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Improving the surface quality and tribological characteristics of 3D-printed titanium parts through reactive electro-spark deposition
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Improving the Surface Quality and Tribological Characteristics of 3D-Printed Titanium Parts through Reactive Electro-Spark Deposition
by Georgi Kostadinov 1ORCID,Todor Penyashki 1,*,Antonio Nikolov 2 andAleksandar Vencl 3ORCID
1
Institute of Soil Science Agrotechnologies and Plant Protection “N. Pushkarov”, Agricultural Academy, Shose Bankya Str. 7, 1331 Sofia, Bulgaria
2
Faculty of Industrial Technology, Technical University of Sofia, Kliment Ochridsky 8, 1000 Sofia, Bulgaria
3
University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade, Serbia
*
Author to whom correspondence should be addressed.
Materials 2024, 17(2), 382; https://doi.org/10.3390/ma17020382
Submission received: 8 December 2023 / Revised: 28 December 2023 / Accepted: 8 January 2024 / Published: 12 January 2024
(This article belongs to the Special Issue Advances in Metal Coatings for Wear and Corrosion Applications)
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Abstract
This work presents the results of research conducted with an aim to improve the surface quality, hardness and wear resistance of titanium alloy Ti6Al4V, obtained via the laser powder bed fusion of metals (PBF-LB/M) process of additive manufacturing (AM) known as the 3D printing of metals. The 3D surfaces were coated via reactive electrospark deposition (RESD) with low-pulse energy and electrode materials of low-melting metals and multi-component hard alloys. The relationship between the electrical parameters of the RESD process and the quality, composition, structure, microhardness and wear resistance of the treated surfaces were investigated and analysed. It was found that the roughness and thickness of the resulting surface layers could be changed by changing the RESD modes within the limits of 2.5–5 µm and 8–20 µm, respectively. RESD processing allowed us to achieve two to five times lower roughness than that of titanium AM surfaces. The microhardness and wear resistance of the RESD surfaces are two to four times higher than those of the titanium substrate. Possibilities for the purposeful synthesis of new wear-resistant phases and compounds and for obtaining surface layers with predetermined thickness and roughness were established. It was shown that the subsequent reaction’s electrospark processing helped to simultaneously reduce the roughness and increase the hardness and wear resistance of the modified surfaces, and can be successfully used instead of the material-energy-labour and machine-intensive finishing treatments of the titanium surfaces obtained after 3D printing
Dielectric and magnetic response of mechanically activated Mn-doped SrTiO3 ceramics
No full textThis research was focused on the influence of manganese (Mn) incorporation at Sr and/or Ti sites on the microstructure, relative dielectric permittivity and specific magnetization of strontium titanate (SrTiO3) ceramics. A solid-state method was used for the preparation of mechanically activated (10, 30 and 120 min) Mn-doped SrTiO3 ceramics with various manganese dioxide (MnO2) weight percentages (1.5, 3 and 6 wt%). Rietveld's analysis showed that the mean crystallite size in doped-activated SrTiO3 ceramics is smaller than in undoped ceramics, which is a consequence of additional crystal structure distortion due to ion substitution. Changes in the Raman spectra indicated dopant incorporation in the SrTiO3 lattice. The microstructural analysis pointed out a decrease in the mean grain size with increasing dopant concentration and time of activation. The highest values of permittivity and magnetization were observed for Mn-doped SrTiO3 ceramic mechanically activated for 120 min. Based on all the above, the optimal electrical and magnetic properties of SrTiO3 ceramics can be achieved by the appropriate choice of mechanical activation time and dopant concentration
