A single-grain approach applied to the modeling of recrystallization kinetics for cold-rolled single-phase metals
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1/30/04
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A Single-Grain Approach Applied to the Modeling of Recrystallization Kinetics for Cold-Rolled Single-Phase Metals S.P. CHEN and S. VAN DER ZWAAG A comprehensive model for the recrystallization kinetics is proposed which incorporates both microstructure and the textural components in the deformed state. The model is based on the singlegrain approach proposed previously. The influence of the as-deformed grain orientation, which affects the stored energy via subgrain size and sub-boundary misorientation, is taken into account. The effects of the deformed grain geometry, the nucleation-site density, and the initial grain size prior to deformation on the recrystallization kinetics are assessed. The model is applied to the recrystallization kinetics of a cold-rolled AA1050 alloy.
I. INTRODUCTION
THE recrystallization kinetics in simple metallic systems is frequently described by JMAK-type models.[1] The basis of the JMAK analysis, which yields the volume fraction transformed (X) against time (t), is X 1 exp (kt n)
[1]
The constant k involves the nucleation rate, or the nucleationsite density, and the growth rate. The exponent n relates to the time dependencies of the nucleation rate, growth, and dimensionality of the growth fronts. The crucial assumption made in deriving the various forms of JMAK is that the nucleation sites are randomly distributed in space, leading to n values of 3 or 4. However, in almost all experimental studies of recrystallization kinetics in aluminum alloys, the exponent n is less than 2. Such a deviation from ideal JMAK behavior is attributed to be the occurrence of concurrent recovery,[2] or a nonuniform distribution of stored energy.[3,4] The occurrence of the simultaneous recovery during recrystallization will reduce the dislocation density and, hence, the stored energy. Consequently, the concurrent recovery should retard recrystallization kinetics and cause a negative deviation from linear JMAK behavior. However, both experiments[5,6] and theoretical predictions[3,7] have shown that concurrent recovery cannot fully explain the observed lower value for n. Hence, a more detailed analysis of the uniformity of stored energy in deformed metals and its effect on the recrystallization behavior seems appropriate. It is well known that the deformation in a polycrystal material is inhomogeneous.[8,9] The inhomogenity is of a dual nature. First, the area along the original grain boundaries undergoes a more severe plastic deformation than that along the average macroscopic level. As a result, a deformation gradient will form in the grain; the original grain boundaries are of highest dislocation density and, therefore, are the main source of recrystallization nuclei, especially for
S.P. CHEN, Postdoctor, formerly with NIMR (Netherlands Institute for Metal Research), Delft University of Technology, is now with NIMR, Faculty of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands. S. VAN DER ZWAAG, Professor, is with the Faculty of Aero
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