ISSN 2594-5327
59º Congresso anual — Vol. 59 , num. 1 (2004)
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Recent results by one of the present authors (T. Miyazaki et al. Metall. Mater. Trans. 30A, 1999, 2783) indicate that classical nucleation and growth theory fail to reproduce the growth kinetics of precipitates in the close vicinity of their solubility limits. These results are rationalized assuming that precipitation proceeds by amplification of fluctuations in the form of spatial concentration waves, i.e., by spinodal decomposition. These results are in agreement with modeling as well as experimental evidences for vapor condensation, which show that the time evolution from the homogeneous non-equilibrium state towards the equilibrium heterogeneous state (i.e. precipitation) proceed nearly at or only after the spinodal line is crossed. In the present work a series of prototype phase diagram calculations is performed based on the Bragg-Williams-Gorskii model, assuming Tsallis' non-extensive entropy. The results show that proper selection of the q-exponent can move the spinodal line towards the actual composition of the alloy in the range of classical nucleation-and-growth regime, justifying the observation of spinodal decomposition in these alloys. The results are considered a strong evidence for the observation of non-extensivity effects in a technologically relevant problem, namely, the aging heat treatment of precipitation hardened alloys.
Recent results by one of the present authors (T. Miyazaki et al. Metall. Mater. Trans. 30A, 1999, 2783) indicate that classical nucleation and growth theory fail to reproduce the growth kinetics of precipitates in the close vicinity of their solubility limits. These results are rationalized assuming that precipitation proceeds by amplification of fluctuations in the form of spatial concentration waves, i.e., by spinodal decomposition. These results are in agreement with modeling as well as experimental evidences for vapor condensation, which show that the time evolution from the homogeneous non-equilibrium state towards the equilibrium heterogeneous state (i.e. precipitation) proceed nearly at or only after the spinodal line is crossed. In the present work a series of prototype phase diagram calculations is performed based on the Bragg-Williams-Gorskii model, assuming Tsallis' non-extensive entropy. The results show that proper selection of the q-exponent can move the spinodal line towards the actual composition of the alloy in the range of classical nucleation-and-growth regime, justifying the observation of spinodal decomposition in these alloys. The results are considered a strong evidence for the observation of non-extensivity effects in a technologically relevant problem, namely, the aging heat treatment of precipitation hardened alloys.
Palavras-chave
Non-extensive thermodynamics, Miscibility gaps, Spinodal decomposition, Bragg-Williams-Gorskii Model, precipitation
Non-extensive thermodynamics, Miscibility gaps, Spinodal decomposition, Bragg-Williams-Gorskii Model, precipitation
Como citar
Schön, Cláudio Geraldo; Miyazaki, Toru.
On the effect of non-extensivity upon the position of the spinodal line for phase separation in binary systems,
p. 2303-2310.
In: 59º Congresso anual,
São Paulo, Brasil,
2004.
ISSN: 2594-5327, DOI 10.5151/2594-5327-3986
