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Stress corrosion cracking of metals and metal alloys
Get PDFMnoga velika oštećenja metalnih konstrukcija, dijelova strojeva izrađenih od metalnih legura te metala općenito mogu uzrokovati velike probleme u radu, poput zastoja u radu, velikih materijalnih gubitaka, narušavanja zdravlja čovjeka, te kontaminacije sastavnica okoliša. Najčešći razlog oštećenja navedenih metala i metalnih legura je korozija, a kao izuzetno razaran i agresivan oblik korozije koji se odvija prilikom djelovanja nekoliko utjecaja, navodi se napetosna korozija.
Napetosna korozija predstavlja primjer lokalne korozije koji nastaje onda kada je promatrani uzorak istovremeno izložen agresivnom djelovanju medija i naprezanju, što najčešće dovodi do stvaranja pukotina i konačnog loma materijala. Pukotine uzrokovane napetosnom korozijom mogu se širiti transkristalno ili interkristalno, odnosno po površini materijala ili uzduž granica metalnog zrna u dubinu.
U ovom radu istražit će se utjecaji koji dovode do pojave napetosne korozije, kao što su utjecaji naprezanja, okoline, strukture materijala, i drugih koji mogu potaknuti razvijanje i napredovanje navedene korozije. Navesti će se posljedice i moguća oštećenja na metalima i metalnim legurama te metode zaštite metala od napetosne korozije.Many major damages of metal structures, machine parts made of metal alloys and metals generally can cause major problems such as work delays, major material losses, damage of human health, and contamination of environmental components. The most common cause of damage of metals and metal alloys is corrosion, and as a highly destructive and aggressive form of corrosion that occurs during the action of several influences, stress corrosion cracking.
Stress corrosion cracking is an example of local corrosion that occurs when the observed sample is simultaneously exposed to the aggressive action of the media and stress, which most often leads to the formation of cracks and the final fracture of the material. Cracks caused by stress corrosion cracking can be transcrystalline or intercrystalline, i.e. across the surface of the material or along the grain boundaries of the metal into depth.
This paper will investigate the effects that lead to stress corrosion cracking, such as the effects of stress, environment, material structure, and others that can stimulate the development and progression of said corrosion. The consequences and possible damages on metals and metal alloys, as well as the methods of metal protection from stress corrosion cracking will be stated
Influence of the technological casting parameters on the microstructure and mechanical properties development of AlSi7Mg0,3 alloy
Get PDFAluminijske legure posjeduju izvrsna mehanička svojstva, fizikalno-kemijska i tehnološka svojstva te su zbog toga pronašle primjenu u automobilskoj, svemirskoj, kemijskoj i prehrambenoj industriji, ali i u elektrotehnici. Primjenu u automobilskoj industriji pronašle su zbog niske gustoće čime se smanjuje masa automobila te se doprinosi smanjenju potrošnje goriva čime se direktno utječe na smanjenje emisije CO2. Jedna od najčešće primjenjivanih legura u autoindustriji je AlSi7Mg0,3 legura. Legura se lijeva u trajne kalupe čime se osiguravaju optimalni uvjeti hlađenja i skrućivanja i postižu bolja mehanička svojstva. S obzirom na geometriju odljevka, lijevanje se provodi tehnologijom gravitacijskog lijevanja sa zakretanjem. U okviru ovog diplomskog rada pokazalo se da različite brzine hlađenja i punjenja kalupa mogu utjecati na razvoj mikrostrukture i mehanička svojstava odljevka. Metalografskim ispitivanjima, osim primarnih αAl dendrita i eutektika (αAl + βSi) uočene su i intermetalne faze na osnovi Fe i Mg. U radu je istražen utjecaj tri različita seta parametara na razvoj mikrostrukture i razvoj αAl u korelaciji s debljinom stijenke: I) optimalni parametri s hlađenjem alata, II) bez hlađenja alata i III) ubrzano punjenje alata. Ispitivanjima je utvrđen pozitivan utjecaj povećanje brzine hlađenja i skrućivanja na usitnjavanje mikrostrukturnih konstituenata, prvenstveno αAl do 25 mm debljine stijenke. Mehaničkim ispitivanjima utvrđene su razlike u vrijednostima vlačne čvrstoće i izduženja za slučajeve I, II i III. U prvom slučaju s optimalnim parametrima lijevanja postižu se najbolji rezultati