Morphology evolution of Ir-Nb-X (XÂ =Â Hf, Ta, or Ti) ternary alloys

The microstructure evolution of nine samples from three Ir-base ternary systems, Ir-Nb-Hf, Ir-Nb-Ta, and Ir-Nb-Ti, was investigated by microstructure observation using scanning electron microscopy (SEM), composition map-analysis using electron probe microscopy analysis (EPMA), and phase determination using X-ray diffraction (XRD) patterns. The fcc/L12 two-phase structure was detected in all the samples. Lattice misfits between fcc and L12 phases were calculated. Ir-Nb-Ta and Ir-Nb-Ti alloys exhibited a microstructure quite similar to that of Ni-base superalloys, and the cuboidal L12 precipitates in Ir-Nb-Ta and Ir-Nb-Ti alloys could maintain up to 1900 °C.