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Pt rare-earth (RE) compounds such as Pt 5 Y have shown great promise as cathode catalysts and can act as strengthening phases in Pt-based alloys as well. The Pt 5 Y was reported to have three different structures but only the Cu 5 Ca-type structure has been elucidated in detail. Here, the atomic structure of another type Pt 5 Y phase in a Pt-Ir-Hf-Y alloy was characterized by transmission electron microscopy (TEM) techniques. Based on the electron diffraction, atomic-scale resolution Z-contrast imaging and elemental mapping results, we proposed a structural model of the Pt 5 Y phase. The ideal structure can be composed of alternating Cu 5 Ca-type sandwich layers and close-packed Pt layers, resulting in a trigonal structure, a = b =5.26 Å, c =26.32 Å, α = β =90° and γ =120° with R32 space group. The finding of the new phase can help us to understand the microstructures of Pt-RE compounds and develop their potential application. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Pt-15Ir-3Hf-0.5Y alloy with good high-temperature strength and ductility is prepared. • No Pt-Hf precipitates but three types of nanoclusters, clusters containing stacking fault, clusters at 1/2 〈0 1 1〉 dislocation core and clusters with short-range order are observed in the alloy matrix. • The alloy has a strong ageing strengthening effect through more and larger clusters formation. A novel ultra-high temperature Pt-15Ir-3Hf-0.5Y (wt.%) alloy was developed for the first time by high vacuum arc-melting, hot rolling and ageing treatment. The microstructures of the as-cast and hot-rolled and then post-aged samples were investigated. The alloy consists of the (Pt,Ir) 5 Y phase and matrix. Through transmission electron microscopy atomic resolution imaging, three types of nanoclusters, clusters containing stacking fault, clusters at 1/2 〈0 1 1〉 dislocation core and clusters with short-range order were observed in the matrix. The hardness at the ambient temperature of the alloy after hot rolling and ageing treatment was up to 443 HV and the tensile strength at 1500 °C was up to 47.8 MPa. Compared with the solid solution strengthened Pt-Ir binary alloys, the addition of Hf and Y can effectively improve the mechanical properties, which were achieved by introducing the combined effects of nanocluster strengthening and grain boundary strengthening of (Pt,Ir) 5 Y phase. Our findings provided new insights into designing the Pt-based superalloy with high strength and ductility. [ABSTRACT FROM AUTHOR]