Coarsening of γ (Ni-Al solid solution) precipitates in a γ' (Ni3Al) matrix

The coarsening behavior of Ni3Al solid-solution precipitates in an MAI matrix was investigated in alloys containing 22.0-22.8 at.% Al aged at 650-800 degrees C for times exceeding 1800 h. The rate constant for coarsening increases with equilibrium volume fraction as predicted by the MLSW theory. The activation energy for coarsening, 314.1 +/- 16.6 kJ mol(-1), agrees very well with results from conventional diffusion experiments. The particle size distributions are not in very good agreement with the predictions of any theory; possible reasons are discussed. The particles become more spherical with decreasing elastic self-energy. The results are consistent with the premise that a strong volume fraction effect is observed so long as diffusion in the matrix phase, and not through the precipitate-matrix interface, controls the kinetics. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.