Impact of chemical composition on tribological properties of AlxCoCrFeNi high-entropy alloys

    Machines. Technologies. Materials., Vol. 15 (2021), Issue 8, pg(s) 323-324

    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


    Investigation of the causes of corrosion of galvanized steel pipes used for hot water supply

    Machines. Technologies. Materials., Vol. 15 (2021), Issue 7, pg(s) 283-286

    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.


    Microcrystallites, granularity and agglomerates of detonation nanodiamonds

    Machines. Technologies. Materials., Vol. 15 (2021), Issue 6, pg(s) 241-243

    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.


    High-entropy alloy of Fe-Ti-Cr-Mn-Si-C system, produced by hot forging from powder mixtures of ferroalloys

    Machines. Technologies. Materials., Vol. 15 (2021), Issue 5, pg(s) 198-200

    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.

  • Phase transformations in high-entropy FeNiCoCrAl alloys during oxidation

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 7 (2021), Issue 1, pg(s) 23-26

    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.

  • Structure transformation in graphite at high-energy ball milling treatment

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 7 (2021), Issue 1, pg(s) 11-13

    The changes in the structure of the crystalline graphite are studied during high-energy ball milling (BM) treatment. It was found by XRD analysis the milling time increasing up to 3.5 h leads to the formation of an amorphous phase in the milling process. After 10 h of ball milling treatment, complete amorphization of graphite takes place. It has been shown by high-resolution electron microscopy the individual particles have complex morphology which depends on the BM time. After 1 h of BM carbon materials characterized by an onion-like structure: the individual particles have a spheroidal shape with a size of ~ 10 nm. However, unlike the previous ones after 10 h of ball milling carbon nanomaterials are characterized by a disordered structure, which is typical for amorphous carbon.


    Quality evaluation of welded joints of various steel welded by GMAW technology

    Industry 4.0, Vol. 6 (2021), Issue 3, pg(s) 87-92

    The paper presents the results of quality evaluation of weldments produced by a mutual combination of different steel grades. Weld joints were made using GMAW technology (method -135 ISO 4063). The type of welding parameters used for the quality of welded joints was monitored. The quality of welded joints was assessed using non-destructive tests. In non-destructive tests, the Visual test according to EN ISO 17637, the Penetration test with colour indication according to EN ISO 22476-12 was used to identify surface defects. The presence of internal errors was assessed by a radiation test according to EN ISO 17636-1. Within the destructive tests, the quality of the welds was assessed by a tensile test according to EN ISO 6892-1, by the test of brittleness of welds according to EN ISO 5173, the course of hardness according to EN ISO 6507-1 was determined on transverse cuts. The bending impact test according to EN ISO 9016 will determine the toughness of the weld metal and heat-affected areas. Metallographic analysis of welds according to EN ISO 17639 was performed on transverse metallographic sections using light microscopy. Based on the performed experiments, recommendations were set, or proposed changes in the welding procedures of the given steel grades.


    Efficiency of processing of recyclate from porous PVC

    Innovations, Vol. 9 (2021), Issue 2, pg(s) 75-77

    The paper presents research on the physical processing properties and morphology of recycled plastics. The scope of work includes conducting the processing of primary PVC and recycled PVC and testing Melt Flow Index and structural investigation of the morphology of materials. In the studies polyvinyl chloride (PVC) Alfavinyl GFM/4-31, was used in the study. This plastic has density of 1230 kg/m3 and hardness of 80 Sh° A. In the experiments, various types of chemical blowing agents were used: Expancel 950 MB80 manufactured by Akzo Nobel. Expancel is a mixture that contains 65 % microspheres in the copolymer of ethylene and vinyl acetate (EVA). The decomposition products of the applied blowing agents mainly include carbon dioxide CO2, a small amount of water H2O and nitrogen N2. The technology for producing the recycled composition is based on the extrusion and compression technology of the compositions obtained. The study of selected physical properties was produced. The research on the structure of manufactured materials, melt flow index MFI, and macroscopic structure are presented.


