This paper discusses the effect of different heat treatment procedures on the microstructural characteristics, damping capacities, and mechanical properties of CuAlNi shape memory alloys (SMA). The ...investigation was performed on samples in the as-cast state and heat treated states (solution annealing at 885 °C/60'/H
O and after tempering at 300 °C/60'/H
O). The microstructure of the samples was examined by light microscopy (LM) and scanning electron microscopy (SEM) equipped with a device for energy dispersive spectrometry (EDS) analysis. Light and scanning electron microscopy showed martensitic microstructure in all investigated samples. However, the changes in microstructure due to heat treatment by the presence of two types of martensite phases (β
and γ
) influenced alloy damping and mechanical properties by enhancing alloy damping characteristics. Heat treatment procedure reduced the alloys' mechanical properties and increased hardness of the alloy. Fractographic analysis of the alloy showed a transgranular type of fracture in samples after casting. After solution annealing, two types of fracture mechanisms can be noticed, transgranular and intergranular, while in tempered samples, mostly an intergranular type of fracture exists.
U radu je dan kratak pregled tehnoloških procesa masovne proizvodnje sirovog čelika u Republici Hrvatskoj (RH) u razdoblju od 1954. do 2020. godine s naglaskom na proizvodnju čelika u razdoblju od ...1992. do 2020. godine. Proizvođači čelika bile su željezare u Sisku i Splitu. Masovna proizvodnja čelika provodila se u Siemens-Martinovim (Sisak) i elektrolučnim pećima (Sisak i Split). Danas se čelik proizvodi samo u ABS Sisak d. o. o. u moderniziranoj elektrolučnoj peći uključujući i primjenu postupaka sekundarne metalurgije (lonac-peć i vakuum otplinjač). Zbog devastacije prerađivačkih kapaciteta (prije 2012. godine) u Željezari Sisak i gašenja proizvodnje čelika u Željezari Split u RH danas nema mogućnosti plastične prerade vlastitog čelika u poluproizvode i/ili gotove proizvode. U RH je u razdoblju od 1954. do 2020. godine ukupno proizvedeno oko 9,3 Mt sirovog čelika (ugljični i niskolegirani čelici). Sažeto je prikazana i uloga visokoškolskog obrazovanja i znanstvenoistraživačkog rada u proizvodnji čelika u RH.
Ovaj rad prikazuje trend proizvodnje sirovog čelika u svijetu u prva dva desetljeća 21. stoljeća. U razdoblju od 2001. do 2020. godine svjetska proizvodnja čelika kontinuirano raste (ukupno je ...proizvedeno 28,5 Gt čelika) uz smanjenje u 2008. (1,6 %) i 2009. godini (7,7 %) zbog globalne financijske i gospodarske krize. Više od pedeset godina čelik se primarno proizvodi pomoću dviju tehnologija: oksidiranjem sirovog željeza (produkt visoke peći) u kisikovim konvertorima pomoću tehničkog kisika te pretaljivanjem starog željeza (čelični otpad) u elektrolučnim pećima. Za proizvodnju kvalitetnijih čelika sve veću ulogu imaju postupci sekundarne metalurgije (dorada čelika u loncu). U 2000. godini u svijetu je proizvedeno 847,2 Mt (udio u kisikovim konvertorima od 58,2 %, a u elektrolučnim pećima od 33,8 %), dok je tijekom 2020. godine proizvedeno 1877,5 Mt čelika, što je porast od 2,2 puta. S obzirom na postupke proizvodnje u 2020. proizvedeno je 73,2 % čelika u kisikovim konvertorima, 26,3 % u elektrolučnim pećima, 0,3 % u Siemens-Martinovim (SM) pećima i 0,2 % ostalim postupcima. Primat proizvodnje čelika je u državama (73,9 % svjetske proizvodnje) i tvrtkama iz Azije. Stupanj recikliranja čelika u razdoblju 2011. – 2019. iznosio je 34 – 37 %. Kina je najveći svjetski proizvođač čelika (od 1996. godine). U razdoblju 2000. – 2020. povećala je proizvodnju čelika za 8,3 puta (sa 127,2 na 1064,8 Mt). Kina je u 2020. godini proizvela 56,6 % svjetske proizvodnje čelika. U razdoblju od 2000. do 2020. godine udio kontinuiranog lijevanja čelika je povećan za oko 10 %, s 87 na 96,6 %.
