MICROSTRUCTURE AND ELEMENTAL ANALYSIS OF POWDER IRON-BASED COMPOSITE MATERIALS

50 8. Zakharova І.V., Royanov V.O. Obґruntuvannia konstruktivnii osoblivostei pul’satora dlia zabezpechennia pul’suiuchogo rozpiliuval’nogo potoku povіtria pri dugovіi metalіzatsії [Substantiation of constructive features of a pulsator for maintenance of a pulsating spray stream of air at arc metallization]. Tekhnologіchnі nauki ta tekhnologії – Technical Sciences and Technologies, 2020, no. 1 (19), pp. 72-78. doi: 10.25140/2411-5363-2020-1(19)-65-71. 9. Roianov V.A., Semenov V.P. Ekonomnolegirovannye poroshkovye provoloki dlia elektrodugovogo napyleniia iznosostoikikh pokrytii [Economically alloyed flux-cored wires for electric arc spraying of wear-resistant coatings]. Vіsnik Priazovs’kogo derzhavnogo tehnіchnogo unіversitetu. – Reporter of the Priazovskyi State Technical University, 1995, vol. 1, pp. 157-160. (Rus.)

In our opinion, graphite and talc can be used as solid lubricants for iron-bronze, which, when combined, give a greater effect than separately. So, talc, having a high adhesive ability, can suppress the efficiency of the interaction of graphite with iron during sintering, keeping it as free as possible, useful for antifriction materials. In addition, these solid lubricants allow the elimination of process lubricants such as zinc stearate from the batch, which has a detrimental effect on the sintering process.
To detect the above effects of solid lubricantsgraphite and talc, a deeper study of the microstructure and the distribution of elements in it of a sintered composition of the «iron-bronze» type is required.
Analysis of recent research and publications. In works [1,2], the kinetics of structure formation of a composite material containing Cu (3%), Sn (1.5%) və Fe (the rest) were used during sintering. It was found that at temperatures above 232°C due to the melting of tin in the system, a liquid phase is formed, however, due to small particles of Fe and Cu oxides, wetting does not occur. With an increase in the sintering temperature to 8500C, active reduction of all particles of the solid phase and their dissolution in the liquid phase take place.
These studies show that the interaction of the liquid phase of tin with iron particles at a sintering temperature of 850C for 1 hour and subsequent cooling lead to the formation of a fine-grained multiphase heterogeneous structure. X-ray diffraction studies have shown that the structure of the sintered samples also contains double chemical phases (Cu 3 Sn, CuSn, FeSn 2 , Fe 3 Sn 2 , FeSn), as well as phases of complex composition.
Purpose of the article is to study the microstructure and elemental analysis of antifriction powder compositions of the «iron-bronze» type.
Presentation of the main material. The chemical composition of the investigated iron-bronze composite materials containing solid lubricants are given in table 1. The mixtures also contain solid lubricantsgraphite and talc together with Cu and Fe. The mixing of the components was carried out in a Y-shaped mixer for 1 hour. The charge was compressed on a Mannesman hydraulic press at pressures of 400, 700, and 1000 MPa, and sintering was carried out in a Koyo Lindberq conveyor furnace at temperatures of 850, 1000, and 1150C in an endothermic gas medium.
The microstructures of the prototypes were studied on a Neofot-21 metallographic microscope, and the distribution of elements on a Camsan X-ray microstructure analyzer.
An examination of the microstructures of all investigated compositions shows that there is almost no pearlite in the structure at 850C (Figure 1). This is primarily due to the fact that talc is adsorbed on the surface of metal particles with a high adhesive ability, which prevents the diffusion of carbon through the iron surface. In addition, it was found that the sintering temperature at 850C is insufficient under the given thermodynamic conditions for carbon diffusion.
Talc and graphite at 850C have thermal stability and shield the surface of copper and iron particles and envelop them. Presumably for the same reason, the wetting of Fe and Cu particles does not occur.
An increase in the sintering temperature of the studied composition to 1000C in the structure of composition A, the pearlite structure prevails over the structure of ferrite with solid lubricants, and in addition, separate light inclusions are visible (Figure 2). 54 An increase in the sintering temperature to 1150C leads to the formation of cementite in the structure of composition A in the form of a network around the pores and at the boundaries of particles.
In rare cases, separate light inclusions do not occur, particles of solid lubricating additives are barely visible (Figure 3).

