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

The features of recrystallization of steels with different chemical composition and type of crystal lattice under laser action were investigated. These processes are of great importance in high-speed laser heating and cooling, as well as in the formation of the microstructure of steels under the influence of residual heat.
It was found that recrystallization under laser action has signs of a dynamic process due to an increase in the dislocation density. In addition, the dislocation substructure of steel is inherited from the initial hot-deformed state. It is shown that the mechanism of laser recrystallization depends on the type of steel, chemical composition, and crystal lattice.
In different steels, the development of primary, collective, and secondary recrystallization was observed. In this case, the change in the grain structure of steels took place against the background of an increased density of dislocations and the formation of a cellular dislocation substructure.

The paper focuses on the application of friction stir welding (FSW) technology for welding of unequal materials based on aluminum alloys. Joints were made from AW 5083 and AW 6082 materials using FSW technology at different weld speed values. The joints were analyzed metallographically, the hardness of the materials was tested across the cross section of the joint and the strength of the joint was tested by destructive static tensile test. At the lowest weld speed, the materials were not perfectly mixed, there was a macroscopically visible gap at the joint location, which was reflected in the lack of joint strength. At the medium and highest weld speed values, a joint with mechanical properties comparable to those of the base material was formed. Metallographically, the bond between the materials was free of any internal defects.

The article describes the concept of a new forging method of circular cross-section blanks in a forging tool, the design of which makes it possible to develop significant alternating deformations in the deformable metal. The results of comparative studies of the microstructure and mechanical properties of AISI-5140H low-alloy structural steel, formed in a new forging tool that implements alternating deformation and in flat strikers are presented.

In this work the possibilities of reducing the roughness and defects of surfaces obtained by 3D printing with selective laser melting (SLM), via reactive electrospark surface modification (ESD) with low-melting AlSi alloys has been shown. The influence of the energy parameters of the ESD process on the roughness, microstructure, microhardness and performance characteristics of the coatings has been studied. Surfaces with new phases and ultrafine crystal-amorphous structure with particle sizes from micro to nano level, with new relief, with thickness up to 15 μm and microhardness up to 11 GPa were obtained, as the initial SLM roughness from Ra = 8-11μm is reduced to Ra=3-5 μm. Possibilities for control of the characteristics of the coatings and purposeful synthesis of new phases by changing the parameters of the spark discharge have been established. The parameters of the ESD process, which provide simultaneous reduction of SLM surface roughness, removal and erasure of the defects and targeted reactive synthesis of new phases with high performance properties and wear resistance, are defined and optimized.

Titanium rich alloys of Ti-Al-C and Ti-Al-B system was synthesised by Spark Plasma Sintering (SPS) and Field Activated Pressure Assisted Sintering (FAPAS) methods with altering sintering temperatures in the range of 950°C-1020°C with different current for the duration of 5 minutes. The initial powders of the composite 85%Ti and 15%Al was processed by High Velocity Energy Distribution (HVED) in a solution of kerosene at the specific energy of 25MJ/kg to reduce the size of the particles to nano-scale. This method of using different parameters of production technology have helped to analyse the most efficient, energy saving, and less waste generation technological process with improved mechanical properties. The metal-based samples were examined by optical and electron microscopy. Mechanical properties of composites were determined by measuring microhardness.
The aim of the investigation was to determine the dependence between parameters of production technology and properties of Ti-AlC composites.

The effect of different heat treatments on the microstructure and mechanical properties of the C45 and S355J2 steel forgings has been presented. Samples of the same forgings, but subjected to the different heating treatments, were prepared and tested by using opticalmicroscopy, tensile machine, and hardness tester. It was observed that the requested mechanical properties of the forgings and uniform structure can be achieved by determining the appropriate heating treatment parameters.

Nickel aluminum bronze with the composition CuAl9Ni3Fe3 was investigated in this paper. After casting, the alloy was annealed at 900 °C followed by quenching. Thermodynamic calculation of the existing phases was performed using the ThermoCalc software. Quenched NAB samples were further aged for 1 h at 300 °C, 350 °C, and 400 °C. During the experiment, the values of hardness and microhardness were examined using standardized Vickers measurement methods. Microstructural analysis was performed using scanning electron microscopy equipped with an energy-dispersive spectrometer. During the precipitation hardening, β’ martensite eutectoidly decomposed into α and κ phases causing an increase in mechanical properties.