mehaničkih svojstava. Fraktografskom analizom utvrđeni su uzroci lošijih mehaničkih svojstava u odljevku. Kako bi se utvrdio uzrok nastalih grešaka provedena je numerička simulacija odljevka te je utvrđena poroznosti nastala uslijed stezanja pri skrućivanju i neusmjereno skrućivanje u toplom mjestu.Aluminum alloys have excellent mechanical properties, physical and chemical and technological properties and therefore found application in the automotive, aerospace, chemical and food industry, but also in electrical engineering. They have been used in the automotive industry because of their low density, which reduce the mass of cars and contributes to the reduction of fuel consumption, thereby directly reducing CO2 emissions. One of the most commonly used alloys in the automotive industry is AlSi7Mg0,3 alloy. The alloy has been poured into die which ensures optimal cooling and solidification conditions and better mechanical properties were achieved. Considering casting geometry, casting is poured by gravity tilt casting technology. Within this paper, has been shown that different cooling speed as well as pouring rates can affect development of casting microstructure and mechanical properties. Metallographic examination reveals primary αAl dendrites and eutectics (αAl + βSi) and other intermetallic phases based on Fe and Mg. In this paper the influence of three sets of parameters was investigated on microstructure development and development of αAl in correlation with wall thickness: I) optimal casting parameters with applied cooling casting die, II) casting parameters without cooling and III) casting parameters with faster pouring rate. A positive impact of increased cooling rate and solidification rate on refinement of microstructural constituents first of all at αAl till 25 mm of wall thicknesses. Mechanical testing revealed difference in tensile strength and elongation values for case I, II, and III. In first case with optimal parameters, the best mechanical properties are obtained. Lower mechanical properties caused by defects in casting were determinate by fractography analysis. In order to determine the cause of the defects, a numerical simulation of the casting was carried. Defects occurred in castings were determinated as shrinkage porosity and unidirectional solidification in hot spots
The Influence of Heat Treatment on Microstructure and Phase Transformation Temperatures of Cu-Al-Ni Shape Memory Alloy
Get PDFIn this paper the results of thermal and microstructural analysis of CuAlNi shape memory alloy before and after heat treatment were presented. The bar of the Cu-12.8 Al – 4.1 Ni (wt.%) alloy obtained by vertical continuous casting technique after casting was submerged to a certain heat treatment procedure. The solution annealing at 850 °C was performed, holding on that temperature for 60 minutes and following water quenching. Afterwards, the tempering at four different temperatures (150 °C, 200 °C, 250 °C and 300 °C) was performed. The microstructural results were obtained by optical and scanning electron microscopy. Thermodynamic calculation of ternary Cu-Al-Ni system under equilibrium is performed by software Thermo-Calc 5. Phase transformation temperatures were determined by differential scanning calorimetry (DSC). The DSC results show the highest values of transformation temperatures in as-cast state. After solution annealing and tempering the transformation temperatures show lower values with exceptional stability of Ms temperature (martensite start temperature)
Identification of Lüders bands using digital image correlation
No full textThis paper presents the characterization of Lüders bands by digital image correlation on niobium microalloyed steel during a static tensile testing.Digital image correlation with the qualitative and quantitative analysis of the Lüders bands on the microalloyed steel was proved asa very precise and suitable method for determining the strain amountin the deformation zone.In this research was determined that the strain amount is the highest in the area behind the Lüders band front and the lowest in the area in front of the Lüders band
Petroleum coke in the production of carbon composites
Get PDFRazvoj društva je određen vještinama proizvodnje i prerade različitih materijala. U prošlosti su određena razdoblja nazvana upravo po materijalima.
