BENEFICIAL EFFECT OF CU CONTENT AND AUSTEMPERING PARAMETERS ON THE HARDNESS AND CORROSION PROPERTIES OF AUSTEMPERED DUCTILE IRON (ADI)

The effect of copper content (0.031 wt.% Cu, 0.32 wt.% Cu, 0.51 wt.% Cu and 0.91 wt.% Cu) on the hardness and corrosion properties of ADI was investigated. Samples austenitization were carried out at 850°C for 60 min followed by its austempering at temperatures from 250°C to 420°C for different time (30 to 60 min) in 50% (KNO3 + NaNO3) salt bath. It was concluded that hardness rises with copper content but decreases with higher austempering temperatures and times. The corrosion properties of the samples with minimum and maximum Cu content were investigated by electrochemical methods in 0.5 M NaCl solution. Samples with a higher copper content have shown higher values of polarization resistance (Rp) and lower values of corrosion current (icorr). After polarization measurements, corroded surfaces were analyzed with SEM/EDS analysis

Utjecaj toplinske obrade na mikrostrukturu i toplinska svojstva traka s prisjetljivosti oblika na bazi bakra

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.Cilj rada bio je istražiti promjene u mikrostrukturi, temperaturama transformacije i toplinskim svojstvima nastale uslijed kaljenja Cu-Al-Mn i Cu-Al-Mn-Ti legura u obliku trake. U radu su prikazani rezultati mikrostrukturne analize i toplinskih svojstava Cu-Al-Mn i Cu-Al-Mn-Ti legura s prisjetljivosti oblika proizvedenih u obliku trake postupkom melt spinning. Mikrostrukturna analiza je provedena prije i nakon kaljenja. Nakon lijevanja istraživane legure su žarene pri 900 °C u trajanju 30 minuta, nakon čega je slijedilo kaljenje u vodi. Mikrostrukturna analiza je provedena optičkim i pretražnim elektronskim mikroskopom opremljenim energetsko disperzijskim spektroskopom te rendgenom. Termodinamički proračun ternarnog Cu-Al-Mn sustava proveden je u ravnotežnim uvjetima pomoću Thermo-Calc 5 programskog paketa. Temperature fazne transformacije određene su diferencijalnom pretražnom kalorimetrijom i mjerenjem električnog otpora. Rezultati mikrostrukturne analize pokazuju prisutnost martenzitne mikrostrukture prije i nakon kaljenja Cu-Al-Mn legure, dok u Cu-Al-Mn-Ti leguri martenzitna mikrostruktura postoji samo nakon kaljenja. Temperature faznih transformacija smanjuju se nakon kaljenja i dodatka titana

The influence of chloride ion concentration on the corrosion behavior of the CuAlNi alloy

The influence of different chloride ion concentration (0.1 %, 0.5 %, 0.9 % and 1.5 % NaCl solution) on the electrochemical behaviour of the cast CuAlNi alloy was examined with electrochemical techniques (open circuit potential measurements, linear and potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS)). After polarization measurements, electrode surfaces were examined with an optical microscope and the SEM/EDS analysis. Polarization measurements revealed that an increase in chloride ion concentration leads to an increase of the corrosion current density values and a decrease of the polarization resistance values, which indicated a higher corrosion attack on the alloy. The examination of alloy surfaces with an optical microscope and the SEM/EDS analysis has shown that there is no indication of pitting corrosion in the 0.1% NaCl solution, but pits were clearly visible on the samples which were examined in the higher chloride concentration solutions. The EDS analysis has shown the existence of copper oxide on the electrode surface and a presence of a small percentage of aluminium in the form of aluminium oxide

The impact of multiwall carbon nanotubes on the photocatalytic properties of imobilizied TiO2

