Jožef Medved

University of Ljubljana

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Maja Vončina

University of Ljubljana

Primož Mrvar

University of Ljubljana

Tilen Balaško

University of Ljubljana

Jaka Burja

Institute of Metals and Technology

Aleš Nagode

University of Ljubljana

Mitja Petrič

University of Ljubljana

BŠ

Barbara Šetina Batič

Institute of Metals and Technology

Stanislav Kores

Talum (Slovenia)

Matjaž Godec

Institute of Metals and Technology

Barbara Simončić

University of Ljubljana

Cooperative Institutions

University of Ljubljana

Institute of Metals and Technology

National Institute of Chemistry

Impol (Slovenia)

University of Maribor

University of Zagreb

Jožef Stefan International Postgraduate School

Jožef Stefan Institute

Talum (Slovenia)

Štore Steel (Slovenia)

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Dilatation analysis of the eutectoid transformation of the as‐cast spheroidal graphite cast iron

Scandinavian Journal of Metallurgy (2002)

Primož Mrvar Milan Trbižan Jožef Medved

It is known that the decomposition of austenite in spheroidal graphite cast iron (SGI) depends on numerous factors. Among them, the cooling rate and microsegregation of alloying elements (Si, Cu, Mn) are derived from the solidification step. The eutectoid transformation of the SGI has been investigated with a new dilatometer that was made for the investigation of cast iron alloys. The temperature dependence of the dilatations, similar to a function of time is shown by the dilatation curves. The investigation of the eutectoid transformation has been examined by the evaluation of dilatation curves, metallographic examinations and chemical compositions. It is possible to exactly follow the eutectoid transformation of austenite, which proceeds according to the stable reaction in ferrite and graphite (γ→α+ graphite) , the metastable reaction in perlite (γ→α+ Fe 3 C) , or dilatometric and differential dilatometric curves, respectively. The ratio between the perlite and ferrite phase in the matrix of the spheroidal graphite cast iron depends upon the extent of each reaction. The temperature difference between the dilatation extremes during the eutectoid reactions, as a function of the ferrite fraction, has been determined. A correlation between the amount of ferrite and the characteristic expansion owing to the graphite precipitation was found.

Dilatometer

10.1034/j.1600-0692.2002.10607.x

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Citations (8)

Effect of Ce on morphology of α(Al)–Al2Cu eutectic in Al–Si–Cu alloy

Transactions of Nonferrous Metals Society of China (2014)

Maja Vončina Jožef Medved Tonica Bončina Franc Zupanič

Morphology

10.1016/s1003-6326(14)63025-9

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Citations (23)

INFLUENCE OF HEAT TREATMENT ON THE HIGH-TEMPERATURE OXIDATION BEHAVIOUR OF CHROMIUM-MOLYBDENUM-VANADIUM ALLOYED HOT-WORK TOOL STEEL

Materiali in tehnologije (2022)

Tilen Balaško Maja Vončina Jaka Burja Jožef Medved

The high-temperature oxidation behaviour of chromium-molybdenum-vanadium alloyed hot-work tool steel was investigated. High-temperature oxidation was investigated in two conditions: soft annealed, and quenched and tempered. The samples were oxidised in a chamber furnace and in an instrument for simultaneous thermal analysis, for 100 h in the temperature range between 400 °C and 700 °C. Metallographic analysis (optical and scanning electron microscopy) was performed to study the microstructural changes in the steel and the oxide layer. Oxidation kinetics were analysed by thermogravimetric analysis, and equations were derived from the results. The kinetics can be described by three mathematical functions, namely: exponential, parabolic and cubic. However, which function best describes the kinetics depends on the oxidation temperature and the thermal condition of the steel. Quenched and tempered samples were shown to oxidise less, resulting in a slower oxidation rate.

Thermogravimetric analysis

Atmospheric temperature range

Thermal oxidation

Hot work

10.17222/mit.2022.406

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Thermodynamic characterization of solidification and defects that occur in Mg-alloy AM60

Journal of Mining and Metallurgy Section B Metallurgy (2017)

Maja Vončina Mitja Petrič Primož Mrvar Jožef Medved

The AM60 alloy was thermodynamically examined using chemical analysis, thermodynamic calculation made by ThermoCalc program, ?in situ? thermal analysis and differential scanning calorimetry (DSC), whereas the microstructure constituents were confirmed using optical and scanning electron microscopy (SEM). At the eutectic temperature of 437 ?C the equilibrium solubility of Al in Mg is 12.6 wt. % Al. On the boundaries of the primary Mg grains the intermetallic compound of Al12Mg17 is precipitating according to the solvus line of the Mg-Al phase diagram. Solidification of the AM60 alloy has been investigated using ?in situ? simple thermal analysis. The investigation of solidification has been taking place by evaluation of the cooling curves in connection with metallographic examinations, differential scanning calorimetry and thermodynamic calculations. All defects, nonmetallic inclusions and intermetallic compounds that occur in investigated AM60 alloy were identified.

