We propose a method for developing new quaternary Ir-Nb-Ni-Al refractory superalloys for ultrahigh-temperature uses, by mixing two types of binary alloys, Ir-20 at. pct Nb and Ni-16.8 at. pct Al, which contain fcc/L1 2 two-phase coherent structures. For alloys of various Ir-Nb/Ni-Al compositions, we analyzed the microstructure and measured the compressive strengths. Phase analysis indicated that three-phase equilibria-fcc, Ir 3 Nb-L1 2 , and Ni 3 Al-L1 2 -existed in Ir-5Nb-62.4Ni-12.6Al (at. pct) (alloy A), Ir-10Nb-41.6Ni-8.4Al (at. pct) (alloy B), and Ir-15Nb-20.8Ni-4.2Al (at. pct) (alloy C) at 1400 ЊC; at 1300 ЊC, three phase equilibria-fcc, Ir 3 Nb, and Ni 3 Al-existed in alloys A and C and four-phase equilibria-fcc, Ir 3 Nb, Ni 3 Al, and IrAl-B2-existed in alloy B. The fcc/L1 2 coherent structure was examined by using transmission electron microscopy (TEM). At a temperature of 1200 ЊC, the compressive strength of these quaternary alloys was between 130 and 350 MPa, which was higher than that of commercial Ni-based superalloys, such as MarM247 (50 MPa), and lower than that of Ir-based binary alloys (500 MPa). Compared to Ir-based alloys, the compressive strain of these quaternary alloys was greatly improved. The potential of the quaternary alloys for ultra-hightemperature use is also discussed.
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