Oxidation behavior of TiN with a Ti interlayer on stainless steel
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Oxidation behavior of TiN with a Ti interlayer on stainless steel 1
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Ming-Hua Shiao , Ching-Chiun Wang , Chien-Ying Su and Fuh-Sheng Shieu 1 Precision Instrument Development Center, National Science Council, Hsinchu 300, Taiwan 2 Department of Materials Engineering, National Chung Hsing University, Taichung 402, Taiwan
ABSTRACT Characterization of the TiN coatings oxidized in air at temperatures at 600 and 700℃ for 30 min was carried out by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). TiN thin films with a Ti interlayer were prepared by hollow cathode discharge ion plating on AISI 304 stainless steel. Both XRD and TEM results show that the TiN coatings and Ti interlayer have columnar structure with (111) and (0002) preferred orientations, respectively. AFM results show the existence of pinholes on the surface of specimens due to electropolishing process of the steel substrate, and the surface roughness (Ra) changes from 3.5 nm for the as-deposited specimen to 11.6 nm after oxidation at 700℃. After oxidation, the TiO2 oxide layer formed on the specimen surface was porous and retained the columnar structure as the original TiN coating. The microstructure of the Ti interlayer gradually changed from columnar to polycrystalline structure due to grain growth. The Auger elemental depth profiling indicated that interdiffusion of the Ti interlayer with steel substrate had occurred during the oxidation process. INTRODUCTION In the past two decades, transition metal nitrides such as TiN, CrN, ZrN, (Ti,Al)N and etc. have been applied extensively in many industries. Base on the advantages of physical properties such as high hardness, low friction coefficient, good adhesion, and excellent wear resistance, titanium nitride has been applied extensively in drill, die mold and cutting tool industries [1-3]. For coating applications, especially in tools and machine parts, a good bonding strength between coating and substrate is required to warrant the service life in the application environment. However, residual stress usually exists in the coatings after deposition is completed. In order to reduce the residual stress a thin metal layer which thermal expansion coefficient between the nitride coating and substrate is often introduced, for e.g., Ti with TiN [4] and Cr with CrN [5]. The performance of the coated component depends not only on the mechanical properties of the hard coatings but also on their oxidation mechanisms [5-7]. Many investigations focused on the mechanism of thermal oxidation of TiN were carried out by X-ray photoelectron spectroscopy (XPS) [8-10]. However, the microstructure and chemistry on the interaction of the TiN coating and steel substrate, even with a Ti interlayer during oxidation process were not still studied much yet. In this study, TiN coatings with an interlayer of Ti were deposited by the hollow cathode discharge ion-plating (HCD-IP) technique on AISI 304 stainless steel. Oxidation behaviors of
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