Quantitative analysis of delta ' precipitation kinetics in Al-Li alloys

The Rietveld method has been applied to X-ray spectra in order to study the precipitated mass fraction of delta' and delta in Al-Li alloys. The method allows us to obtain quantitatively the delta' and delta precipitate mass f ractions, and their evolution with aging time. Furthermore, this method als o gives directly the cell parameter evolution of the matrix phase and indir ectly the mean half radius of S' precipitates through an appropriate calibr ation curve. Experimentally, this calibration has been approached by previo usly studying the evolution of the mean half radius of delta' by transmissi on electron microscopy (TEM). Thermoelectric power has also been shown to b e a powerful technique to study the microstructural evolution of Al-Li allo ys, bring sensitive to the different stages of precipitation associated to the delta' and delta phases. The comparison of the different experimental r esults allow us to stablish a clear difference between the precipitation ki netics and the hardening kinetics. (C) 2000 Acta Metallurgica Inc. Publishe d by Elsevier Science Ltd All rights reserved.