The effect of annealing temperature on the recrystallization kinetics of commercially pure aluminum
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Communications
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The Effect of Annealing Temperature on the Recrystallization Kinetics of Commercially Pure Aluminum
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N.H. LIN, C.P. CHANG, and P.W. KAO ( d ) 37~'C
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O v e r the last few decades, the classic Johnson-MehlAvrami-Kolmogorov (JMAK) equation[~-3] X = 1 - exp (-kt"), where X is the fraction of recrystallized material, t is time, and k and n are constants, has been the most widely used equation for modeling primary recrystaUization in deformed metals. Theoretically, it can be proved that n = 4 if all recrystallized nuclei are formed randomly, the nucleation rate remains constant, the growth rate is three dimensional isotropic, and the growth rate remains the same during growth. If nucleation only occurs at time zero, then n = 3, and this is called site saturation. If heterogeneous nucleation on one or two dimensions occurs, and the growth is less than three dimensional, n < 3 is predicted, t4] However, over the last few decades, many experimental results t5-8] gave n < 3 (typically between 1 and 2) whereas metallographical evidence was not found for nucleation that was limited to less than three dimensions. A detailed review of this problem has recently been given by Roller e t al. [9] there is no need to repeat their discussion here. Rollet e t al. used computer simulation to prove that when considering inhomogeneous distribution of stored energy in a deformed matrix caused by orientation dependence of flow stress of polycrystals, n is much less than the theoretical value. The reason for this is that when there is an inhomogeneous distribution of stored energy, recrystallized nuclei are not randomly distributed, and the growth rate varies so that the application of the JMAK equation is inappropriate. Although Rollet e t al. tg] beautifully used computer simulation to provide the explanation for the low value of n, it would be even more convincing if there were experimental proof of their conclusion. There are two ways to do this. The direct way is to study the recrystallization kinetics of a deformed material that has homogeneous stored energy in it, and the indirect way is to try to obtain a recrystallization condition that satisfies the assumption for the JMAK equation. The former way seems unlikely to be achieved because, in any crystal, limited slip systems result in variations of dislocation activity in three-dimensional space, which gives inhomogeneous distribution of stored energy. The latter way is more likely to be achieved because nucleation and growth are both thermally activated processes, it is expected that if sufficient energy can be provided to the material, then the effect of inhomogeneous distribution of stored energy can be minimized. This is to say that at a very high annealing temperature, viable nucleati
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