Oxidation of Ni-toughened nc-TiN/a-SiN x nanocomposite thin films
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Xianting Zeng Singapore Institute of Manufacturing Technology, Singapore 638075 (Received 28 February 2005; accepted 6 July 2005)
Oxidation behavior of Ni-toughened reactively sputtered composite thin films of nanocrystalline TiN and amorphous SiNx [denoted as nc-TiN/a-SiNx(Ni)] was explored to understand the oxidation mechanism. The films were deposited on silicon substrate using a magnetron sputtering technique. Oxidation was carried out from 450 °C up to 1000 °C. The nature of the oxidation was determined using x-ray photoelectron spectroscopy. The microstructure of the oxidized films was studied using grazing incidence x-ray diffraction. The topography was characterized using atomic force microscopy. It was determined that the oxidation of the nc-TiN/a-SiNx(Ni) thin film proceeds primarily through a diffusion process, in which nickel atoms diffuse outward and oxygen ions inward. The oxidation takes place by progressive replacement of nitrogen with diffused oxygen. Five regions were identified in the oxidized layer from surface into the film. For films doped with 2.1 at.% Ni, a threshold temperature of 850 °C was determined, below which, excellent oxidation resistance prevails but above which, oxidation takes place at exponential rate, accompanied by abrupt increase of surface roughness.
I. INTRODUCTION
The use of hard coatings in engines, machines, tools, and other wear resistant components has achieved a high level of commercial success.1 Nanocomposite hard films have received much attention recently because they have improved mechanical2–4 properties due to the size effect;5,6 thus they become prime candidates for use in dry machining and related applications. Veprek et al.7 reported that films of nanocrystalline TiN and TiSi2 imbedded in amorphous Si 3 N 4 and amorphous TiSi 2 achieved a hardness of 105 GPa via chemical vapor deposition. Zhang et al.8,9 prepared nc-TiN/a-SiNx nanocomposite thin films with hardness about 40 GPa through reactive magnetron sputtering. However, for practical industrial applications, the highest hardness is not the primary goal. Instead, a combination of hardness, toughness and, in many cases, oxidation resistance, is a)
Address all correspondence to this author. e-mail: [email protected] This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www. mrs.org/publications/jmr/policy.html. DOI: 10.1557/JMR.2005.0357 2754
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J. Mater. Res., Vol. 20, No. 10, Oct 2005 Downloaded: 16 Mar 2015
sought after. To overcome the brittleness of bulk ceramics, usually a second ductile phase is incorporated10–12 or nanometer-sized metal particles are added13,14 to improve toughness. This also applies to thin films and coatings. Musil and co-workers embedded crystalline nitrides in metallic Cu,15,16 Ni,17–19 and Y,20 etc., for improved toughness. It is obvious that there are two aspects of reasons for choosing Ni: (i) oxidation resistanc
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