Jožef Medved

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

Abstract The effect of Ce addition on the morphology of the α(Al)–Al 2 Cu eutectic in Al–Si–Cu alloy was investigated using thermal analysis, light microscopy, scanning electron microscopy, focused ion beam and energy dispersive analysis. The results show that the eutectic α(Al)–Al 2 Cu forms within small space between dendrites, silicon and AlSiFeMn plates. Eutectic Al 2 Cu is not lamellar but degenerated. However, Al 2 Cu in Ce-modified alloys is more compact. Ce partially dissolves in Al 2 Cu, which is a viable reason for the formation of coarser Al 2 Cu. The addition of Ce also increases the microhardness of the α(Al)–Al 2 Cu eutectic by almost 10% compared with the basic Al–Si–Cu alloy.

Microstructural evolution in Al–Mn–Cu–(Be) alloys

This study investigates the effects of alloying elements on the microstructural evolution of Al-rich Al–Mn–Cu–(Be) alloys during solidification, and subsequent heating and annealing. The samples were characterised using scanning electron microscopy, energy dispersive X-ray spectroscopy, synchrotron X-ray diffraction, time-of-flight secondary-ion mass spectroscopy, and differential scanning calorimetry. In the ternary Al94Mn3Cu3 (at%) alloy, the phases formed during slower cooling (≈1 K s−1) can be predicted by the known Al–Mn–Cu phase diagram. The addition of Be prevented the formation of Al6Mn, decreased the fraction of τ1-Al29Mn6Cu4, and increased the fraction of Al4Mn. During faster cooling (≈1000 K s−1), Al4Mn predominantly formed in the ternary alloy, whereas, in the quaternary alloys, the icosahedral quasicrystalline phase dominated. Further heating and annealing of the alloys caused an increase in the volume fractions of τ1 in all alloys and Be4Al (Mn,Cu) in quaternary alloys, while fractions of all other intermetallic phases decreased. Solidification with a moderate cooling rate (≈1000 K s−1) caused considerable strengthening, which was reduced by annealing for up to 25% in the quaternary alloys, while hardness remained almost the same in the ternary alloy.

Thermal Analysis of the Mg-Al Alloys

Multi-crystalline silicon ingot casting using directional crystallisation is the most costeffective technique for the production of Si for the photovoltaic industry. Non-uniform cooling conditions and a non-planarity of the solidification front result, however, in the build-up of stresses and viscoplastic deformation. Known defects, such as dislocations and residual stresses, can then occur and reduce the quality of the produced material. Numerical simulation, combined with experimental investigation, is therefore a key tool for understanding the crystallisation process, and optimizing it. The purpose of the present work is to present an experimental furnace for directional crystallisation of silicon, and its analysis by means of numerical simulation. The complete casting procedure, i.e., including both the crystallisation phase and the subsequent ingot cooling, is simulated. The thermal field has been computed by a CFD tool, taking into account important phenomena such as radiation and convection in the melt. The transient thermal field is used as input for a thermo-elasto-viscoplastic model for the analysis of stress build-up and viscoplastic deformation during the process. Numerical analysis is employed to identify process phases where further optimisation is needed in order to reduce generated defects.

The effect of cooling rate on the solidification and microstructure evolution in duplex stainless steel

The effects of the cooling rate on the solidification and microstructure evolution in the duplex stainless steel SAF 2205 was studied using DSC and light microscopy. A ferritoscope was used to measure the ferrite content. It was revealed that the cooling rate has an influence on the δ-ferrite nucleation temperature and the width of the solidification interval. Moreover, with an increase in cooling rate, the content of δ-ferrite increases, while the quantity of austenite in the ferrite matrix decreases and its morphology changes to acicular. A two-cycle DSC experiment made possible a more accurate interpretation of the collected data.

