Diffusion Phenomena: Aspects of Characterization and Experiments

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Authors: H. Becker, D. Heger, A. Leineweber, David Rafaja
Abstract: The influence of Spark Plasma Sintering / Field Assisted Sintering Technology applying pulsed direct current up to the root-mean-square current densities of 129 A/cm2 on the interfacial reactions in Al - Fe - Al stacks was investigated at temperatures between 500°C and 600°C. Independently of the current density and current direction, thin Al13Fe4 and wide Al5Fe2 phases were detected in the diffusion couples. The Al5Fe2 phase consisted of columnar grains having a {001}-fiber texture. Al13Fe4 was found in the form of discontinuous spots at the Al/Al5Fe2 interface. The interface between Al5Fe2 and Fe was highly fringed. The layer growth kinetics of Al5Fe2 was parabolic. The growth rate was strongly enhanced in the SPS/FAST experiments as compared to the conventional diffusion experiments, independently, on the current direction. It is suggested that the enhanced growth rates are a result of temperature gradients existing in a typical Spark Plasma Sintering device. Possible effects of thermomigration and electromigration are discussed.
Authors: A.S. Barros, Adrina P. Silva, Ivaldo Leão Ferreira, O.L. Rocha, A.L. Moreira
Abstract: This paper presents a theoretical-experimental study for the prediction of the interfacial heat transfer coefficient during the horizontal directional solidification of an Al-3wt.%Cu alloy on water cooled stainless steel chill under transient heat flow conditions. Eight thermocouples were connected with the casting and the time-temperature data were recorded automatically. The thermocouples were placed at 5, 10, 15, 20, 30, 50, 70 and 90 mm from the metal-mold interface. A numerical technique which compares theoretical and experimental thermal profiles was used to measure the heat transfer coefficient values. This has permitted the evaluation of the variation of this thermal parameter along the solidification which is represented by a power equation that shows the time dependence during the process given by hi = constant (t)-n, which represents the best fit between the experimental and calculated curves. The obtained results also include the variation of both primary and secondary dendritic arm spacings of alloy analyzed as a function of heat transfer coefficient. These dendrite arm spacings were found to decrease as the values of this coefficient are increased. Finally, an experimental law of the Hall-Petch type is proposed relating the resulting microhardness to the heat transfer coefficient investigated.
Authors: Martin Vlach, Ivana Stulikova, Bohumil Smola, Tomáš Kekule, Veronika Kodetova, Jaroslav Malek
Abstract: The effect of hot rolling on mechanical and electrical properties, microstructure and recrystallization behaviour of the AlMnScZr alloy was studied. The mould-cast alloy and the alloy after hot rolling at 300 °C was studied during step-by-step quasilinear annealing from 200 °C up to 600 °C with heating rate 100 K/h followed by subsequent isothermal annealing at 600 °C/5 h. Precipitation reactions were studied by electrical resistometry, differential scanning calorimetry and hardness measurements. Transmission electron microscopy and electron backscatter diffraction examination of specimens quenched from temperatures of significant resistivity changes were used to identify microstructural processes responsible for these changes. Only occasional irregular sharp-edged polygonal particles of the AlMnFeSi system were found in the as-prepared state of the mould-cast alloy. The as-prepared state of the hot-rolled alloy was characterized by a dispersion of fine coherent Al3Sc and/or Al3(Sc,Zr) particles and furthermore a fine (sub) grain structure was observed. The hardening effect in the alloys is due to presence and/or precipitation of the Sc,Zr-containing particles with L12 structure. The distinct resistivity changes of the alloys are mainly caused by precipitation of Mn-containing particles. Two-stage development of the Al6Mn phase (in (sub) grain interiors and at (sub) grain boundaries) in the hot-rolled alloy was observed. The presence of Sc,Zr-and Mn-containing particles has an anti-recrystallization effect that prevents recrystallization minimally up to 600 °C and annealing of 1 hour in the hot-rolled alloy. The apparent activation energy for the Al3(Sc,Zr)-phase and Al6Mn-phase precipitation was also determined. The activation energy values obtained in the hot-rolled AlMnScZr alloy are comparable to those observed in the hot deformed AlMnScZr alloys prepared by powder metallurgy.
Authors: Andrzej Golabczak, Andrzej Konstantynowicz, Marcin Golabczak
Abstract: In the paper a new method has been proposed for the determining of the very fine machining uniformity over the elaborated surface and could be applied to different machined materials and machining procedures. The proposed methodology is relatively simple and is essentially formulated in the few subsequent steps: taking surface roughness 3D profile accordingly proposed scheme; estimation of the roughness statistical parameters: Rp, Rv, Rt, Ra, Rq, Rskew, Rkurt, and if need be – surface rugosity Ru; calculation of the centroid of the obtained data due to the measurement fields, calculation of the barycentre of the obtained data with the weighting variable chosen for the appropriate evaluation of the surface machining uniformity. As the main Cartesian coordinates of the centroid calculation we propose (Rskew, Rkurt), although other data organization schemes have also been provided as the example solutions. The final evaluation of the surface machining uniformity is based upon the Euclidean distance between the centroid and barycentre of the surface roughness data. The proposed method has been applied to experimental results obtained with the AFM technique used on samples of the polished AZ31 magnesium alloy. The surface machining procedure comprised of four stages performed with using different abrasive media, finally lead to the highest grade of the surface roughness.
