Ab initio study of elastic properties of Ir and Ir3X compounds

Elastic constants and moduli of face-centered cubic Ir and its L1(2) intermetallic compounds Ir3X (X=Ti,Ta, Nb, Zr, Hf, V) have been determined using ab initio density functional theory calculations within the generalized gradient approximation. With the tetragonal, trigonal, and isotropical lattice distortions, elastic constants C-11, C-12, C-44, and bulk modulus B are derived from the second derivative of the total energy as a function of volume. The calculated Young's modulus E, shear modulus G, Poisson's ratio v, and the ratio R-G/B of G over B are then used to examine mechanical properties of Ir and Ir3X compounds. By analyzing R-G/B and Cauchy pressure C-12-C-44, the brittle-ductile behavior of the materials is assessed. Based on the modulus difference DeltaG between the gamma matrix (Ir) and gamma' precipitates (Ir3X), the gamma' strengthening effect in the gamma matrix is studied. (C) 2003 American Institute of Physics.