Dynamic scaling of the decomposition structure of Chromindur during aging at 5250C

The distinction between the spinodal evolution of structure and the nucleation and growth of distinct precipitates is not clear. In the original Cahn-Hilliard treatment of spinodal decomposition, one expects to observe the development of a scattering maximum indicative of a kinetically favored decomposition-fluctuation wavelength. The size or scale of this wavelength was expected to be fixed in time with only a growth of scattered intensity as the fluctuation grew in amplitude. At long aging times a dynamic scaling having a t/sup 1/3/ dependence is expected for the structure whether the structure evolved by spinodal decomposition or by nucleation and growth. Consequently, in the decomposition process, dynamic scaling laws could be expected to have time exponents from zero to 1/3. In the current study of Chromindur (Fe-28 wt % Cr-10.5 wt % Co), a series of coupons were solution heat treated at 9250C for 2 h, quenched into icy brine, and aged at 5250 for times up to almost 500 h. The peak position in the small-angle scattering pattern was followed as a function of time. It was found that a time exponent of 0.10 appears to apply to the decomposition for up to 20 h. A time exponent of 0.25 then applies from approximately 20 h to almost 500 h. No t/sup 1/3/ dependence was seen for the times examined