The effects of Ir addition on the microstructural characteristics of Ni-based single crystal superalloys have been investigated using atom probe field ion microscopy (APFIM) and the results were compared with numerical estimations obtained from the Monte Carlo simulations (MCS) and the cluster variation method (CVM). The alloy investigated was TMS-79 (Ni-12.6 at% Al-7.7 at% Cr-4.6 at% Mo-2.7 at% Ta-1.8 at% Ir). APFIM analysis revealed that Ir atoms have a slight preference to partition into the γ-phase and to substitute for the Al site in the γ′ precipitates, which showed agreement with numerical estimations by CVM and MCS. The possible effect of Ir additions on the mechanical properties is briefly discussed.
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