Precipitation kinetics in a Cu-4 mass%25 Ti alloy
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abstract
The precipitation kinetics in a Cu-4 mass%25 Ti alloy was studied using SEM, TEM, XRD and Vickers hardness. A Cu-4 mass%25 Ti alloy was prepared, homogenized, solution treated and then aged at 673, 773 and 873 K for times between 0.6 to 720ks. 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 β′ (Cu4Ti) preceded to that of the equilibrium phase β phase (Cu3Ti), which formed through cellular precipitation. The coarsening process of β′ phase followed the LSW theory for diffusion-controlled growth. The activation energy for this coarsening process was determined to be about 190 ± 10 kJ·mol-1. The discontinuous precipitation of β phase has an activation energy of about 207 kJ·mol-1 and an exponent time of about one. The highest hardness and fastest transformation kinetics occurred at aging temperatures of 673 and 873 K, respectively.
