Precipitation hardening of Ir-Nb and Ir-Zr alloys

The authors previously developed refractory superalloys based on platinum-group metals with fcc and L12 two-phase coherent structures. The refractory superalloys are potentially useful at ultra-high temperature, at which Ni-based superalloys can not be used. From among the platinum-group metals, they selected Ir as the base material because its melting temperature (2447 C) is higher than that of Ni (1455 C) and because Ir, with an fcc structure, can be equilibrated with the L12 structure phase. Preliminary results demonstrated the superior strength of Ir-based refractory superalloys above 1200 C. Those results also revealed that precipitation hardening occurs and is affected by the shape of the precipitate. The precipitate shape of Ir-based alloys heat-treated at 1200 C is affected by the lattice misfits between the matrix and precipitates. In this study, the authors investigated the precipitation hardening mechanism by observing dislocation structures in deformed samples of Ir-Nb and Ir-Zr alloys using bright-field imaging and dark-field weak-beam imaging techniques with a transmission electron microscope (TEM)