Investigation on microstructure and fracture of quaternary Ir-based alloys

The microstructure and the fracture of the new developed Ir-Nb-Ni-Al and Ir-Ta-Ni-Al were investigated. At 1300 degrees C, three-phase equilibrium-fee, L1(2)-Ni3Al and Ir3Nb were observed in alloys Ir-5Nb-62.4Ni-12.6Al, Ir-15Nb-20.8Ni-4.2Al and three-phase equilibrium-fee, L1(2)-Ni3Al and Ir3Ta existed in alloys Ir-3.75Ta-67.4Ni-12.6Al and Ir-11.25Ta-20.8Ni-4.2Al; four-equilibrium-fee, B2-IrAl, L1(2)-Ni3Al and Ir3Nb or Ir3Ta were observed in alloy Ir-10Nb-41.6Ni-8.4Al or Ir-7.5Ta-41.6Ni-8.4Al. At 1400 degrees C, the three-phase equilibrium existed in all of the alloys. The compressive strengths at 1200 degrees C were from 79 to 616 MPa. The compressive strain of the quaternary was greatly improved compared with ir-based alloys (below 10%). The lowest one was 18. The precipitation hardening of quaternary alloys can be caused by the precipitate-shearing mechanism. The compressive strength of quaternary alloys can be attributed to the precipitation and solid solution hardening as well as to the interface strengthening.