Industry development, Earth’s population growth, ever increasing need for greater pharmaceuticals production causes irreversible changes in the environment. Photocatalysis is a process that leads to complete decomposition of pharmaceuticals to non-hazardous degradation products under the influence of solar radiation in the presence of a photocatalyst. A photocatalyst, such as titanium dioxide (TiO2), is required for photocatalysis. The efficiency of using TiO2 is limited due to the high energy banned zone (3-3.2 eV) so only UV-A light, which makes up 5% of solar radiation, activates the photocatalyst. In order to overcome the problem of prohibited zones and to shift the light response threshold of TiO2 into the visible part of the spectrum, different methods can be used. One of the methods showing the potential is the use of multiwall carbon nanotubes (MWCNT). In this paper a TiO2 / MWCNT composites with various concentrations of MWCNT were prepared. The concentrations of MWCNT ranged from 1.5, 5, 10, 25, 50 and 100 wt. % MWCNT relative to the mass of TiO2. It was observed that the concentration of MWCNT affects the photocatalytic activity of the composite obtained. Photocatalytic activity was followed by a degradation of salicylic acid, in a pilot reactor followed by UV-ViS spectrometry, as a modal solution and an example of a pharmaceuticals present in the water. The prepared catalysts were characterized by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX)

Sensitive Electrochemical Determination of Folic Acid Using ex–situ Prepared Bismuth Film Electrodes

The electrochemical behavior of folic acid (FA), at the electrochemically prepared ex situ bismuth film (BiF) on glassy carbon electrode, clearly indicates electrocatalytic nature of the prepared film toward FA reduction (at –0.55 V). Scanning electron microscopy is used for morphological characterization of the prepared BiF. Accordingly, we establishing an electrochemical procedure based on square wave cathodic stripping voltammetry, preceded by accumulation of FA on the BiF electrode (BiFE). This analytical method is optimized and its analytical performance is presented. This electrode displays a two linear response range: 0.1 to 1.0 μmol L–1 and 1.0–10.0 μmol L–1 with sensitivity of 20.10 μA μmol–1 L and 2.28 μA μmol–1 L, respectively. Developed method was validated in compliance with spectrophotometric method. Excellent recovery and standard deviation obtained with BiFE revealed great analytical potential of the proposed method which was applied for the determination of FA in pharmaceuticals formulation. This work is licensed under a Creative Commons Attribution 4.0 International License

Značajke masovne proizvodnje sirovog čelika u Republici Hrvatskoj od 1954. do 2020. godine

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

The impact of multiwall carbon nanotubes on the photocatalytic properties of imobilizied TiO2

Industry development, Earth’s population growth, ever increasing need for greater pharmaceuticals production causes irreversible changes in the environment. Photocatalysis is a process that leads to complete decomposition of pharmaceuticals to non-hazardous degradation products under the influence of solar radiation in the presence of a photocatalyst. A photocatalyst, such as titanium dioxide (TiO2), is required for photocatalysis. The efficiency of using TiO2 is limited due to the high energy banned zone (3-3.2 eV) so only UV-A light, which makes up 5% of solar radiation, activates the photocatalyst. In order to overcome the problem of prohibited zones and to shift the light response threshold of TiO2 into the visible part of the spectrum, different methods can be used. One of the methods showing the potential is the use of multiwall carbon nanotubes (MWCNT). In this paper a TiO2 / MWCNT composites with various concentrations of MWCNT were prepared. The concentrations of MWCNT ranged from 1.5, 5, 10, 25, 50 and 100 wt. % MWCNT relative to the mass of TiO2. It was observed that the concentration of MWCNT affects the photocatalytic activity of the composite obtained. Photocatalytic activity was followed by a degradation of salicylic acid, in a pilot reactor followed by UV-ViS spectrometry, as a modal solution and an example of a pharmaceuticals present in the water. The prepared catalysts were characterized by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX)

