Surface characterisation of plasma-nitrided iron by X-ray photoelectron spectroscopy

The nitriding by plasma has the potential to improve the tribological and m echanical properties on a number of substrates, and offers various advantag es as compared with other methods used in the modification of surfaces. We prepared four samples by nitriding the iron substrates in a gas mixture (80 % H-2 and 20% N-2) under a pressure of 9.0 mbar, discharge frequency of 10 kHz and temperature of 773 K, for periods of 1, 2, 4 and 6 h. We characteri sed the samples by scanning electron microscopy (SEM), X-ray diffraction (X RD) and microhardness techniques, and detected the presence of Fe4N and Fe2 -3N phases. We employed X-ray photoelectron spectroscopy (XPS) to obtain ch emical-state and quantitative information of the plasma-nitrided iron surfa ces. In situ cleaning was carried out by argon ion bombardment. The Fe 2p(3 /2) photoelectron peaks for all samples presented three components, associa ted with Fe-0, Fe2+ and Fe3+, while the N 1s lines showed two components, t he main one due to iron nitride and the other is connected with oxidised ni trogen. (C) 1999 Elsevier Science B.V. All rights reserved.