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Numerical analysis of metallographic preparation effect on the hardness of titanium alloy
No full textLegure titana zbog svojih dobrih svojstava imaju sve veću primjenu u biomedicini. Međutim, u svrhu poboljšanja određenih svojstava dizajniraju se legure na bazi titana s novim kemijskim sastavima. Kako bi se one mogle karakterizirati na zadovoljavajući način, prethodno moraju biti adekvatno pripremljene. Ispravna metalografska priprema ispitnih uzoraka je pretpostavka za kvalitetno promatranje, identificiranje te evaluaciju mikrostrukturnih značajki. Stoga se parametri brušenja i poliranja moraju odabrati tako da pripremljena površina uzorka bude reprezentativna. S obzirom na to da su za već poznate standardizirane legure ti parametri dobro poznati, kod razvoja novih, ali sličnih materijala, potrebno je utvrditi odgovaraju li ti uvjeti i za pripremu novih sastava. Ukoliko to nije slučaj, potrebno je naći optimalne parametre metalografske pripreme tih sastava. U ovom radu je 12 uzoraka eksperimentalne legure uloženo u epoksidnu masu radi lakšeg rukovanja. U svrhu utvrđivanja utjecaja metalografske pripreme varirana su dva najutjecajnija parametra: vrijeme i sila brušenja, dok je brzina rotacije brusne ploče bila konstantna. Nakon brušenja najvećom gradacijom brusnog papira, uzorci su promatrani pod svjetlosnim mikroskopom kako bi se utvrdilo stanje površine. Zatim im je određena tvrdoća, kao mehaničko svojstvo koje se najčešće ispituje pri karakterizaciji materijala, metodom po Vickersu različitim opterećenjima indentora. Nakon toga, uzorci su polirani u istim uvjetima, te im je ponovno određena tvrdoća. Dobivene vrijednosti tvrdoće numerički su analizirane te su utvrđene odgovarajuće funkcionalne ovisnosti izmjerene tvrdoće o parametrima brušenja (vrijeme i sila) te o sili utiskivanja indentora.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. Proper metallographic preparation of test specimens is a prerequisite for quality observation, identification and evaluation of microstructural features. Therefore, the grinding and polishing parameters must be selected so that the prepared sample surface is representative. Given that these parameters are well known for already known, standardized alloys, in the development of new but similar materials it is necessary to determine whether these conditions are suitable for the preparation of new compositions. If this is not the case, it is necessary to find the optimal parameters of metallographic preparation of these compositions. In this paper, 12 samples of experimental alloy were embedded in the epoxy mass for easier handling. In order to determine the influence of metallographic preparation, 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, as a mechanical property that is most often tested in the characterization of materials, 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 indenter indentation force were determined
Influence of modification on microstructure degradation of AlSi12 alloy exposed to the corrosion environment
No full textThe corrosion resistance of aluminum-silicon (Al- Si) foundry alloys is a result of microstructure development influenced by melt treatment and solidification. As a part of the main eutectic (αAl + βSi), βSi particles are cathodic with respect to the αAl matrix enabling micro-galvanic couple formation and localized corrosion. Despite its high polarization and low current density, increase in the eutectic (αAl + βSi) will contribute to the microstructure degradation of an alloy in corrosive environment. The research was performed in order to estimate the influence of eutectic βSi particles size on the microstructure degradation of AlSi12 alloy with mixed morphology of eutectic (αAl + βSi). The results of light microscopy indicated preferred initiation and progress of cavities involving modified eutectic (αAl + βSi) with eutectic βSi particles of smaller average particle size. The unmodified eutectic (αAl + βSi) with lamellar morphology and dendrites of primary αAl phase were not visually affected by degradation. The average cavity size and pH value of the solution increase with the increasing exposure time, while microstructure degradation rate decreases
Influence of Copper Addition in AlSi7MgCu Alloy on Microstructure Development and Tensile Strength Improvement
