A protective nanocrystalline aluminum oxide layer forms during oxidation of Al-implanted TiN thin film coating on stainless steel substrate. TiN itself has poor chemical stability at elevated temperatures in an oxidizing atmosphere. Implantation of Al-ions to a TiN film, prepared by hollow cathode discharge ion plating (HCD-IP), at 4.5 × 1017 ions·cm-2 has greatly improved thermal oxidation resistance at temperatures up to 973 K and for periods up to 20 h in a pure oxygen atmosphere. Al-implantation significantly reduced the oxidation rate of the TiN. The apparent activation energy for oxidation increased with increasing Al-dose. At the initial stage of oxidation, free metallic aluminum and/or new AlN- or more likely (Ti, Al)N-reacted with oxygen prior to oxidation of TiN. The thin aluminum oxide layer formed on the implanted samples was dense and free from surface flaws. This layer is thought to act as a barrier to oxygen migration protecting the TiN film from further oxidation. The diffusion of Al-atoms was a driving mechanism to activate the protection of TiN at high oxidation temperatures. The alteration of the oxidation kinetics and mechanism of the implanted TiN in an oxygen atmosphere is a consequence of the effective modification of oxide properties through Al incorporation.
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