Chemical state of nitrogen in a high nitrogen face-centered-cubic phase formed on plasma source ion nitrided austenitic stainless steel

Abstract

A single high nitrogen face-centered-cubic phase (γN) was formed on the plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel. Auger electron spectroscopy and x-ray photoelectron spectroscopy, in conjuction with ion beam sputtering, were used to determine the chemical composition and bonding of nitrogen in the γN phase. The chemical composition of the γN phase was shown as a formula with atomic fraction (Fe0.60,Cr0.22,Ni0.18)2N. The γN phase possessed weaker Cr–N ionic-type bonds and stronger Fe–N ionic-type bonds, compared with the stoichiometric nitrides. The Cr2p3∕2 binding energy was 1.1eV lower than that of CrN and Cr2N phases (at 575.5eV). The chemical shift of the Fe–N bonding compared with the Fe–Fe bonding was nearly 2.1eV. The N1s binding energies showed that the nitrogen was in the chemical state with iron (at 396.6eV) and chromium (at 397.7eV). All the chromium appeared to be in the Cr–N bond. A part of iron was also observed in the nitride state, and all the nickel was contained in the metallic state.