Defect and Diffusion Forum Vol. 420

Abstract: Four main diffusion laws: 1D diffusion in a planar bulk sample or random walks along a straight line x=α₁t^1/2; 3D diffusion or random walks from a point source and forming small spherical particle: x=α₂t^1/3; 1D+1D diffusion or random walks along a straight plane with simultaneous outflow into balk: x=α₃t^1/4; 1D+2D diffusion or random walks along a straight line with simultaneous outflow into balk: x=α₄t^1/6 are analysed theoretically using mathematical modelling and appropriate physical models. Convex shape of the diffusion profile near the top along a dislocation pipe with simultaneous outflow into balk is predicted. It is shown that the cone angle near the top is increasing with time. Literature experimental data are used for analysis.

Abstract: As it is well established, Stokes law has been used to calculate the time required to precipitate a particle in a fluid under specific conditions such as sphericity, laminar flow, differences on densities (particle and fluid) and fluid viscosity for a specific gravity force (g). However, when the separation under 1-g takes days or months and it is crucial to estimate that time in just minutes, the separation time at 1-g can be estimated making a relationship with any other g (n). However, in any centrifuge the n value is not reached instantaneously but in a specific time and during this time the g-value is never constant, but it is always growing (at the first stage). Then, after reaching the n-value, the centrifuge could stay at that value for a certain time and then, (the third stage) the n value will change again, this time decreasing. Therefore, the aim of this study is to establish a mathematical model that considers the acceleration and deceleration periods and expresses them as equivalents of the n period by using a numerical approach [1-3]. It is expected the g-equivalent concept increases the certainty of the separation time estimation.

Abstract: Is it possible to quantify in General Relativity, GR, the entropy generated by Super-Massive Black Holes, SMBH, during its evaporation time, since the intrinsic Hawking radiation in the infinity that, although insignificant, is important in the effects on the thermal quantum atmosphere? The purpose was to develop a formula that allows us to measure the entropy generated during the evaporation time of different types of SMBH of: i. remnant BH of the binary black holes’ merger, BBH: GW150914, GW151226 and LTV151012 detected by the Laser Interferometer Gravitational-Wave Observatory, LIGO, and ii. Schwarzschild, Reissner-Nordström, Kerr and Kerr-Newman, and thus quantify in GR the “insignificant” quantum effects involved, in order to contribute to the validity of the generalized second law, GSL, that directly links the laws of black hole mechanics to the ordinary laws of thermodynamics, as a starting point for unifying quantum effects with GR. This formula could have some relationship with the detection of the shadow’s image of the event horizon of a BH. This formula was developed in dimensional analysis, using the constants of nature and the possible evaporation time of a black hole, to quantify the entropy generated during that time. The energy-stress tensor was calculated with the 4 metrics to obtain the material content and apply the proposed formula. The entropy of the evaporation time of SMBH proved to be insignificant, its temperature is barely above absolute zero, however, the calculation of this type of entropy allows us to argue about the importance of the quantum effects of Hawking radiation mentioned by authors who have studied the quantum effects with arguments that are fundamentally based on the presence of the surrounding thermal atmosphere of the BH.

Abstract: The present study has been undertaken to study the microstructure and microhardness of the multi-component B–C–N diffusion coatings developed on AISI M2 high-speed steel substrate at 560 and 650 oC for 1 and 4 h for each temperature respectively. The investigation of the coatings was fulfilled using scanning electron microscopy, energy dispersion spectroscopy and X-ray diffraction analysis. Additionally, Vickers microhardness measurements were performed. The results showed that varying conditions of the thermochemical treatment led to a variety of coatings in the sense of their microstructure and phase composition.

Abstract: The main objective of this work was to obtain information about the hydrogen diffusion behaviour in a cold-worked austenitic stainless steel (X3CrMnNiMoN17-8-4) in which deformation-induced martensite formation occurs during mechanical deformation. Three different states of pre-deformation (31 %, 39 % and 49 %) that showed induced phase transformation from austenite to α’martensite as well as the solution-annealed material were part of this study. All samples were charged with hydrogen in a 0.1 M NaOH solution. This charging took place electrolytic with 10 mA cm^-2 at three different temperatures (50 °C; 65 °C and 80 °C) in the double cell according to Devanathan and Stachurski. Due to the very slow diffusion of hydrogen through austenite, the samples were not charged until the equilibrium state was reached. To find out the necessary diffusion parameters, the data were fitted with numerical optimisation. Using this method, the effective diffusion coefficients of charging could be determined for all material states. The study also contains microscopic analyses to visualize the effect of cold working on the microstructure of the material. The appearance of α’-martensite significantly contributes to the susceptibility to hydrogen uptake leading to increasing diffusion coefficients in relation to higher pre-deformation.