Optimisations in continuous casting of Cu based alloys by numerical simulation

Experimental study and numerical model for the thermo-mechanical properties in continuous casting (CC) of Cu-Al alloys is presented. This is a prerequisite basis for further development of Cu based shape memory alloys (SMA) with various alloying elements (like Ni or Mn). A coupled thermo-mechanical numerical simulation of the CC process is implemented and applied to the full non-equilibrium process conditions. In the experimental part, we used simple yet effective vertical continuous casting system. For the quantitative comparison, we implemented a special temperature measurement system within a graphite crystalliser that enables us to monitor the temperature profile at several spots around the solidification front in real time. The present analysis of the various process parameters’ effect on the solidification process includes: casting speed, thermal contact conductivity, liquid metal temperature, and cooling system set up. For microstructural examination we prepared samples from rods that were subsequently investigated by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDXS) analysis. Comparisons of the experimental results and numerical simulation were carried out. We developed a comprehensive numerical simulation model that quantitatively describes non-equilibrium time- dependent temperature profile, solid fraction and microstructure features in as cast state. Results from the coupled thermo-mechanical and microstructural simulations compare favourably with experimental data suggesting the casting speed as a key parameter in process optimisation

Optimisations in continuous casting of Cu based alloys by numerical simulation

Experimental study and numerical model for the thermo-mechanical properties in continuous casting (CC) of Cu-Al alloys is presented. This is a prerequisite basis for further development of Cu based shape memory alloys (SMA) with various alloying elements (like Ni or Mn). A coupled thermo-mechanical numerical simulation of the CC process is implemented and applied to the full non-equilibrium process conditions. In the experimental part, we used simple yet effective vertical continuous casting system. For the quantitative comparison, we implemented a special temperature measurement system within a graphite crystalliser that enables us to monitor the temperature profile at several spots around the solidification front in real time. The present analysis of the various process parameters’ effect on the solidification process includes: casting speed, thermal contact conductivity, liquid metal temperature, and cooling system set up. For microstructural examination we prepared samples from rods that were subsequently investigated by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDXS) analysis. Comparisons of the experimental results and numerical simulation were carried out. We developed a comprehensive numerical simulation model that quantitatively describes non-equilibrium time- dependent temperature profile, solid fraction and microstructure features in as cast state. Results from the coupled thermo-mechanical and microstructural simulations compare favourably with experimental data suggesting the casting speed as a key parameter in process optimisation

ANALIZA MIKROSTRUKTURE ZLITINE CuAlNiMn Z OBLIKOVNIM SPOMINOM PRED NATEZNIM PREIZKUSOM IN PO NJEM

In this paper the results of a microstructural analysis before and after fracture along with the mechanical properties and hardness of the CuAlNiMn shape-memory alloy are presented. The melting of the alloy was carried out in a vacuum-induction furnace in a protective atmosphere of argon. The alloy was cast into an ingot of 15 kg. After casting the alloy was forged and rolled into rods with a diameter of approximately 10 mm. A microstructural characterization was performed with light microscopy (LM) and scanning electron microscopy (SEM) equipped with energy-dispersive spectrometry (EDS). Martensitic microstructure was observed in the rods after the deformation. The fractographic analysis of the samples after the tensile testing revealed some areas with intergranular fracture. However, the greater part of the fracture surface indicated the pattern of transgranular brittle fracture. The results of the tensile tests showed the tensile strength of 401.39 MPa and elongation of 1.64 %. The hardness of the CuAlNiMn alloy is 290.7 HV0.5.V prispevku so predstavljeni rezultati analize mikrostrukture pred prelomom in po njem skupaj z mehanskimi lastnostmi in trdoto zlitine CuAlNiMn z oblikovnim spominom. Taljenje zlitine je bilo izvedeno v vakuumski pe~i v za{~itni atmosferi argona. Zlitina je bila ulita v ingot mase 15 kg. Po litju je bila zlitina kovana in zvaljana na premer pribli`no 10 mm. Karakterizacija mikrostrukture je bila izvedena s svetlobno mikroskopijo (SM) in vrsti~no elektronsko mikroskopijo (SEM), opremljeno z energijskim disperzijskim spektrometrom (EDS). Analizirana je bila martenzitna mikrostruktura zlitine CuAlNiMn pred izvedenim nateznim preizkusom. Izvedena sta bila natezni preizkus in meritve trdot. Fraktografska analiza je pokazala ve~ podro~ij z interkristalnim in pogosto transkristalnim krhkim prelomom. Rezultati nateznega preizkusa so pokazali, da je natezna trdnost 401,39 MPa in raztezek 1,64 %. Trdota zlitine CuAlNiMn je 290,7 HV0,5