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The microstructure of alloy B in large amounts consists of fine light inclusions and cementite in large amounts. In some places, these particles, surrounding the pearlite matrix, form a continuous lattice. The alloy matrix consists of finely dispersed pearlite, which is characteristic of copper.
To study the chemical composition of particles in a Camsan X-ray spectral microscope analyzer, an analysis of the microstructures was carried out at selected points of the alloys of composition B and C (Figure 4).
According to the data in table 2, the chemical compositions at different points differ sharply. For example, an alloy of composition B consists of solid Fe-Cu-Sn at high iron concentrations at points 1, 2 and 6 (97.88; 98.76; 94.38 wt.%).
The number of elements in individual particles is given in table 2. At the same time, copper is the predominant element at points 3 and 4. The boundaries of these elements are Fe-Cu-Sn solid solutions with an increased copper content (34.22 wt.%). The number of non-metallic inclusions is very small, which indicates the destruction of the talc structure at a heating temperature of 1500C and the complete disappearance of free graphite.
It was found that an alloy of composition B consists of a Fe-Cu-Sn solid solution based on iron and copper. However, due to the high content of copper and tin in the alloy, the chemical composition of the points differs significantly from the corresponding points of the alloy consists of B, that is, they are rich in copper and tin.
At points 3 and 4, a significant amount of non-metallic elements (graphite and talc) was found, which confirms the thermal stability of talc at a temperature of 1000C.
The presence of talc, which spreads along the pores and between particles, significantly reduces the interaction between the liquid and the solid phase.
The results of chemical analysis in micrographs show that as a result of sintering Fe, Cu, Sn, an iron-bronze structure is formed. The matrix of such alloys consists of Fe-Cu-Sn solid solutions of variable composition based on iron. This indicates the heterogeneity of the sintered composite structure.
To confirm these assumptions, we carried out a phase X-ray diffraction analysis of the ironbronze composite powder material. Diffractometric curves were plotted on DRON-2.0 on filtered iron rays. As seen from

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The absence of diffraction effects characteristic of Sn and Zn in diffractograms is probably due to their solubility in Fe and Cu cells. This is due to the low melting points of Sn (232C) and Zn (420C), on the other hand, their ionic radii, which make it possible to isomorphically replace Cu and Fe ions with Sn and Zn ions (their difference is no more than 15%).
According to the formula below, the stability of Cu and Fe cells is slightly different from that of pure Cu and Fe. 2 2 2 () a d nk h k    , where d, n, k, l, h are coefficients. Comparison of the diffraction effects of Fe and Cu shows that the sample of alloy of composition A at 800C contains a small amount of Cu, which is mainly represented by iron. Fig. 5 -Diffractometric curves of iron-bronze samples. Compositions: 1, 2, 3 -A; 4, 5, 6 -B; və 7 -C; pressing pressure, MPa: 1, 2, 3 -700; 4, 5, 7 -1000; 6 -400; sintering temperature, C: 1 -800; 2, 5 -1000; 3, 6 -1150; 4, 7 -850 Since sample 3 with such a composition with an increase in the sintering temperature to 1000C has only traces of copper, this confirms the above-mentioned statement that copper particles with a liquid tin phase at a temperature of 800C are isolated and copper has not yet dissolved in iron.
In samples 4 and 5 of composition B, sintered at 850 and 1000C, the amount of Cu or Cu-Sn is almost two times higher than in the composition of alloy A. The largest amount of Cu and Cu-Sn is recorded in sample 6 with a content of B, sintered at 1150C.