Face centered cubic and L1₂ two-phase structure of Ir-Nb-Zr alloys

The phase constitution of Ir-Nb-Zr alloys with a composition below 25 at% (Nb+Zr) was investigated by microstructure observation using scanning electron microscopy (SEM), composition analysis using electron probe microscopy analysis (EPMA), and phase identification using X-ray diffraction analysis (XRD). Partial isothermal sections of the Ir-Nb-Zr ternary system were determined at 1773, 2073, and 2373 K. It was found that the f.c.c. and L1₂ two-phase regions, which are shown in the Ir-Nb and Ir-Zr binary systems, were connected from the Ir-Nb side to the Ir-Zr side in the Ir-Nb-Zr ternary system. The potential of Ir-Nb-Zr alloys as high-temperature materials is discussed in terms of the microstructure and the lattice misfit between the f.c.c. and L1₂ phases.