OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Ti‒Fe, Al‒Fe, and also Ti‒Al‒Fe‒O, taking into account the oxidation of the chip [20‒22, 24‒25]. In this regard, it is relevant to study the powder products synthesized under vacuum sintering conditions due to the interaction of matrix components (Ti, Al) with the treated steel chip. Thus, the aim of this study is an analysis of the structural-phase state of sintered powder products with different combinations of matrix components when using the grinded steel chip. An evaluation of the interaction of the treated steel chip with titanium and aluminum powder components will allow determining possible research areas for achieving acceptable properties in terms of compositions control, processing modes, and consolidation conditions. Materials and methods For experimental research, the powder mixtures were prepared using both industrial powders of titanium (TPP-8 with a dispersion of < 125–160 μm), aluminum (PA-4, < 100 μm), and a powder from grinded and sieved to 300 μm, additionally oxidized steel 45 chip. The initial state of the chip is shown in Fig. 1. Waste from milling workpieces made of steel 45 without using cutting fluids was used for the research. It was assumed that a significant part of the oxide film would be formed on the chip as a result of this technological operation. The X-ray diffraction analysis of the steel 45 chip showed an almost standard set of characteristic phases of this steel. Consequently, no noticeable number of oxides (10‒15 vol. % Fe2O3) was formed (Fig. 2, a). It is obvious that an increased oxygen content is present, but it is distributed in the form of local small (possibly nanoscale) oxide inclusions that are beyond the sensitivity of an X-ray diffractometer. In this regard, it was decided to oxidize further the chip using the simplest and most accessible way, such as keeping the chip in water for 48 hours. As another method of oxidation, a prevalent method of air annealing in a muffle furnace was used (up to 400 °С). However, the Fe2C precipitation (Fig. 2, b) occurred in the chip after such heat treatment. Therefore, the preference was given to the oxidation in water. As a result, the Fe2O3 phase was formed in sufficient volume (Fig. 2, c). Grinding of small chip pieces was carried out using a vibrating mill in the presence of steel balls in a ratio of 20:1 (balls/chip). Such treatment made it possible to stimulate further the formation of iron oxides. The chip was grinded into various fractions as the result of vibration grinding. After that, particles up to 300 µm have been sieved out. Smaller fractions were not sieved out, since its output was less than 10 % of the processed chip volume. The compositions of the mixtures used provided several options of combining components: Al + chip (steel 45); Ti + chip (steel 45) and Ti + Al + chip (steel 45). The components ratio in the mixtures was determined based on possible interaction reactions. For the first option (Al + chip (steel 45)), the number of interacting components should be enough to initiate the iron reduction reactions from the Fe2O3 iron oxide formed in the steel chip. For the second option, the powder fraction of the processed steel chip in titanium corresponded to an area comparable with the limiting solubility of iron in titanium [25]. The third option of the mixture corresponded to the composition, in which the selected ratio of components could stimulate both reduction reactions (metallothermy) and synthesis of intermetallics. The powder mixtures used in the experiments are presented in Table 1. The powders were mixed in an axial mixer for 4 hours. The obtained mixtures were pressed using a cylindrical mold with a floating punch to obtain samples with 10–15 mm in height and 10 mm in diameter. The studied samples with an initial porosity of 25–30 % were sintered in a vacuum furnace at a temperature Fig. 1. Chip appearance after milling a steel 45 workpiece
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