Ugljični materijali su materijali sastavljeni od ugljika pri čemu se isključuju spojevi ugljika s drugim elementima.Bez ugljičnih materijala je nezamisliv život današnjeg čovjeka.Osim tradicionalnih ugljičnih materijala koje čovjek poznaje odavno, kao što su čađa i ugljen, u zadnjih nekoliko desetljeća razvijaju se novi ugljični materijali poput grafena, ugljičnih vlakana, ugljičnih kompozitnih materijala, nanocjevčica itd.
U radu je dan pregled relevantne literature koja se odnosi na povezanost naftnog koksa kao tradicionalnog ugljičnog materijala i ugljičnih kompozita kao suvremenih ugljičnih materijala. Razrađena su poglavlja koja počinju s pojmom i podjelom materijala općenito, zatim kompozitnih materijala općenito i naftnog koksa. Nakon toga opisana je proizvodnja ugljičnih kompozita i navedena su njihova svojstva i upotreba.The development of society is determined by the skills of producing and processing of various materials. In the past, the certain periods of civilization have been named precisely by materials.
Carbon materials are materials made of carbon, excluding carbon compounds with other elements.Without carbon materials the life of a modern manis unimaginable.In addition to the traditional carbon materials that people have known long ago, such as carbon black and coal, new carbon materials such as graphene, carbon fibers, carbon composite materials, nanotubes etc. are being developed over the last few decades.
This paper presents a review of relevant literature related to the connection of petroleum coke as a traditional carbon material and carbon composites as modern carbon materials. The chapters that begin with the definition and classificationof materials in general, in addition, composite materials in general, and petroleum cokehave been elaborated. After that the production of carbon composites is described and their properties anduse are listed
Microstructural analysis of welded joined pipes achived by TIG procedure
Get PDFU ovome radu napravljen je teorijski pregled postupaka elektrolučnog zavarivanja s detaljnim opisom postupka elektrolučnog zavarivanja netaljivom elektrodom pod zaštitom inertnog plina. Opisan je osnovni princip elektrolučnog zavarivanja te je istaknut utjecaj ključnih parametara na kvalitetu zavarenog spoja. Navedeni su uređaji i vrste elektroda koji se primjenjuju kod elektrolučnog zavarivanja s netaljivom elektrodom pod zaštitom inertnog plina.
U eksperimentalnom dijelu rada provedena je metalografska analiza mikrostrukture sučeono zavarenog spoja cijevi i redukcije. Iz zavarenog spoja cijevi izrezani su ispitni uzorci iz četiri različite zone koje obuhvaćaju oba osnovna materijala cijevi, zonu taljenja i zonu utjecaja topline. Nakon rezanja ispitni uzorci su u uređaju za vruće izostatsko prešanje uloženi u praškastu vodljivu masu, nakon čega su brušeni, polirani i nagriženi nitalom kako bi se provela metalografska analiza. Provedenim metalografskim ispitivanjima zaključilo se da zona utjecaja topline ima sitnozrnatu strukturu, a zona taljenja lijevanu strukturu.This paper provides a theoretical overview of welding procedures with a detailed description of the arc welding procedure with infusible electrode protected by inert gas. The basic principle of arc welding is described and the influence of key parameters on the quality of the welded joint is emphasized. The devices and types of electrodes that are used for electrostatic welding with an inert gas protection are listed.
