Nitriding of yttria-stabilized zirconia in atmospheric pressure microwave plasma
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R.P. Cardoso and T. Belmonte Institut Jean Lamour, Nancy-Universite´, CNRS, 54042 Nancy Cedex, France
C.A. Figueroa, C.A. Perottoni, J.E. Zorzi, and G.V. Soaresa) Universidade de Caxias do Sul, 95070-560 Caxias do Sul, Rio Grande do Sul, Brazil
I.J.R. Baumvol Universidade de Caxias do Sul, 95070-560 Caxias do Sul, Rio Grande do Sul, Brazil; and Universidade Federal do Rio Grande do Sul, Instituto de Fı´sica, 91501-970 Porto Alegre, Rio Grande do Sul, Brazil (Received 4 February 2009; accepted 23 March 2009)
High temperature plasma nitriding of yttria-partially-stabilized zirconia in atmospheric pressure microwave plasma was investigated. The morphological, mechanical, and physicochemical characteristics of the resulting nitrided layer were characterized by different methods, such as optical and scanning electron microscopy, microindentation, x-ray diffraction, narrow resonant nuclear reaction profiling, secondary neutral mass spectrometry, and x-ray photoelectron spectroscopy, aiming at investigating the applicability of this highly efficient process for nitriding of ceramics. The structure of the plasma nitrided layer was found to be complex, composed of tetragonal and cubic zirconia, as well as zirconium nitride and oxynitride. The growth rate of the nitrided layer, 4 mm/min, is much higher than that obtained by any other previous nitriding process, whereas a typical 50% increase in Vickers hardness over that of yttria-partially-stabilized zirconia was observed. I. INTRODUCTION
Surface nitriding of zirconia is a convenient route to obtain a superior material that has the bulk properties of a high-hardness, high-toughness ceramic, namely yttriapartially-stabilized zirconia and the surface properties of zirconium nitride or oxynitride.1–9 Indeed, the partially stabilized tetragonal phase of zirconia (ZrO2) doped with 3 mol% Y2O3 (3Y-PSZ) has high hardness (Vickers hardness 12 GPa) and high fracture toughness (6–12 MPa m1/2).9,10 Zirconium nitride (ZrN), on the other hand, is a refractory material that is even harder than ZrO2 (Vickers hardness 15 GPa)8,9 and shows good thermal and electrical conductivity.11 In addition, ZrN presents very high thermal stability,11–13 is resistant to wear, corrosion, and abrasion,13–15 and has a gold-like color.16–18 Furthermore, nitriding of zirconia is essentially performed by partial or full replacement of N for O, which is responsible for the excellent adhesion between the nitrided layer and the substrate.9,19,20 The composite obtained by surface nitriding of zirconia finds relevant applications as a protective coating of cutting tools and dies,11,14 as a diffusion a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0245 J. Mater. Res., Vol. 24, No. 6, Jun 2009
barrier and an electrical contact in integrated circuits,12 as well as in decorative coatings.21,22 In the latter, the ubiquitous formation of zirconium oxynitrides (ZrOxNy) in nearsurface regions of nitrided zirconia has been investigated, exploring the fact that the oxygen co
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