The development of novel industrial cast and wrought (C&W) disk alloys with required combination of strength, creep and fatigue resistances is always desired and a challenge to material researchers. Recently, in the High Temperature Materials 21 Project (HTM21) led by the Japanese National Institute for Materials Science (NIMS), we proposed an innovative concept to design disk alloys. This concept is based on combining the characters of two kinds of γ−γ′ two-phase alloys (Ni-base and Cobase alloys) and leads up to some promising candidate alloys that can be processed by normal C&W processing route and shows at least a 30°C increase in temperature capability over the current C&W U720Li disk alloy. This paper shows the design idea, workability and mechanical properties of some Ni-Co-base alloys. Furthermore, full-scale-disk forgings were processed successfully for the evaluations of the processing ability and microstructure of new Ni-Co-base disk alloys, which demonstrated the advantages and possibility of Ni-Co-base disk alloys at the component level.
The effects of nickel content on the properties of the polycrystalline Ir 85 Nb 15 refractory superalloy were studied. To examine the possibility of replacing Ir with Ni in Ir 85-X Nb 15 Ni X , we varied the nickel content from 0 to 50 at. pct. The yield strength of the Ir 75 Nb 15 Ni 10 alloy was 2150 MPa at room temperature, much greater than that of the binary Ir 85 Nb 15 alloy, and 728 MPa at 1473 K, similar to that of the binary alloy. The fracture mode of an Ir 85-X Nb 15 Ni X alloy changed from predominantly intergranular in fcc and L1 2 two-phase Ir 85 Nb 15 to transgranular in the two-phase Ir 75 Nb 15 Ni 10 alloy and a mixture of intergranular and transgranular in the other tested alloys when the Ni content exceeded 20 pct. The Ni addition also increased the compression ductility for Ni content up to 50 at. pct. The maximum compression ductility was approximately 13 pct, obtained from Ir 65 Nb 15 Ni 20 . Ir 85-X Nb 15 Ni X two-phase refractory superalloys with X Յ 10 were superior to the binary Ir 85 Nb 15 alloy as an ultrahigh-temperature structural material in terms of strength, fracture behavior, and density.
The microstructural evolution and mechanical properties were examined in a Ni-based superalloy, TMW-4, with high Co and Ti contents at temperatures ranging from 700°C to 1200°C for various times up to 1000 hours. The results showed that solution treatments (temperatures: from 1100°C to 1200°C; time: 4 hours) essentially affected the fraction and size of primary and secondary c¢ precipitations and grain size. No g-Ni 3 Ti phase was observed in all solution heattreatment samples. On the other hand, small amounts of g phase were observed in the samples after homogenization at 1220°C and aging at temperatures ranging from 1000°C to 1175°C. Based on the investigations, a time-temperature-transition (TTT) curve for the g-phase formation was constructed. These microstructural effects were successfully combined to obtain an increase of tensile properties in terms of both strength and ductility.
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