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Recovery and recrystallization of the deformed, orderable alloy (Co78Fe22)3V

Published online by Cambridge University Press:  31 January 2011

R.W. Cahn*
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom
M. Takeyama*
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831–6115
J.A. Horton
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831–6115
C.T. Liu
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831–6115
*
a)Address correspondence to this author.
b)Current address: National Research Institute for Metals, 2–3–12 Nakameguro, Meguro-ku, Tokyo 153, Japan.
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Abstract

An alloy of composition (Co78Fe22)3V, which orders to an L12 superlattice below a critical temperature (Tc) of 910 °C, was rolled to 25–50% reduction in the initially ordered condition and annealed at various temperatures above and below Tc and examined by hardness, tensile testing, optical and electron microscopy and dilatometry, in order to study the progress of recovery and recrystallization. Recrystallization was severely retarded on annealing below Tc; close to Tc, recrystallization was ≈ 300 × slower in the ordered than the disordered range. Although recrystallization started promptly, predominantly at grain boundaries, very rapid recovery-softening of the unrecrystallized regions progressively reduced the driving force for recrystallization and slowed it down drastically. However, at 770°and 500 °C, recovery-softening was replaced by some recovery-hardening (i.e., strain-age hardening). Above Tc, recrystallization was complete in a few seconds and a special annealing method was needed to measure such times accurately. Dilatometric measurements showed that most of the order destroyed by rolling was restored long before recrystallization began, but the restoration was never complete unless the alloy was heated up through Tc and then slow cooled. Electron microscopy showed no sign of any antiphase domains in recrystallized grains except for a few isolated domain boundaries on annealing at 770 °C. A model is proposed to rationalize the incidence of recovery-softening or strain-age hardening at different annealing temperatures.

Type
Articles
Copyright
Copyright © Materials Research Society 1991

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