Fundamental and Innovations in Plasma Assisted Diffusion of Nitrogen and Carbon in Austenitic Stainless Steels and Related Alloys

Abstract

An improvement of the surface properties of austenitic stainless steels and nickel‐based alloys is obtained by low temperature plasma assisted nitriding (PAN), plasma assisted carburizing (PAC) and plasma assisted nitrocarburizing (PANC). At low temperature, PAN treatment produces a peculiar phase usually called expanded austenite, S phase, m phase or γN phase. Replacing nitrogen by hydrocarbon for conducting a low temperature PAC gives a carburized layer containing the carbon expanded austenite phase (γC). These two phases can simultaneously be obtained by combining hydrocarbon and nitrogen in the gas phase through a low temperature PANC. Several fundamental aspects concerning the expanded austenite phases are presented in this paper.

Austenite modification of AISI 316L SS by pulsed nitrogen ion beams generated in dense plasma focus discharges

“…In addition, Christiansen et al [39] have produced stress free expanded austenite as a fine powder, showing that it has a well defined fcc structure. This finding proves that the X-ray diffraction peak deviations from the fault free positions observed in other experiments can be attributed to the lattice distortion due to the stress induced during the nitriding mechanisms themselves [41][42][43]. Furthermore, Xu et al [33] using the arc-source ion nitriding concept, have found that the amount of lattice expansion from planes of (200) is always larger than that from (111) at a specific depth, and along the full expanded austenite layer.…”

Diffusion profiles after nitrocarburizing austenitic stainless steel

“…Treatments that combine dissolution of both carbon and nitrogen, here denoted as "nitrocarburizing", can also be applied to the same material -successively or simultaneously. Unusual composition profiles have been obtained in this way [2][3][4][5][6][7][8][9][10][11]. In particular, when simultaneously nitrocarburizing (with a gas containing both nitrogenand carbon-bearing molecular species), two distinct regions are formed at the alloy surface: a nitrogen-rich layer at the outer surface and a carbon-rich layer beneath it.…”

Effect of bombarding steel with Xe+ ions on the surface nanostructure and on pulsed plasma nitriding process

“…Nevertheless, the non-bombarded sample side shows characteristic bi-layers case: one thin layer (~1.5 m) at the bottom of the layer (indicated by an arrow in Figure 7) followed by a thicker one (~8.6 m). The presence of a bi-layers case is characteristic of standard nonbombarded nitriding process [30,33]. On the other hand, the micrograph corresponding to the pre-bombarded side of the sample shows a compact nitride monolayer.…”