Decomposition of a metastable bcc phase in rapidly solidified Ni-9 at.% Zr and Ni-8 at.% Zr-1 at.% X alloys

M. Chandrasekaran, G. Ghosh, D. Schryvers, M. De Graef, L. Delaey, G. Van Tendeloo

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

A metastable body centred cubic (bcc) phase with lattice parameter a = 0-280 ± 0-005 nm is obtained upon rapidly solidifying Ni-9 at.% Zr and Ni-8 at.% Zr-1 at.% X (= Si, Ti, Mo) alloys. This bcc (A2) phase and its decomposition behaviour are studied by X-ray diffraction, differential scanning calorimetry (DSC), conventional transmission electron microscopy, transmission electron diffraction and high resolution electron microscopy. Both continuous heating experiments in DSC and ex-situ isothermal annealing studies suggest that the bcc phase is relatively more stable in the ternary alloys. Upon aging, the bcc phase decomposes into equilibrium phases (αNi) and Ni5Zr. While (αNi) forms directly from the bcc phase, formation of layered structures precedes the formation of the other equilibrium phase Ni5Zr. Using hexagonal representation, the lattice parameters of the layered structure in the ordered state are a≈ 0-471 nm and c≈l-612nm and those in the disordered state are a≈0-471 nm and c≈0-403 nm. The morphology of the decomposition products at a very early stage is found to be dominated by strain energy. The microstructural evolution as a function of temperature is also reported and discussed.

Original languageEnglish (US)
Pages (from-to)677-701
Number of pages25
JournalPhilosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties
Volume75
Issue number3
DOIs
StatePublished - Mar 1997

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Materials Science(all)
  • Condensed Matter Physics
  • Physics and Astronomy (miscellaneous)
  • Metals and Alloys

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