Study of the Eutectoid Transformation in the As-Cast Spheroidal Graphite Cast Iron with 'in Situ' Dilatation Analysis – Method for Quality Control

The eutectoid transformation of the spheroidal graphite cast iron (S.G.I.) has been investigated with “in situ” dilatometer, which was made for the investigation of the cast iron alloys. The investigation of the eutectoid transformation has been taking place by evaluation of the “insitu” dilatation curves in connection with metallographic examinations, chemical analyses and thermodynamic calculations of the phase equilibriums. By dilatometric curves it is possible to follow the exact eutectoid transformation of austenite. On a basis of numerous quantitative relations, as the relation between the ferrite and pearlite fractions in the as-cast SGI, which was determined by the analysis of the dilatometric curves and the composition, the ratio between ferrite and pearlite in the microstructure could be determined in a very short time. From the kinetics of austenite transformation and temperature dependence of the ferrite or pearlite growth the following characteristic temperatures of the eutectoid transformation have been established: the ferrite nucleation o Tα , the beginning of the ferrite growth Tα , and pearlite growth Tp , respectively. Kinetic curves, which show the fraction of the single microstructure constituents in the microstructure in dependence of the transformation time for mainly ferrite SGI, are good represented by the physical sigmoidal Boltzmann model.

Thermal analysis of indefinite chill cast iron modified with ferrovanadium and ferrotungsten

Melt modification is a method commonly used when enhancing mechanical and microstructural properties of various alloys. The addition of heterogeneous nucleation sites generally refines the given microstructure and enhances the toughness of the material. Ferroalloys based on high-melting elements require a longer incubation time in the melt which makes them liable candidates for modification agents. A research on the effect of melt modification was conducted on an indefinite chill cast iron alloy commonly used for working layers in rolls. The goal of the research was to determine the effect of ferrovanadium and ferrotungsten melt treatment with the use of thermal analysis along with thermodynamic modelling using the CALPHAD approach. The results show a decrease in the measured liquidus temperature of the modified alloy along with a possible second eutectic reaction hidden inside the main graphite/cementite eutectic reaction. Scanning electron microscopy revealed small and evenly distributed MC type carbides rich in V with W and other carbide-forming elements. The results presented in this work enable a better understanding of the impact melt modification has on the development of microstructure and subsequently the improvement in mechanical properties of the alloy.

Combining polyNiPAAm/chitosan microgel and bio-barrier polysiloxane matrix to create smart cotton fabric with responsive moisture management and antibacterial properties: influence of the application process

Smart cotton fabric with simultaneous temperature and pH responsive moisture management and antibacterial properties was prepared by applying poly-(N-isopropylacrylamide)/chitosan microgel in combination with bio-barrier-forming sol–gel precursor dimethyloctadecyl (3-(trimethoxysilyl)propyl) ammonium chloride. Two application processes were used: one-step, which included deposition of a mixture of PNCS microgel and Si-QAC mixture (PNCS/SiQ (1S)), and two-step, comprising deposition of PNCS microgel followed by Si-QAC (PNCS + SiQ (2S)) and vice versa, i.e., deposition of Si-QAC followed by the PNCS microgel (SiQ + PNCS (2S)). Different analysis, i.e., nuclear magnetic resonance, thermogravimetry and dynamic light scattering were used to characterize the poly-(N-isopropylacrylamide)/chitosan microgel, while scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy analysis were employed to determine the morphological and chemical properties of the modified cotton samples. Their functional properties were assessed by the moisture content, water vapor transmission rate, water retention capacity and antibacterial activity against Escherichia coli. While Si-QAC granted excellent antibacterial activity, it also influenced swelling/deswelling activity of the poly-(N-isopropylacrylamide)/chitosan microgel. Accordingly, it slightly impaired moisture content and water retention capacity at conditions when microgels swell but increased water repulsion from the poly-(N-isopropylacrylamide)/chitosan microgel at conditions that trigger its coil-to-globe transition. The application process greatly influenced the washing fastness of the coatings, and the PNCS + SiQ (2S) application process appeared most promising. In this case, the poly-(N-isopropylacrylamide)/chitosan microgel acted as a carrier for the sol–gel precursor dimethyloctadecyl (3-(trimethoxysilyl)propyl) ammonium chloride, causing its gradual release to the fiber surface triggered by a variation of temperature and pH and thus preserving its excellent antibacterial activity after five laboratory washings. To assure complete synergistic activity of both components in the coating, further optimization of the sol–gel precursor dimethyloctadecyl (3-(trimethoxysilyl)propyl) ammonium chloride concentration is necessary.Graphical Abstract

