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Y.W. Bao, M.S. Li, J.Y. Wang, and Y.C. Zhoua) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China (Received 4 June 2008; accepted 21 August 2008)

The oxidation behavior of Zr2[Al(Si)]4C5 and Zr3[Al(Si)]4C6 in air has been investigated. The oxidation kinetics of bulk Zr2[Al(Si)]4C5 and Zr3[Al(Si)]4C6 at 900–1300 °C generally follow a parabolic law at a very short initial stage and then a linear law for a long period with the activation energy of 237.9 and 226.8 kJ/mol, respectively. The oxide scales have a duplex structure, consisting of mainly an outer porous layer of ZrO2, Al2O3, and aluminosilicate/mullite, and a thin inner compact layer of these oxides plus remaining carbon. The oxidation resistance of Zr2[Al(Si)]4C5 and Zr3[Al(Si)]4C6 has been improved compared with Zr2Al3C4, and is much better than ZrC due to larger fraction of protective oxidation products, Al2O3 and aluminosilicate/mullite.

I. INTRODUCTION

ZrC is characterized by high melting point, high hardness and modulus, relatively good thermal shock resistance, and chemical inertness.1,2 It also has high strength at elevated temperatures.2 It is thus a good candidate material for ultrahigh-temperature applications. However, the intrinsic brittleness and poor oxidation resistance limit its extensive applications.1–5 To overcome these problems, Zr2Al3C4 were recently developed by adding Al into ZrC; Zr2Al3C4 shows superior oxidation resistance, strength, specific stiffness, and toughness compared to ZrC.6–10 However, as a high-temperature structural material, the oxidation resistance of Zr2Al3C4 ceramic at high temperature is still unsatisfactory. The oxidation kinetics of Zr2Al3C4 follow the linear law above 800 °C because no protective Al2O3 scales formed on the substrate.9 Recently, we improved the high temperature oxidation resistance of Zr2Al3C4 by silicon pack cementation.10 It was found that a series of protective oxidation products, such as aluminosilicate glass, mullite, and ZrSiO4, retarded inward diffusion of oxygen during the oxidation of siliconized Zr2Al3C4. In addition, another layered ternary carbide, Al4SiC4, exhibits good oxidation resistance up to 1600 °C due to the formation of a continuous aluminosilicate glass that can fill up

II. EXPERIMENTAL

a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0411 J. Mater. Res., Vol. 23, No. 12, Dec 2008

http://journals.cambridge.org

pores and cracks between the grains at high oxidation temperatures.11,12 Achievements in siliconized Zr2Al3C4 and Al4SiC4 imply that the oxidation resistance of Zr2Al3C4 ceramic can possibly be improved by incorporating Si into the Zr-Al-C system. Recently, Zr2[Al(Si)]4C5 and Zr3[Al(Si)]4C6 were identified in the Zr-Al-Si-C system.13,14 Moreover, it was reported that quaternary Zr-Al-Si-C ceramics processed thermoelectric properties superior to those of ternary Zr2Al3C4 and Zr3Al3C5 carbides. Recently, we synthesized Zr2[Al(Si)]4C5 and Zr3