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Submitted on 1 Jan 1977
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THE STATE OF ORDER IN QUENCHED CuPt
ALLOY
J.-P. Chevalier, W. Stobbs
To cite this version:
JOURNAL DE PHYSIQUE Colloque C7, supplkment au no 12, Tome 38, dkcembre 1977, page C7-172
THE STATE OF ORDER
IN QUENCHED CuPt ALLOY
J.-P. CHEVALIER (*) and W. M. STOBBS (**)
Cavendish Laboratory, Cambridge, England
RksumB. - Nous avons Ctudie l'ordre local dans C u P t trempe. Abstract. - W e have studied local order in quenched CuPt alloy.
Dark field stereo images in quenched CuPt alloy [l] using short-range order (SRO) scattering show that the local order is of microdomain form. These micro- domains have the L1, structure and range in size from 10
A
to 100A.
They have irregular shapes and micro- domains of the four ordering variants interlock to fill space. Microdiffraction with a 20A
electron probe, using a field emission gun scanning transmission electron microscope [2] confirmed these results, and analysis of the microdiffraction intensities suggests that these domains are imperfectly ordered with order parameter of about 0.5. These results can be compared with those of Walker [3], obtained using both roomtemperature and high temperature X-Ray diffraction. We consider the misfit, due to ordering, between microdomains ordered on different ( I11 } planes. This misfit varies with the degree of order in the microdomains ordered on different ( l l l } planes. lattice imaging [4] a model is proposed for the arran- gement of microdomains in order to accomodate misfits.
Finally, we take this opportunity to propose an operational definition of the term microdomain, appropriate to quenched alloys (i.e. alloys in which the state of order is static). On the basis of our obser- vations on quenched CuPt we propose to define
microdomain as :
1) A region that is three-dimensionally bound. 2) This region has to have a true crystal superstruc- ture even if imperfectly ordered. Conceptually if the size of the region is increased we obtain a large crystal with that superstructure.
3) The size of the region has to be larger than the size of the superlattice unit cell, if the microdomain is perfectly ordered and substantially larger, if the microdomain is imperfectly ordered.
4) We suggest that this definition of microdomain distinguishes it from clusters (e.g. [5, 61) and that this distinction is physically meaningful.
References
[l] CHEVALIER, J.-P. and STOBBS, W. M., Electron Mzcroscopy, ed. D. Brandon (pub. Tal. International) 1976 p. 515. [2] CHEVALIER, J.-P. and CRAVEN, A. J., Phil. Mug. 36 (1977) 67. [3] WALKER, C. B., J. Appl. Phys. 23 (1952) 118.
[4] CHEVALIER, J.-P., PhD Thesis, University of Cambridge (1977). [5] KIKUCHI, R., J. Physique Colloq. 38 (1977) C7.
[6] DE RIDDER, R., VAN TENDELOO, G., VAN DYCK, D., AME- LINCKX, S., J. Physique Colloq. 38 (1977) C7.
(*) Laboratoire de Mttallurgie Structurale des Alliages Ordon- nbs. Ecole Nationale SupCrieure de Chimie de Paris, 11, rue Pierre- et-Marie-Curie 75231 Paris, France.
(**) Dept. of Metallurgy and Materials Sciences, University of Cambridge Pembroke St., Cambridge CB 23 QZ, England.
