RADIATION-INDUCED HOMOGENEOUS PRECIPITATION IN UNDERSATURATED SOLID-SOLUTIONS

TEM study of 1 MeV electron irradiated Al 1.9 at% Zn solid solution shows that Zn precipitates form, under irradiation, at temperatures well above the Zn solvus temperature outside irradiation. The corresponding upward shift of this temperature is dose rate dependent. This new example of radiation-induced precipitation exhibits unexpected features, which are not accounted for by the available models: (1) no correlation exists between the location of the precipitates and that of the point defects sinks; (2) the precipitation of incoherent β phase with atomic volume smaller than that of the matrix, and of coherent G.P. zones both occurs; (3) the size of the incoherent β precipitates saturates at large dose. A general mechanism for solute concentration fluctuations under irradiation is proposed which qualitatively accounts for the formation of coherent G.P. zones and for the nucleation of solute clusters with more complex structures. A reanalysis of Russell's model [16] for the growth of incoherent precipitates shows that it may qualitatively account for the observed behavior of the β phase precipitates. © 1979.