International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

In this work it was studied the influence of low-carbon steel wire annealing at different temperatures from 500 to 750 °C that was obtained by cold drawing on its structure and properties. It was sown that bigger work-hardening during the drawing process leads to the decreasing of collective recrystallization starting temperature, which could resulting in obtaining less plastic properties than are appear after lower annealing temperatures with additional loss of strength. The found effects give valuable information for cases when it is desirable to obtain the minimal strength or the maximum plasticity of the wire.

Powder high-entropy alloys (HEA) of TiCrFeNiC equioatomic composition were synthesized by hot forging (HF). The phase composition and parameters of the fine structure of the alloys are determined. It is shown that at all annealing temperatures of the alloys their phase composition does not change significantly and consists of two solid solutions of substitution – FCC and BCC and two carbide phases – TiC and Cr3C2. The mechanical properties of the alloys are at a rather high level – so the maximum strength of the alloy was 2243 MPa and the hardness is more than 62 HRC, which can be explained by the effect of high entropy and in situ synthesis of carbides in the manufacture of alloys.

For simulation of processes of compaction or forging of products from powder materials, a method of permeable elements is proposed. The essence of the method is to use elements whose shape is regulated in advance, and, unlike the finite element method, where the elements coincide with the material volumes and their masses are unchanged, here the masses elements are variable, and material can flow between adjacent cells. Examples of using the method for modeling the processes of forging of porous preforms in closed and open dies, as well as in a closed die with a compensation cavity, are presented.

Using an originally developed laboratory controlled air cooling automatic device regimes of controlled fasted normalization of low and middle carbon steel were studied. Significant improving of the steel structure was shown. The proposed technologies of controlled air cooling could be useful for small metal products of middle carbon steels heat treatment as an advanced normalization process.

The possibilities of Fe-Al intermetallic system production by vacuum sintering and impact consolidation of powder bodies, as well as the influence of the regimes of the methods used on the structure and properties of iron aluminides were studied in the article. Mixture of iron and aluminum powders were used for fabrication of iron aluminide Fe₃Al. The powder samples were compacted and vacuum sintered at temperatures of 1250, 1350, 1400 and 1450 °C, and also using hot forging at a temperature of 1050 °C and 1150 °C. It is shown, that the increase of density is observed only at a temperature of 1400 °C. At sintering temperature of 1450 °C the samples reach a density of 6,35 g/cm³, which is 94% of the theoretical value. Only the use of hot forging makes it possible to obtain nonporous samples. It is shown, that bending strength, fracture toughness and hardness increase with increase of sintering temperature, but higher values of this parameters have the samples, produced with use of hot forging.

Effective modification not by expensive nano-powders but by relatively large ones (up to several microns) and capable to dissolve when entering into the melt and become additional crystallization centers at its start point was shown. That provides a metal structure refinement and, consequently, increases the whole complex of mechanical properties. The optimal process parameters of refractory compounds disperse powders modification were proposed.

The effect of metal phase composition in the Fe-based + (2 % glass) powdered composites on the basic mechanical and tribological properties of the composites, made by means of sintering and hot forging, have been investigated. As a basis for the metallic phase of the composite the mixtures of iron powders with additives of graphite, B₄C, BN and Cu at different ratio were used. It was shown that at sintering of metal-glass material the reaction of glass phase with oxides on the surface of iron powder particles takes place, resulting in a change of glass phase chemical composition. The results of materials mechanical properties investigations had shown that the highest strength properties and hardness have the composites with the content of the initial powder mixture of 5% Cu and 2% B₄C, while the best tribological properties have the composites with 2% B₄C, 5% Cu and 1% BN.

The results of investigations of the structure and the elastic characteristics of the aluminum-matrix composites of Al-TiC system, produced by hot forging in accordance with different technological schemes are presented. It is shown that the materials obtained by hot forging differ in appreciable anisotropy, which is characterized by the elongation of the particles of the matrix phase in the direction normal to forging force. Hereupon the resulting values of both normal elasticity modulus and shear modulus in the plane normal to the direction of the deforming force during hot forging, are of 12-15% higher than the corresponding characteristics in the direction of deformation. For all of the above manufacturing processes the elastic characteristics of the investigated aluminum-matrix composites exceed by 40-70% (depending on the direction of sounding) the Young modulus of aluminum, and the respective characteristics of the shear modulus are higher by 8-15%.

Properties of polycrystalline nanodiamond powder after treatment under oxidizing alkali melts of sodium nitrate and sodium hydroxide were investigated. It is established that the dried initial product contains the particles with size up to 100 microns, which are easily broken by ultrasonic treatment to size about 15 micron. A comparative grain-size analysis of samples before and after treatment of oxidative alkaline melts showed that the average grain size is reduced to 6 microns and the particles of less than 1 micron are formed. It is shown that after treatment in the oxidative alkaline melt final material does not contain non-diamond carbon and the dried powder of polycrystalline diamond practically does not aggregate.

The results of investigations of basic physical and chemical properties for aluminosilicate melts of different compositionsis presented. It is shown that the highest values of surface tension and adhesion was observed for the basalt melts, whereas neutral aluminosilicate glass melts without iron oxides in their composition are characterized by a high value of contact angle and the lowest values of surface forces. The insertion in the melt of ZrO₂ increases significantly wetting angles, surface tension and adhesion throughout the temperature range as compared with the same melts without zirconia. Basalt melts differ by lower viscosities and significantly less sensitivity to the effects of additives on viscosity of zirconium oxide as compared to the andesite-basalt melts.

The feachures of structure and phase formation of TiC hardened Fe-based alloy at in-situ thermal synthesis from mixtures of TiH₂, Fe, graphite and Ni powders had been investigated. It was shown that after synthesis at 1200 ⁰С the structure of the alloy is a skeleton of titanium carbide grains of various shapes and sizes from 1 to 20 µm cemented with Fe-based binding substance mostly located around the titanium carbide grains. The phase composition of the obtained alloy includes mainly phases of titanium carbide and α-Fe. In the case of using the initial mixture with the Ni in the composition of the alloy along with the titanium carbide solid solution of Ni in alpha-iron and Ni-based compounds were identified. When Ni is used instead of Fe in initial powder mixture it leads to a noticeable refinement of the alloy grain structure: the size of the carbide grains is generally not more than 5-7 microns. With the decrease in Ni content in the mixture and respectively increase of iron content at the same Ti and graphite content, the particle size increases markedly and approaches with 5 % of Ni to the particle size of the alloy obtained from the mixture containing no Ni.

Structural investigations performed by the methods of X-ray diffractometry and scanning electron microscopy of electrodeposited iron-based coatings revealed common and specific features and regularities of influence of nickel and chromium on their structure formation. Significant changes in surface morphology, crystallographic texture and microhardness of the electrodeposited coatings caused by the insertion of nickel and chromium in the sulfate iron-plating electrolyte were found and compared.