In the experimental part, a metallographic analysis of the microstructure of the welded pipe and reduction welds was performed. From the welded tube joint, test samples were cut out of four different zones, covering both of the basic materials, the melting zone and the heat transfer zone. After cutting, the test samples were placed in a hot isostatic press with a powdered conductive mass, after which they were crushed, polished and eroded with nital to perform metallographic analysis. The metallographic investigations carried out concluded that the zone of heat influence has a fine-grained structure and the melted zone has the cast structure
Analysis of welded low-carbon steel properties
Get PDFU radu je dan teorijski pregled postupaka zavarivanja metalnih materijala. Poseban
osvrt je dan na postupke elektrootpornog točkastog zavarivanja. Kako je elektrootporno
točkasto zavarivanje najčešće korišteni postupak spajanja u automobilskoj industriji, poseban
osvrt je dan na parametre zavarivanja i njihov utjecaj na konačnu kvalitetu zavara. Opisane su
najčešće greške koje se javljaju u zavaru pri točkastom zavarivanju, kao i metode kojima su
vršena strukturna ispitivanja i mjerenje tvrdoće zavarenih spojeva. U eksperimentalnom
dijelu na prethodno zavarenim uzorcima uzimanih iz limova s tri tipa vozila, provedena je
metalografska priprema uzoraka brušenjem i nagrizanjem. Nagrizanje je provedeno u dvije
otopine, prvo u otopini nital (0,5 % HNO 3 u destiliranoj vodi) kako bi odredili početnu
strukturu, a nakon ponovnog poliranja otopinom Klemm 1, kako bi utvrdili postojanje
zaostalog austenita. Nakon strukturnih istraživanja provedeno je mjerenje makro i mikro –
tvrdoće u području zavara. Time se istražio utjecaj strukturnih promjena u području zavara na
svojstva zavarenog spoja, točnije tvrdoća. Iz rezultata ispitivanja i provedenih analiza
zaključeno je kako tijekom elektrootpornog točkastog zavarivanja ispitivanih limova dolazi
do pojave zaostalog austenita u strukturi u zoni utjecaja topline i zoni taljenja. Također
uočena je pojava dendritnog rasta zrna i martenzit u zoni taljenja. Izmjerene vrijednosti
tvrdoće pokazuju kako uslijed promjene strukture dolazi i do značajne promjene u
izmjerenim vrijednostima tvrdoće u odnosu na osnovno stanje. Najviši iznosi tvrdoće
izmjereni su u zoni taljenja kod svih uzoraka. Također su i u zoni utjecaja topline izmjerene
više vrijednosti tvrdoće u odnosu na tvrdoću polaznog materijala. Dokazano je kako uslijed
zavarivanja dolazi do pojave zaostalog austenita u području zone utjecaja topline i zone
taljenja, te mjestimične pojave martenzta u zoni taljenja, što za posljedicu ima porast
vrijednosti tvrdoće u području zavara.Thepaperprovides a theoreticaloverviewofweldingprocedures for metallic
materials. Since spot weldingisthe most commonlyusedwelding procedure inautomotive
industry, specialattentionisgiven to weldingparametersduring spot weldingandtheir
impact on finalweldquality. In thepaper are alsodescribedthe most commonerrorsthat
occurduring spot welding, andthemethodsthat are used for structuraltestingand for
measurementofweldhardness. In theexperimentalpartthemetallographicpreparationof
specimenswasperformed on previouslyweldedspecimenstakenfromsheetsfromthree
typesofvehiclebygrindingandetching. Etchingwascarriedoutintwosolutions, firstin
NITAL solution (0.5% HNO 3 indistilled water) to determinetheinitialstructure, andafterre-
polishingwithKlemm 1 solution to determinetheexistenceofresidualaustenite. After
structuralstudies, themeasurementofmacroandmicro - hardnessintheweldareawas
performed. Theeffectofstructuralchanges on thepropertiesoftheweldedjoint, namely
hardness, wereinvestigated. Fromthe test resultsandperformedanalyzes, itcanbe
concludedthatduringtheelectricresistance spot weldinginthetestedsteelsheetsthereis
occurrenceofresidualausteniteinthestructureoftheheataffective zone andmelting zone.
