Available online at www.sciencedirect.com Journal of the European Ceramic Society 32 (2012) 1813–1820 Multiple crack healing of a Ti 2 AlC ceramic Shibo Li a,b,∗ , Guiming Song b , Kees Kwakernaak b , Sybrand van der Zwaag c , Wim G. Sloof b a Center of Materials Science and Engineering, School of Mechanical and Electronic Control Engineering, Beijing Jiaotong University, Beijing 100044, China b Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands c Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands Received 23 November 2011; received in revised form 4 January 2012; accepted 16 January 2012 Available online 6 February 2012 Abstract A highly attractive self-healing material would be one which combines excellent mechanical properties with a multiple healing capability. Self- healing ceramics have been studied for over 40 years to obtain some performance recovery and to prevent material failure during service, but so far only materials with the capability of single healing event per damage site have been realized. Here we report on a self-healing Ti 2 AlC ceramic capable of repeatedly repairing damage events. The Ti 2 AlC ceramic achieves at least seven healing cycles after repeated cracking at a given location. The main healing mechanism at high temperature is the filling of the cracks by the formation well adhering -Al 2 O 3 and the presence of some rutile TiO 2 . For healed samples, the flexural strength returned or even slightly exceeded the virginal strength. The fracture toughness recovery has been quantified for multiple healing cycles. © 2012 Elsevier Ltd. All rights reserved. Keywords: Carbides; Crack healing; Electron microscopy; X-ray methods; Mechanical properties 1. Introduction Advanced ceramics with extraordinary mechanical, thermal and electrical properties have been used in a wide range of appli- cations. The main drawback of these ceramics is their brittle character that makes them sensitive to the presence of surface cracks, resulting in loss in performance or even a sudden catas- trophic failure. Inspired by healing processes in nature, for some years material scientists have tried to develop self-healing engi- neering materials combining adequate mechanical properties and autonomous crack healing ability to restore their load bear- ing capacity. 1–3 The earliest crack healing study on a ceramic, viz. corundum could be traced back to the year 1966. 4 After that damage repair in some oxide ceramics such as ZnO, MgO, UO 2 , Al 2 O 3 has been investigated. 5–7 The main crack healing mechanism for these oxide ceramics is grain growth similar to the mechanism responsible for densification during sinter- ing. Since then, another crack healing mechanism driven by ∗ Corresponding author at: Center of Materials Science and Engineering, School of Mechanical and Electronic Control Engineering, Beijing Jiaotong Uni- versity, Beijing 100044, China. Tel.: +86 10 51685554; fax: +86 10 51685554. E-mail address: shbli1@bjtu.edu.cn (S. Li). oxidation has been developed for SiC, Si 3 N 4 and ternary car- bides as well as their composites. 8–14 This is potentially a very attractive concept because the additional atoms required to fill the crack are automatically supplied by the gaseous environ- ment and the material itself had not to be ‘weakened’ to allow self healing. For such system, both the ceramic matrix and the gaseous environment act as “reservoirs” for providing the heal- ing agent. It is reasonable to believe that multiple healing events in such ceramics should be possible. However, over 40 years, autonomous healing of ceramics has only been demonstrated for single or one-time-only healing event and the effect of such healing on the mechanical properties was not quantified either. Recently, a novel ternary ceramic, viz. Ti 2 AlC has attracted much attention. Ti 2 AlC belongs to the so-called MAX-phase family, where M is an early transition metal, A is mostly a group IIIA or IVA element, and X is either C or N. 15 Ti 2 AlC has an unusual combination of attractive properties up to high temper- atures, such as high strength, high oxidation resistance, ductility and nonsusceptibility to thermal shock. These properties make Ti 2 AlC attractive for high temperature applications in which the material is exposed to thermal cycles, mechanical loading and oxidative environments. Such conditions are encountered in installations for power generation or propulsion, raw material production, recycling, etc. Hence, autonomous crack healing is 0955-2219/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2012.01.017