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Phase Diagram Evaluations: Section II

Al-Ir-Zr (Aluminum-Iridium-Zirconium) V. Raghavan

Recently, [2005Miu] determined a partial liquidus projection and an isothermal section at 1650 °C for Ir-rich alloys of this system.

Binary Systems The Al-Ir phase diagram in the Ir-rich region determined by [2005Miu] depicts a eutectic reaction between (Ir) and IrAl (B2, CsCl-type cubic) at 30.5 at.% Al and 2020 °C. The other Al-Ir phases are: Ir2Al5 (cubic, space group Pm 3n), IrAl3 (D018, Na3As-type hexagonal), Ir4Al13 (monoclinic), and Ir2Al9 (D8d, Co2Al9-type monoclinic). The Ir-Zr phase diagram [Massalski2] has the following intermediate phases: Ir3Zr (L12, AuCu3-type cubic), Ir2Zr (C15, MgCu2type cubic), bIrZr (B2, CsCl-type cubic), Ir3Zr5 (D88, Mn5Si3-type hexagonal), IrZr2 (C16, CuAl2-type tetragonal) and IrZr3 (aV3S-type tetragonal).

alloys: 70Ir-20Al-10Zr and 70Ir-24Al-6Zr (atomic percent). The samples were annealed at 1650 °C for 24 h. The phase equilibria were studied with scanning electron metallography, wavelength dispersive x-ray spectroscopy, and differential thermal analysis. The partial liquidus projection constructed by [2005Miu] is shown in Fig. 1. In the Ir-rich region, a ternary eutectic reaction E was proposed by [2005Miu]. Fig. 2 shows the partial isothermal section at 1650 °C. In the solid solution based on Ir3Zr, Al substitutes for Zr up to the solubility limit of 7.4 at.%. No ternary phases were found in this region. The previously known ternary compounds Al16Ir7-8Zr6 (Mn23Th6-type cubic) and AlIrZr (MgZn2-type hexagonal) lie outside the investigated range.

Reference

Ternary Phase Equilibria With starting metals of 99.99% Al, 99.9% Ir, and 99.6% Zr, [2005Miu] arc-melted under Ar atm two Ir-rich ternary

2005Miu: S. Miura, K. Ohkubo, Y. Terada, Y. Kimura, Y. Mishima, Y. Yamabe-Mitarai, H. Harada, and T. Mohri, Phase Equilibria in the Ir-Rich Portion of the Ir-Al-X (X: Ti, Zr and Hf) Ternary Systems, J. Alloys Compd., 2005, 393, p 239-247

Fig. 1 Al-Ir-Zr partial liquidus projection for Ir-rich alloys [2005Miu]

Fig. 2 Al-Ir-Zr partial isothermal section at 1650 °C for Ir-rich alloys [2005Miu]

Journal of Phase Equilibria and Diffusion Vol. 29 No. 4 2008

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