OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 to 2.5 % in sintered samples is confirmed by the data of elemental analysis of gaseous impurities, performed using the LECO ONH-836 analyzer. The results of X-ray diffraction analysis of sintered samples of the Ti + chips (steel 45) composition make it possible to identify the titanium base as a non-equilibrium solid solution based on α-Ti, the fraction of which reaches 91 vol. %. The remainder is free iron (9 vol. %) at the locations of fragments particles of the steel chip. The variant, when during the sintering process the powdered oxidized chip simultaneously interacts with titanium and aluminum, is shown in Fig. 8. The ratio of components admits both the cross-synthesis initiation of intermetallic compounds and the iron reduction reaction from oxide inclusions on steel chip particles. The actual phase composition (Fig. 8, a) shows that in this case the large volume (about 67 vol. %) of the non-equilibrium phase of the solid solution based on α–Ti is formed, where both a part of aluminum and oxygen can diffuse. The formation of another non-equilibrium phase up to 12 vol. %, the stoichiometry of which is close to AlFe2 (according to the PDF 4+ database file cabinet), can occur at the boundary of steel chip particles upon contact with aluminum particles. Also, in the sintered sample from this composition, X-ray diffraction analysis determined the iron content up to 21 vol. %, perhaps some of it is the reduction reaction product from the formed oxide phases on the grinded oxidized steel chip when interacting with aluminum. The oxide phases were not explicitly determined by X-ray diffraction analysis despite the oxygen presence, which was identified by the analyzer at a level of 1.8 %. It is obvious that the selected ratio of components (Ti, Al and grinded steel 45 chip) and the oxidation degree of the chip (not more than 30 vol. % Fe2O3) did not provide the required amount of reduction reaction products (Fe2O3 + Al → Al2O3 + Fe). Considering the variants of compositions presented in the work using the treated steel chip, it can be unequivocally stated that the grinded oxidized chip is an active interacting component in the studied compositions. The oxide phase presence on fragmented chip particles not only doesn’t prevent the reactiondiffusion interaction with other components, but also promotes the implementation of additional reaction processes. As an indirect confirmation of such processes, one can use the results of the analysis of volumetric changes in compacts after sintering. Table 2 shows the changes in the volumes of sintered compacts, with the exception of the mixture with aluminum (Al + chips (steel 45)) which has lost its initial shape due to an intense exothermic reaction. Negative values show volumetric growth of compacts due to the formation of new phases, migration of elements from one group of components to another, formation of pores in place of molten aluminum which, in turn, migrated to other components, increasing the volume of their grains, etc. The most notable volume increase of compacts is observed after sintering of the last variant of the Ti + Al + chips (steel 45) mixture. Here, several diffusion processes associated with aluminum migration а b Fig. 8. Phase composition (a) and microstructure (b) of sintered specimens from Ti + Al + chips (steel 45) mixture; 1 – solid solution area based on α-Ti; 2 – area rich in free iron; 3 – area corresponding to the nonequilibrium AlFe2 phase
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