Corrosion resistance properties of reactive plasma-sprayed titanium composite coatings

Among thermal spraying methods, an attractive technical possibility lies in the fabrication of protective coatings or free-standing components by mean s of reactive plasma spraying (RPS) techniques. Using reactive gases, such as nitrogen or methane, it is possible to synthesize hard nitride or carbid e phases in reactive metals like Ti, Cr or Al. In this investigation compos ite titanium-nitrides/titanium coatings produced by RPS through a controlle d atmosphere plasma spray system (CAPS), were electrochemically tested to e valuate their corrosion behaviour. Two environments were selected: a neutra l (0.5 M NaCl) and an acid aqueous solution (0.5 h 5 NaCl + 1 M HCl). The i nfluence of porosity and nitrogen content on the corrosion resistance has b een investigated. Polarization curves of coated samples, detached coatings, AISI304 substrate and commercially pure titanium (grade 2) are also report ed and discussed. The corrosion resistance of coated samples was found to b e mainly dependent on porosity values, thus optimization of plasma spraying parameters assumes a fundamental role to obtain wear and corrosion resista nt deposits. (C) 2000 Elsevier Science S.A. All rights reserved.