No full textCommercial AlSi7Mg alloy represents the usual choice for complex geometry casting production. The market imperative to improve mechanical properties imposed the design of new chemical composition of AlSi7MgCu alloy with high content of Cu (up to 1.435 wt.%). This represents a challenge in order to achieve advanced properties. The interaction of a number of alloying (Si, Mg, Cu) and trace elements (Fe, Mn) influenced a wide range of complex reactions occurring and therefore leading to intermetallic phase precipitation. The characterization of novel chemical composition interaction and its solidification sequence was achieved by modelling an equilibrium phase diagram, simultaneously performing both thermal analysis and metallographic investigations. Copper influence was indicated in the whole solidification process starting with infiltration in modified Chinese script phase Al15(Fe,Mn,Cu)3Si2, beside common intermetallic Al5FeSi. Copper addition encourages formation of compact complex intermetallic phases Al5Cu2Mg8Si6 and Al8(Fe,Mn,Cu)Mg3Si6. Solidification ended with secondary eutectic αAl + Al2Cu + βSi. Microstructure investigation allows volume reconstruction of the microstructure and distribution of particular phases. Chemical compositions enriched in copper content and developed microstructural constituent through solidification sequence of AlSi7MgCu alloy contribute to a significant increase in mechanical properties already in an as-cast state
Microstructure and properties of silicon alloyed compacted graphite irons (CGI)
No full textThe microstructure, tensile properties and hardness of 25 mm thick compacted graphite iron samples alloyed with 3,01, 3,22, 3,61, 3,97 and 4,29 wt. % Si were analyzed in this paper. It was found that Si promotes and strengthens ferrite. Metallic matrix of compacted graphite iron sample alloyed with 3,01 wt. % Si consisted of 98,1 % ferrite and 1,9 % pearlite. Fully ferritic metallic matrix was obtained in compacted graphite iron samples alloyed with 3,22, 3,61, 3,97 and 4,29 wt. % Si. Nodularity varied from 8 to 13 %. Yield strength increased from 246 to 447 N/mm2, tensile strength increased from 318 to 496 N/mm2, hardness increased from 160 to 227 HBW, and elongation decreased from 3,6 to 1,6 % with an increase in Si content from 3,01 to 4,29 wt. %. Analyzed Si alloyed compacted graphite iron samples have a very uniform hardness and higher ratio Rp02/Rp02 than conventional ferritic, ferritic-pearlitic and pearlitic compacted graphite iron grades
Dynamic modelling of the biomass gasification process in a fixed bed reactor by using the artificial neural network
No full textBiomass gasification enables the transformation of biomass feedstock into syngas suitable for further energy conversions. Mathematical models of gasification are not only valuable tool for the design and optimization of the processes, but could be also employed for online prediction and process control. In this work, the potential of using nonlinear autoregressive networks with exogenous inputs (NARX) for predicting the gasification process when a lower amount of experimental data is available was studied. The analysis of using an open-loop NARX network for an online prediction of the syngas composition in a downdraft gasifier at different data recording frequency was performed. The predicted results showed that by decreasing the data recording frequency, the prediction error increases. Furthermore, the possibility of improving the NARX network at lower data recording frequency was analysed by expanding the training dataset to reduce discrepancies between predicted and measured results. Inclusion of four data sets made neural network more robust and flexible for operating with fewer data points. Practical significance of results can be seen in the application of open-loop network for online prediction and control of the gasification process at lower data recording frequency as a part of a model predictive control module
Monitoring of CO2 emmissions in electric-arc furnace steel production
No full textEmisije ugljik (IV)-oksida, CO2, nastale iz antropogenih izvora,predstavljaju sve veći problem u smislu onečišćenja atmosfere te direktno utječu na klimatske promjene koje mogu ostaviti katastrofalne posljedice za planet i čovječanstvo. S ciljem smanjenja emisija štetnih plinova na globalnoj razini te razini članica EU donesena je zakonska regulativa kojom se nastoji ograničiti emisije stakleničkih plinva na razinu koja neće štetno djelovati na okoliš.Kyoto protokol, ratificiran od 55 država, definira smanjenje stakleničkih plinova: ugljik (IV)-oksida (CO2), metana (CH4), dušik (I)-oksida (N2O), klorofluorougljikovodika (HFC-i i PFC-i) i sumporovog heksafluorida (SF6).Direktivom 2003/87/EZ Europskog parlamenta i vijeća od 13.10.2003. definirano je trgovanje emisijskim jedinicama stakleničkih plinova unutar članica EU zajednice. Zakonski se obvezuje svako postrojenje koje proizvodnim procesom emitira stakleničke plinove, na izradu godišnjeg izvješća o emisijama nastalim tijekom proizvodnje.
