Investigation of ordering kinetics in Cu 3 Au with the tomographic atom probe
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Investigation of ordering kinetics in Cu3 Au with the tomographic atom probe S. Duval and S. Chambreland Groupe de M´etallurgie Physique, UMR CNRS 6634, Universit´e de Rouen, F-76821, Mont Saint Aignan Cedex, France
A. Loiseau Laboratoire de Physique du Solide/ONERA, BP 72, F-92322 Chˆatillon Cedex, France
D. Blavettea),b) Groupe de M´etallurgie Physique, UMR CNRS 6634, Universit´e de Rouen, F-76821, Mont Saint Aignan Cedex, France (Received 29 May 1997; accepted 24 September 1997)
Kinetics of congruent ordering in Cu3 Au at 350 ±C was investigated by means of a three-dimensional atom probe. This instrument, called a Tomographic Atom Probe (TAP), enables atomic resolution images of a small volume (10 3 10 3 100 nm3 ) of the material reconstructed in the three dimensions of space. The time evolution of ordered domains at 350 ±C shows that a t 1/2 law is followed as soon as 5 min. For this aging time, the nucleus diameter is close to 1.7 nm. This scaling law was observed even before domains came into contact (t 50 min). Competitive growth was observed to start as soon as 5 min. The number density was observed to decrease rapidly up to t 50 min. A slower decrease was observed when domains begin to impinge. Experimental conditions and requirements as well as advantages of TAP as compared to HREM for the study of ordering are discussed in detail.
I. INTRODUCTION
The ordering kinetics of first-order phase transitions have been of continuous interest for three decades. Theoretical (for a general review, see Refs. 1–6), experimental (an extensive list of references can be found in Ref. 7), and computer simulation (see, for instance, Refs. 8–13) studies on this very fascinating problem abound. The phenomena have been studied in various systems and among them, chemical order-disorder transitions in binary alloys are convenient model systems of investigation. Results show that distinct physical regimes can be distinguished: nucleation and ordering, growth, and coarsening. A large focus of interest has been the nonequilibrium scaling and apparent universality in late stage growth kinetics.14,15 In the coarsening regime, the system can be characterized by a single length scale Lstd, the average size of an ordered domain at time t.1 Evidence from theory, simulations, and experiments indicates that universal laws exist for Lstd in the form of characteristic power law t n and that n 0.5 when the domain growth is driven by the curvature of the domain walls.16 In contrast to coarsening, the early stages of
a)
Address correspondence to this author. e-mail: [email protected] b) Also with the Institut Universitaire de France. 1502
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 6, Jun 1998
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ordering, that is, nucleation and ordering, are much less known and understood since they are basically difficult to study experimentally.17 These early stages immediately follow the quench (fast or sluggish) of the alloy from an initial disord
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