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

Studies of the impact of high voltage electric discharge (HVED) treatment on the dispersion and phase composition of 87,5 % Al + 12,5 % Cu powder system were performed. It was shown that HVED treatment in kerosene with specific treatment energy of 5 MJ/kg leads to the decrease of mean diameter of treated powder from 15 to 13 μm, and the increase of specific treatment energy leads to the decrease of mean diameter of treated powder from 15 to 6 μm. X-ray diffraction analysis shows that CuAl2 and Al4C3 are synthesized in all considered treatment regimes.
HVED treatment with increased specific treatment energy leads to the increase of quantity of synthesized Al4C3 phase. The use of “three point – plane” electrode system instead of “point – plane” during HVED treatment of 87,5 % Al + 12,5 % Cu powder system leads to the increase of quantity of synthesized Al4C3 and CuAl2 phases, while the efficiency of powders dispersion slightly decreases. Up to 40% of particles in powder mixture, treated by HVED in kerosene with the use of “three point – plane” electrode system, have diameter close to the diameter of the initial powder mixture

Sn-Ag powder alloy of eutectic composition is demanded in the production of powders for soldering pastes used in electronics. Non-eutectic alloy has found its application in catalysis for CO2 reduction, in 3D printing, as the promising material for lithium ion batteries. In this work the way of synthesis of Sn–Ag nanostructured powder alloy with near-eutectic composition based of cementation reaction in the system Sn0/Ag+ in aqueous solutions was proposed. The peculiarities of alloy powder synthesis in acid and slightly acid solutions were studied. Factors influencing on powder microstructure, phase and elemental composition were identified. Electrochemical behavior of tin in aqueous solutions for silver deposition was studied by potentiometric method.

The low-temperature method of Sn–Ni–Zn powders synthesis by cementation of tin and nickel with zinc powder from acidic solutions with the formation of “zinc core – porous nickel shell – external tin layer” structures has been proposed. The method provides metals ratio control in wide ranges (7–41 at. % of tin, 38–86 at. % of nickel and 7–24 at. % of zinc) by variation of the process duration. X-ray phase analysis data give evidence on the presence of β-Sn and Zn phases as well as NiZn3 and NiSn intermetallics in the powders obtained. Differential scanning calorimetry data show the availability of Sn–Zn eutectic with the melting point at 171.2 °C in the powders with high tin content (30–40 at. %). The formation of the ternary intermetallic τ1 phase (Ni3+xSn4Zn) has been established to occur as a result of the powders heating at 260 °C. The discovered low-temperature phase transformation in Sn–Ni–Zn system at 260 °C is of interest for electronic equipment assembly processes that include consecutive stages of soldering and resoldering.

The possibility of high energy synthesis of Ti–Al–C system powder grain refiner by using high voltage electric discharges for treatment of powder mixtures of 75 % Ti + 25 % Al and 85 % Ti + 15 % Al composition in kerosene with subsequent briquetting by spark plasma sintering is shown in present work. It is found out that high voltage electric discharge treatment of powders leads to the increase of dispersity as well as to synthesis of new carbon containing phases during chemical interaction between system components and products of working hydrocarbon liquid destruction. The possibility of controlling this process by changing initial composition of powders, specific treatment energy and spatial distribution of plasma formations by changing electrode system type is shown. It is also shown that changing master alloy synthesis parameters allows controlling inoculation efficiency. Thereby it is possible to achieve surface or volumetric inoculation, so selective increasing of plastic or strength properties of Ni-based cast superalloys becomes possible. Introduction of 0.01 % of synthesized grain refiner during the casting of SM88U (СМ88У) superalloy allows decreasing mean grain size from 1…2 mm to 0.2…0.5 mm. Tensile strength of inoculated superalloy at the temperature of 900˚С was 68 MPa while their stress rupture strength increased by 20 % in average. Composition and properties of inoculated alloys comply with standard technical documentation, which allows their usage for the
production of gas turbines blades.

