Specific volume and elastic properties of glassy, icosahedral quasicrystalline and crystalline phases in Zr-Ni-Cu-Al-Pd alloy

Elastic properties, phase composition, microstructure and specific volume changes in the Zr65Ni10Cu5Al7.5 Pd-12.5 glassy alloy during progressive devitrification have been studied by ultrasonic pulse, X-ray diffractometry, transmission electron microscopy and Archimedean methods, respectively, in terms of structure and properties change. On heating the glassy alloy initially forms an icosahedral phase and then a mixture of tI12 Zr2Niss and beta-Zr-ss crystalline phases after annealing at 993 K for 300 s, and lastly tI12 Zr2Nss, tI6 Zr2Pd and hP9 Zr6Al2Ni crystalline phases after prolonged annealing at 993 K for 7.2 ks. In an as-solidified state the alloy shows high Poisson's and K/G ratios of 0.42 and 7, respectively. These parameters are responsible for its good ductility. The structural changes are accompanied by decreases in specific volume, bulk modulus, Lame parameter and Poisson's ratio. Small specific volume changes upon primary devitrification suggest a close relation between the glassy and the icosahedral structures. The existence of the icosahedral local order, which exhibits rigidity for three-dimensional shear deformation with mixed mode 11 mode 111, may be responsible for good elasticity of the glassy alloy. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.