The effects of platinum group metals (PGMs) addition on microscopic characteristics of Ni-Al-PGM ternary and Ni-base single crystal superalloys were investigated. Several Ni-19at%Al-Xat% PGM (PGM: Ru, Rh, Pd, Ir and Pt) ternary alloys were prepared by arc-melting in order to understand the distribution of PGMs in y and y ' two phases. It is found from differential thermal analysis (DTA) that among PGMs, Ir and Ru increase the melting points whereas Pt and Pd decrease the melting points. These

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... loys were successfully solution treated at 1300°C for 4h. After ageing treatment, all Ni-19Al-1PGM alloys form y and y ' two-phase structure, while 9at% addition of Ir, Ru, Rh and Pd leads to the precipitation of PGM-enriched phase which is different from both y and y ' phases, except for a Ni-19Al-9Pt alloy which maintains y and y ' two-phase structure. SEM-EDX analysis revealed that Ir and Ru have a preference to partition to the y phase while Pt, Pd and Rh have a preference for the y ' phase. Microscopic distribution of Ir and Ru in multi-component Ni-base single crystal superalloys were also investigated. Atomprobe field ion microscopy (APFIM) revealed that partitioning behaviour of Ir in multi-component Ni-base single crystal superalloys depends on alloy composition. For Re-free alloy TMS-79, Ir atoms have a small preference to be located in the y phase, while for Recontaining TMS-80, Ir tends to partition to the y ' precipitates. On the other hand, Ru is found to prefer the y phase in Re-containing TMS-91. These results suggest that among alloying elements, 'competition of partitioning' takes place in multi-component alloys. The order of alloying elements having stronger preference to the y phase can be summarized as Re > Cr > (MO, Ru, Co) > w > Ir.