Defect and Diffusion Forum Vol. 413

Abstract: We remind the reader to some common features of metallic and oxide glasses. We then introduce the radiotracer method for diffusion studies, which can be applied for both types of glasses. We provide an overview on diffusion in metallic glasses in which we consider both types of metallic glasses – conventional and bulk metallic glasses. In the last part we discuss diffusion and ionic conduction in oxide glasses. For ionic glasses, conductivity measurements are an important complement to tracer diffusion studies. We remind the reader to the method of impedance spectroscopy. We discuss results for soda-lime silicate glasses, single alkali borate glasses and mixed alkali borate glasses and present evidence for collective jump processes in glasses.

Abstract: Cathode materials based on lithium-metal-oxide compounds are an essential technical component for lithium-ion batteries, which are still being researched and continuously improved. For a fundamental understanding of kinetic processes at and in electrodes the Li diffusion is of high relevance. Most cathode materials are based on the layered LiCoO₂ (LCO) and LiNi_0.33Mn_0.33Co_0.33O₂ (NMC₃₃₃). In the present study Li tracer self-diffusion is investigated in polycrystalline sintered bulk samples of sub-stoichiometric Li_0.9CoO₂ at 145 °C ≤ T ≤ 350 °C and compared to Li_0.9Ni_0.33Mn_0.33Co_0.33O₂ in the temperature range between 110 and 350 °C. For analysis, stable ⁶Li tracers are used in combination with secondary ion mass spectrometry (SIMS). The Li tracer diffusivities D^* of both compounds with a sub-stoichiometric Li concentration are identical within error limits and can be described by the Arrhenius law with an activation enthalpy of (0.76 ± 0.13) eV for LCO and (0.85 ± 0.03) eV for NMC₃₃₃, which is interpreted as the migration energy of a single Li vacancy. This means that a modification of the transition metal (M) layer composition within the LiMO₂ structure does not significantly influence lithium diffusion in the temperature range investigated.

Abstract: In this paper, the diffusion isotope effect and diffusion mechanism are investigated by means of molecular dynamics simulations in two liquid alloys, Ni-Ag and Ni-Cu. The values for the diffusion isotope effect parameter allow for the estimate of the number of atoms which are moving cooperatively in a basic diffusion event as experienced by a given atomic species. It is shown that the composition dependence of N_D is typically very small. However, the temperature dependence of this parameter is much more pronounced. In addition, it is shown that, on average, in these alloys and temperatures considered, N_D is limited to the range: 5<N_D<17. This is consistent with results of molecular dynamics simulations on the average coordination number calculations. This would suggest that, together with a given atom, depending on temperature, the neighbouring atoms are all involved in the basic diffusion event.

Abstract: The aim of this work is to investigate chemo-resistivity properties of natural rubber-carbon nanostructure composite, that’s why a change of diffusion characteristics and reversibility of electro-chemical properties of the composite with different degree values of crosslinks have been analysed. The composites are made from natural rubber (polyisoprene) as matrix material and high structure carbon black as electro-conductive filler. In order to investigate diffusion characteristics of volatile organic compounds (VOC) in relation to chemo-resistive response of composites simultaneous mass, length and electrical resistance change measurements of the samples, when samples are held in VOC and after exposures to VOC were carried out. Electrical resistance increase mechanism in the composite advances with the composite structure development during vulcanization.

Abstract: The paper considers the theoretical foundations of softening of iron ore materials in a blast furnace (the so-called ‘cohesion zone’). The dependences of the temperature range of softening of iron ore materials (the temperatures of the beginning and ending of softening) on the degree of reduction are calculated and experimentally obtained. Physical modelling of the softening process of reduced iron ore materials was carried out using the Russian State Standard No 26517-85. The results of calculations of the location and shape of the cohesion zone in the blast furnace for iron ore materials with different metallurgical characteristics are presented.

Abstract: The present study has been undertaken to compare the microstructure of the plain carbon steel, containing 0.65 carbon, which was formed during varying isothermal and continuous cooling conditions following austenitisation at the same temperature and soaking time. After austenitisation, one set of samples was subjected to isothermal treatment which was carried out at a temperature varying in the range of 650–400 °C, and the other one was continuously cooled to ambient temperature using different cooling rates ranging from 500 to 1.4 °Cs^–1. The metallographic examination of the samples was fulfilled using light and TEM microscopy. Additionally, Vickers hardness measurements were performed.

