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The precipitation kinetics in a Cu-4 mass% Ti alloy was studied using SEM, TEM, XRD and Vickers hardness. A Cu-4 mass% Ti alloy was prepared, homogenized, solution treated and then aged at 673, 773 and 873 K for times between 0.6 to 720 ks. The XRD and TEM results indicated that the phase decomposition occurred by spinodal decomposition during the early stages of aging. The growth kinetics of composition modulation wavelength is very slow at the early stages of aging. The precipitation of metaestable 0 (Cu 4 Ti) preceded to that of the equilibrium phase phase (Cu 3 Ti), which formed through cellular precipitation. The coarsening process of 0 phase followed the LSW theory for diffusioncontrolled growth. The activation energy for this coarsening process was determined to be about 190 AE 10 kJÁmol À1 . The discontinuous precipitation of phase has an activation energy of about 207 kJÁmol À1 and an exponent time of about one. The highest hardness and fastest transformation kinetics occurred at aging temperatures of 673 and 873 K, respectively.

Phase decomposition was studied during aging of an Fe-32 at%Cr alloy by means of TEM, hardness and the numerical solution of the linear Cahn-Hilliard differential partial equation using the explicit finite difference method. Results of the numerical simulation permitted to describe appropriately the mechanism, morphology and kinetics of phase decomposition during the isothermal aging of this alloy. The growth kinetics of phase decomposition was observed to be very slow during the early stages of aging and it increased considerably as the aging progressed. The morphology of decomposed phases consisted of an interconnected irregular shape with no preferential alignment for short aging times and a further aging caused the change to a plate shape of the decomposed Cr-rich phase aligned in the h110i directions of the Fe-rich matrix. The increase in hardness seems to be associated with the coherency and nanometer size of the spinodally-decomposed phases in the aged alloy.

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