High-temperature synthesis in TI+AL powder mixture exposed to gamma irradiation. The features of intermetallic phases formation

Abstract

The purpose of the work presented is to study the processes of phase formation in mechanically activated Ti + Al powder mixture which was exposed to low doses of gamma radiation. A two-stage treatment of the initial powder mixture of the specified composition was conducted. At the first stage, the mixture was mechanically activated in order to achieve a high quality of contact between the reactants. At the second stage, the mixture was subjected to gamma irradiation in order to form a wide transition zone in the contact area. The irradiated mixture was heated by the external heating source. To study the processes of phase formation, the technique of time-resolved X-Ray diffraction was used. The comparative analysis of intermetallic phases formation sequences for irradiated and non-irradiated mixtures was carried out. It was found that the heterogeneous reactions pathways are significantly different for these cases. The detailed analysis of parallel and consecutives reactions was carried out at various stages of high-temperature synthesis taking into account the structure of the Ti–Al equilibrium diagram. It was found that the most probable mechanism of heterogeneous reaction in unirradiated mixture is the predominant dissolution of titanium with the formation of intermetallic phases TiAl, TiAl3. In the irradiated mixture, on the contrary, the flow of aluminum atoms dominates, which leads to the formation of the only synthesis product of the TiAl composition. In the case of forced cooling of the mixture after thermal explosion (TE), a uniform distribution of reactants is observed in the whole volume of the sample of the irradiated mixture which is similar in composition to the TiAl compound.