The distribution of Ir in Ni-base single-crystal superalloys

The microscopic distribution of Ir in Ni-N-Ir ternary alloys and Ni-base single crystal superalloys was investigated. It is found from SEM-EDS analysis that in Ni-18at%Al-Ir ternary alloys, Ir has a preference to partition to the gamma phase. On the other hand, partitioning behaviour of Ir in multicomponent Ni-base single crystal superalloy changes depending on alloy composition. Atomprobe field ion microscopy (APFIM) revealed that for Re-free alloy TMS-79, Ir atoms have a small preference to be located in the gamma phase, while for Re-containing TMS-80, Ir tends to partition to the gamma' precipitates. These results suggest that among alloying elements, 'competition of partitioning' takes place in multi-component alloys. The experimental results were compared with numerical estimations by cluster variation method (CVM) and showed reasonable agreement.