U ovom pregledu prikazan je dio znanstvenih istraživanja pri razvoju legura s prisjetljivošću oblika (engl. Shape Memory Alloy, SMA) na bazi bakra na Metalurškom fakultetu Sveučilišta u Zagrebu u ...razdoblju od 2006. do 2022. godine u suradnji s brojnim visokoškolskim i znanstvenim institucijama u regiji. Istraživane su sljedeće legure SMA: CuAlNi, CuAlMn, itd. Provedeno je fizikalno modeliranje uključujući numeričku simulaciju razvoja mikrostrukture i toplinsku analizu tih legura. Legure SMA rađene su u lučnoj, visokofrekventnoj i indukcijskim pećima pomoću tri različite tehnologije lijevanja: brzo skrućivanje, lijevanje u metalne i/ili grafitne kokile te kontinuirano lijevanje u šipke. Nakon toga odabrane legure su toplo i hladno valjane. Provedena je toplinska obrada (austenitizacija uz naknadno gašenje u vodi i žarenje) i karakterizacija funkcionalnih svojstava legura SMA u različitim stanjima. Za karakterizaciju, osim ispitivanja mehaničkih svojstava, primijenjene su brojne visokosofisticirane metode: optička mikroskopija (OM), pretražna (SEM) i transmisijska elektronska mikroskopija (TEM), energetsko disperzijska-spektroskopija (EDS), pretražna diferencijalna kalorimetrija (DSC), dinamičko-mehanička analiza (DMA), rendgenska difrakcija (XRD), elektrokemijska impedancijska spektroskopija (EIS) itd. Već pri lijevanju kod pojedinih legura SMA, a posebice nakon toplinske obrade austenitizacijom uz naknadno gašenje u vodi, utvrđena je martenzitna mikrostruktura koja je osnovni preduvjet za svojstvo prisjetljivosti oblika. Na temelju provedenih istraživanja po većini parametara (plastičnost, korozijska otpornost itd.) može se zaključiti da su se najbolje pokazale legure CuAlMn.
Kao rezultat provedenih istraživanja na legurama SMA, prema podatcima iz baze CROSBI (na dan 23. prosinca 2022.), istraživački tim objavio je 33 rada u časopisima (od kojih su 23 rada u časopisima indeksiranim u bazi podataka Web of Science), 74 rada u zbornicima međunarodnih konferencija, 18 sažetaka u zbornicima konferencija te pet ostalih radova. Također, obranjena je jedna doktorska disertacija te je izrađeno i obranjeno 12 završnih i 25 diplomskih radova u području tehničkih znanosti iz znanstvenih polja metalurgije i kemijskog inženjerstva.
The aim in this work was to investigate the change in microstructure, phase transformation temperatures, and thermal properties due to the quenching of the investigated Cu-Al-Mn and Cu-Al-Mn-Ti ...alloys in ribbon form. This paper presents the results of microstructure analysis and thermal properties of Cu-Al-Mn and Cu-Al-Mn-Ti shape memory alloys produced in ribbon form by melt spinning technique. The microstructural analysis was carried out before and after quenching. After casting of the investigated alloys, annealing at 900 °C for 30 min was performed, followed by water quenching. The microstructural analysis was carried out by optical and scanning electron microscopy equipped with an energy dispersive spectrometer and by X-ray diffractometer. Thermodynamic calculation of a ternary Cu-Al-Mn system in equilibrium condition was performed using Thermo-Calc 5 software. Phase transformation temperatures were determined by differential scanning calorimetry and electrical resistance measuring. The results of microstructural analysis show the presence of martensite microstructures before and after quenching in the Cu-Al-Mn alloy, while in the Cu-Al-Mn-Ti alloy martensite microstructure exists only after quenching. Phase transformation temperatures decreased after quenching and titanium addition.
•The presence of sulphate ions does not significantly affect the dissolution mechanism of the alloy.•Corrosion products mostly contain oxides and chlorides of Al, Mn and Cu.•The Cualmn alloy ...undergoes general corrosion in the studied solutions.•The growth dynamic of the spontaneous surface film in the tested solutions is different.•The stability of the surface film increases with the immersion time and the presence of sulphate ions.
The electrochemical behaviour of a CuAlMn alloy in a 0.5 M NaCl solution with the addition of different concentrations of Na2SO4 (0.1, 0.3, and 0.5 M) was investigated by observing the change in open circuit potential (EOC) with time, applying polarization methods and electrochemical impedance spectroscopy (EIS). The damage to the metal surface was determined by optical microscopy and SEM/EDS analysis.
Although the increase in the content of sulphate ions in the NaCl solution reduces the corrosion current and increases the polarization resistance, their presence does not affect the CuAlMn dissolution mechanism. The anodic reaction of Cu dissolution is controlled by the diffusion of soluble CuCl2− species from the electrode surface into the bulk solution. Surface analysis showed a uniform dissolution of the investigated alloy.
The corrosion resistance of CuAlMn at EOC is a consequence of forming a natural surface film. The experimental conditions (immersion time and presence of sulphate ions) increase the stability of the surface layer (the resistance, compactness, and thickness of the surface layer increase). Moreover, in the presence of sulphate ions, a subsequent ordering of the structure of the surface layer takes place during stabilization at the open circuit potential which is a consequence attributed to the formation of adsorbed species such as Cu(SO4)ads and/or Cu(OH)ads on the electrode surface.
