| Numéro |
J. Phys. Colloques
Volume 48, Numéro C6, Novembre 1987
34th International Field Emission Symposium / 34ème Symposium International d'Emission de Champ
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| Page(s) | C6-373 - C6-378 | |
| DOI | https://doi.org/10.1051/jphyscol:1987661 | |
J. Phys. Colloques 48 (1987) C6-373-C6-378
DOI: 10.1051/jphyscol:1987661
ORDERING AND DISORDERING PHENOMENA AT/NEAR THE SURFACE OF D1a TYPE ORDERING ALLOYS
T. Kingetsu1, M. Yamamoto2 et S. Nenno21 New Materials Research Laboratories, Nisshin Steel Co., Ichikawa, Chiba 272, Japan
2 Department of Materials Science and Engineering, Osaka University, Suita, Osaka 565, Japan
Abstract
Ordering and disordering phenomena at/near the surface of D1a type ordering alloys (Ni4Mo and Ni4W) were studied by field-ion microscopy experimentally and by theoretical calculation based on a broken bond model and Bragg-Williams approximation. The main experimental results are as follows : (i) an ordered phase nucleates preferentially at surfaces with certain low index orientation based on the fcc matrix (immediately below Tc), (ii) surface layers of specimens become disordered (around 0.9Tc) and (iii) faceting based on the ordered structure occurs (around 0.8Tc). In the theoretical calculations, (i) surface energy, (ii) surface free energy, (iii) equilibrium degree of order and (iv) surface nucleation rate were obtained. The calculated results explain peculiar phenomena in the above experimental results.