Gamma double prime precipitation kinetic in Alloy 718

Gamma double prime (gamma ''), precipitation was studied in Alloy 718 using isothermal and isochronal aging heat treatments applied between 943 and 1003 K. It is shown, that the coarsening behavior of gamma '' precipitates follows the coarsening kinetic predictions of the Lifshitz-Slyozov-Wagner (LSW) theory. The activation energy for gamma '' growth has been determined as equal to 272 kJ mol(-1) and seems to be controlled by volume diffusion of mobium in the matrix. The energy of the gamma ''/matrix interface, Gamma, has been found to be 95 +/- 17 mJ m(-2) by assuming that the gamma '' precipitates adopt a disk shape which minimizes the total energy. This energy includes a volume distortion term calculated from the Eshelby inclusion theory and a surface component which is assumed to be isotropic. This interfacial energy is discussed and compared with the energy of gamma'/matrix and gamma ''/matrix interfaces in other superalloys. The constant K '' of the LSW law time dependence has been calculated using the value of interfacial energy and the activation energy of gamma '' precipitates coarsening and is found to be in good agreement with our experimental values. (C) 2007 Elsevier B.V. All rights reserved.