high-temperature nickel alloy using combined surface engineering technology

Abstract

To increase the oxidation resistance of the Inconel 718 Ni alloy, a hybrid technology is proposed that combines electro-spark alloying (ESA) and magnetron sputtering (MS). Multiphase ZrSiB (ESA), ZrSiB, MoSiB, and CrAlSiB (MS) electrodes were obtained by self-propagating high-temperature synthesis. The study of the structure, composition and properties of single- and double-layers has been carried out. ZrB2 (73 wt.%), Si (21 wt.%), Ni and NiSix traces (<5 wt.%) were detected in the ESA-layer. The ESA-layer had a hardness of 19 GPa and elastic modulus of 351 GPa. The ZrSiB MS-layer contained a h-ZrB2 phase with a 4 –17 nm crystallites and Si-based amorphous regions. The layer hardness and elastic modulus were equal to 22 and 256 GPa, respectively. The MoSiB MS-layer had a conical structure, contained the h-MoSi2 and B-based amorphous phases. The layer showed hardness of 27 GPa and elastic modulus of 389 GPa. The Cr2Al, CrBx, and CrSi2 phases were found in the CrAlSiB MS-layer with hardness of 19 GPa and elastic modulus of 260 GPa. The 4.8 µm oxide film was formed on the surface of the Ni alloy after annealing in air at 900°C. The depth of the oxidation for ZrSiB / ZrSiB, MoSiB / ZrSiB, and CrAlSiB / ZrSiB MS-ESA coatings was 9.2, 0.4, and 0.12 µm, correspondingly. The ESA-layer acts as barrier to reduce the diffusion of elements from the substrate. Two-layer MoSiB / ZrSiB and CrAlSiB / ZrSiB coatings increase the oxidation resistance of the Ni alloy by 12 and 40 times, respectively, and can be recommended for deposition onto aircraft engine parts.