Transformation of nano icosahedral phase in Zr65Al7.5Ni10Cu17.5-xPdx (x=0 to 4) glassy alloys

J. Saida et al., Transformation of nano icosahedral phase in Zr65Al7.5Ni10Cu17.5-xPdx (x=0 to 4) glassy alloys, MATER TRANS, 42(8), 2001, pp. 1497-1501
Citations number
Categorie Soggetti
Material Science & Engineering
Journal title
ISSN journal
1345-9678 → ACNP
Year of publication
1497 - 1501
SICI code
We investigated the transformation behavior from gassy to icosahedral and/o r fcc Zr2Ni phases in the Zr65Al7.5Ni10Cu17.5-xPdx (x = 0 to 4) glassy allo y,, with low oxygen contents of less than 400 ppm mass%. The primary phase is a metastable single fcc Zr2Ni phase in the x = 0 alloy and a single icos ahedral quasicrystal line phase in the 2 to 4 at%Pd alloys. The mixture pha se of icosahedral and fcc Zr2Ni precipitates at the initial crystallization stage in the x = I alloy. It is therefore confirmed that the icosahedral p hase is formed by the addition of 1 at% Pd to the Zr-Al-Ni-Cu glassy alloy. The icosahedral and Zr2Ni particles have grain sizes in the diameter range of 500 to 1000 nm and arc in an isolated state for (lie sample annealed at a temperature near the crystallization temperature. A significant redistri bution leading to the enrichment of Zr in the icosahedral phase is confirme d. Moreover, it is recognized that Ni and Cu are rejected from the icosahed ral phase. We also observed the enrichment of Zr and Ni and the rejection o f Cu in the Zr2Ni phase, No significant difference in Al content is observe d among the icosahedral, Zr2Ni and residual glassy phases. The Pd content i n the icosahedral phase is the same as that in the Zr2Ni phase. The differe nce of Zr, Ni and Cu contents among the icosahedral, Zr2Ni and remaining gl assy phases is in the range of 2 to 9 at%. No significant difference in the Pd content is observed between the icosahedral and Zr2Ni phases. Consideri ng that the diameter of the primary phase decreases significantly with incr easing Pd content, it is suggested that Pd plays a dominant role in the inc rease in the number of nucleation sites of the icosahedral phase. Moreover, it is strongly suggested that the icosahedral phase originates from the ic osahedral short-range order with an increase of nucleation rate as a result of the addition of noble metal.