Influence of the chemical composition of the matrix on the structure and properties of monolithic SHS composites

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 3 2021 Introduction The technological development of new composite materials formed by the SHS method has been carried out for about 50 years, but there are still many unresolved issues. Throughout the development of wear- resistant SHS -composites, main focus is usually drawn towards the hardening phase – carbides and borides, which ensures high values of hardness and wear-resistance [1-5]. SHS method is mostly known in the area of development of new powder materials [6-8]. There is not enough attention paid to monolithic SHS - composites, which are used mostly as instructional materials. The expansion of the scope of application of monolithic SHS composites, associated with the expansion of the range of its strength characteristics, makes it important to identify the role of the metal matrix. Phenomenon of secondary pattern formation is not studied enough in such composites. Data around the influence of eutectic systems that inevitably happen during the synthesis of multicomponent systems, such as Fe-Ni-Ti-C-B and Ni-Cr-Ti-C-B [9–16] is contradictory. Particular difficulties exist when it comes to obtaining non-porous monolithic composites, used for the details and construction elements, experiencing abrasion on a large surface area. A danger of cracking and rapid destruction exists with the mechanical loading, particularly with shock loads. In order to reach a satisfactory combination of wear-resistance and durability, it is important to pay particular attention to metal matrix and processes happening during the secondary structure formation within the metal matrix as well as discovering additional ways for structural changes, chemical composition and matrix properties, which eventually leads to changes of composition characteristics as a whole. In connection with the above, studies of the influence of a metal matrix on the properties of SHS composites are relevant, since it will make a certain contribution to the creation of scientific foundations for the production of highly wear- resistant materials with high strength indicators. The main aim of this work was to conduct a comparative analysis of the structure and properties of SHS composites of the Fe-Ti-C-B, Fe-Ni-Ti-C-B, Fe-Ni-Cr-Ti-C-B and Cu-Ti-C-B systems. Materials and research methods Monolithic SH S composites of different chemical composition obtained by the technology described in [23, 24] are studied. Initial powder mixture consists of thermotactic and matrix components. Thermally reactive components (TRC) are titanium powders, boron carbide B 4 C. Percentage calculation of those com- ponents in TRC was made on the condition of a reaction (1) in stoichiometric proportion: 4Ti + C + В 4 С → 2TiС + 2TiB 2 . (1) Matrix components are powders Fe, Cr, Ni, Сu. The following powders were utilized: titanium PTM- 1 (particle size 15-45 µm), boron carbide M20 (12-20 µm), technical carbon P-804T (1–4 µm), iron PGRV-3 (40–100 µm), nickel PNK-UTZ (1–20 µm), copper PMR-1 (40-100 µm), chrome PH1M (20–100 µm). Initial powders were put into a ball mill with a 5-liter capacity together with grinding balls made out of ball-bearing steel SHH15. Powder mass ratio in relation to the mass of balls was 1:3. Mixing type: dry. Mixing time: 12 hours. It was previously shown that the minimum porosity of the Fe-Ni-Ti-C-B composites is obtained when the content of TRC in the powder mixture is no more than 30 wt. % [25–29]. The chemical composition of powder mixtures for the production of SHS composites is shown in Table 1. Steel pipe container made of a low-carbon structural steel (St3 grade) was filled with the obtained pow - der mix. Initial compacting of the powder mix was achieved with a special snap. Then the initial sample was immersed in an electric furnace and heated up to the temperature of exothermic reaction (1,030 ˚С). After SHS completion hot sample was transferred to a hydraulic press and compacted with a weight of not less than 250 MPa, in order to eliminate porosity. As a result, sandwich plates were obtained, the appearance of which is shown in Fig. 1. Structure of those composites was investigated on a scanning electron microscope TESCAN VEGAII XMU. Rockwell hardness was measured on a hardness tester. Local chemical composition of phases was