Journal of Alloys and Compounds 395 (2005) 263–271 Phase equilibria in Ir-rich portion of Ir–Al–X (X: V, Nb and Ta) ternary systems Seiji Miura a,* , Kenji Ohkubo a , Yoshihiro Terada b , Yoshisato Kimura c , Yoshinao Mishima c , Yoko Yamabe-Mitarai d , Hiroshi Harada d , Tetsuo Mohri a a Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo 060-8628, Japan b Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan c Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan d High Temperature Materials Group, National Institute for Materials Science, Sengen 1-2-1, Tsukuba, Ibaraki 305-0047, Japan Received 18 October 2004; accepted 9 November 2004 Available online 19 January 2005 Abstract Isotherms of the Ir-rich portion of the Ir–Al–X (X: V, Nb, Ta) systems composed of fcc-Ir solid solution ((Ir) ss ), Ir-based L1 2 intermetallic compounds Ir 3 X and B2–IrAl are presented as a second report of a series of investigations on the phase equilibria in the (Ir or Rh)–Al–X (X: Ti, Zr and Hf, or, V, Nb and Ta) ternary systems. In both Ir–Al–Nb and Ir–Al–Ta systems fcc/L1 2 /B2 three-phase equilibrium is found. In Ir–Al–V system, Ir solid solution and Ir 3 V have close compositions each other and fcc/L1 2 /B2 three-phase equilibrium is expected. No ternary compound is observed in all of the isotherms. Solid solubility of each phase is confirmed by chemical analysis by wavelength dispersive X-ray spectroscopy (WDS). The direction of the solubility lobe of L1 2 –Ir 3 X with Al addition is explained in terms of the nearest neighbor interactions. Liquidus surfaces are also established by taking into account the microstructure of as-cast alloys, differential thermal analysis (DTA) data, and the Ir–Al and the Ir–X binary phase diagrams reported previously. © 2004 Elsevier B.V. All rights reserved. Keywords: Intermetallics; Scanning electron microscopy; High temperature alloys 1. Introduction Recently, as candidates for new heat resisting materials, al- loys based on high melting-point metals with a face centered cubic crystal structure, such as Ir and Rh, have been focused [1–4]. They show good high temperature mechanical prop- erties which can be partially attributed to an excellent high temperature strength of dispersed Ir- and Rh-based L1 2 com- pounds with which a similar microstructure with the com- mercial Ni-based superalloys is obtained [5,6]. Therefore, these alloys are expected to have a much higher application temperature range than that of Ni-based alloys. * Corresponding author. Tel.: +81 117066347; fax: +81 117067812. E-mail address: miura@eng.hokudai.ac.jp (S. Miura). Present authors have investigated the physical properties, such as thermal conductivity and coefficient of thermal ex- pansion, of Ir- and Rh-based L1 2 compounds [7–10]. Al- though these physical properties are inevitable to assess the applicability of these materials for high temperature use, phase diagrams are also quite important in order to obtain prospects of developing suitable phase selection and occur- rence of the microstructure evolution of the materials. Espe- cially, phase diagrams including Al are inevitable; it is be- cause the B2 intermetallic compound IrAl and presumably RhAl and their alloys show good oxidation resistance caused by the self-organization of Al 2 O 3 outer-layer on the Ir or Rh inner-layer during oxidation as was demonstrated by Hosoda and co-workers [11–18]. The self-healing oxidation resistant structure through the consumption of the IrAl compound is expected to be applicable as an oxidation-resistant “smart” 0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.11.029