Abstract: The magnesium AZ31B alloy has been utilized in a variety of applications within the automotive and aviation industries due to its high specific strength, low-cost processing, and low density. However, the AZ31B alloy generally has poor ductility and limited workability at room temperature. The objective of this study was to develop a manufacturing processing technique to increase the potential uses of this alloy. The methodology includes cold rolling and annealing using small pass reductions until the samples reached a final thickness of 1.78 mm (0.07 in). The samples were cut into 10.16 mm (0.4 in), 7.62 mm (0.3 in), and 5.08 mm (0.2 in) thicknesses prior to cold rolling and were rolled in 0-, 45-, and 90-degree rolling directions. The grain shapes and sizes were examined via optical microscopy. Tensile testing was conducted to determine the strength and ductility. Scanning electron microscopy (SEM) images were taken to evaluate fractured surfaces. All processes including rolling direction and furnace cooling or air cooling after annealing produced similar results of medium strength (245-250 MPa in ultimate strength, 122-127 MPa in yield) and greater than 22.5% elongations in very thin sheets. Samples rolled along the 45-degree direction produced the highest percent reduction in thickness.

Abstract: Aluminium bronze alloys are special copper alloys that have a machinability rate from 20 to 40% compared to free cutting brasses, so the cutting parameters and type of tools suitable for machining of these materials may be very different for other copper alloys. Also, due to the relative high costs of the raw material, the absence of contamination of the chips by cutting fluids improve its intrinsic resales value and encourage the use of machining process without coolant. The aim of this work is to evaluate the tool wear mechanisms in the finishing machining of the Cu-10wt%Al-5wt%Ni-5wt%Fe aluminium-bronze alloy with carbide and cermet inserts at different cutting speeds under dry machining condition. The turning of material showed lower surface roughness in higher speed conditions and better dimensional stability at lower speeds. It was observed the formation of continuous chips, but of little volume occupied. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of tool wear show the adhesion as the main tool wear mechanism, followed by abrasion. At the lower cutting speed, the adhesion wears affected significantly the surface finish, reducing the tool life in comparison to the higher speeds.

Abstract: Metallurgical characteristics of iron ore agglomerates of various basicity (reducibility, strength after reduction (LTD_+6.3), temperatures of the beginning and ending of softening) have been investigated. The phase composition (XRD) of iron ore agglomerates and their microstructure were analyzed by optical microscopy. Various dependences of influence of the basicity of iron ore agglomerates on their metallurgical characteristics with respect to the proportion of phase components that have been obtained. It has been shown that an increase in the proportion of stabilized silicoferrite (SFCA) in the agglomerate has a positive effect on their strength after reaction, which will further increase the productivity of the blast furnace and significantly reduce dust emission.

Abstract: Microwave absorbing materials are applied in stealth, communications and information processing technologies. This kind of material dissipates an electromagnetic wave by converting it into thermal energy. The nanostructuration of materials became a reliable route over the years to enhance the dielectric and magnetic properties, which induce the required interaction. Nanostructured Fe-Co alloys are soft magnetic materials that make them promising candidates for microwave absorption when combined with other materials. The aim of our study was therefore to investigate the microwave absorption properties of based nanocomposites. The nanocomposites were obtained by the solution dispersion method. Nanocrystalline alloys elaborated by mechanical alloying (MA) in a high-energy planetary ball mill (RETSCH PM400) were dispersed into commercial epoxy resin matrix to form thin polymer nanocomposites. The grain size refinement and structural properties changes during milling process were characterized using powder’s X-ray Diffraction (XPERT PRO MPD diffractometer) at different milling durations. XRD spectra analysis show that a grain size refinement of 4.54 nm was reached after 60h milling accompanied with 1.2 % microdeformations. Obtained powders were shaped in small discs for which resonant cavity measurements were undertaken. The based nanocomposites have been subject to an experiment of two-port S parameters measurement in a rectangular waveguide (R120). The microwave experiments involved a Network Analyzer (VNA). Obtained results in terms of reflection losses show a good absorbing characteristic over the [8-15] GHz microwaves band.