Microstructural and cavitation erosion testing was carried out on Cu-12.8Al-4.1Ni (wt. %) shape memory alloy (SMA) samples produced by continuous casting followed by heat treatment consisting of ...solution annealing at 885 °C for 60 min and, later, water quenching. Cavitation resistance testing was applied using a standard ultrasonic vibratory cavitation set up with stationary specimen. Surface changes during the cavitation were monitored by metallographic analysis using an optical microscope (OM), atomic force microscope (AFM), and scanning electron microscope (SEM) as well as by weight measurements. The results revealed a martensite microstructure after both casting and quenching. Microhardness value was higher after water quenching than in the as-cast state. After 420 min of cavitation exposure, a negligible mass loss was noticed for both samples. Based on the obtained results, both samples showed excellent cavitation resistance. Mass loss and morphological analysis of the formed pits indicated better cavitation resistance for the as-cast state (L).
A comparative corrosion study of Cu and Cu-Al, Cu-Al-Ni, Cu-Al-Mn and Cu-Al-Mn-Ni in 0.5 mol dm-3 NaCl solution was performed using an open circuit potential, potentiodynamic polarization and ...electrochemical impedance spectroscopy measurements (EIS). Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) analysis was used to evaluate corrosive damage on the sample surface after polarization measurements. The reported results suggest that the alloying elements have reduced cathodic and anodic current densities in the Tafel region, increased anodic currents at higher anodic potentials, and slightly displaced corrosion potential towards more positive values. Overall, impedance increased in the following order: Cu < Cu-Al < Cu-Al-Ni < Cu-Al-Mn < Cu-Al-Mn-Ni. This indicates that Cu alloys possess better corrosion resistance. SEM and EDS analysis after polarization measurements showed uniform dissolution of pure Cu, as well as the presence of a surface oxide layer, consisting of a mixture of the corresponding alloying elements, on all investigated alloys. Aggressive anodic polarization severely damaged the barrier layers on the Cu alloy specimens.
Background/Aim. The epidemic of typhus lasted for sever-al months in the Kingdom of Serbia during the First World War, and a vast number of people lost their lives. The objective of the paper was to ...investigate how the Politika, Belgrade daily newspaper, informed the then Serbian public about the epidemic of typhus in the Great War. Methods. By using statistical and historical-critical method, the analysis of all texts published in the Politika from February 1915, when the Serbian government and the Supreme Command allowed the press to write about the epidemic of typhus, until the outbreak began to calm down at the beginning of May 1915, was performed. Results. In the observed period, among the texts dedicated to the typhus epidemic, news about people who died of typhus (obituaries), news about the epidemic itself, as well as affirmative texts about the feats of doctors. There were more texts about allies? military missions than about Serbian Army Medical Corps. The reporting was balanced and highly professional. Conclusion. In the period February?May 1915, a number of different articles about the typhus epidemic in Serbia during the Great War were published in the daily newspaper Politika. The reporting was well-balanced, ethical and highly professional.
The corrosion behaviour of Cu-Al-Ni alloy in 0.5 mol dm–3 H2SO4 solution was investigated by electrochemical methods including open circuit potential measurement, electrochemical impedance ...spectroscopy measurements, linear and potentiodynamic polarization. Measurements were performed in 0.5 mol dm–3 H2SO4 at temperatures 20 and 40 °C. After polarization testing, corroded electrode surfaces were ultrasonically cleaned in deionized water and examined by light and scanning electron microscopy, while the elemental composition at individual points of the alloy surface was determined by EDS analysis. The results of the investigations revealed the occurrence of intergranular corrosion on the Cu-Al-Ni surface, which became more pronounced with increasing temperature.
Korozijsko ponašanje Cu-Al-Ni legure u 0,5 mol dm–3 H2SO4 otopini ispitivano je elektrokemijskim metodama kao što su mjerenje potencijala otvorenog strujnog kruga, mjerenje metodom elektrokemijske impedancijske spektroskopije, linearne i potenciodinamičke polarizacije. Mjerenja su provedena u 0,5 mol dm–3 H2SO4 pri temperaturama od 20 i 40 °C. Nakon polarizacijskih mjerenja korodirane površine elektroda ultrazvučno su očišćene u deioniziranoj vodi i ispitane svjetlosnim i pretražnim elektronskim mikroskopom, dok je elementarni sastav na pojedinim točkama na površini određen EDS analizom. Rezultati ispitivanja pokazali su da dolazi do interkristalne korozije na površini Cu-Al-Ni legure, čiji intenzitet raste s povećanjem temperature elektrolita.
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