Influence of N-, P- and Si-based Flame Retardant Mixtures on Flammability, Thermal Behavior and Mechanical Properties of PA6 Composite Fibers

This research investigated the influence of two flame retardant (FR) mixtures consisting melamine cyanurate (MeCy) and aluminum diethylphosphinate (AlPi), and MeCy and sodium aluminosilicate (SASi) at different weight ratios, on the flammability, thermal behavior and mechanical properties of polyamide 6 (PA6) composite yarns produced by meltspinning. The morphological and chemical properties of PA6/FR filaments were investigated by scanning electron microscopy and Fourier-transform infrared spectroscopy, flame retardancy by vertical burning test UL-94, thermal behavior by thermogravimetric and differential scanning calorimetric analyses, and mechanical properties by tensile tests. The results indicate that within the UL 94 V2 rating, the composite yarns differed significantly from each other in their burning and dripping behavior. The incorporation of both mixtures, MeCy+AlPi and MeCy+SASi, into the PA6/FR yarns significantly decreased the afterflame time relative to pristine PA6, confirming a lower production of flammable volatiles. This phenomenon was attributed mainly to MeCy, which caused an immediate extinguishment of the flame after the withdrawal of the igniting flame. Compared to one component MeCy, the incorporation of the MeCy+SASi mixture enhanced the thermooxidative stability of the PA6/FR yarns because of their additive effect at higher concentrations. In contrast, an antagonistic effect was obtained for the MeCy+AlPi mixture, irrespective of the concentration. Since the incorporation of MeCy+SASi did not drastically reduce the tensile properties of filaments, this mixture enables the production of the PA6/MeCy+SASi composite yarns with the enhanced flame retardancy and thermo-oxidative stability.

Development of Innovative Al–Si–Mn–Mg Alloys with High Mechanical Properties

In modern practice standard materials do not satisfy the rigorous requirements for applications. Paper represents thermodynamic modeling of innovative aluminium alloys with better mechanical properties for high temperature applications. Using different combinations of alloying elements in specific temperature regions the information of which specific phase (solid solution, intermetallic compound) is formed. Alloys systems Al–X–Y (X = Si, Mn, Mg; Y = Zr, Mo) were investigated using thermodynamic equilibrium calculations (ThermoCalc), thermal analysis, and optical and scanning electron microscopy, in order to analyze the corresponding properties. Determination of chemical composition and types of phases, amount of phase and study of equilibrium and non-equilibrium processes, the characteristic solidification temperatures and mechanical properties for laboratory and industrial aluminium alloys was done.

Thermodynamic characterization of aluminium corner of Al–Cu system with various Nd additions

The effect of various neodymium additions on the characteristic solidification temperatures and on the microstructure development of the laboratory-prepared binary alloy AlCu5.5 was investigated. The aluminium corner of ternary system Al–Cu with various Nd additions was investigated using thermal analysis, differential scanning calorimetry and optical and scanning electron microscopy. The presence of Nd phases was confirmed using X-ray diffractometer. Microhardness of α-Al in AlCu5.5 alloy containing various Nd additions was analysed. The results show that the addition of neodymium raises eutectic (α-Al + Al2Cu) solidification temperature and solidus temperature, which leads to a narrower solidification interval. It was also confirmed that Nd formed two binary eutectics (α-Al + Al2Cu(Nd)) and (α-Al + Al8Cu4Nd). The addition of Nd also caused the increase in microhardness of α-Al phase.