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Strain hardening during superplastic deformation of A1-7475 alloy

Published online by Cambridge University Press:  31 January 2011

H. E. Adabbo ,
G. González-Doncel ,
O. A. Ruano ,
J. M. Belzunce  and
O. D. Sherby
H. E. Adabbo*
Affiliation:
Centro Nacional de Investigaciones Metalúurgicas, C.S.I.C., Av. de Gregorio del Amo 8, 28040 Madrid, Spain
G. González-Doncel
Affiliation:
Centro Nacional de Investigaciones Metalúurgicas, C.S.I.C., Av. de Gregorio del Amo 8, 28040 Madrid, Spain
O. A. Ruano
Affiliation:
Centro Nacional de Investigaciones Metalúurgicas, C.S.I.C., Av. de Gregorio del Amo 8, 28040 Madrid, Spain
J. M. Belzunce*
Affiliation:
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305
O. D. Sherby
Affiliation:
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305
*
a)Permanent address: Instituto de Investigaciones en Ciencia y Tecnología de Materiales, CONICET, Juan B. Justo 4302, Mar del Plata (7600), Argentina.
b)Permanent address: Cristalería Espanola, Carr. Madrid-Barcelona km 34.5, 28800 Alcalá de Henares, Spain.
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Abstract

Strain hardening dominates the deformation process in fine-grained A1-7475 alloy in the temperature range 400 to 515 °C. It is shown that anomalously low stress exponents are obtained as a result of strain hardening in strain-rate-change tests. In order to measure stress exponents in a quasi-steady state condition, the samples must be initially deformed at a relatively high stress (≍ 10 MPa) to a relatively high strain (∊ ≍ 0.5) before initiating a strain-rate-change test. Such a procedure revealed that a stress exponent about equal to two and an activation energy (141 kJ/mole) nearly equal to the activation energy for lattice diffusion are obtained. The results are interpreted in terms of a model involving grain boundary sliding accommodated by slip following the Gifkins' “core and mantle” concept. It is proposed that strain hardening is associated with the development of a boundary-dislocation structure in the mantle region in a manner similar to the development of subgrains in the core of a grain when slip is the principal deformation mode.

Type
Articles
Information
Journal of Materials Research , Volume 4 , Issue 3 , June 1989 , pp. 587 - 594
Copyright
Copyright © Materials Research Society 1989

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