omega phase in individual latent tracks induced by irradiation of alpha-titanium with megaelectronvolt fullerenes

摘要

Evidence is obtained for the existence of a hexagonal omega phase in individual latent tracks (i.e. in the vicinity of the ion paths) induced in hcp alpha-Ti after irradiation at 80K at low fluences with 30MeV C_(60) ions. The orientation relationships between the alpha and omega phases are those previously observed by Dammak et al. in 1993 when the omega phase is obtained after irradiation at high fluences with gigaelectronvolt monomers at low temperatures (i.e. (002)_(alpha)||(21-bar0)_(omega) and [100]_(alpha)||[00l]_(omega)). Parallel moire fringes, due to the overlapping of the structure of the omega phase with the alpha matrix, are observed in bright-field images obtained with (020)_(alpha)||(030)_(omega)) reflection conditions. The spacing of these fringes is very close to the value of 3.2 nm expected from the interplanar distances d_((020))~(alpha) and d_((030))~(omega). After irradiation at 300K, such fringes are also observed but the track structure cannot be established unambiguously. This dependence of the irradiation temperature is related to the temperature-pressure structural properties. The present transmission electron microscopy observations are compared with those obtained by Dammak et al. in 1996 and 1999 in the case of irradiation with gigaelectronvolt monomers for which it has been established that an overlapping of tracks is necessary to induce the alpha -> omega on transformation.