Al-C-Ir (Aluminum-Carbon-Iridium)

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Phase Diagram Evaluations: Section II

Al-C-Ir (Aluminum-Carbon-Iridium) V. Raghavan

Recently, [2002Kim] determined an isothermal section at 1100 °C for this system in the Ir-rich region. No ternary carbide of the E21, Co3AlC-type was found.

Binary Systems In the Al-C system, the stoichiometric compound Al4C3 (D71-type rhombohedral) is present. The Al-Ir phase diagram [Massalski2] depicts the following intermediate phases: Ir2Al9 (D8d, Co2Al9-type monoclinic), Ir4Al13 (monoclinic), IrAl3 (D018, Na3As-type hexagonal), Ir2Al5 (or IrAl2.7, cubic), and IrAl (B2, CsCl-type cubic). The C-Ir system [Massalski2] is of the simple eutectic type, with the eutectic temperature at 2296 °C.

Ternary Phase Equilibria Starting with high purity elemental powders, [2002Kim] prepared by means of arc-melting under Ar atm (or spark Fig. 2 Al-C-Ir partial liquidus projection [2002Kim]

plasma sintering in vacuum) just one alloy with the composition 66.7Ir-22.2Al-11.1C (in atomic percent). This composition corresponds to a possible ternary carbide with the stoichiometry of Ir3AlC0.5. Alloy samples were annealed at 1100 °C for 72-144 h. The phase equilibria were studied with electron microscopy, x-ray diffraction and electron probe microanalysis. Differential thermal analysis was carried out at a heating/cooling rate of 10 °C per min. The microstructure showed primary crystals of (Ir), IrAl (B2) phase, and graphite. There was no evidence for the presence of a ternary carbide. The partial isothermal section at 1100 °C and the liquidus projection constructed by [2002Kim] are shown in Fig. 1 and 2 respectively.

Reference

Fig. 1 Al-C-Ir partial isothermal section at 1100 °C [2002Kim]

2002Kim: Y. Kimura, K. Iida, and Y. Mishima, Microstructures and Phase Equilibria of the Transition Metal Corner in the Rh-Al-C and Ir-Al-C Ternary Systems, Intermetallics, 2002, 10, p 933-944

Journal of Phase Equilibria and Diffusion Vol. 29 No. 1 2008

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