Newly developed niobium-based superalloys for elevated temperature application

Niobium(Nb)-based alloy is one of the candidate materials for ultra-high temperature applications, because of its high melting point, a good ductility at room temperature and a moderate density. Making a best use of these merits in Nb, a series of Nb-based superalloys have been developed for hot components of gas turbines. During the development, a solidsolution and a dispersion strengthening mechanisms were fully utilized through the additions of such alloying elements as Mo, W, Si, Hf and C. Typical composition of the strongest Nb-based alloy developed from this study is as follows: Nb-16Si-5Mo-15W-5Hf-5C(at%) with creep rupture life over 100 h under 150 MPa at 1500 DGC. Further studies toward an establishment of sufficient oxidation and corrosion resistance of the alloys at such high temperatures as 1500 DGC is now under way based on the idea of diffusion barrier coatings. (AU)