Isotope exchange investigation of nitrogen redistribution in expanded austenite

Sequential plasma and gaseous nitriding of Fe–18Cr–10Ni–3Mo stainless steel at 390°C with 14N and 15N isotopes followed by denitriding in flowing hydrogen was investigated. Redistribution of plasma-inserted nitrogen atoms (15N) by subsequent gaseous nitriding (14N) was observed. Denitriding after plasma- and gaseous nitriding resulted in predominant retraction of 14N, and only a minor amount of 15N. The nitrogen isotope diffusion behaviour is explained by two different states of nitrogen bonding and short-range ordering between nitrogen and chromium

Atom probe tomography characterization of nitrogen induced decomposition in low temperature plasma nitrided 304L austenitic stainless steel

International audienc

Atom probe tomography characterization of nitrogen induced decomposition in low temperature plasma nitrided 304L austenitic stainless steel

International audienc

Magnetic properties of single crystalline expanded austenite obtained by plasma nitriding of austenitic stainless steel single crystals

Ferromagnetic single crystalline [100], [110], and [111]-oriented expanded austenite is obtained by plasma nitriding of paramagnetic 316L austenitic stainless steel single crystals at either 300 or 400 C. After nitriding at 400 C, the [100] direction appears to constitute the magnetic easy axis due to the interplay between a large lattice expansion and the expected decomposition of the expanded austenite, which results in Fe- and Ni-enriched areas. However, a complex combination of uniaxial (i.e., twofold) and biaxial (i.e., fourfold) in-plane magnetic anisotropies is encountered. It is suggested that the former is related to residual stress-induced effects while the latter is associated to the in-plane projections of the cubic lattice symmetry. Increasing the processing temperature strengthens the biaxial in-plane anisotropy in detriment of the uniaxial contribution, in agreement with a more homogeneous structure of expanded austenite with lower residual stresses. In contrast to polycrystalline expanded austenite, single crystalline expanded austenite exhibits its magnetic easy axes along basic directions. © 2013 American Chemical Society.Peer Reviewe

The Nature and Origin of "Double Expanded Austenite" in Ni-Based Ni-Ti Alloys Developing Upon Low Temperature Gaseous Nitriding

International audienceGaseous nitriding of Ni-4 wt pct Ti alloy plates led to the development of double expanded austenite (gamma (N1) and gamma (N2)) at the surface of the nitride plates. Grazing-incidence X-ray diffraction analysis demonstrated that the component gamma (N1) is located close to the surface and the component gamma (N2) is located at a certain depth below the specimen surface, in correspondence with a layered character of the nitrided zone beneath the surface as revealed by optical microscopy. Electron probe microanalysis, atom probe tomography, and Laue microdiffraction analysis did not reveal a significant difference in nitrogen content of the gamma (N1) and gamma (N2) sublayers. By X-ray diffraction stress analysis it was shown that the only significant differences of the two expanded austenite layers is a pronounced difference in compressive stress parallel to the surface: the gamma (N1) layer is subjected to a huge compressive stress, as large as a few GPa, whereas a relatively modest stress prevails in the gamma (N2) layer