ω phase individual latent tracks induced by irradiation of α-titanium with megaelectronvolt fullerenes
Résumé
Evidence is obtained for the existence of a hexagonal ω phase in individual latent tracks (i.e. in the vicinity of the ion paths) induced in hcp α-Ti after irradiation at 80 K at low fluences with 30 MeV C60 ions. The orientation relationships between the α and ω phases are those previously observed by Dammak et al. in 1993 when the ω phase is obtained after irradiation at high fluences with gigaelectronvolt monomers at low temperatures (i.e. (002)α∥(21̄0)ω and [100]α∥[001]ω). Parallel moiré fringes, due to the overlapping of the structure of the ω phase with the α matrix, are observed in bright-field images obtained with (020)α(∥(030)ω) reflection conditions. The spacing of these fringes is very close to the value of 3.2 nm expected from the interplanar distances d(020)α and d(030)ω. After irradiation at 300 K, 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 α → ω transformation.