METASTABLE PHASE FORMATION UNDER IRRADIATION

A short survey is presentd of recent advances in the theory of stability criteria for phase under irradiation. The reason why standard thermodynamical criteria do not apply is discussed. As an example we show that among the many cases of irradiation induced stabilization of metastable phases, some are simple enough to deserve a detailed quantitative theoretical interpretation. Such is the case for the Ni4Mo compound where irradiation-induced inversion of the respective stability of two ordered structures was first reported, as well as irradiation-induced bistability. A Lyapunov function formalism is used to describe quantitatively the competition between the chemically driven formation of compounds with their ballistic destruction and to assess the respective stability of various compound structures under irradiation. Good quantitative agreement with the reported behavior is achieved. We argue that a similar type of approach might be useful for predicting the type of phase to be stabilized by mechanical alloying.