FORMATION AND ANNEALING BEHAVIOR OF DEFECT CLUSTERS IN ELECTRON OR HE-ION IRRADIATED TI-RICH TI-AL ALLOYS

In order to clarify the effect of He atoms on the formation and anneal ing behavior of defect clusters in Ti-Al alloys, a Ti-47 at.% Al inter metallic compound has been irradiated with electrons and He-ions. Heli um-ion irradiation enhances the nucleation of defect clusters, especia lly of interstitial loops, at temperatures from 623 to 773 K in both g amma-TiAl and alpha(2)-Ti3Al grains of the sample. However, there is l ittle difference between the annealing temperature ranges of defect cl usters in TiAl grains formed by He-ion or electron irradiation at 623 K, The dot-shaped clusters and interstitial loops grow scarcely during annealing, but are annihilated by annealing up to 923 K. Cavities are formed after irradiation with He-ions below 10 dpa at 773 K, but no c avities are formed by electron irradiation up to 30 dpa. The cavities in gamma-TiAl and alpha(2)-Ti3Al grains survive after annealing even a t 1053 K for 1.8 ks, keeping their density and diameter to be nearly t he same as those in the as-irradiated grains.