Nitriding Kinetics of Inconel 600

Ni-based alloys are preferred as structural materials over austenitic stainless steels in nitrogen containing atmospheres like in neutron detectors due to severe problem of nitriding of stainless steels and subsequent loss of nitrogen. Extensive work has been carried out in literature on the nitriding behavior of austenitic stainless steels whereas similar information on Ni-based alloys is very few. Hence, to assess the nitriding kinetics of a Ni-based alloy (Inconel 600) nitriding experiments were carried out. Inconel 600 was plasma nitrided at temperatures in the range of 450–600 °C for time durations of 1 to 24 h. Evolution of the microstructure and kinetics of nitrided layer formation and its growth were investigated using various experimental techniques like electron probe micro-analysis and electron microscopy. Nitriding at a temperature of 600 °C for 24 h resulted in the formation of a nitrided zone of ~ 14 μm thickness. Inconel 600 was found to get internally nitrided resulting in the formation of nano-meter sized fcc CrN precipitates in Cr depleted Ni–Fe based matrix phase. Diffusion coefficient and activation energy values for the diffusion of nitrogen in fcc Ni-based matrix were evaluated using the studies on kinetics of growth of nitrided layer. These values were compared with the available information in literature on other Ni–Cr–Fe alloys.