Impact of Nanocellulose Loading on the Crystal Structure, Morphology and Properties of PVDF/Magnetite@NC/BaTiO3 Multi-component Hybrid Ceramic/Polymer Composite Material
No full textThe hybrid multifunctional magnetic organic/inorganic composite materials, with addition of optimal filler type and quantities are attractive due to wide range of potential application, from various pressure sensors, through smart packaging, to tissue engineering and medicine. The structural, morphological and magnetic properties of polyvinylidene fluoride/nanocellulose/magnetite@BaTiO3 hybrid films were investigated. The presented study revealed significant impact of nanocellulose (NC) content on formation of the polymorphs of PVDF, responsible for ferro-, piezo- and pyroelectric properties. The structural characterization, XRD and Raman measurements confirmed enhancement of the β and γ phases when the loading of NC higher then 4 wt% in multi-component hybrid films. The saturation magnetization value gradually raises with increasing amount of NC and reaches its maximum value of 41.2 emu/g at content of 4 wt% NC. Further, addition of NC decreases saturation magnetization value regardless of constant amount of magnetite, indicating optimal content of NC substrate for co-precipitation of Fe3O4 onto NC matrix.This is the peer reviewed version of the paper: Janićijević, Aleksandra, Pavlović, Vera P., Kovačević, Danijela, Đorđević, Nenad, Marinković, Aleksandar, Vlahović, Branislav, Karoui, Abdennaceur, Pavlović, Vladimir B., Filipović, Suzana, "Impact of Nanocellulose Loading on the Crystal Structure, Morphology and Properties of PVDF/Magnetite@NC/BaTiO3 Multi-component Hybrid Ceramic/Polymer Composite Material". Journal of Inorganic and Organometallic Polymers and Materials (2024), https://doi.org/10.1007/s10904-023-02953-
ГУБИТАК ЕНЕРГИЈЕ НА РЕШЕТКАМА
No full textВодозахвати пумпних постројења (водоводи, постројења за пречишћавање
отпадних вода, итд.) и хидроелектрана поседују решетке за спречавање уласка отпадних материја у проточни тракт постројења. Правилним: избором, конструисањем, одређивањем губитка и одржавањем решетке, знатно се утиче на енергетску ефикасност хидро постројења.
Локални губитак на решеткама је један од важних параметара при пројектовању пумпних и
турбинских постројења. Постоји већи број емпиријских израза различитих аутора за
одређивање губитка енергије на решетки. У раду је извршена упоредна анализа 10 израза, на
основу којих су одређени губици за решетку са кружним и решетку са правоугаоним обликом
профила шипки. Губици су одређени за углове нагиба решетке од: 90°, 45°, 35°, 25° и 15° и
брзине дострујавања воде од: 0,3; 0,5; 0,7; 0,9 и 1,1 m/s. Уочавају се одређена одступања
добијених резултата. Пошто се вредност губитка не решетки најпоузданије одређује
моделским испитивањем, приказано је и идејно решење инсталације за хидрауличка
испитивања у каналу са променљивим нагибом у лабораторији Катедре за хидрауличне
машине и енергетске системе, Машинског факултета.[https://ieep-2024.drustvo-termicara.com/content/files/c43d337.pdf
Experimental validation of the FE model of a composite beam
No full textIn order to design a composite beam of a contemporary unmanned air vehicle with vertical
take-off and landing capability, a finite element (FE) model was developed. Structure is
assumed as layered carbon-fiber shell, and is supposed to endure aerodynamic and gravitational
loads. The composite beam was manufactured and experimentally tested in accordance with
the expected operational load regimes (corresponding to 30%, 50%, 70% and 100% throttle).
