Atomic resolution observations of solute-atom segregation effects and phase transitions in stacking faults in dilute cobalt alloys-II. Analyses and discussion

R. Herschitz*, D. N. Seidman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

Solute atom segregation effects to individual stacking faults in Co-0.96 at.% Nb and Co-0.98 at.% Fe alloys have been investigated using the atom-probe field-ion microscope (Part I). In this paper a deconvolution procedure is developed. This procedure in combination with the experimental results is used to demonstrate that the solute concentration profile associated with a stacking fault is extremely narrow-it falls off to the solute concentration of the matrix within less than 4 Å. The thermodynamics of solute-atom segregation is discussed in light of the experimental observations. It is shown that a simple Langmuir-McLean segregation isotherm-which assumes no interaction between the segregating atoms-can not be used to interpret our experimental results. However, the results can be explained qualitatively by a Bragg-Williams model, which takes into account the first-nearest-neighbor interaction between atoms. This isotherm predicts the occurrence of a phase transition in the plane of the stacking fault. A partial molar heat of segregation of - 20meV atom-1 and a first-nearest-neighbor interaction energy parameter of -65meV atom-1 are consistent qualitatively with our experimental observations. The experimentally observed transition from an unsaturated (disordered) to a saturated (ordered) stacking fault is broader than the one predicted by the Bragg-Williams model. Possible reasons for this difference are discussed.

Original languageEnglish (US)
Pages (from-to)1565-1576
Number of pages12
JournalActa Metallurgica
Volume33
Issue number8
DOIs
StatePublished - Jan 1 1985

ASJC Scopus subject areas

  • Engineering(all)

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