Improved Hardness, Wear and Corrosion Resistance of Inconel 718 Treated by Hot Wall Plasma Nitriding

In this study, Inconel 718 superalloy was treated using the hot wall plasma nitriding (HWPN) technique. This treatment was performed in 75% N-2 + 25% H-2 atmosphere at temperatures 400, 450, and 500 degrees C for 6 h. Through this process, the chamber wall temperature was 400 degrees C. X-ray diffraction, scanning electron microscopy, and micro-hardness measurement were used to characterize the modified samples. The pin-on-disk method was used to examine the wear behavior of the samples. Potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution were utilized to study corrosion characteristics. The results showed that the nitrided layers with appropriate thickness still form at moderate treatment temperature. Moreover, surface hardness increased up to about four times after HWPN (at 500 degrees C). Nitriding at 450 degrees C produced a higher corrosion resistance, a considerable increase in surface hardness, improved wear resistance, and the most expanded fcc-phase (gamma(N)) among all samples.