OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 3 2023 Ta b l e 2 Phase composition of mechanically activated mixtures after additional annealing in vacuum depending on the degree of compaction Mixture composition Modes of compaction and heat treatment of MA mixture Volume content of phases, % Compaction Heat treatment Fe2Ti (15-336) FeTi (19-636) Fe (6-696) Ti (5-682) TiN0.9 (31-1403) ? 2Fe + Ti Loose mixture 1,000 °С, 1 hour 73.3 2.2 24.5 – – – 1,150 °С, 2 hours 74.5 4.8 20.7 – – – 1,250 °С, 2 hours 73.2 3.1 23.7 – – – Compacted sample 1,250 °С, 2 hours 84 – 16 – – Fe + Ti Loose mixture 1,000 °С, 1 hours 89.5 7.9 – 0.7 – 1.9 1,150 °С, 2 hours 83.4 4.5 – – 7.4 4.7 1,250 °С, 2 hours 84.0 1.1 – 6.8 4.5 1.6 Compacted sample 1,250 °С, 2 hours 85 15 – – – – significant amount of unreacted iron remains. It can be explained by a sufficientlywide region of homogeneity of the Fe2Ti compound (fig. 1). In annealed Fe + Ti mixtures, the Fe2Ti phase is also the main phase, while the content of the target FeTi phase does not exceed 7.9 vol. %. Perhaps, one of the reasons for the multiphase nature of the annealing products is the mechanically activated mixtures were annealed in a loose mixture. In order to increase the specific reactive surface area, the mechanically activated mixtures were pressed, and the compacts were subjected to high-temperature diffusion annealing under the same conditions as the mixtures in loose mixture. The phase composition of the annealed compacts (Table 2) differs from the phase composition of the mixtures in loose mixture by the absence of undetermined phases, unreacted titanium and titanium nitride, the small content of which is determined in the annealed mixtures. However, there were no qualitative changes in the phase composition. The Fe2Ti intermetallic compound remained the main phase in the compacts of both compositions. At the same time, the content of the target phases increased due to a decrease in the content of unreacted iron (for the 2Fe + Ti composition) and secondary-side phases (for the Fe + Ti composition). Conclusions 1. In mechanically activated powder mixtures of compositions corresponding to Fe2Ti and FeTi binary intermetallic compounds, exothermic reactions occur under heating, causing temperature elevation and the formation of a small amount of intermetallic compounds. 2. Under the modes of mechanical activation of mixtures used in the study it is impossible to synthesize single-phase intermetallic compounds in thermal explosion reaction. 3. The predominant formation of the Fe2Ti compound is explained by a thermodynamic stimulus: the negative enthalpy of Fe2Ti formation is twice that of the FeTi compound. References 1. Sandrock G. A panoramic overview of hydrogen storage alloys from a gas reaction point of view. Journal of Alloys and Compounds, 1999, vol. 293–295, pp. 877–888. DOI: 10.1016/S0925-8388(99)00384-9. 2. Delogu F., Cocco G. Сompositional effects on the mechanochemical synthesis of Fe–Ti and Cu–Ti amorphous alloys by mechanical alloying. Journal of Alloys and Compounds, 2003, vol. 352, iss. 1, pp. 92–98. DOI: 10.1016/ S0925-8388(02)01109-X.
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