Phase stability of decomposed Ni-Al alloys under ion irradiation - art. no. 224113

The disordering of a decomposed Ni-12 at. %-Al alloy under irradiation with 300-keV Ni+ ions is studied in direct comparison to homogeneous Ni3Al at v arious temperatures. For that, the degree of long-range order is quantitati vely determined by electron diffractometry. Heterogeneous alloys disorder s ignificantly 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 e xperimental results are compared with model calculation based on a Cahn-Hil liard-type continuum model. At higher temperatures the model yields a corre ct description of the experiments. However, discrepancies at room temperatu re suggest a direct coupling of local composition and degree of order durin g the collision cascade. This interpretation is further supported by Monte Carlo simulations of overlapping cascade events.