Aleksei Obrosov | BTU Cottbus (original) (raw)

Papers by Aleksei Obrosov

Metals, Dec 19, 2018

A deep surface modified TiZr layer was fabricated by high-intensity low-energy titanium ion impla... more A deep surface modified TiZr layer was fabricated by high-intensity low-energy titanium ion implantation into zirconium alloy Zr-1Nb. Gas-phase hydrogenation was performed to evaluate protective properties of the modified layer against hydrogen permeation into Zr-1Nb alloy. The effects of ion implantation and hydrogen on microstructure, phase composition and elemental distribution of TiZr layer were analyzed by scanning electron microscopy, X-ray diffraction, and glow-discharge optical emission spectroscopy, respectively. It was revealed that TiZr layer (~10 µm thickness) is represented by α + α(TiZr) lamellar microstructure with gradient distribution of Ti through the layer depth. It was shown that the formation of TiZr layer provides significant reduction of hydrogen uptake by zirconium alloy at 400 and 500 • C. Hydrogenation of the modified layer leads to refinement of lamellar plates and formation of more homogenous microstructure. Hydrogen desorption from Ti-implanted Zr-1Nb alloy was analyzed by thermal desorption spectroscopy. Hydrogen interaction with the surface modified TiZr layer, as well as its resistance properties, are discussed.

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Sep 1, 2022

Microhardness variations across the friction stir welded (FSW) and impulse friction stir welded (... more Microhardness variations across the friction stir welded (FSW) and impulse friction stir welded (IFSW) AA2024-T351 joints have been elucidated by the transformations of the S-Al 2 CuMg phase with a special focus on a distinguished hardness peak within the heat-affected zone (HAZ) of the impulse welds. The increase in hardness within the stir zone (SZ) originated from the partial re-precipitation of the initial Guinier-Preston-Bagaryatsky zones (GPB) and metastable S needles, previously dissolved.) Formation and growth of stable S precipitates via coalescence accounted for the softening through the thermo-mechanically affected zone (TMAZ). The peak strengthening within the HAZ of the IFSW joints was mainly caused by the dense needle-shaped S particles, which can be explained by a mutual influence of the process specific temperature and strain cycles. Dislocations and subgrain boundaries introduced to the material due to plastic deformation facilitated the nucleation of strengthening S precipitates in the HAZ. It demonstrates that the impact of deformation should be considered by the characterization of the precipitation development in the HAZ.

Materials, Mar 31, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Journal of Materials Engineering and Performance, Sep 29, 2022

The effect of heat treatment at various temperatures (650, 850, 1050, and 1100°C) and dwell times... more The effect of heat treatment at various temperatures (650, 850, 1050, and 1100°C) and dwell times (10 min and 1 h) on the metallurgical and microstructural evolution as well as on the related tensile properties of stainless steel 316L processed by selective laser melting (SLM) has been systematically evaluated. The metallurgical and microstructural features such as defects, stability of the columnar-cellular structure and substructure, second phase particles, and phase transformation imparted by SLM and heat treatment have been discussed. It has been shown that the processing conditions specific to SLM significantly alter the kinetics of phase evolution compared to standard welding techniques which affects the accuracy of the prediction. The influence of these characteristics on tensile properties and hardness was elucidated. It was disclosed that with increasing heat treatment temperature there was a gradual increase in elongation but a decrease in strength related to the dislocation density and the development of the microstructure.

Results in physics, Dec 1, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Materials, Oct 22, 2020

The microstructural and functional behavior of TiNi-based wires with a silver content of 0-1.5 at... more The microstructural and functional behavior of TiNi-based wires with a silver content of 0-1.5 at.% was evaluated. The concentration range for Ag doping determined for the TiNi wires with potential for the medical industry was 0-0.2 at.%. Microstructure analysis of TiNi wires with different silver contents at room temperature indicated a multiphase structural state. Various internal structures with tangled grain boundaries were formed by intense plastic deformation. The nanocrystalline structure and phase state of wire with the minimum silver content (0.1 at.% Ag) provide full shape recovery, the greatest reversible strain, and optimal strength and ductility. TiNi ingots with a high Ag content (0.5-1.5 at.%) cracked under minimum load due to excess silver that crystallized along the grain boundaries and broke cohesion bonds between the TiNi grains.

