Microstructure and elemental analysis of powder iron-based composite materials

Abstract

This article studies the kinetics of structure formation of a composite powder material containing solid lubricants such as graphite, talc and zinc stearate. For the experiments were prepared charge containing powders, wt.%: Cu – 4-18; Sn – 1-2.0; C – 1.5-2.5; talc – 2.0-3.5; zinc stearate – 0.5, Fe – the rest. Mixing of powders was carried out in a Y-shaped mixer, pressing of charges was carried out on a hydraulic press at pressures of 400-1000 MPa, and sintering of compacts – in a conveyor furnace in a protective gas (endothermic gas) in the temperature range 850-1150°C. There is no pearlite in the microstructure of iron-bronze sintered at 850°C. This is due to the adsorption capacity of talc on the surface of iron particles, which prevents the diffusion of carbon into the iron crystal lattice. An increase in the sintering temperature to 1000°C leads to the formation of pearlite in the structure of iron-bronze, while pearlite prevails over ferrite. This indicates the partial burnout of talc from the surface of the iron particles and the open paths of carbon diffusion. At a sintering temperature of 1150°C, a pearlite structure and a network of light inclusions are formed in the microstructure of iron-bronze samples. The study of the chemical composition of light inclusions with a micro-X-ray spectral analyzer showed that these inclusions contain solid solutions of variable compositions either Fe-Cu-Sn, Cu-Fe-Sn or Cu-Sn-Fe. To confirm these assumptions, X-ray phase analysis was performed. The diffraction patterns of these samples are reflections of Fe and Cu. The absence of diffraction effects characteristic of Sn is due to its solubility in the Cu lattice. This is due to the low melting point of Sn (232°С) and its ionic radius, which allows the isomorphic substitution of Cu and Fe ions with Sn ions (their difference is no more than 15%)