Mechanical and thermodynamic properties of the Ir-Nb-Zr intermetallic system

The mechanical and electronic properties of the high melting intermetallic compounds Ir-3(NbxZr1-x) are examined. The Ir-Nb-Zr system contains two related high temperature L1(2) intermetallic phases, Ir3Nb and Ir3Zr, with similar lattice parameters and melting points of 2450 degrees C and 2280 degrees C, respectively. Microhardness and compression tests show that Ir3Nb possesses a significantly higher strength than Ir3Zr, despite their marked similarities in electronic structure and cohesive properties. Furthermore, studies of ternary L1(2) compounds of composition Ir-3(NbxZr1-x) show that their strength changes continuously between the two binary systems. This study was undertaken to explore the differences in the strength of Ir3Nb and Ir3Zr and to correlate experimental results to theoretical studies. Total energy electronic structure calculations confirm the similarity in the cohesive properties of the binary compounds and point to differences in the density of states at the Fermi level as a possible reason for their dissimilar mechanical properties. First-principles electronic structure calculations were also carried out along a tetragonal Bain distortion for both Ir3Nb and Lr3Zr. The observed microhardness differences between these two intermetallic compounds correlate well with the calculated shear elastic constants (c(11)-c(12))/2 Finally, the total energy calculations are combined with the Cluster Variation Method in order to calculate the Ir-rich comer of the ternary phase diagram.