Akademik Veri Yönetim Sistemi
JOURNAL OF MATERIALS SCIENCE, cilt.29, sa.1, ss.15-25, 1994 (SCI-Expanded)
The early stage coarsening behaviour of delta' (Al3Li) precipitates and composite precipitates, consisting of beta' (Al3Zr) core enveloped by a delta' shell, in an Al-2.5% Li-0.1 5% Zr alloy has been studied at 443, 473 and 503 K by conventional transmission electron microscopy using superlattice dark-field images. Coarsening kinetics of delta' precipitates was found to exhibit considerable deviation from the t1/3 law corresponding to diffusion control at 473 and 503 K. This deviation may be explained either by the operation of a surface-reaction controlled coarsening mechanism represented by t1/2 law, or by the presence of a slower precoarsening stage preceding diffusion-controlled coarsening. The particle-size distributions of delta' precipitates were not in accordance with either the earlier theoretical predictions or the normal distribution. They were symmetrical or slightly skewed to the left, and particle sizes twice the average were observed. The coarsening kinetics of composite precipitates, was found to be rather different from that of delta'; a diffusion model which yields t1/n law with n changing from 1/4 to 1/6 as the coarsening progresses, was predicted. The composite precipitates have exhibited quite a narrow and rather symmetrical size distribution.