U ovom radu dan je detaljan prikaz polugodišnjeg izračuna emisija CO2 za 2019. godinu koje nastaju tijekom proizvodnje čelika u čeličani ABS SISAK d.o.o.Nadalje,definirane su zakonske obveze čeličana, dan je opis procesa, definirani sutokovi izvora emisija te jedan iznos emisije otpadnog CO2 u elektrolučnoj peći, dobiven metodom proračuna.Emissions of carbon dioxide, CO2, from anthropogenic sources are a growing problem in terms of air pollution and directly affect climate change, which can have catastrophic consequences for the planet. Therefore, many legal acts and international agreements have been signed in global to implement cleaner technology production and reduce greenhouse gas emissions.The Kyoto Protocol, ratified by 55 countries, defines the reduction of greenhouse gases: carbon (IV)-oxide (CO2), methane (CH), nitrogen (I) -oxide (N2O), chlorofluorocarbons (HFCs and PFCs) and sulfur hexafluoride (SF6). Directive 2003/87/EC of the European Parliament and of the Council of 13.10.2003.establishing a scheme for greenhouse gas emission allowance trading within the Member States.Every plant that emits greenhouse gases during the production process is legally obliged to prepare an annual report on emissions from production.
In this paper, a detailed overview of the semi-annual calculation of CO2 emissions for 2019. that occur during steel production in the steel plant ABS SISAK d.o.o. is presented. Furthermore, the legal obligations of steels, description of the process, the flows of emission sources and the amount of waste CO2 emissions in the electric arc furnace determined by the calculation method, are defined
Mathematical modeling of the influence parameters during formation and propagation of the Lüders bands
No full textIn this study, an analysis of the influence parameters measured by the static tensile test, thermography and digital image correlation was performed during formation and propagation of the Lüders bands. A new approach to the prediction of stresses, maximum temperature changes and strains during the Lüders band formation and propagation is proposed in this paper. Application of the obtained mathematical models of influence parameters gives a clear insight into the behavior of niobium microalloyed steel at the beginning of the plastic flow, which can improve product quality and reduce costs during the forming of microalloyed steels with the appearance of the Lüders bands. The obtained models of influential parameters during formation and propagation of the Lüders bands have been developed by the regression analysis method. The proposed mathematical models showed low deviations of calculated results ranging from 1.34% to 12.37%.The local stress amounts, important in the forming of microalloyed steels since indicating surface roughness and plastic flow possibilities during the Lüders band propagation, are obtained by the mathematical model. It was found that stress amounts increase during the Lüders band propagation in the area behind the Lüders band front. The difference in stress amount between the start of the Lüders band propagation and advanced Lüders band propagation is 25.53 MPa
Application of adsorption in purification of waste water
No full textDa bi se osigurala voda odgovarajuće kvalitete ili da bi se iz nje uklonila onečišćenja primjenjuje se velik broj različitih metoda. Odabir metode za pročišćavanje otpadnih voda ovisi o vrsti onečišćenja, ponovnoj primjeni pročišćene vode, ali i o ekonomskim čimbenicima. Danas se najčešće primjenjuje adsorpcija. Ovo je vrlo jednostavna i učinkovita metoda. Tom metodom moguće je ukloniti anorganska onečišćenja poput iona teških metala, ali i organska onečišćenja. U ovom završnom radu dan je pregled osnovnih pojmova vezanih za adsorpciju kao i pregled čimbenika koji utječu na mogućnost odvijanja adsorpcije, odnosno njezinu primjenu. Literaturno su obrađene najčešće adsorpcijske izoterme i kinetika adsorpcije. Poseban naglasak je stavljen na mogućnost korištenja adsorpcije kao metode za pročišćavanje otpadnih voda.A large number of different methods are applied to ensure proper quality of water or to remove contaminants from it. The choice of method for waste water treatment depends on the type of pollution, the reuse of the purified water, but also on economic factors.Today adsorption is most commonly used.It is a very simple and effective method.This method can eliminate inorganic contaminants, such as heavy metal ions, but also organic contaminants.This final paper provides an overview of the basic concepts related to adsorption, as well as an overview of the factors that influence the ability of adsorption to take place, i.e. its application.The most common adsorption isotherms and adsorption kineticsare processed.Particular emphasis is placed on the possibility of using adsorption as a method for purification of waste water
Microstructure characterization and phase transformations of Cu-Al-Mn-Ag alloys
No full textCu-Al-Mn legure s prisjetljivosti oblika postale su vrlo atraktivne za komercijalnu primjenu u bioinženjerstvu, dentalnoj industriji te u proizvodnji senzora i aktuatora, i sve više zamjenjuju uporabu vrlo skupe Ni-Ti legure, s obzirom na njihovu nisku cijenu koštanja, veliku superelastičnost te izrazitu duktilnost. Efekt prisljetljivosti oblika u istraživanim legurama posljedica je bezdifuzijske martenzitne transformacije, koja podrazumjeva promjenu kristalne strukture materijala. Dodavanjem mangana osnovnoj binarnoj Cu-Al leguri, proširuje se područje -faze, ključnoj fazi za postizanje martenzitne strukture, `-faze, čime se povećava duktilnost materijala te sposobnost njenog hladnog deformiranja. Daljnjim dodavanjem mikrolegirajućih elemenata ternarnoj Cu-Al-Mn leguri, može se utjecati na smanjenje veličine zrna, čvrstoću materijala, pomak faznih transformacija te efekt prisjetljivosti oblika.
