Properties of the Ir85Nb15 two-phase refractory superalloys with nickel additions

The effects of nickel content on the properties of the polycrystalline Ir85Nb15 refractory superalloy were studied. To examine the possibility of replacing Ir with Ni in Ir85-XNb15NiX, we varied the nickel content from 0 to 50 at. pct. The yield strength of the Ir75Nb15Ni10 alloy was 2150 MPa at room temperature, much greater than that of the binary Ir85Nb15 alloy, and 728 MPa at 1473 K, similar to that of the binary alloy. The fracture mode of an Ir85-XNb15NiX alloy changed from predominantly intergranular in fcc and L1(2) two-phase Ir85Nb15 to transgranular in the two-phase Ir75Nb15Ni10 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 Ir65Nb15Ni20. Ir85-XNb15NiX two-phase refractory superalloys with X less than or equal to 10 were superior to the binary Ir85Nb15 alloy as an ultrahigh-temperature structural material in terms of strength, fracture behavior, and density.