Phase stability and transformations in the Zr2NiCu1-x amorphous system

TitlePhase stability and transformations in the Zr2NiCu1-x amorphous system
Publication TypeJournal Article
Year of Publication2008
AuthorsKramer MJ, Xu M, Ye YY, Sordelet DJ, Morris JR
Journal TitleMetallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
Date PublishedAug
Type of ArticleProceedings Paper
ISBN Number1073-5623
Accession NumberISI:000256886600013
Keywordsalloys, CHARACTERISTICS, CRYSTALLIZATION, CU-NI GLASS, dynamics, kinetics, selection, short-range order, supercooled liquid, THERMAL-STABILITY, ZR METALLIC GLASSES

Since Ni and Cu differ by only one valence electron, yet have nearly identical atomic sizes (1.27 vs 1.28 angstrom for Cu and Ni, respectively), the amorphous Zr2NiCu1-x system is ideal for isolating the effects of electronic structure on short- and medium-range order and the concomitant influence of both the structure and order on devitrification pathways. Thermal analysis, time-resolved high-energy X-ray diffraction (HEXRD), and transmission electron microscopy (TEM) were used to follow metastable and stable crystalline phase formation during devitrification. Using HEXRD, we observed that the first devitrification product in the Zr2Ni system is the C16 structure, if oxygen is kept sufficiently low, while the Zr2Cu system forms the C11b structure. For x = 0.25, the initial devitrification involves forming coexisting C11b and C16 phases. When Ni is increased to x >= 0.50, the initial devitrification only involves the C16 structure. These results are in complete accord with electronic structure calculations showing that the enthalpy of formation for the C11b phase is favored for x = 0, while enthalpies for C11b and C16 are nearly identical for x = 0.25; the C16 phase has the most negative enthalpy for all compositions in which x > 0.25.

Alternate JournalMetall. Mater. Trans. A-Phys. Metall. Mater. Sci.