OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Aluminum was added to the steel 45 chip according to the assumption that this mixture is an activeinteracting Fe–Al–O composition. In this case, several parallel-sequential reactions can be initiated, including a reduction reaction. As it is known, the formation of several intermetallic compounds (Fe3Al, FeAl, FeAl2, Fe2Al5 и FeAl3) is possible in the Fe–Al system according to the equilibrium state diagram [25]. The reduction reaction is not excluded if the Fe2O3 iron oxide is presented in the treated chip: Fe2O3 + Al → Al2O3 + Fe. Both the formation of intermetallic compounds and aluminothermy are exothermic reactions, which can significantly increase the current heating temperature. In this case, the sintering process can turn into a thermal explosion. Aluminum interacts with grinded particles of oxidized steel 45 chip under the condition of a new powder product synthesis with a complex phase composition (Fig. 4). This powder material can be considered as a resource for various additive manufacturing technologies or as a precursor in other powder mixtures. At first glance, it can be assumed that the basis of the synthesized particles from a mixture of aluminum and the treated chip is a metal matrix with needle-like inclusions of iron aluminides and inclusions of the Al2O3 oxide phase (Fig. 5). The calculation of the phase ratio in the synthesized product showed that the significant part of the volume belonged to the FeAl (up to 30 vol. %) and Al2O3 (up to 17 vol. %) phases. The XRD also detects free iron (23 vol. %) and aluminum (15 vol. %). According to the main chemical element distribution map (Fig. 6), iron and oxygen are distributed within the volume of the synthesized particles. Aluminum is also present there, but in combination with iron (FeAl) or in the form of Al2O3 oxide. Areas with predominant iron content prevail directly in the volume of particles, while free aluminum is concentrated at their periphery (Fig. 6, c). The interaction of the treated steel chip with titanium was considered using the example of the Ti + chips (steel 45) composition, where titanium was the basis, and the chip was an alloying additive, unlike the previous mixture. In this case, no extreme reactions were expected; the process was carried out under typical solid phase sintering conditions. The chosen sintering temperature (1,000 °С) is low for this composition, while a possible liquid phase (eutectic) in the Ti–Fe system is formed at 1,085 °С according to the equilibrium state diagram. Therefore, a titanium phase is predominantly observed with a small inclusion of free Fig. 4. Phase composition of the sintered powder product from Al + chips (steel 45) mixture а b Fig. 5. Microstructure of the powder product obtained by sintering a mixture of Al + chips (steel 45): the general grain view of powder particles (a) and the internal structure (b)
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