Abstract: Strength characteristics of iron ore agglomerates of various basicity (mechanical strength and abrasion resistance, thermomechanical strength) have been investigated. The chemical and phase compositions of iron ore agglomerates, their microstructure and local chemical composition were analyzed. Dependences of the strength characteristics of iron ore agglomerates of various basicity on the morphology of silicate bond have been obtained. Dependences of influence of basicity of iron ore agglomerates on their strength characteristics depending on the proportion of phase components are obtained. It has been shown that an increase in the proportion of stabilized silicoferrite (SFCA) in the composition of agglomerates has a positive effect on their thermomechanical strength, which will increase the productivity of the blast furnace and significantly reduce the emission of dust.

Abstract: Nuclear relaxation caused by diffusion of ¹¹¹In/Cd probe atoms was measured in four phases having the tetragonal FeGa₃ structure (tP16) using perturbed angular correlation spectroscopy (PAC) and used to gain insight into diffusion processes in phases having more than one diffusion sublattice. The three indide phases studied in this work have two inequivalent and interpenetrating In-sublattices, labeled In1 and In2, and nuclear quadrupole interactions were resolved for probes on each sublattice. The phases are line-compounds with narrow field-widths. Diffusional relaxations, fitted using an exponential damping ansatz, were measured at the two opposing boundary compositions as a function of temperature. “High” and “low” relaxation regimes were observed that are attributed to In-poorer and In-richer compositions, under the reasonable assumption that the atomic motion occurs via an indium-vacancy diffusion mechanism. Relaxation was observed to be greater for tracer atoms starting on In2 sites in the indides immediately following decay of ¹¹¹In into ¹¹¹Cd, which is attributed to a preference of daughter Cd-tracer atoms and/or indium vacancies to occupy In1 sites. Activation enthalpies for relaxation are compared with enthalpies for self-diffusion in indium metal.

Abstract: Increasing durability of catalysts used in fuel cells is a necessary condition for their widespread commercialization. Fulfilling this condition requires understanding the catalyst degradation mechanism to propose how to reduce it. Transmission electron microscopy can help solve this problem thanks to the fact that it enables direct observation and thus unambiguous interpretation of the processes taking place. For this purpose, Identical Location Transmission Electron Microscopy (IL-TEM) was applied for observations of a commercial catalyst (platinum nanoparticles with a diameter of about 2 nm deposited on Vulcan carbon black) before and after durability tests. Obtained results may contribute to the development of better models of phenomena occurring during cell operation.

Abstract: Niobium is added to carbon steels in small amounts (< 0.1weight %), thus being called a microalloying element, to increase mechanical strength and toughness. When added to steel, niobium is partly soluble in the matrix and another part combines with carbon and nitrogen forming a family of Nb_xC_yN_z precipitates (niobium carbides, nitrides or carbonitrides), where the values of x, y, z depend on the temperature and the chemical composition of the steel. The effects of niobium dissolved in the matrix or as precipitates are distinct and sometimes antagonistic. Thus, two samples of the same carbon steel microalloyed with niobium may differ in: microstructure, ferritic grain size or interlamellar spacing of the pearlite, depending on the thermomechanical processing to which they were submitted, which will result in different mechanical properties. In order to make good use of the possible beneficial effects of adding niobium to carbon steels, it is necessary to clearly understand its complex physical metallurgy. To analyze the effects of niobium, six steels were used (0.2/0.4/0.8 C/ 1 Mn, with and without the addition of 0.03 Nb, weight %). Using an ARL ion microprobe, with oxygen ions and mass spectroscopy reading on niobium steel, after partial isothermal transformation at 700 oC, we observed the partition of niobium between ferrite and austenite. Thus, the formation of ferrite is slower, shifting the TTT curve to longer times and separating the pearlite and bainite bays. The same occurs in continuous cooling transformation, where the diffusional components (ferrite, pearlite and bainite) are formed at lower temperatures and with a longer time. With pearlite forming at lower temperatures, there is a decrease in the interlamellar spacing, increasing its hardness and, consequently, the mechanical strength. Niobium also forms carbonitrides, and these finely precipitated particles anchor the grain boundary, making it difficult to move and thus producing a smaller austenitic grain size than in steel without the addition of niobium, increasing mechanical strength and toughness of steel.