Characteristics of Cr-Al-N-O Thin Films Prepared by Pulsed Laser Deposition
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Characteristics of Cr-Al-N-O Thin Films Prepared by Pulsed Laser Deposition Makoto Hirai, Hajime Saito, Tsuneo Suzuki, Hisayuki Suematsu, Weihua Jiang and Kiyoshi Yatsui Extreme Energy-Density Research Institute, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, JAPAN. ABSTRACT Chromium aluminum oxynitride (Cr-Al-N-O) thin films have been successfully prepared by pulsed laser deposition (PLD). Experiments were carried out by changing surface area ratio of the targets (SR = SAlN / (SCr2N + SAlN)) from 0 to 100 %. The composition of the thin film prepared at SR = 75 % was determined to be Cr0.11Al0.39N0.25O0.25 by Rutherford backscattering spectroscopy (RBS). The hardness of the Cr-Al-N-O thin film was found to be above HV 4000 when the aluminum content in cations (x) was 25 at. %. The high hardness can be explained by solid solution hardening and/or increasing bulk modulus. The oxidation of the Cr-Al-N-O thin film occurred above 900 ˚C. From the result of grazing angle X-ray diffractometry (GXRD), the oxidation resistance of the Cr-Al-N-O thin film was found to be improved due to the fact that Cr2O3 and α-Al2O3 grains are formed at the outermost surface of the thin film. INTRODUCTION Hard coatings of nitrides have been prepared by physical vapor deposition (PVD). Chromium nitride (CrN), titanium nitride (TiN) and titanium aluminum nitride (Ti-Al-N) are widely used as the coatings for cutting tools in industries. In fact, Ti-Al-N has been known to exhibit the highest hardness (HV 3000) and oxidation temperature (800 ˚C) among these coatings [1,2]. However, to increase the lifetime of the coatings used under severer conditions, it is necessary to improve these properties further. Recently, much attention is paid for chromium aluminum nitride (Cr-Al-N). One of the reasons is that CrN has the highest solubility limit for aluminum nitride (AlN) among transition metal nitrides with B1 (NaCl) structure [3]. It can be related by that solid solution hardening is effective when the solubility limit is large. In addition, among metals and alloys, better oxidation behavior is achieved not only by chromium but also aluminum. An aluminum sesquioxide (Al2O3) layer, which is formed on the surface of aluminum bulks, inhibits the oxidation proceeds. Thus, Cr-Al-N is expected to improve the oxidation characteristics of CrN. Although Cr-Al-N thin films have been prepared by PVD [3,4], a comprehensive understanding of hardness and oxidation behavior is still poor. Several studies showed that the nitride thin films prepared by PVD contain the oxygen of approximately 10 at. % [5-7]. It is therefore necessary to characterize the thin films in the chromium aluminum oxynitride (Cr-AlN-O) system. We have already prepared Cr-Al-N thin films containing oxygen by pulsed laser deposition (PLD) [8]. The aim of this investigation is to reveal hardness and oxidation behavior of the Cr-Al-N-O thin films.
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EXPERIMENTAL DETAILS Thin films were deposited by the irradiation of a Nd: yttrium aluminum garnet (λ = 355 nm) laser beam onto
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