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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Fe4N by Materials Project

Fe4N crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. there are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a linear geometry to four equivalent Fe and two equivalent N atoms. All Fe–Fe bond lengths are 2.60 Å. Both Fe–N bond lengths are 1.84 Å. In the second Fe site, Fe is bonded to twelve equivalent Fe atoms to form FeFe12 cuboctahedra that share corners with twelve equivalent FeFe12 cuboctahedra, faces with six equivalent FeFe12 cuboctahedra, and faces with eight equivalent NFe6 octahedra. N is bonded to six equivalent Fe atoms to form NFe6 octahedra that share corners with six equivalent NFe6 octahedra and faces with eight equivalent FeFe12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe4N by Materials Project

Fe4N crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Fe sites. In the first Fe site, Fe is bonded to twelve Fe atoms to form FeFe12 cuboctahedra that share corners with six equivalent FeFe12 cuboctahedra, corners with six equivalent NFe6 octahedra, edges with twelve equivalent FeFe12 cuboctahedra, faces with twelve equivalent FeFe12 cuboctahedra, and a faceface with one NFe6 octahedra. The corner-sharing octahedral tilt angles are 42°. There are a spread of Fe–Fe bond distances ranging from 2.44–2.58 Å. In the second Fe site, Fe is bonded in a 3-coordinate geometry to three equivalent Fe and three equivalent N atoms. All Fe–N bond lengths are 1.92 Å. N is bonded to six equivalent Fe atoms to form NFe6 octahedra that share corners with twelve equivalent FeFe12 cuboctahedra, edges with six equivalent NFe6 octahedra, and faces with two equivalent FeFe12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of nitriding on mechanical and microstructural properties of Direct Metal Laser Sintered 17-4PH stainless steel

In this work, the effect of the nitriding process on microstructure and mechanical properties of additively manufactured (AM) 17-4PH stainless steel is investigated. The nitriding was performed at 530 °C, 560 °C, and 580 °C for 2 h. The nitriding process improves the hardness and surface roughness of the AM 17-4PH steel. Detailed microstructural characterizations of both as-built and nitride samples are performed using an optical microscope, scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction technique. It reveals that the nitride layer thickness increases with nitriding temperature. A distinct transition layer between the substrate and nitride layer is observed in the 560 °C and 580 °C nitride samples. The nitriding process develops almost equiaxed grain microstructure with new secondary phase precipitates, whereas in the as-built material, the grains are primarily columnar along the AM process build direction. Specifically, the nitriding process introduces γ-Fe4N, ε-Fe3N, CrN, and Ni3N precipitates. The increase in Ni- and Cu-rich precipitates with the nitriding temperature explains the observed improvement in the hardness and surface roughness. Furthermore, the nitriding process does not alter the substrate's initial weak crystallographic texture.

17-4PH steel↗