Strength behavior of Ir-based refractory superalloys

The microstructure and compression strength of Ir-based binary alloys, Ir-V, -Ti, -Nb, -Ta, Hf, and -Zr alloys, up to 2000 degrees C were investigated. These alloys have been suggested as "refractory superalloys" which are defined as the alloys with an fcc and L1(2) two-phase coherent structure and with yet higher melting temperature. The fee and L1(2) two-phase structure was observed in the Ir-based alloys by a transmission electron microscope. Precipitate shape was observed to depend upon the lattice parameter misfit between the fee matrix and L1(2) precipitates. Cuboidal L1(2) 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. The Ir-Nb, Ta, -Hf, and -Zr alloys displayed superior strength throughout the temperature range. Precipitation hardening was investigated in the Ir-Nb and Ir-Zr alloys, 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. Precipitate morphology and distribution were changed by heat treatment in Ir-Nb alloy. The strength of sample with precipitates distributed uniformly was higher than that of the strength of the sample with precipitates aligned along(010) directions and wide fee matrix.