Electrochemical behavior of silver in tungstate-molybdate melts was studied by potentiometric and voltammetric methods. The electrode process was identified as a single-electron reversible one. The effect of silver on the electrochemical deposition of molybdenum carbide coatings and their electrochemical corrosion behavior in a sodium polysulfide melt was studied.

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.

A complex approach to obtainment of titanium carbide hard metals, which consists of utilization of high density energy flows of high voltage electric discharges (HVED) for dispersion and activation of particles of powders mixture of 80 % Ti + 20 % Fe composition and synthesis of carbide phase and subsequent consolidation of obtained powders mixture by high density electric current with spark plasma sintering (SPS) method. Connection between specific cyclic energy of treatment of “kerosene – Ti + Fe powders mixture” disperse system and changes of dispersity, shape and phase composition of powders and physical and mechanical properties (hydrostatic density, hardness, thermal conductivity, wear resistance, dynamic strength) of materials consolidated from them is found. Tungstenless titanium carbide hard metals, which have high specific values of strength and wear resistance, hardness of which is higher than 82 HRA, and thermal conductivity of such materials is insignificantly lower than thermal conductivity of VK6 alloy, were obtained

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 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.

The impact of current shape during consolidation of Fe – Ti – C – B system materials on the physio-mechanical properties of obtained specimens is studied in present paper. It is experimentally found that the use of method of decrease of voltage surge on output Schottky diodes of SPS device and the decrease of operation time of overcurrent protection in power circuit of SPS generator allowed changing current harmonic composition which lead to an increase of properties of consolidated Fe – Ti – C – B specimens – porosity decreased from 15.8 to 2.8 %, hardness increased from 50 to 55 HRC, loss of mass during abrasive wear decreased from 2 to 0.5 mass. %, and bending strength increased from 750 to 1500 MPa. It is found out that increase of input power during consolidation from 1.3 to 7.5 kJ/s by changing current harmonic composition leads to an increase of physico-mechanical characteristics of Fe – Ti – C – B system metalmatrix composites. Density of consolidated specimens increased from 75 to 95 %, their hardness increased from 35 to 50 HRC, loss of mass during abrasive wear decreased from 10 to 1 mass. % and their bending strength increased from 400 to 1100 MPa.

Regularities of the influence of spark plasma sintering heating rate on the structure and properties of dispersion-strengthened materials based on Fe – Ti – C – (B) system are studied. Increasing heating rate of the samples from 10 °C/s to 20 °C/s induced by increasing current rise rate leads to decrease the average grain size in the material matrix of the Fe – Ti – C – B system from 2.5 to 1.5 microns. This allows to increase hardness from 48 HRC up to 70 HRC and wear resistance 7 times compared to R6M5 (full analog of HSS M2) steel during SPS consolidation in the mode with a heating rate of 20 °C/s and isothermal exposure 1100 °C for 180 s.

The capabilities of powder hot forging for manufacturing of Fe₃Al intermetallics and effect of forging and following thermal treatment routines on their structure and properties had been investigated. Fe₃Al intermetallic powders were produced by means of thermal synthesis at 1000°С in vacuum from a mixture of Fe and Al elemental powders. Hot forging of consolidated preforms had been carried out from 1000, 1050, 1100 and 1150°С and afterwards the hot forged preforms were subjected to supplementary sintering in vacuum at 1100÷1450°С. It is foud, that thermal synthesis of Fe + 14% Al powder mixture results in formation of Fe₃Al phase. Sintering of hot forged specimens result in increasing of strength and crack growth resistance, which values enhance with increasing of sintering temperature. Otherwise the hardness of hot forged intermetallics decreases after their sintering. The influence of modes of treatment on the structure and properties of the materials was investigated. It has been established that the strength and fracture toughness of the intermetallics obtained from milled blend after hot forging had the higher values as compared with the alloy made from the batch without its milling.