Improvement of oxidation-resistance of NiCrAlY coatings by application of CrN or CrON interlayer
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Yao, Q.M. Wang, Z.B. Bao, J. Gong, and C. Suna) Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
X. Jiang Institute of Materials Engineering University of Siegen, Paul-Bonatz-Str. 9-11, Siegen 57076, Germany (Received 20 March 2007; accepted 24 July 2007)
NiCrAlY coatings with and without CrN or CrON interlayer as diffusion barrier were deposited on superalloy DSM11 by arc ion plating (AIP). The oxidation performance of the coating systems was evaluated by isothermal oxidation tests at 1100 °C for 100 h. The element interdiffusion and oxidation behavior of the coating systems were described. It was found that the NiCrAlY coatings provided protective effect for the DSM11 substrate. However, serious interdiffusion between the coatings and substrate resulted in rapid degradation of the coatings. The addition of CrN or CrON interlayer between the coatings and substrate markedly decreased the interdiffusion. CrON interlayer performed better than CrN interlayer, which was attributed to the excellent diffusion barrier ability of Al2O3 layer formed in the interlayer at high temperature. Also, the NiCrAlY/CrON coating system exhibited more effective protection for DSM11 than the NiCrAlY/CrN coating system.
I. INTRODUCTION
MCrAlY (M ⳱ Ni, Co or both) coatings, with good balance of oxidation, hot corrosion, and mechanical properties, are widely used on turbine engine blades/ vanes both as standalone overlays and as bond coats for thermal barrier coatings (TBCs).1–4 NiCrAlY coatings, with low-cost and facilitated element design, are still important among MCrAlY-type coatings.5–8 At 900 or 1000 °C, NiCrAlY coatings could offer satisfying protection for the underlying substrates by formation of protective scales of Al2O3 or Cr2O3 on the coating surface during service. However, when temperature rose up to 1100 °C, the coatings would degrade rapidly.5,7 It was ascribed that at 1100 °C the intensive interdiffusion accelerated protective scales spalling and continuous protective scales of alumina (or chromia) were not regenerated because of the depletion of Cr and Al elements. Therefore, element interdiffusion was the main reason for the fast degradation of NiCrAlY coatings at 1100 °C.5
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0062 J. Mater. Res., Vol. 23, No. 2, Feb 2008
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To limit the element interdiffusion and thereby improve the oxidation resistance of coatings, developing an interlayer as diffusion barrier between the coatings and substrate was a favorable solution.9–13 CrON coatings, with the combined properties of chromium nitride (CrN) coatings and chromium oxide (Cr2O3) coatings, were investigated widely. By changing the O2/N2 flow ratios in physical vapor depostion (PVD) process, the structures and properties of CrON coatings were varied.14–16 As diffusion barrier, CrON coatings could effectively suppress the interdiffusion below 1100 °C.13 However, at higher tem
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