Phase stability of decomposed Ni-Al alloys under ion irradiation

Abstract

The disordering of a decomposed $\mathrm{Ni}\ensuremath{-}12\mathrm{at}.%\ensuremath{-}\mathrm{Al}$ alloy under irradiation with 300-keV ${\mathrm{Ni}}^{+}$ ions is studied in direct comparison to homogeneous ${\mathrm{Ni}}_{3}\mathrm{Al}$ at various temperatures. For that, the degree of long-range order is quantitatively determined by electron diffractometry. Heterogeneous alloys disorder significantly faster than the homogeneous intermetallic. In addition, their disordering rate depends on the precipitate size of the microstructure. At 823 K a steady state with an intermediate degree of order is reached. The experimental results are compared with model calculation based on a Cahn-Hilliard-type continuum model. At higher temperatures the model yields a correct description of the experiments. However, discrepancies at room temperature suggest a direct coupling of local composition and degree of order during the collision cascade. This interpretation is further supported by Monte Carlo simulations of overlapping cascade events.