Transactions of Nonferrous Metals Society of China, Nov 1, 2019

Abstract The effect of sintering temperature (1073–1373 K) on the structural and tribological pro... more Abstract The effect of sintering temperature (1073–1373 K) on the structural and tribological properties of nanostructured ball-milled β-type Ti–15Mo samples was investigated. The prepared samples were characterized using various apperatus such as X-ray diffractometer, scanning electron microscope (SEM) and ball-on-plate type oscillating tribometer. Wear tests were conducted under different applied loads (2, 8 and 16 N). Structural results showed that the mean pore and crystallite size continuously decreased with increasing sintering temperature to reach the lowest values of 4 nm and 29 nm at 1373 K, respectively. The relative density of the sintered sample at 1373 K was as high as 97.0%. Moreover, a higher sintering temperature resulted in higher relative density, greater hardness and elastic modulus of the sample. It was observed that both the friction coefficient and wear rate were lower in the sample sintered at 1373 K which was attributed to the closed porosity.

International Journal of Precision Engineering and Manufacturing-Green Technology, Jul 12, 2021

Nowadays, the recycled fine aggregate sourced from construction and demolition waste is not frequ... more Nowadays, the recycled fine aggregate sourced from construction and demolition waste is not frequently used in manufacturing of epoxy resin coatings. Therefore, the main novelty of the article is to prepare green epoxy resin coatings modified with recycled fine aggregate in a replacement ratio of natural fine aggregate ranged from 20 to 100%. The microstructural properties of the aggregates and epoxy resin were analyzed using micro-computed tomography, scanning electron microscopy and nanoindentation. The macroscopic mechanical properties were examined using pull-off strength tests. The highest improvement of the mechanical properties was observed for epoxy resin coatings modified with 20% of natural fine aggregate and 80% of recycled fine aggregate. It has been found that even 100% of natural fine aggregate can be successfully replaced using the recycled fine aggregate with consequent improvement of the pull-off strength of analyzed epoxy resin coatings. In order to confirm the assumptions resulting from the conducted research, an original analytical and numerical failure model proved the superior behavior of modified coating was developed.

Metals, Nov 12, 2017

Ti-Al-N coatings were deposited on high-speed steel substrates by filtered vacuum arc deposition ... more Ti-Al-N coatings were deposited on high-speed steel substrates by filtered vacuum arc deposition (FVAD) during evaporation of aluminum and titanium cathodes. Distribution of elements, phase composition, and mechanical properties of Ti-Al-N coatings were investigated using Auger electron spectroscopy (AES), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nanoindentation, respectively. Additionally, tribological tests and scratch tests of the coatings were performed. The stoichiometry of the coating changes from Ti 0.6 Al 0.4 N to Ti 0.48 Al 0.52 N with increasing aluminum arc current from 70 A to 90 A, respectively. XRD and TEM showed only face-centered cubic Ti-Al-N phase with preferred orientation of the crystallites in (220) direction with respect to the sample normal and without precipitates of AlN or intermetallics inside the coatings. Incorporation of Al into the TiN lattice caused shifting of the (220) reflex to a higher 2θ angle with increasing Al content. Low content and size of microdroplets were obtained using coaxial plasma filters, which provides good mechanical and tribological properties of the coatings. The highest value of microhardness (36 GPa) and the best wear-resistance were achieved for the coating with higher Al content, thus for Ti 0.48 Al 0.52 N. These coatings exhibit good adhesive properties up to 30 N load in the scratch tests.

Journal of Materials Engineering and Performance, Sep 24, 2019

Aiming to develop alloys with better properties for orthopedic applications, the focus of the pre... more Aiming to develop alloys with better properties for orthopedic applications, the focus of the present research was to evaluate the effect of Mo at.% content on structural, mechanical, and tribological properties of hot isostatically pressed Ti-xMo (x = 4, 8, 12, 15, and 20 at.%) alloys. The structural evolution, mechanical properties, and tribological behavior of the nanostructured Ti-xMo alloys were evaluated using x-ray diffraction, scanning electron microscope, and ball-on-disk tribometer. Wear tests were conducted under different applied loads of 2, 8, and 16 N. Experimental results indicated that the structural evolution and morphological changes of the milled alloys were sensitive to their molybdenum (Mo) content. The morphological characterization showed that the crystallite size and the particle size decreased with increasing Mo content (at.%) reaching the lowest values of 27 and 26 nm in the case of Ti-15Mo and Ti-20Mo, respectively. On the other hand, the coefficient of friction and wear rates were found to be decreasing with increasing Mo content.

Metals, Nov 5, 2016

Coating growth and mechanical properties of nanolamellar Cr 2 AlC coatings at various sputtering ... more Coating growth and mechanical properties of nanolamellar Cr 2 AlC coatings at various sputtering power were investigated in the present study. Cr 2 AlC coating was deposited on the IN 718 superalloy and (100) Si wafers by DC magnetron sputtering at different sputtering powers. The structure and properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. It was found that coatings had columnar structure with nanocrystalline substructure. Deposition rate increased with the sputtering power. XRD results showed the presence of the Cr 2 AlC MAX phase, intermetallic AlCr 2 and Cr 7 C 3 carbide phases, along with the change in preferential coating growth orientation. TEM observations confirmed the occurrence of these phases, and the SAED patterns demonstrated significant texture of the coatings. Hardness values were measured in the range between 11-14 GPa, showing a slight increase with the sputtering power.

