Morphology evolution of Ir–X–Al (X = Nb or Zr) ternary alloys

The microstructure evolution of four samples belonging to two Ir-based ternary systems, Ir–Nb–Al and Ir–Zr–Al, has been investigated by microstructure observation using scanning electron microscopy (SEM), phase composition analysis using electron probe microscopy analysis (EPMA) methods, and phase structure determination using X-ray diffraction (XRD) patterns. An fcc/L12 two-phase structure was detected in all of the samples. One Ir–Nb–Al alloy with a composition near the Ir side of the phase diagram has been found to exhibit a microstructure similar to that of Ni-based superalloys with cuboidal L12–Ir3Nb precipitates embedded in an fcc–Ir matrix. The lattice misfit between the fcc and L12 phases of these samples has been estimated.