Stoga je u ovom radu istražen utjecaj srebra na mikrostrukturu i temperature faznih transformacija Cu-Al-Mn legura. Cu-Al-Mn-Ag legure pripremljene su taljenjem u elektrolučnoj peći te lijevane u cilindrični kalup, dimenzija 8 mm x*1,2 cm. Termodinamički proračun i mehanizam skrućivanja Cu-Al-Mn legura proveden je programom Thermo-Calc, korištenjem termodinamičkih podataka prema Miettinenu. Simultanom tehnikom toplinske analize, diferencijalnom pretražnom kalorimetrijom/termogravimetrijom (STA DSC/TG) određene su temperature transformacija Cu-Al-Mn-Ag legura, dinamičkim mjerenjima kroz 2 ciklusa zagrijavanje/hlađenje, u atmosferi argona. Mikrostrukturna ispitivanja provedena su optičkom mikroskopijom (OM) te skenirajućom elektronskom mikroskopijom (SEM), dok je energijsko disperzijskom spektrometrijom (EDS) određen kemijski sastav istraživanih sustava. Rezultati mikrostrukture korelirani su sa promjenom sastava Cu-Al-Mn-Ag legure i udjelom srebra te pomakom temperatura transformacija.Cu-Al-Mn shape memory alloys became very attractive for commercial use in the bioengineering, dental industry and in the high-demand industry for sensors or actuators, and they are frequently used instead of very expensive Ni-Ti alloy, due to their low cost, superelasticity and high ductility. Shape memory effect is a consequence of the diffusionless martensitic transformation, which implies a change of crystal structure. Addition of manganese to binary Cu-Al alloy, broadens -phase region, parent phase for formation of martensitic structure, `-phase, what increase ductility and cold workability of material. Further addition of alloying elements influences to decreasing of grain size, changes of phase transformation temperatures, mechanical properties and shape memory effect.
In this paper, the effect of silver addition on the microstructure and transformation temperatures of Cu-Al-Mn alloys was investigated. Cu-Al-Mn-Ag alloys were prepared by melting in the electric-arc furnace and casted in the moulds dimensions 8 mm*1.2 cm. Thermodynamic calculation and solidification mechanism was performed by software Thermo-Calc 5, with thermodynamic data according to Miettinen. Transformation temperatures of Cu-Al-Mn-Ag alloys were carried out by simultaneous thermal analysis differential scanning calorimetry/thermogravimetry (STA DSC/TG) through two dynamic cycles in the argon atmosphere. Microstructural investigations were performed by optical microscopy (OM) and scanning electron microscopy (SEM), while chemical content of specimens was determined by energy-dispersive spectrometry (EDS). Microstructural results were correlated with silver content in Cu-Al-Mn-Ag alloy as well as transformation temperatures
Numerical simulation in optimization of thin-walled EN-GJL-200 casting
No full textImplementation of new strategies and concepts such as "Near net shape castings" and "Right for the first time" represent an imperative for nowadays foundry production. High material utilization, with minimal number of forming operations and defects avoiding is the main goal for casting producers. Therefore, numerical simulation as a part of CAD/CAE technologies represents an indispensable tool for achieving competitiveness on global market. Numerical simulation of casting poring and solidification represents a description of physical phenomena based on mathematical model. The application of computer numerical simulations, which are based on complex and comprehensive mathematical models such as Fourier law, found its significant application in consideration of thermal processes in the foundry. Numerical simulation enables analogical display of metallurgical processes by calculation and graphical disposition of the process from the pouring to the final casting solidification. Solidification process is very complex process which comprehends knowledge related to material and technology behaviour and interactions. Complexity of metal casting consists from element interactions and mass transfer during solidification, and technological development including heat transfer. The most useful numerical method is finite difference method due to its simplicity, but the finite element method is more accurate and does not have any limitation with respect to the complexity of geometric shapes. The focus of this investigation was optimization of pouring and solidification process of thinwalled EN-GJL-200 casting using numerical simulation. Complex geometry of thin-walled casting represents the challenge due to crusted parts and stress bending of casting in existing technological set up. Numerical simulation optimization reveals changes in technological parameters of gating system, venting system and support. Optimization enables even filling of castings in order to prevent an extensive thermal overload and consequently stress of particular parts of castings