Available online at www.sciencedirect.com Journal of the European Ceramic Society 32 (2012) 1395–1403 Oxidation behavior of electrically conductive / SiAlON composites with segregated network of TiCN Ali C ¸ elik, Erhan Ayas, Etem Halil, Alpagut Kara ∗ Department of Materials Science and Engineering, Anadolu University, Iki Eylul Campus, Eski¸ sehir, Turkey Available online 15 April 2011 Abstract The oxidation behavior of novel electrically conductive / SiAlON composites with a continuous network of 2.5–10 vol% TiCN particulates was investigated. Composites, produced by coating spray dried granules with nano TiCN particles by a simple blending method, were gas pressure sintered at 1990 ◦ C for 1 h under 10 MPa N 2 pressure. Oxidation tests were carried out between 800 ◦ C and 1200 ◦ C in air for 2 and 48 h in atmosphere of dry air. Below 1000 ◦ C, the formation of TiO 2 crystals on the surfaces of TiCN particles was observed. Before the glass transition temperature of intergranular phase (T g < 1000 ◦ C), it was revealed that oxidation is controlled by the diffusion of oxygen into pre-formed TiO 2 particles. Above T g , liquid glass dissolves the intergranular phase elements such as Ti, Y, and Si at the interface between TiCN and SiAlON particles. Migration of Ti towards the (opening point of the TiCN network) surface was found to be the main reason for the formation of subsurface porosity that slows down Ti diffusion through the surface. Moreover, it was detected that at high temperatures surface porosity filled by the intergranular glassy phase. Consequently, the oxidation rate was found to be decreased due to the slower oxygen diffusion. © 2011 Elsevier Ltd. All rights reserved. Keywords: Composites; SiAlON; TiCN; Electrical conductivity; Oxidation 1. Introduction Si 3 N 4 and SiAlON ceramics are important structural materials due to their superior mechanical, thermal and chem- ical properties both at room and high temperatures. While wear resistance, hardness, toughness and creep resistance of Si 3 N 4 /SiAlON can be improved considerably by the dispersion of the secondary carbides, nitrides or borides, 1–7 electrical prop- erties can also be improved by the addition of some functional phases. 8–13 Conductive Si 3 N 4 /SiAlON based composites are candidate materials for the applications such as heat exchangers, heaters, ignitiors that operates at high temperatures contain- ing oxygen and/or oxidant substances (water vapor and carbon dioxide oxygen atmosphere). Therefore, the behavior of these composites against to oxygen at high temperatures is critical and has been subjected to a series of studies. 14–20 TiN and TiCN particulates are the most preferred rein- forcing phases to make Si 3 N 4 /SiAlON ceramics electrically conductive due to not only low electrical resistivity but also unique combination of mechanical properties. There are vari- ∗ Corresponding author. Tel.: +90 222 3213550-6584; fax: +90 222 3222943. E-mail address: akara@anadolu.edu.tr (A. Kara). ous approaches to produce such composites. The most common method is the direct dispersion of TiN/TiCN particles in Si 3 N 4 matrix by conventional powder processing routes. 7–9 In these types of composites, homogeneous dispersion of minimum amount of secondary phase without degrading densification and mechanical features is very critical, since it affects the electrical conductivity. However, the dispersion of a secondary phase is a difficult task to achieve. Therefore, in situ formation of homo- geneously distributed nano conductive particles is an alternative method to this approach. 21–23 Obtaining good electrical conduc- tion by this method is also challenging, since process parameters must be controlled precisely to avoid the grain growth and accordingly separation of conductive particles from each other. A new method to obtain a continuous network in these types of composites has been developed by Ayas and Kara. 24 In this method, spray dried SiAlON granules with an average diameter of 100 m were coated with nano-TiCN particles by dry mixing of these two components. Consequently, low resistivity values (≈10 -2  m) were achieved with the incorporation of as low as 5 vol% of TiCN after gas pressure sintering. For such ceramics, it is important to evaluate the thermal sta- bility and degradation of mechanical and functional properties of such composites at high temperatures. In the present work, oxidation behavior of / SiAlON composites with different 0955-2219/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2011.03.028