• PDF / 268,588 Bytes
• 1 Pages / 593.972 x 792 pts Page_size
• 17 Downloads / 260 Views

DOWNLOAD

REPORT

---

Section II: Phase Diagram Evaluations

Al-Hf-Ir (Aluminum-Hafnium-Iridium) 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 Hf-Ir phase diagram [Massalski2] has the following intermediate phases: Ir3Hf (L12, AuCu3-type cubic), IrHf, Ir3Hf5 (D88, Mn5Si3-type hexagonal) and IrHf2 (Ti2Ni-type cubic).

was 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 sketched by [2005Miu] is shown in Fig. 1. In the Ir-rich region, a U-type transition reaction L + Ir3Hf M (Ir) + IrAl was proposed by [2005Miu]. Figure 2 shows the partial isothermal section at 1650 °C. In the solid solution based on Ir3Hf, Al substitutes for Hf up to 5.1 at.%. No ternary phases were found in this region. The previously known ternary compounds Al16Hf6Ir8 (Mn23Th6-type cubic) and AlIrHf (MgZn2-type hexagonal) fall outside the investigated range. In view of the very limited results of [2005Miu], the data in Figs. 1 and 2 may be considered tentative.

Ternary Phase Equilibria

Reference

With starting metals of 99.99% Al, 95% Hf, and 99.9% Ir, [2005Miu] arc-melted under Ar atm an Ir-rich alloy of composition 70Ir-20Al-10Hf (atomic percent). The sample

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-Hf-Ir partial liquidus projection for Ir-rich alloys [2005Miu]

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

368

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