High-temperature oxidation and hot corrosion of Cr 2 AlC Z.J. Lin a,b , M.S. Li a , J.Y. Wang a , Y.C. Zhou a, * a Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China b Graduate School of Chinese Academy of Sciences, Beijing 100039, China Received 26 May 2007; received in revised form 8 July 2007; accepted 11 July 2007 Available online 27 August 2007 Abstract High-temperature oxidation and hot corrosion behaviors of Cr 2 AlC were investigated at 800–1300 °C in air. Thermogravimetric–dif- ferential scanning calorimetric test revealed that the starting oxidation temperature for Cr 2 AlC is about 800 °C, which is 400 °C higher than other ternary transition metal aluminum carbides. Thermogravimetric analyses demonstrated that Cr 2 AlC displayed excellent high- temperature oxidation resistance with parabolic rate constants of 1.08 · 10 12 and 2.96 · 10 9 kg 2 m 4 s 1 at 800 and 1300 °C, respec- tively. Moreover, Cr 2 AlC exhibited exceptionally good hot corrosion resistance against molten Na 2 SO 4 salt. The mechanism of the excel- lent high-temperature corrosion resistance for Cr 2 AlC can be attributed to the formation of a protective Al 2 O 3 -rich scale during both the high-temperature oxidation and hot corrosion processes. Ó 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Cr 2 AlC; Hot pressing; Oxidation; Hot corrosion; Microstructure 1. Introduction M n+1 AX n phases (where n is 1, 2, or 3; M is an early transition metal; A is an A-group element; and X is either C or N) display a unique combination of properties, including low density, high elastic modulus, easy machin- ability, excellent thermal shock resistance and damage tol- erance. Ti 3 SiC 2 [1–6], Ti 3 AlC 2 [7–11] and Ti 2 AlC [12–17] are representative members that have been extensively studied. Although Ti 3 AlC 2 and Ti 2 AlC exhibit good high-temperature oxidation resistance in air [8,12,13], these two compounds suffer from serious Na 2 SO 4 -induced hot corrosion attacks [9,15]. Therefore, the search for new MAX phases for both high-temperature oxidation and hot corrosion resistance is important. Na 2 SO 4 is the pre- dominant salt involved in the hot corrosion process. Previ- ous investigations demonstrated that Cr 2 O 3 and Al 2 O 3 had lower solubility in molten Na 2 SO 4 under common combus- tion environments [18]. And alloys with a higher Cr con- centration generally display better hot corrosion resistance. Thus, it is expected that compounds in the Cr–Al–C system may exhibit good resistance against both high-temperature oxidation and hot corrosion. Cr 2 AlC, the only layered ternary carbide identified in the Cr–Al–C system, has received increasing attention in recent years. Jeitschko et al. [19] discovered Cr 2 AlC in the 1960s; Schuster et al. [20] later confirmed the presence of this car- bide during the investigation of the ternary M 2 AlC (M = Ti, V and Cr) phase diagram. Theoretical work by Sun et al. [21,22] and Wang et al. [23,24] has demonstrated that Cr 2 AlC possesses a high elastic stiffness. Experimen- tally, Schneider et al. [25] first fabricated polycrystalline Cr 2 AlC films by a magnetron sputtering method and obtained the structural parameters; and the present authors synthesized single-phase bulk Cr 2 AlC ceramic [26]. The average grain size was about 30 lm. The results showed that Cr 2 AlC possesses a relatively high hardness and dis- plays good oxidation resistance. Tian et al. [27] also reported the fabrication of bulk Cr 2 AlC material, and pre- sented some of its mechanical and thermal properties. 1359-6454/$30.00 Ó 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2007.07.024 * Corresponding author. Tel.: +86 24 23971765; fax: +86 24 23891320. E-mail address: yczhou@imr.ac.cn (Y.C. Zhou). www.elsevier.com/locate/actamat Acta Materialia 55 (2007) 6182–6191