Static forces, simulating two thrust forces generated by propellers connected to electric engines
and loads from the tail surfaces, were introduced as illustrated in Fig. 1 (left). Strain was
measured at six locations distributed along the beam. A very good comparison between
numerical and experimental results is achieved. Slight discrepancies can be attributed to
manufacturing omissions, insufficient knowledge of mechanical properties of the laminas
making-up the composite structure, and simplifications and idealizations of the numerical
model
PROGRAMMING AND VERIFICATION OF THE MACHINING PROGRAM FOR A TEST WORKPIECE FOR A MACHINE WITH A HORIZONTAL ROTARY AXIS
No full textThis paper presents the testing of the working accuracy of a 3-axis CNC mill. The machine has two
translational axes and a horizontal rotary axis, with the structure A'OXZ. For this machine, a postprocessor was
developed utilizing the kinematic equations. In this study, a specialized test piece was designed and machined to verify
the accuracy and reliability of both the postprocessor and the machine. The test piece was designed with specific
geometric features intended to evaluate the performance of the machining system and the postprocessing program
under various operational scenarios. PTC Creo Parametric software was used for part design and toolpath generation
processes. The generated toolpath was tested in a virtual machining environment on a virtual machine using Vericut
software. The final test piece will be machined on the machine, ensuring an evaluation of the machining system's
performance
INACCURACY ANALYSIS OF CHEBYSHEV’S MECHANISM
No full textConverting rotary motion into rectilinear motion can be very useful in mechanical applications. This type of conversion is mostly achieved using specific types of joints. However, it can be convenient to use mechanisms that can convert rotary motion into rectilinear motion for a specific engineering purpose. The mechanisms with this possibility are called Straight-line generators. The mechanism described in this paper is part of this group, and it is called Chebyshev's mechanism. Chebyshev's mechanism consists of four connected links with proportional dimensions. It is important to point out that this mechanism and most mechanisms from the Straight-line generators group do not generate the perfect straight line. The generated line is an approximate straight line with a changeable deviation from the perfect straight line. This paper shows how the parameters of the mechanism impact the deviation, how the generated line can be described, and what the generated line specifics are.Editor: Dr Boris Dumnić, full professor, dean
Technical treatment and design: Dr Đorđe Vukelić, full professor
Dr Milana Ilić Mićunović, assistant professor
MSc Aleksandar Milošević, assistan
Novel insights into the problem of enthalpy and entropy convergence in thermal decomposition of coal slag using the data from non-isothermal kinetic measurements
No full textThis study provides insight into benefits of thermo-chemical conversion of coal slag as recovery process into value-added products. This research involves kinetic analysis of process conducted through non-isothermal thermal analysis measurements, with additional raw material characterization. Kinetic results showed that decomposition proceeds through two consecutive reactions steps (first one, including anorthite P1̅ → I1̅ phase transition, and then production of incongruent melting product (ternary system: CaO·Al2O3·2SiO2 (CAS2), where viscosity of slag changes), and second one including dehydration and formation of meta-muscovite, and subsequently, thermal disruption of muscovite de-hydroxylated phase, which proceeds with breaking of octahedral Al–O bonds), and one single-step reaction (attributed to CO-reduction of hematite to magnetite). Thermodynamic results showed an existence of physically meaningful isokinetic temperature (Tiso), which corresponds to active vibrational frequency of surroundings of SiO2 reaction site, manifested through Si‒O bond weakening by catalytic reaction of freed hydroxide ion (OH−). It was concluded that at temperature T = Tiso, the course of process loses its dependence on temperature and pressure, regulating changes between thermodynamic parameters, through enthalpy-entropy compensation (EEC) effect
Experimental Investigation of the Aerodynamic Performance of a Ducted Propeller
No full textIn flight conditions up to transonic speeds (M < 0.8), there is no more effective element for creating thrust than a propeller. However, duct-free propellers have significant flaws that can affect flight performance: higher thrust demands necessitate a larger propeller diameter, leading to increased mass; noticeable losses at the blade tips occur when local velocities reach transonic speeds (0.8 < M < 1.2); and there are large aero-acoustic emissions due to flow instability and separation on the blades.
Installing a duct around the propeller reduces the propeller load by changing the stream tube flow field. Another benefit of the duct is the creation of additional thrust force, further increasing the efficiency of the propeller of a given diameter. Tip losses can be significantly reduced, and many studies have shown that ducted propellers offer significant potential in reducing sound emissions.
In this study, several test ducts with different exit diameters and inlet lip radii were designed to determine their effect on ducted propeller performance. The ducts were 3D printed using an FDM printer, then sanded and painted to prepare them for testing. All ducts were integrated onto a commercially available 12-inch diameter propeller driven by an electric BLDC motor.
Static and dynamic tests of the propulsion system were performed on a test stand at the wind tunnel facility of the Faculty of Mechanical Engineering in Belgrade. During testing, measurements of thrust force, rpm, and electrical power were performed. Additionally, to investigate the propulsion system's noise emission, sound volume measurements were performed and compared to those obtained for the duct-free propeller. Preliminary analysis of the results shows an improvement in efficiency and noise emission in some test cases, demonstrating the potential for enhancing aerodynamic performance through relatively simple modifications to the propulsion system
Environmental and Social Assessment of SHPP Komalj - Expertise
No full textM103 - The expertise is done for Deloitte Consulting co. The investor was EIB (European Investment Bank)