Abstract
We study experimentally the local chemistry and atomic structure of heterophase interfaces on an atomic scale. In this work, the heterophase precipitate/matrix interfaces of small molybdenum nitride precipitates in an α-iron matrix are investigated on a subnanometer scale by 1-dimensional atom-probe field-ion microscopy (1D-APFIM) and 3-dimensional atom-probe microscopy (3DAPM). Molybdenum nitride precipitates are generated by annealing Fe-2 at.% Mo-X, where X = 0.4 at.% Sb or 0.5 at.% Sn, at 550°C, in an ammonia/hydrogen atmosphere. Internal nitridation at this temperature produces thin, coherent platelet-shaped molybdenum nitride precipitates. 1D-APFIM selected area analyses are efficient in determining the composition of the precipitates and it is found that a possible Sn or Sb segregation at coherent matrix/precipitate interfaces is either nonexistent or below the detection limit of 1D-APFIM. 3DAPM analyses, however, provide significantly better counting statistics and detect a small, but significant segregation of Sb at the matrix/precipitate interface with a Gibbsian interfacial excess of 0.30±0.15 nm-2. This is in distinct contrast to the segregation behavior of Sn or Sb at the interfaces of semicoherent coarse precipitates produced by internal nitridation at 600°C, for which much larger Gibbsian interfacial excesses of Sn or Sb, up to 7±3 nm-2, have been measured. In contrast, the thin platelets are either coherent or have significantly fewer misfit dislocations than is geometrically necessary for a full compensation of the lattice parameter misfit between precipitate and matrix. This demonstrates that Sn or Sb segregation with an appreciable Gibbsian interfacial excess is related to the presence of misfit dislocations at the interfaces of the coarse precipitates.
Original language | English (US) |
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Pages (from-to) | 257-264 |
Number of pages | 8 |
Journal | Interface Science |
Volume | 9 |
Issue number | 3-4 |
DOIs | |
State | Published - Nov 2001 |
Funding
This research was supported by the National Science Foundation (Bruce A. MacDonald, grant officer) under Grant DMR-9728986. D. I. received partial support through the Max Planck Research Prize of D.N.S. and from the Deutsche Forschungsgemeinschaft. The authors wish to thank Ms. Ellen J. Siem for her contributions to this research as a result of an undergraduate research project with financial support from the REU program of the National Science Foundation. Special thanks are due to Mr. Jason T. Sebastian for his experimental assistance and useful discussions.
Keywords
- Gibbsian interfacial excess
- Heterophase interfaces
- Internal nitridation
- Iron-molybdenum alloys
- Segregation
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- General Materials Science
- Condensed Matter Physics