Solvus

10.2298/jmmb160609009v

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Citations (3)

A cross-section approach to measuring the shadow economy

Journal of Policy Modeling (2006)

Marta Orviská Anetta Čaplánová Jožef Medved John Hudson

10.1016/j.jpolmod.2006.04.009

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Influence of cooling rates on temperatures phase transitions and on microstructure of aluminium alloy EN AW‐5083

Materialwissenschaft und Werkstofftechnik (2012)

Natalija Dolić Jožef Medved Primož Mrvar Faruk Unkić

Abstract The casting of different forms and dimensions of aluminium alloy EN WA‐5083 test samples and the usage of different types of mould materials resulted in achieving different cooling rates of samples. The methods used were simple thermal analysis, using casting into a measuring cell made by the Croning process and using casting into a cone‐shaped measuring cell, as well as simultaneous thermal analysis using the method of differential scanning calorimetry. Significant temperature phase transitions and times of solidification were determined, and the dependence model of the solidification time on the sample cooling rate was obtained. Determining the mean number of grains per unit area on samples after having performed the simple thermal analysis and differential scanning calorimetry makes it possible to develop a dependence model of the mean number of grains per unit area on the cooling rate. These models are the basis for carrying out numerical simulations of solidification and microstructure development in the cone‐shaped measuring cell, and the comparison of the distribution of the mean number of grains per unit area obtained by simulation with the one obtained experimentally. The obtained results represent a part of the preliminary tests of the microstructure development of industrially cast ingots of EN AW‐5083 alloy depending on the local ingot cooling rate.

Ingot

Cooling curve

10.1002/mawe.201200929

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Electrical Resistivity of Al-Cast Alloys in the Range of Solidification

CRC Press eBooks (2019)

M. Petri Jožef Medved Sebastjan Kastelic Maja Vončina Primož Mrvar

The aim of this paper is to explain the electrical resistivity change during solidification and connect it with the thermal analysis and solidification course. The problem at conducting the “in situ” measurement by four-point technique is the electrode material, which often oxidizes during measurements causing high contact resistance and providing incorrect results. Various materials were tested and aluminum electrodes chosen. The advantage of aluminum electrodes is that they melt within the specimen immediately after being poured and cause no interface resulting with any contact resistance. Pure aluminum, hypoeutectic alloy AlSi7Mg, and eutectic AlSi12 alloys were tested. Resistivity of Al–Si alloys is increasing with Si content. Grain refinement and modification of β Si were employed. Grain refinement has any effect on electrical resistivity. Modification of β Si phase causes decrease of electrical resistivity. The electrical resistivity curves give information similar as cooling curves from thermal analysis measurements.

Contact resistance

Electrical contacts

10.1201/9781351045636-140000202

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High-Temperature Oxidation Behavior of Tool Steel with Increased Thermal Conductivity

Oxidation of Metals (2022)

Tilen Balaško Maja Vončina Jaka Burja Barbara Šetina Batič Jožef Medved

High-Temperature Corrosion

10.1007/s11085-022-10119-1

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Citations (5)

In situ prepared polyamide 6/DOPO-derivative nanocomposite for melt-spinning of flame retardant textile filaments

Polymer Degradation and Stability (2019)

Jelena Vasiljević Marija Čolović Ivan Jerman Barbara Simončić Andrej Demšar

A novel flame retardant polyamide 6 (PA6)/bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-derivative (PHED) nanocomposite textile filament yarns were developed. The scalable production approach includes in situ water-catalyzed ring-opening polymerization of ε -caprolactam in the presence of the flame retardant PHED followed by melt-spinning of nanocomposite filament yarns and production of knitted fabrics. The specific chemical structure of the PHED additive enabled its excellent miscibility with molten ε-caprolactam and the uninterrupted polymerization of ε -caprolactam. The produced PA6/PHED nanocomposite was characterized by the preserved molecular structure of the polyamide 6 and uniformly distributed nano-dispersed FR at concentrations of 10 and 15 wt %. The PA6/PHED nanocomposite structure was successfully preserved after the melt-spinning processing. The PA6 nanocomposite filament yarns at the applied 15 wt %. loading of PHED showed (a) increased thermo-oxidative stability compared to neat PA6 up to 500 °C, with a 43% higher residue at 500 °C and (b) self-extinguishment of fiber strand and knitted samples within 1 s in standard vertical flame spread tests (ASTM D6413), followed by the significant reduction of the melt-dripping and the melt-drop flammability. Additionally, 1.2 mm-tick PA6/PHED bar samples achieved a V0 rating in UL94 vertical burning test at the applied 10 wt % concentration of PHED. This innovative and scalable approach could pave the way for the production of new-generation nanocomposite PA6 filament yarns with self-extinguishing properties at the macro-scale, which would be highly beneficial for increasing fire safety, whilst maintaining the use of a DOPO derivative at the minimum level. A new scalable approach is established to produce the first-ever polyamide 6/DOPO-derivative nanocomposite filament yarns and knitted fabrics with superior flame retardancy and self-extinguishing properties. The in situ approach for the incorporation of the organophosphorus additive of specific chemical structure in the PA6 matrix guarantees its uniform distribution and nanodispersion as well as the successful melt-spinning of textile filaments with highly effective flame retardancy, whilst maintaining the use of a DOPO-derivative at the minimum level. • Flame retardant PA6/PHED nanocomposite was produced by in situ polymerization approach. • Textile filament yarns were successfully melt-spun from produced nanocomposites. • PHED increased thermo-oxidative stability of PA6 up to 500 °C, with 43% higher residue at 500 °C. • Self-extinction within 1 s for PA6/PHED fiber strand and knitted fabric was achieved in vertical flame spread tests (ASTM D6413). • UL94 V-0 rating was achieved for 1.2 mm-tick PA6/PHED bar samples with 10 wt % of PHED.

Melt spinning

Caprolactam

In situ polymerization

10.1016/j.polymdegradstab.2019.05.011

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Citations (49)

Medium term plans and results in Slovak agriculture.

Jožef Medved

Slovak

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