Therewasalsoobservedtheoccurrenceofdendriticgraingrowthandmartensitestructurein
themelting zone. Measuredhardnessvalues show thatdue to thechangeinstructure, thereis
a significantchangeinthemeasuredhardnessvalues relative to thestarting metal. The
highesthardnessvalues weremeasuredinthemelting zone at allsamples. Also, intheheat
affected zone themeasuredhardnessvaluesweremuchhigherrelative to the as received
material. Ithasbeenshownthatdue to theweldingthereisoccurrenceofretainedaustenitein
theheataffected zone andthemelting zone, andtheoccasionalappearancemartensiteinthe
melting zone, whichresultsinincreaseofhardnessintheweldedarea
Microstructural characterisation of casted ingot of the CuAlMn alloy
Get PDFU ovom radu provedena je mikrostrukturna karakterizacija CuAlMn legure s prisjetljivosti oblika. Ispitivanje je provedeno na uzorcima legure u lijevanom i toplinski obrađenom stanju. Ispitivana legura dobivena je taljenjem tehnički čistih elemenata bakra, aluminija i mangana ciljanog kemijskog sastava Cu – 8.6%, Al – 9,9% Mn (mas.%). Toplinska obrada uzorka provedena je na temperaturi od 900 °C u vremenskom periodu od 15 minuta nakon čega je usljedilo hlađenje vodom. Mikrostrukturna karakterizacija CuAlMn legure provedena je optičkom mikroskopijom i pretražnom elektronskom mikroskopijom opremljenom s energetsko disperzijskim spektrometrom. Rezultati su pokazali da uzorci posjeduju dvofaznu (α + β) mikrostrukturu u lijevanom stanju, dok je nakon toplinske obrade zamijećena samo martenzitna mikrostruktura. Provedeno je ispitivanje mikrotvrdoće Vickersovom metodom te rezultati pokazuju veću tvrdoću nakon toplinske obrade.In this research a microstructural characterisation of CuAlMn shape memory alloy has been performed. The research was performed on alloy samples in as-cast and heat treated state. The tested alloy was obtained by melting technically pure elements of copper, aluminium and manganese with a targeted chemical composition of Cu – 8.6%, Al – 9,9% Mn (wt.%). The heat treatment of the sample was carried out at a temperature of 900 °C for a period of 15 minutes after which it was cooled with water. Microstructural characterization of the CuAlMn alloy was performed by optical microscopy and scanning electron microscopy equipped with an energy dispersion spectrometer. The results showed that the sample had a two – phase (α + β) microstructure in as-cast state while after heat treatment only a martensitic microstructure was observed. Microhardness testing was performed using the Vickers method and the results show higher hardness after heat treatment
Water hardness
No full textTvrdoća vode u prirodi je uzrokovana otapanjem kalcijevih i magnezijevih soli. Voda koja dopire do pojedinih dijelova Zemlje se razlikuje, te je vrlo važno konstantno kontrolirati njezinu tvrdoću kako bi do potrošača dolazila sukladno propisanim vrijednostima. Tvrda voda stvara probleme u industriji kao i u domaćinstvu jer može izazvati materijalne štete, usporiti industrijske procese ili ih u potpunosti onemogućiti. U ovom radu dan je pregled osnovne podjele tvrdoće vode i procesa omekšavanja. Tvrdoća vode se otklanja omekšavanjem koje se provodi potpuno ili djelomično, u toplim ili hladnim uvjetima. Otklanjanje tvrde vode iz industrije se može provesti dodatkom tvari za omekšavanje, ali i pomoću ionskih izmjenjivača.Hard water is caused by dissolution of calcium and magnesium salts. Water that reaches certain parts of Earth is different. It is important to always control water hardness, so it could reach the consumer in recommended values. Hard water causes problems in industry but as well in households. It can cause material damage, slow down industrial process or stop it all together. In this work it is given the overview of basic water hardness types and ways to soften it. Hard water softens partially or completely in warm or cold environment. Hard water removal in industry can be conducted with softening substances or ion exchanger
Numerical simulation of welding distortions in large structures with a simplified engineering approach
No full textThis paper presents an efficient thermo-elastoplastic method for the prediction of welding-induced distortions in a large panel structure. It is based on a shell/3D modeling technique which was proposed and experimentally validated in the authors’ previous study. Two numerical examples are analyzed to evaluate the accuracy and efficiency of the present method. In the first example, the recommendations for the estimation of the minimum 3D zone size in the shell/3D model reported in the authors’ previous work are verified, in comparison with the full 3D model, on a T-joint model consisting of plates with different thicknesses. It is shown that the shell/3D modeling technique provides a significant reduction in the computational time needed for the simulation of the welding process and thus enables efficient thermo-elastoplastic analyses on large structures. In the second example, the proposed model is validated on a large panel structure by corresponding the experimental data and inherent strain solutions from the literature