Application of heterogeneous nucleation theory to precipitate nucleation at GP zones

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The accelerated nucleation of precipitates at GP zones is explained using heterogeneous nucleation theory. Nucleation at zone : matrix boundaries is encouraged by several factors: 1) the chemical interfacial energy of zone : matrix boundaries can significantly decrease the interfacial energy barrier to nucleation; 2) destruction of quenched-in excess vacancies at incoherent portions of the nucleus surface may make the change in the volume free energy significantly more negative; 3) the crystal structures of the zone and matrix are identical and parallel which permits the nucleus to be faceted in both phases. Some additional assistance to nucleation at GP zones is provided by: 4) the accelerated diffusivity resulting from the presence of excess vacancies and 5) the large area of zone : matrix boundary per unit volume of matrix. These factors can more than compensate for the decreased solute supersaturation due to the formation of GP zones and provide an explanation for the enhanced nucleation of precipitates in the presence of GP zones. © 1976 The Metallurgical of Society of AIME.

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Metallurgical Transactions A