First principles calculation reveals that ideal mechanical strengths of L1(2) Ir3Nb are higher than those of L1(2) Ir3Hf, and that Hf and Nb atoms have different effects on the brittle behavior of Ir, i.e., the Ir3Hf bulk seems less brittle than fcc Ir, while Ir3Nb becomes more brittle. Densities of states suggest that the chemical bonding formed in Ir3Nb should be stronger and more directional than that in Ir3Hf. Calculation also shows that compared with pure Ir bulk, the bond strengths of (1 0 0)-I and (1 1 0) Ir/Ir3X (X = Hf, Nb) interfaces have increased, while the bond strengths of (1 0 0)-II and (1 1 1) Ir/Ir3X interfaces have decreased, due to the formation of the interface. In addition, it is found out that the (1 0 0)-I interfaces are energetically favorable with negative interface energies, which is good agreement with similar experimental observations in the literature. (C) 2010 Elsevier BM. All rights reserved.