High temperature strengths of Ir-based refractory superalloys

The microstructure and compression strengths of Ir-based binary alloys (Ir-X, where X is V, Ti, Ta, Nb, Hf, or Zr) at temperatures between room temperature and 1800°C were investigated. Several Ir-based alloys displayed superior strength throughout the temperature range. An fcc and L1₂ two-phase structure was observed in the Ir-based alloys by a transmission electron microscope and is believed to be an important element of the strength performance. Precipitate shape was observed to depend upon the lattice parameter misfit between an fcc matrix and L1₂ precipitates. Cuboidal L1₂ precipitates were formed in the Ir-Nb and Ir-Ta alloys with lattice misfit about 0.3%. Plate-like precipitates were formed in the Ir-Hf and Ir-Zr alloys with lattice misfit about 2%, and these precipitates formed a three-dimensional maze structure. Precipitation hardening was investigated in the Ir-Nb and Ir-Zr alloys, but was larger in the Ir-Zr alloy. We observed different deformation mechanisms, shearing mechanism and bypass mechanism in the Ir-Zr and Ir-Nb alloys, respectively.