Plasma nitriding response at 400 °C of the single crystalline Ni-based superalloy MC2

Plasma nitriding of MC2, a single crystalline (γ/γ′) Ni-based superalloy, was performed at 400 °C for 1 and 4 h. Owing to its monomodal γ′ particle size distribution, MC2 was used as a model material in an attempt to investigate the behavior of precipitates during the nitriding of a γ matrix. The nitrogen profiles, the morphology, and the nature of the phases in the nitrided layer were characterized by glow discharge optical emission spectroscopy, scanning electron microscopy, and X-ray diffraction. The γ matrix appeared to be nitrided similarly to the γ solid solution in austenitic stainless steels with the development of an expanded γN phase. The amount of nitrogen in the γ matrix varies from ~30 at.% at the surface till ~20 at.% at the interface with the non nitrided matrix. On the contrary, the γ′ precipitates accommodate no more than few at.% of nitrogen. This disparity modifies the morphology and the average γ channel width increased by ~25 %.