Improvement of high-temperature oxidation resistance of titanium nitride and titanium carbide films by aluminum ion implantation

Thermal oxidation behaviors of aluminum ion implanted titanium nitride and titanium carbide films have been studied in a dry oxygen atmosphere. TiN and TiC films of approximately 2 mu m in thickness were prepared on 18-8 stainless steel (corresponding to AISI 304) substrates by hollow cathode discharge ion plating. Aluminum ion implantation was performed at an energy of 50 keV with doses of 1 x 10(17) and 3 x 10(17) ions cm(-2). Continuous oxidation tests were carried out on TiN and TIC films implanted with Al, and oxidation inhibition was evaluated from their mass gain. The structure of oxide layers formed by oxidation was characterized using an X-ray diffractometer (XRD). Surface morphology and cross-sectional evaluations of the oxides were carried out by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical bonding states of elements in surface layers of films. The oxidized surface of as-deposited TIN films have rutile TiO2 above the temperature of 873 K, and those of as-deposited TiC films have anatase TiO2 below 873 K or rutile TiO2 above 873 K. However, Al implantation caused the oxidation rate of TiN and TIC films to slow down at the initial stage of oxidation. In the case of TIN films implanted with 3 x 10(17) Al cm(-2) and oxidized at 1073 K for 2 h, the Al-2p XPS spectrum reveals oxide states as Al2O3, although no oxides were found on XRD patterns. The same phenomenon has been recognized on TiC films that were implanted with 3 x 10(17) Al cm(-2) and oxidized at 773 K for 2 h. The Al oxides formed on the Al implanted TiN and TIC films are considered to improve the oxidation of these films. The oxidation behaviors of the Al implanted TiN and TIC films are similar to that of the TiAlN films. (C) 1998 Elsevier Science S.A.