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

An experimental study was carried out to develop a technique for manufacturing a high silicon Al-Si-Ni sintered alloy with a coefficient of thermal expansion close to steels. A stage of hot forging was added to overcome porosity and improve silicon inclusions morphology to obtain better mechanical properties. Liquid and solid phase regimes of sintering were studied for the material made of the elemental components powders mixture as well as of a pre-alloyed powder. The impracticality of liquid-phase sintering modes is shown for this type of material primarily because of the tendency to liquid-phase exudation. It was proposed to carry out a solid-state vacuum sintering with subsequent hot deformation. Only the pre-alloyed powder is suitable for the technique; the other way, it leads to the course and sometimes, not equilibrium intermetallic inclusions will form in place of nickel particles because of the insolubility of Ni in solid Al. It is shown the possibility of successful plastic deformation of this material after sintering despite its extremely low ductility, which helps successfully overcome porosity and improve the characteristics of the microstructure of the material.

In this paper the physical model for high pressure water atomization of metal melts using hydraulic nozzle of a vortex type was proposed. The developed model assumes, that due to high speed water flow with significant centrifugal component of its velocity vector the rarefaction is formed, which causes intensive air suction leading to the formation of rotating gas (vapor-air) layer of toroid-like shape, providing a gap between the water flow and the metal stream. Thus water stream is separated from the heated surface of metal stream and the formation of particles during crystallization of melt droplets occurs due to surface tension mainly in this vapor-air layer. The cooling of melt droplets in the gas-water leads to the formation of spherical powder particles. The proposed model correlates well with the known experimental data on the production of spherical powders using a vortex-type annular hydraulic nozzle.

The effect of TiB2 additives on the sintering temperature, structure, and mechanical properties of materials based on the Fe-FeCr800 system is investigated. It was shown that the introduction of titanium diboride additives leads to the activation of compaction and to a 50–70ºС decrease in the sintering temperature of the pressed composites based on iron. It has been studied that the addition of titanium diboride in the range of 0.38-0.74 (% wt.) provides, with a slight increase in hardness, an increase of 20-25% of the flexural strength of the composite 65Fe-35 FeCr800800 (% wt.), and also provides the formation of a multiphase, microheterogeneous structure of the matrix-filled composite type, which consists of chromium steel of the X6Cr17 type, double iron-chromium carbides M7C3, M3C and complex carboborides of the Me3(CB) type.

Using computer modelling with originally developed semi empirical physical grounded models a study was carried out to investigate influence of previous hot deformation on carbonitrides formation from austenite in low-carbon micro-alloyed steel. Studied in the article is an influence of degree and rate of the deformation on processes of nucleation and growth of Nb and Ti carbonitride particles. The model helps to predict not only process of changing in number and average size of the particles but also to estimate their final size distribution. One of additional peculiarities of the developed model is its ability to predict composition of the cabinetries formed in certain conditions. The model takes into account process of recrystallization and returning, which affect carbonitrides precipitation and are influenced by it. Acceleration was shown of both nucleation and growth rates of the particles due to increasing of deformation degree and strain rate. Another result is that previous deformation significantly affects size distribution function of the particles precipitated with rather lesser effect on their average size. Kinetic curves and final size distribution plots are given.

The influence of temperature of sintering on structure formation, phase composition, microhardness of components of powder composite 65 % wt. Fe – 35 % wt. FH800 were investigated. It has been established that the increase in the temperature of sintering from 1050 ºС to 1250 ºС leads to some increase in volumetric shrinkage, density and decrease in porosity of samples of material which was made from coarse-grained source powders of industrial production components. It was found that the sintering of green compacts in the range of 1000-1300 ºС causes significant changes in the chemical and phase composition of the carbide component of the composite, which are described by a series of phase transformations: M7C3 → M3C (1000-1150 ºС) → M7C3 (1200 ºС) → M3C (1250-1300 ºС)

Equiatomic alloys TiCrFeNiCuC were made by two methods of powder metallurgy – vacuum sintering and hot forging followed by annealing. In the process of sintering the TiCrFeNiCuC blanks, the influence of entropy of mixing resulted in the formation of solid substitution solutions mainly on the basis of the FCC lattice, and also formed titanium carbide (TiC0.74). In samples obtained by hot forging and subsequent annealing, two carbides TiC and Cr3C2 were found, and titanium carbide being formed with lower carbon content (TiC0.58). In addition, the forged samples showed significantly higher values of the defect of the crystalline structure, which leads to increase in their hardness.

Analysis of the structural state and phase composition of surface metal layers after combined treatment of steel which includes preliminary surface plastic deformation of the workpiece, electrospark doping with use of rotating disk electrode 2 mm thick, made of WCCo hard alloy and subsequent surface ball smooth rolling, has been performed. It was shown that the use of combined treatment provides a gradient-layered structure with low surface roughness. Phase composition of the obtained layer consist of ferritic α-Fe phase and a number of carbide phases formed during the interaction of the electrode material with steel: F3W3C, WC and W2C semi-carbide. Wear resistance of the material after treatment exceeds similar properties of the original carbon steel up to 4 times.

The results of the estimation for the influence of titanium diboride content in the initial powder mixture on the basic mechanical properties at the tests on tension and compression are presented. It is shown that the porosity of sintered at 1250 0C preforms from TiH2-TiB2 powder mixture increases with increasing of titanium diboride content in the initial charge, which is due to the manifestation of the Frenkel effect at sintering. The values of tensile strength, hardness and elastic modulus, despite some porosity growth of the sintered alloy, increase with the addition of 5 % of TiB2 powder, while increasing the content of the high modulus component in the mixture to 10 % leads to decrease in the level of these characteristics. The plasticity of sintered alloys monotonically decreases with increasing of the boride component content. At compression tests, the yield point and the compressive strength increase monotonically with increase in TiB2 content, despite the increase in porosity of the latter, due to a significantly lower effect of porosity on the value of the resistance to deformation in compression compared with tension. The use of hot forging of sintered powder preforms leads to increase of strength properties and hardness of the composites.

An experimental electron-beam technology for obtaining tube billets from NiCrAlY alloys used as cathodes for the deposition of heat-resistant coatings by the ion-plasma method has been developed. It is established that coatings applied to gas turbine blades of aircraft engines using cathodes of electron beam melting meet the requirements of Motor-Sich JSC TU for this type of products.

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 electrochemical behavior of dimeric tungsten complexes in metaphosphate-containing melts is studied potentiometrically and voltammetrically. The electrodeposition of tungsten and tungsten coatings from halide-oxide and oxide melts and the correlation between the properties of deposits and the conditions of  electrolysis are investigated.

The specifications for manufacturing of relit (WC + W2C) granular powder by the method of explosive evaporation of condensation in vacuum using electron-beam technologies are presented. It is established that when depositing material on cooled surfaces, it is possible to refine the precipitation products by metallic and non-metallic impurities, depending on the elasticity of their vapors.