Minitsky A. Development of physical and technological basics for production of high-density powder materials

The dissertation is devoted to the solution of an important scientific and technical problem of development and manufacturing of high-density economically alloyed powder materials on the basis of iron with high physical and mechanical characteristics for application under extreme conditions of operation. Comprehensive studies of the plating process of iron powdersby copper and cobalt are conducted, and the dependence of physical and technological characteristics of the powders on the coating film thickness is found out. The main parameters which affect the process of deposition of the coatings on iron powder particles are determined. The possibility tocontrol the coating thickness (in the range of 12–20 μm) by changing the deposition kinetics is found out.The process of compaction of composite iron powders in the conditions of static pressing is analyzed by means of the mathematical equations which describe the density dependences on the pressure of compaction. The possibility of fabrication of materials for electrotechnical application on the base of composite powders of the Fe–Co system with high density and high magnetic characteristics with low total losses upon magnetization reversal at a level of 19–21 W/kg is shown, that allows to use the materials for production of magnetic circuits designed for operation in both constant and variable fields of industrial frequency. The influence of loading conditions, nature and physical properties of the powders on the degree of compaction during pressing is studied. The process of second compaction of the powder systems in the conditions of static pressing is investigated, and the main factors affecting the efficiency of compact densification are revealed. It is found out that the second compaction of iron–graphite mixes enhances the strength of the compacts by 5 times, that is caused both by higher density and increase in the surface area of iron–iron contacts. The possibility of manufacturing long semi-products by static pressing and second compaction of powder mixtures of brittle and ductile materials, including hard alloys WC-Co and Cr3C2-Ni, is found out. The process of second compaction of iron powders under conditions of triaxial compression in a high-pressure chamber is investigated; it is found out that the compact densification depends on the internal friction of particles and the forces in the axial and radial directions. For the first time, the efficiency of obtaining high-density and high-strength Fe-based powder materials by free deposition is shown, which is explained by the contribution of shear deformations into the densification process. The expediency of additional densification by free deposition of multilayer briquettes on the example of iron-graphite samples with different content of graphite in layers is shown, which provides a gradient of properties. The effect of thermomechanical treatment on the densification processes, phase composition, microstructure and properties of powder materials is investigated. It is shown that hot free forging of powder systems can be used to expand the range of composites from metal and cermet powders. The results of research showed the prospects of processing metal waste from shavings of ‘ШХ-15’ steel using free hot forging with previous deposition of powder briquettes. Non-porous composites based on ‘ШХ-15’ shavings and various components added with high strength (1600–1700 MPa) and ductility have been fabricated. The influence of chemical and structural perfection of compacts on the mechanical properties of economically alloyed steels and composites is investigated. For the first time, the influence of the type of porous 3D frame structure, namely the orientation of unit cells, on the nature of deformation of materials is determined. The processes of infiltration of porous iron frames produced by powder metallurgy methods (including 3D printing technologies) by Al-based melt under conditions with a pressure gradient are studied. The minimum size of pores (400 μm),which provides full filling of a porous framework with Al-based melt, is determined. As a part of the dissertation, powder materials have been developed and fabricated that can be widely used as structural, tribotechnical, electrical and special purpose materials. Magnetic materials based on the composite powders have been developed for operation in alternating fields of industrial frequency, which have low losses upon magnetization reversal and at the same time retain high magnetic characteristics. The materials for high-current contacts based on metalworking waste of heavy alloys infiltrated by copper with erosion resistance at the level of industrial pseudo-alloys have been developed. A technology of producing carbide cores is worked out; these cores passed ballistic tests which confirmed that they can be used for the production of armor-piercing ammunition for small arms.