Characterization of thin solid films containing yttrium formed by electrogeneration of base for high temperature corrosion applications Jean-Michel Brossard, Josseline Balmain, Juan Creus, Gilles Bonnet * Laboratoire d’Etudes des Mate´riaux en Milieux Agressifs, Universite´ de La Rochelle-Avenue Michel Cre´peau, 17000 La Rochelle, France Received 26 June 2003; accepted in revised form 16 January 2004 Available online 15 April 2004 Abstract Mixed water – ethyl alcohol solutions of Y(NO 3 ) 3 , 6H 2 O at 0.01 M were used for cathodic electrodeposition of Y(OH) 3 thin films on Ni – 20 wt.% Cr – 1.5 wt.% Si substrate. Y(OH) 3 , xH 2 O deposits were obtained using a conventional three electrode cell. Current density and duration of deposition were optimized in order to obtain thin (<1 Am), uniform and adherent films. These deposited films were further transformed by thermal treatment into Y 2 O 3 coatings, expected to increase the high temperature oxidation resistance of the substrate. Thermal stability, microstructure and formed phase of as deposited films and thermally treated films were characterized by differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron and atomic force microscopies (SEM, AFM), inductively coupled plasma- optical emission spectroscopy (ICP-OES) and X-ray diffraction. D 2004 Elsevier B.V. All rights reserved. Keywords: Electrochemical deposition; Thin film; Yttrium oxide; Chromium alloy 1. Introduction Rare earth (RE) oxide thin films exhibit important phys- ical, chemical and thermal properties which are of great interest for numerous technological applications such as electrochemical sensors [1] , high T c superconductive REBCO thin films [2], optical coatings [3], protective coat- ings [4], etc. In this last case, it is well known that rare earth elements [5] or RE oxide films [6] improve the high temper- ature behaviour of chromia- and alumina-forming alloys. The chromia-forming alloys lifetime can be enhanced by any of the following mechanisms: (i) decrease of the Cr content required to develop a continuous Cr 2 O 3 protective layer; (ii) reduction of oxidation rate; and (iii) increase of oxide scale adherence and spallation resistance. The more typical tech- niques used to obtain thin (<1 Am) RE oxide films for corrosion protection are magnetron sputtering [7], chemical vapour deposition (CVD) [8] , metallo-organic CVD (MOCVD) [9], sol–gel [10] and electrophoresis [11]. How- ever, the cathodic electrolytic deposition method, described by Switzer [12], is emerging as an attractive substitute to the above-mentioned techniques to obtain various hydroxide/ oxide deposits [12–16] or co-deposits [17,18]. This process is achieved via precipitation of metal ions present in aqueous or mixed water –ethanol solutions [19,20] with electrogen- erated base, forming a hydroxide deposit on the metallic substrate. An appropriate thermal treatment allows the con- version of the hydroxide film into the corresponding oxide film. This way is an alternative to the method using organic solvents to produce RE containing films, commonly employed to avoid release of H 2 gas bubbles produced by water reduction at the typical deposition potentials of reactive elements. This technique also presents important advantages such as a good control of film thickness and morphology, by con- trolling bath composition and deposition parameters. Fur- thermore, the electrodeposition technique requires low cost equipment, permits film formation on complex shaped sub- strates, and deposition rate is higher than with other methods. The purpose of this work is to determine the adequate parameters of cathodic electrolytic deposition of Y(OH) 3 films from mixed water–ethyl alcohol solutions of Y(NO 3 ) 3 , 6H 2 O to obtain, after thermal treatment, thin, adherent and uniform Y 2 O 3 films for high temperature purposes. 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.01.019 * Corresponding author. Tel.: +33-05-46-45-82-63; fax: +33-05-46-45- 72-72. E-mail address: gilles.bonnet@univ-lr.fr (G. Bonnet). www.elsevier.com/locate/surfcoat Surface & Coatings Technology 185 (2004) 275– 282