Structural and phase transformations in quenched and aged Zr-Ir alloys

X-ray diffraction, optical metallography, transmission electron microscopy, and hardness measurements were used to study the phase composition and mic rostructure of quenched and aged Zr-lr alloys containing from 0.25 to 5 at. % iridium. It was established that a two-phase microstructure of the packet type, consisting of the alpha-phase and a beta-phase enriched with iridium , forms during quenching of the alloys containing up to 1 at.% iridium. A m etastable omega-phase forms in the alloys containing from 1.5 to 5 at.% iri dium. The omega-phase particles have an equiaxed shape after quenching. Dur ing aging, the omega-phase particles grow and adopt a cubic shape, and the lattice of the omega-phase becomes more perfect. The interfacial planes of the omega-phase particles are the {100}(beta)parallel to{201}(omega) planes . The aging time, required for the transition into the equilibrium (alpha+Z r3Ir) state, depends on the temperature of the aging and on the iridium con tent in the ahoy. The stability of the omega-phase in the Zr-lr alloys is l ess than in the Zr-Ru and Zr-Os alloys. (C) 2000 Elsevier Science S.A. All rights reserved.