High-entropy alloys were first extensively described in 2004 [1]. Despite the increasing scientific interest in these materials, there is still much to discover. The AlCoCrFeNi alloy is one of the most popular HEAs. Scientists often study the mechanical properties of this alloy and the effect of varying the different component contents on its properties [2,3]. There are also studies on the effects of alloying additives on structure and properties [4,5]. In this study, high-entropy alloys were obtained by induction melting. The influence of aluminium content and titanium addition on tribological properties of AlxCoCrFeNi alloy was tested. Furthermore, the alloys were characterised by X-ray diffraction (XRD), hardness, and microstructure examination. The occurring wear mechanisms and tribological properties of the tested high-entropy alloys were analysed and compared with the results obtained for C45 steel. The received results confirm the influence of Al content in AlxCoCrFeNi alloy and Ti addition on tribological properties

The object of the study is the part of the galvanized steel pipe (about 1-meter-long) supplied by the customers, which was used to supply hot water inside the residential building and which has corroded during exploitation of 5 years. To clarify the situation, quality of surface coating and microstructure of the obtained galvanized steel pipe was analysed. Electrical stray currents of the pipeline installed in the building were measured. The sample of the hot water was taken and analysed at the certificated laboratory.
The aim of the investigation was to determine the possible causes of the hot water supply pipe corrosion during sufficiently short time of exploitation.

Energy-saturated materials are considered to be a source of cheap energy, while detonation synthesis is a new promising form of the basic technology for producing nanodiamonds and other super hard and ceramic nanomaterials. Nanodiamonds is a unique product that combines both the properties of diamond and the advantages of nanostructures. The given work investigated the synthesis products, obtained under industrial conditions, while having detonation of a mixture of trinitrotoluene (TNT) with gecsogen (RDX) and RDX with graphite. The sizes of microcrystallites were, estimated by X-ray diffraction analysis and particle grain size according to the measurement of specific surface area, agglomerate in water suspension after treatment by ultrasound. There was, shown the evolution of nanod iamonds particle sizes and microstructures, both in the primary synthesis products and after enrichment from non-diamond forms of carbon and technological impurities. Changes in the microstructure indicate a high reactivity of nanodiamonds. The obtained results can be useful for studying the mechanism of synthesis and practical application of detonation nanodiamonds.

The peculiarities of the structure and phase composition of the high-entropy alloy of the TiCrFeMnSiC system obtained from the powder mixture of ferrotitanium, ferrochrome and ferrosilicon-manganese ferroalloys are considered in the work. The technological scheme of alloy production included joint grinding of the mixture in a planetary mill, consolidation of the blanks, their heating to 1100 0C, hot forging on the arc press and subsequent annealing of hot-forged samples at 1200 0C. According to the results of X-ray analysis of the obtained alloy, it was found that the main phase of the alloy is the BCC phase with the parameter of the cubic lattice a = 0.2868 nm, which is a solid solution based on alloying components of the original charge. The phase composition of the composite also recorded ti tanium carbide TiC with FCC lattice with the parameter a = 0.4319 nm, which corresponds to a stoichiometric composition of about TiC0.6 and a small amount of FCC phase of iron-chromium carbide (Cr, Fe)23C6 with lattice parameter a = 1.0645 nm. The material has a high hardness (up to 60-61 HRC), which can provide high resistance of this multicomponent alloy.

The evolution of phase composition and mechanical properties and the formation of oxide layers on Fe40–xNiCoCrAlx (x = 5 and 10 at.%) alloys in long-term oxidation at 900 and 1000 °C were studied. In the initial cast state, depending on the aluminum content and valence electron concentration, the alloys contain only an fcc solid solution (VEC = 8 e/a) or a mixture of fcc and bcc phases (VEC = 7.75 e/a). Thin continuous oxide scales containing Cr2O3 and NiCr2O4 spinel formed on the surface of both alloys oxidized at 900°C for 50 h. A further increase in the annealing time to 100 h leads to the formation of aluminum oxide Al2O3 in the scale on the Fe30Ni25Co15Cr20Al10 alloy, having high protective properties. An increase in the oxidation temperature to 1000°C results in partial failure of the protective layer on the
alloy with 10 at.% Al. Long-term holding at 900°C (100 h) + 1000°C (50 h) does not change the phase composition of the Fe35Ni25Co15Cr20Al5 alloy matrix, being indicative of its high thermal stability. In the two-phase Fe30Ni25Co15Cr20Al10 alloy, the quantitative ratio of solid solutions sharply changes: the amount of the bcc phase increases from 4 to 54 wt.% and its B2-type ordering is observed. The mechanical characteristics of the starting alloys and those after long-term high-temperature annealing were determined by automated indentation. It is shown how the hardness (HIT) and the elastic modulus (E) of alloys change after oxidation, depending on the Al content.