CHARACTERIZATION OF MECHANICAL-PROPERTIES IN THE IR-NB-ZR INTERMETALLIC SYSTEM

The mechanical properties of very high melting intermetallic compounds are examined in the Ir-Nb-Zr system. The Ir-Nb-Zr system contains two related high temperature L1(2) intermetallic compounds, Ir3Nb and Ir3Zr, with similar lattice parameters and melting points of 2450 and 2280-degrees-C respectively. Microhardness and compression tests show that the Ir3Nb possesses twice the strength of the Ir3Zr despite their marked similarities in electronic structure and cohesive properties. Furthermore, preliminary studies of a ternary L1(2) compound of composition Ir0.71Nb0.21Zr0.08 show that it has a high temperature strength greater than that of either of the binary systems. 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 behavior.