Polymers, Dec 20, 2017

The scaffolds made of polycaprolactone (PCL) are actively employed in different areas of biology ... more The scaffolds made of polycaprolactone (PCL) are actively employed in different areas of biology and medicine, especially in tissue engineering. However, the usage of unmodified PCL is significantly restricted by the hydrophobicity of its surface, due to the fact that its inert surface hinders the adhesion of cells and the cell interactions on PCL surface. In this work, the surface of PCL nanofibers is modified by Ar/CO 2 /C 2 H 4 plasma depositing active COOH groups in the amount of 0.57 at % that were later used for the immobilization of platelet-rich plasma (PRP). The modification of PCL nanofibers significantly enhances the viability and proliferation (by hundred times) of human mesenchymal stem cells, and decreases apoptotic cell death to a normal level. According to X-ray photoelectron spectroscopy (XPS), after immobilization of PRP, up to 10.7 at % of nitrogen was incorporated into the nanofibers surface confirming the grafting of proteins. Active proliferation and sustaining the cell viability on nanofibers with immobilized PRP led to an average number of cells of 258 ± 12.9 and 364 ± 34.5 for nanofibers with ionic and covalent bonding of PRP, respectively. Hence, our new method for the modification of PCL nanofibers with PRP opens new possibilities for its application in tissue engineering.

Hydrogen degradation is a serious problem in industrial applications like power plants (boilers, ... more Hydrogen degradation is a serious problem in industrial applications like power plants (boilers, turbines), marine structures, car and aircraft components, as it leads to failures as well as to deterioration of properties. Inconel 718 is one of the most commonly used materials for these applications. Different metal nitrides like TiN coatings have been deposited in past to prevent hydrogen degradation, which are also known for their high hardness and good wear resistance [1, 2]. However, reports on hydrogen degradation of CrN coatings, which shows better oxidation and corrosion resistance, higher temperature stability and lower friction coefficient than TiN [3, 4] has not been reported till now. Despite a lot of publications about CrN films, up to now the effect of hydrogenation on mechanical and tribological properties of CrN coatings is still not completely understood. In the current work CrxN coatings were deposited by Direct Current Magnetron Sputtering (dcMS) on Inconel 718 substrate at different chamber pressures and substrate voltages. Substrate voltage is one of the most important process parameters which determines the structure of the coating and the adhesion between substrate and coating. Simultaneously a study of the chamber pressure is also needed to understand the deposited structure and growth rate because at higher pressures the high number of argon atoms reduce the number of ionized ions available for the deposition leading to low deposition rates [5]. Gas-phase hydrogenation of the samples was performed at a temperature of 600° C and hydrogen pressure of 2 atm. It was found that CrxN coatings are resistant against hydrogen exposure as compared to uncoated surfaces. The results of changes in the mechanical, tribological properties and phase composition of the coatings after hydrogenation are discussed. Coating microstructure was studied by scanning electron microscopy (SEM). The mechanical properties of the coatings were characterized by means of nanoindentation and scratch test.

Coatings, Jan 8, 2019

This paper describes the influence of silicon carbide (SiC) coating on hydrogen sorption kinetics... more This paper describes the influence of silicon carbide (SiC) coating on hydrogen sorption kinetics of zirconium alloy E110 (Zr-1Nb). Amorphous SiC coating of 1.5-µm thickness was deposited on Zr-1Nb alloy substrate by direct current magnetron sputtering of composite cathode. Hydrogen absorption by SiC-coated Zr-1Nb alloy significantly decreased due to low hydrogen permeability of the coating. Hydrogenation tests show that SiC coating provides protective properties against hydrogen permeation in the investigated temperature range of 350-450 • C. It was shown that hydrogenation of uncoated Zr-1Nb leads to formation of δ hydrides at 350 • C and δ and γ hydrides at higher temperatures whereas in the SiC-coated Zr-1Nb alloy only δ hydrides formed. Gradient hydrogen distribution through the SiC coating and H trapping in the carbon-rich interface was observed. The adhesion strength of the coating was~5 N. Hydrogenation up to 450 • C for 5 h does not degrade the adhesion properties during scratch testing.

