OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Volumetric changes and transformation of the pore structure are additional indirect indicators of structural and phase changes in powder materials. Thus, volume changes were calculated for the samples of those powder mixtures compositions that retained its shape. Volume changes were defined as the relative change in the samples volume before and after sintering: 0 0 0 V V V V V − ∆ = ,% (2) where V0. – the initial sample volume; V – the sample volume after sintering. Structural studies were carried out using optical microscopy, X-ray diffraction analysis and energy dispersive microanalysis (AXIOVERT-200MAT optical microscope, Shimadzu XRD–6000 X-ray diffractometer, CuKα radiation, TESCAN MIRA 3LMU scanning electron microscope). The phase composition was analyzed using the PDF 4+ databases, as well as the POWDER CELL 2.4 full-profile analysis program using the Rietveld phase quantification. Results and discussions Control compacts were prepared from the powder of grinded oxidized chip and sintered along with the samples of other compositions investigated to understand the behavior of treated chip from steel 45 during sintering. The general view, morphological features and detected phases of the sintered processed chip are shown in Fig. 3. The sintered chip microstructure shows the specific shape of fragmented steel particles, where small oxide inclusions are observed (Fig. 3, b). X-ray diffraction analysis of the sintered treated chip showed the degradation of the initial oxide Fe2O3 with the transition to FeO monoxide (Fig. 3, c). a b c Fig. 3. General view (a) of a sintered compact made of processed chips, its microstructure (b) and phase composition (c)
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