    Regularities of influence of electron beam technology on heat resistance of optical elements in precision instrument-making

    Machines. Technologies. Materials., Vol. 14 (2020), Issue 5, pg(s) 206-209

    Existing experimental researches show that in order to prevent the destruction of optical elements of modern opto-electronic devices (discs as the light filter linings for IR devices, the input protective windows of laser sighting systems for observation in IR areas of the spectrum, semispherical fairings of IR devices for homing and observation of objects, lightguides for laser medical devices, etc.), electron beam method becomes promising, as it provides cleaning of surfaces, increases their microhardness, makes them more resistant to external influences. The results of experimental studies to improve the properties of the surface layers of elements from optical ceramics after their processing with a moving electron beam with a heat density Fn = 106…1.6∙107 W/m2 and moving speed V = 10-3…10-1 m/s (increase in the surface microhardness from 1.2 … 2.9 GPa (raw elements) to 5.7 … 6.4 GPa (processed elements), the occurrence of hardened layers with a thickness of 210… 230 microns). It has been established that the improvement of these properties leads to an increase in the resistance of elements to external thermal effects: an increase of 1.3…1.7 times the critical values of external heat flows and their exposure times, exceeding which leads to the destruction of elements and the failure of devices for the studied range of change of external pressure is 105…107 Pa; increasing the maximum allowable values of thermoelastic stresses in elements from 50…140 MPa to 160…370 MPa at heating temperatures of 300…1200 K.


    Comparison of corrosion resistance of traditional and modern alternative pipeline steel

    Machines. Technologies. Materials., Vol. 14 (2020), Issue 4, pg(s) 172-176

    The paper presents results of research aimed at comparing selected properties of two types of pipe steels, conventional 17G1S-U steel and alternative S960QL steel. The steels were compared in terms of their chemical composition, microstructure, hardness and corrosion resistance. Static electrochemical corrosion tests were performed on the materials, namely electrochemical impedance spectroscopy (PEIS) and linear polarization (LP) in two electrolytes. The results show different chemical composition and microstructure of materials. 17G1S-U steel has a row-like ferritic-pearlitic structure with a hardness of 200 HV 0.1. S960QL steel has a martensitic structure with a hardness of 353 HV 0.1. Steels showed very close corrosion rate in both electrolytes.

  • Electrodeposition of copper on cold rolled copper substrate

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 6 (2020), Issue 1, pg(s) 11-14

    The microscopic and macroscopic views of copper electrodeposits obtained on plastically deformed copper substrates of different deformation degrees have been investigated. Experiments have been performed under galvanostatic conditions. There appear, depending upon the degree of reduction realized during substrate rolling, three types of deposit: epitaxial, homogenous and texture. Epitaxial growth is observed on unreformed substrate and on the substrates with lesser deformation degree (up to 60 %). With the increase of the substrate reduction degree, heterogeneous type of the deposit appeared and the phenomenon of twinning was stated. On very much deformed substrates, as well as in presence of organic additives, field oriented texture type of the deposit is obtained. On very deformed substrates macroscopic uneven deposits appeared, with the linear structure which follows the direction of substrate rolling. Possible explanations of this phenomenon are given.


    “Equal-channel angular pressing-drawing” technology

    Machines. Technologies. Materials., Vol. 14 (2020), Issue 1, pg(s) 28-30

    This article describes the technology of the combined process “equal-channel angular pressing-drawing”. The analysis of the influence of this process on the structure and mechanical properties of aluminum, copper and steel wires is given. The results of the study showed that the proposed combined deformation method “equal-channel angular pressing-drawing” has a significant advantage over the existing technology for the production of high-strength wire. This deformation method due to the combination of two deformations: severe plastic deformation in a matrix with parallel channels and the process of deformation through a drawing die, allows to get a wire with an ultra-fine structure and a high level of mechanical properties, the required size and shape of the cross section in a small number of deformation cycles.