INSTABILITY OF ORDERED PRECIPITATES DUE TO LOCAL DISORDERING AND ATOMIC MIXING UNDER IRRADIATION

A time-dependent Ginzburg-Landau (TDGL) model for rime-evolution of lo cal degree of order S and local concentration X was employed in studyi ng dissolution dynamics of ordered precipitates under irradiation with energetic particles. In the simulation, the irradiation effect was ta ken into account as random formation of small zones, in which disorder ing and atom mixing occur momentarily. The process depends sensitively on dose rate of irradiation. In the case of a high dose rate, the pre cipitates disappear in two separate steps. The ordered structure is qu ickly destroyed and then the precipitates dissolve into the matrix of a disordered phase. In comparison, the disordering and the dissolution proceed at the same time when the dose rate is significantly low. The precipitates with locally disordered regions shrink with time. Fine o rdered precipitates are newly formed in thp matrix in the latter case. It is suggested that the moderate irradiation with a low dose rare is available for refinement of ordered precipitates. (C) 1997 Elsevier S cience B.V.