Synthesis, characterization and properties of intensified plasma-assisted nitrided superalloy Inconel 718

Superalloy Inconel 718 (IN-718) was nitrided at relatively low temperatures (< 500 °C) by intensified plasma-assisted processing (IPAP). The structural characteristics of the nitrided layers at the surface were investigated by X-ray diffraction analysis and X-ray photoelectron spectroscopy. The IPAP-treated alloy was composed of a ∼4 μm thick single-phase layer followed by a ∼25 μm nitrogen diffusion zone. The results showed that the nitride phase formed from the anisotropic expansion of the original alloy unit cell in a similar way to that observed in the Fe–Cr–Ni system (AISI 316 austenitic stainless steel). The electron binding energy characteristics of the various elements involved in the single-phase were revealed for the first time. Micro indentation experiments showed that IPAP nitriding for 3 h caused at least a four-fold increase in the surface hardness. The nitrided surfaces were found to possess significantly improved wear and corrosion resistance. The present results show that low temperature IPAP nitriding is an effective surface treatment for IN-718.