Journal of Materials Science, Aug 3, 2021

Magnetron sputtering is one of the most commonly used deposition techniques, which has received c... more Magnetron sputtering is one of the most commonly used deposition techniques, which has received considerable attention in industrial applications. In particular, owing to its compatibility with conventional fabrication processes, it can produce and fabricate high-quality dense thin films of a wide range of materials. In the present study, nitrogen (N) was combined with pure vanadium in order to form binary nitride to improve its mechanical and tribological performance. To evaluate the influence of nitrogen on the structure of the as-deposited vanadium nitride (VN) coatings, the following techniques were used: XPS, XRD, SEM, AFM and optical profilometry. The residual stresses were determined by the curvature method using Stoney's formula. The hardness and Young's modulus were obtained by nanoindentation measurements. The friction behavior and wear characteristics of the films were evaluated by using a ball-ondisk tribometer. The obtained results showed that the N/V ratio increased with increasing the N 2 flow rate while the deposition rate decreased. The preferred orientation was changed from (200) to (111) as the N 2 flow rate increased with Handling Editor: Catalin Croitoru.

Conference Papers in Science, May 5, 2015

The wear of metallic components used in gas and steam turbines due to erosive sand particles lead... more The wear of metallic components used in gas and steam turbines due to erosive sand particles leads to a tremendous decrease in their lifetime. This wear can be reduced by the use of suitable erosion resistant coatings resulting in lower maintenance costs. In this context, multilayer Cr/CrN PVD coatings using an industrial coater were designed and applied on Inconel 718, a material which finds its application in gas turbines. A variation in the bimodal period has been induced in order to achieve an optimal coating architecture providing optimum properties needed for the erosion resistant coatings. The coating was deposited using a single Crtarget with an induction of N 2 during the nitriding phase at a temperature of 480-500 ∘ C and the coating thickness of 24-26 m was kept constant throughout. The erosion tests were conducted at angles of 30 ∘ , 60 ∘ , and 90 ∘. The sand used for the test is an irregular shaped SiO 2. The erosion tests were followed by a detailed microscopic examination of the eroded coating structure in combination with nanoindentation and scratch tests.

The minerals, metals & materials series, 2020

Surface investigation: x-ray, synchrotron and neutron techniques, May 1, 2018

The influence of plasma-immersion titanium-ion implantation on the hydrogen saturation of E110 zi... more The influence of plasma-immersion titanium-ion implantation on the hydrogen saturation of E110 zirconium alloy is described. Titanium ions are implanted from the metal plasma of an arc discharge at an accelerating-pulse bias potential of 1.5 kV (the pulse-repetition frequency is 100 kHz, and the pulse length is 5 μs) for 30 min. The phase composition, morphology, and valence state of the alloy surface layer are studied. Comparative analysis of changes in the hardness and wear resistance of the alloy subjected to implantation is performed. It is demonstrated that the rate of hydrogen penetration into the surface-doped alloy decreases substantially at a gas-phase hydrogenation temperature of 400°C.

Materials today communications, Jun 1, 2021

Abstract Replacement of toxic and expensive vanadium (V) in medical grade titanium alloys with ch... more Abstract Replacement of toxic and expensive vanadium (V) in medical grade titanium alloys with cheaper and non-toxic elements such as iron (Fe) or niobium (Nb), is an important step forward in developing safer and less expensive biomaterials. Evaluating the effect of different process parameters such as the milling time on the properties of these newly developed alloys helps in understanding and controlling their behavior. Hence, in this study, the influence of ball-milling duration (2, 6, 8, 12 and 18 h) on crystalline structure, phase evolution, densification, and mechanical characteristics of biomedical nanocrystalline Ti-6Al-4Fe (wt. %) alloys is investigated. X-ray diffraction (XRD) confirmed that after 6 h of milling, aluminum (Al) and Fe completely dissolved into Ti matrix to form a solid solution of Ti (Al, Fe). XRD further revealed that the crystallite size decreased from 56 to 30 nm and the micro-strain increased with an increase in milling time. A decrease in porosity along with an increase in density is also observed for the alloys with increasing milling time. Moreover, the values of porosity obtained for the developed Ti-6Al-4Fe alloys ranged from 1 to 12 %, which is comparable to the porosity of one of the cortical bones making it a potential candidate for bone replacements. Microhardness measurements showed that the hardness of the Ti-6Al-4Fe alloys was greater than the hardness of the conventional Ti-6Al-4V alloys. It was observed that the Ti-6Al-4Fe alloy fabricated with the powders milled for 2 h showed the lowest value of Young’s Modulus. Milling time also had a significant effect on the surface roughness of the alloy samples, which showed a decreasing trend with increasing milling times.

Materials research express, Oct 23, 2019