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

Pelton mini hydro-turbine, more concretely its turbine circle buckets was completely damaged during explotation conditions i.e. working time of about two years and half. Because turbine was ensured in ensured company, representatives of the company engaged court expert prof Cvetkovski to perform investigations (analysis) and to determine the reasons for these accidents. Normally working time of the Pelton turbine is about ten years, but there is examples that it can work even twenty years if construction and maintains of turbine was properly done. Therefore, the purpose of the conducted expert examination is to analyze the causes, effects and potential solutions for the damaged Pelton turbine. This report covers the technical aspects, the mechanisms that contribute to the appearance of defects, that is, damage of the buckets of the Pelton turbine. In order to find the reason of failure of the turbine buckets, as first complete visual inspection of the turbine wheel was performed. As additional investigation was performed chemical analysis of the buckets, measuring of its hardness and metallographic investigation (determination of type and quantity of non-metallic inclusion and microstructure).

This paper investigates the influence of aging parameters (temperature and time) on thermal, mechanical and structural properties of the EN AW-6060 aluminum alloy. Thermal diffusivity and hardness were measured after applied heat treatments followed by investigation on scanning electron and transmission electron microscopes. Heat treatments included: solutionizing at 550°C for 1 hour followed by quenching in ice water; after quenching samples were aged at two separate temperatures of 180°C and 200°C for 1-8 hours. The results show that hardness gradually increases with aging time achieving peak value of 95 HV10 after aging at 180°C for 5 hours. Thermal
diffusivity also increases with both aging time and temperature achieving peak values after aging at 200°C for 4 hours. SEM/EDS analysis show the existence of finely distributed precipitates containing Mg, Si and Fe. TEM investigation confirms the existence of rod-shaped precipitates several nanometers in length.

Mechanical tests of 5- and 6-component high-entropy alloys, which were obtained for the first time by the method of hot forging, were carried out. The test results showed a fairly high hardness and strength of the obtained alloys. The TiCrFeNiC alloy (without annealing) has the highest mechanical properties. Its high strength is due to solid-solution hardening, as well as the formation of carbides in situ. Fractographic studies showed mostly quasi-brittle destruction of alloy samples.

The hardness of iron-nickel coatings during the restoration of worn parts is an important factor determining the service life of machines. This mechanical property depends on many factors, the simultaneous influence of which cannot be taken into account in conventional experiments. Therefore, we have made an attempt to simultaneously use the complex methods of similarity theories and planning multifactorial experiments to study the hardness of iron-nickel coatings. The composition of the electrolyte was obtained by us with a copyright certificate for the invention No. 700568, Moscow, 1989, Katsitadze J.V.,. Kikabidze D . N . “Electrolyte for obtaining plated iron-nickel alloy”. This approach to the issue allows taking into account the simultaneous influence of a large number of factors on the optimization parameter, obtaining reliable and reasonable results in the form of regression equations, optimizing the process of restoring machine parts with an iron-nickel electrolytic alloy and generalizing the results obtained.
In the article, the influence of technological similarity criteria on the hardness of iron-nickel coatings is explored, the response function is obtained depending on the dimensionless similarity criteria and the corresponding mathematical model is used to carry out targeted experiments according to the Box-Benkin plan. As a result of mathematical processing of the obtained data, an adequate regression equation was derived, according to which the optimal electrolyte composition and electrolysis conditions have been

Aluminum belongs to the group of light metals, which as pure aluminum does not have good enough mechanical properties for most engineering requirements. Therefore, in order to improve the exploitation properties of aluminum, it undergoes an alloying process, where different chemical elements are added to it, each of which has its own different role. Alloying is carried out mostly to increase hardness and tensile strength, then to increase machinability and stiffness, and sometimes toughness and castability. The most important chemical elements used for alloying aluminum are magnesium, copper, silicon, zinc and manganese, while chromium, titanium and iron are used as impurities. This paper presents the parameters of descriptive statistic mechanical properties of aluminum alloys EN AW-6060 (AlMgSi0,5).

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.

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.

This paper presents the results of an investigation conducted on samples of high-quality heat-treated carbon steel using the magnetic noise method. The objective of the work was to find the proper informative parameters for identifying the obtained s tructures with different hardness. To this end, samples were prepared using quenching and tempering heat treatment at different temperatures , from 150°C to 500°C. After microstructural analysis and hardness measurements, the samples were investigated using the magnetic noise method. The signals were visualized and analyzed using a digital oscilloscope and the Multi Instrument 3.8 software program. The RMS informative parameters and the registration time of the magnetic noise signals were used to identify the obtained microstructures with different characteristics and hardness.

Titanium alloys due to their good properties are increasingly used in biomedicine. However, in order to improve certain properties, titanium-based alloys with new chemical compositions are designed. In order to be characterized in a satisfactory manner, they must first be adequately prepared. In this paper the two most influential parameters were varied: grinding time and force, while the speed of rotation of the grinding wheel was constant. After grinding with the highest gradation of grind paper, the samples were observed under a light microscope to determine the condition of the surface. Then their hardness was determined by the Vickers method with different indenter loads. After that, the samples were polished under the same conditions, and their hardness was determined again. The obtained hardness values were numerically analyzed and the corresponding functional dependences of the measured hardness on the grinding parameters (time and force) and on the indentation force were determined.

Due to the mechanical properties (toughness, elongation, tensile strength) that characterize ductile iron, its application in foundry technology is becoming more pronounced every day. The chemical composition and heat treatment of ductile iron have a great influence on the required mechanical properties. Given the operating conditions, the main purpose of heat treatment of ductile iron is to change the desired mechanical properties. Since the specific mechanical properties of ductile iron are generally related to the regularity of the mined graphite nodules, the main objective in production is to produce ductile iron with the highest possible percentage of ductility. In the experimental part of the paper, microstructure and hardness tests were carried out on specimens of ductile iron NL 400 and NL 700 before and after heat treatment by soft annealing (ferritization) and improvement. It was found that the type and corresponding parameters of heat treatment significantly affect the microstructure and the achieved hardness values of the ductile iron test specimens.

The research of the technology of obtaining new copper-ferrochrome composite material has been done. The results of its structure and properties analysis are presented. The material structure consists of the copper base, non-dissolved coarse inclusions of ferrochrome, diffused zones, forming around these inclusions and phases, having formed in the place of completely dissolved inclusions of ferrochrome fine particles. The material has good mechanical properties and a high wear resistance due to the formed solid solutions of the carbides in the copper.

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.