Authors: D. Saidi, M. Bouaziz, A.P. Babichev, M.A. Djema, K. Hamouda
Abstract: The present paper examines the influence of the tribofinishing process on the surface state of steel parts XC48, while taking into account the variation in hardness and mass. The tribofinishing process is a mechanical-chemical process, which comprises the use of low frequency impact vibration in the presence of abrasive and chemical additives [1]. The treatment regime (frequency and amplitude) has a great influence on geometrical, mechanical and metallographic treated surfaces. The improvement of the surface quality is determined as a function of the treatment time from 30 to 240 minutes. The tribofinishing process has many technical and economic advantages for the treatment of mechanical parts of simple and complex shapes, which have a better surface finish and improved life of parts etc.
Authors: Marcel Mandel, Wladimir Kietov, Lutz Krueger
Abstract: The corrosion behaviour of a high-alloy CrMnNi steel was investigated electrochemically in a 0.5 M sulphuric acid solution. The characteristic regions of the active, passive and transpassive state for the material were monitored by means of acoustic emissions. To this end, the steel was potentiostatically polarised and the acoustic emission signal was recorded on the specimen’s surface at a distance of 5 cm from the location of corrosion. Analysis of the acoustic emission signals revealed an increase in signal intensity due to hydrogen bubble formation when the material was cathodically polarised. Furthermore, for anodic polarisation, a continuous decline in the signal-time correlation occurred when the material was polarised in the active/passive state, whereas a sharp point of inflexion and drastic reduction in intensity was recognised when the material was polarised in the passive state. Moreover, a further increase in signal intensity was observed when the transpassive state was reached. The increase at transpassivity was related to the onset of oxygen bubble formation at the electrode.
Authors: N. López-Perrusquia, M.A. Doñu Ruiz, D. Sánchez Huerta, J. Noriega-Zenteno, J.V. Cortés-Suarez
Abstract: This paper studies the formation of iron boride on the surface in ductile iron 100-70-03 class exposed to a thermochemical treatment boron dehydrated paste. The formation of iron boride layers Fe2B/FeB-type were obtained at temperatures of 1173 K, 1223 K and 1273 K, with exposure times of 8 hours of treatment. The study consisted in evaluating the growth kinetics of the boride layer on the surface of ductile iron boriding. Also the boride layers were determined by the XRD method, EDS. Also evaluated fracture toughness technique Vickers microindentation 15 and 30 microns from the surface with different loadings of iron boride microindentation formed on the surface.
Authors: Solange T. Fonseca, Amilton Sinatora, Antonio J. Ramirez, Domingos J. Minicucci, Conrado R. Afonso, Paulo Roberto Mei
Abstract: To understand the effect of vanadium on the austenite decomposition of a 0.7 %C steel used in railway wheels the Continuous Cooling Transformation (CCT) diagrams were obtained and the microstructures analyzed with optical, SEM, TEM and XRD techniques. Vanadium refined the austenitic grain (12 and 6 μm for 7C and 7V, respectively), what can be explain by the presence of fine (10 nm in diameter) V4C3 precipitates, which restricts the austenitic grain growth. In addition, vanadium, in solid solution, reduced the pearlite interlamelar spacing (0.13 and 0.11 μm for 7C and 7V, respectively) by depressing the initial temperature pearlite formation (644 and 639 °C for 7C and 7V, respectively). He increased the ferrite volume fraction from 1 to 3 % at cooling rate of 1 oC/s, due the fact that vanadium is a ferrite stabilizer. Vanadium addition did not affect the initial temperature for martensite formation, but increased the hardenability with martensite formation at slower cooling rates (10 and 5 oC/s for 7C and 7V, respectively). For higher cooling rates (20 to 100 oC/s), the austenite transformation to martensite at room temperature was incomplete and all steels presented martensite and retained austenite, which volumetric fraction was near the same for both steels varying from 20 to 40 %.
Authors: P. González-Aguirre, Hervé Fontaine, C. Beitia, R. Pastorello, J. Ohlsen, J. Lundgren
Abstract: In order to better understand the sorption and outgassing mechanism of gases in relation to wafers containers (FOUP), we have measured HF gas transport coefficients for different FOUP polymers. Gas sorption is governed by surface adsorption, followed by diffusion and solubility. Cross contamination between FOUP and wafer occurs when polymers outgas contaminants into the surrounding environment. Diffusion is the key parameter to understanding cross contamination within the FOUP environment. In this work, we present the transport coefficients obtained for gaseous HF at cleanroom conditions (Patm, 21 ± 2°C & 40% RH) using the sorption kinetic method, based on Fick’s law, for thin films (<80μm) of polycarbonate (PC), polyetherimide (PEI) and a low absorbing polymer named Entegris Barrier Material (EBM) that constitute FOUPs. The resulting kinetic curves show Fick’s behavior, where obtained HF diffusion coefficients are between 3.7 X10-10 and 42 x10-12 cm2/s and are significantly lower than diffusion coefficients obtained for H2O using a gas permeation method. Nevertheless, the similar order of magnitude between the HF and the H2O permeability coefficients obtained by the two methods validates the sorption kinetic method. Finally, the obtained coefficients were used in numerical simulation in order to forecast polymer behavior.
Authors: Shelley Lorimer, Ryan Boehnke, Brigida Meza
Abstract: The mechanisms of mass transfer in thermal solvent enhanced oil recovery processes and the influence of grid size in the numerical simulation of these processes is not well understood [1, 2]. The literature has indicated that, experimentally, solvent fronts progress more rapidly that what can be predicted using current approximations [3]. It has also been shown that under certain modelling conditions with coarser grid meshes, the influence of numerical errors can be substantial. The equations that govern thermal/solvent multiphase flow through porous media are extremely complex and it is very difficult to decouple the contribution of the mass transfer mechanisms from the thermal effects. This paper was written to increase the understanding of the mass transfer mechanisms in hybrid thermal solvent recovery processes through sensitivity study using a numerical solution of the linear one dimensional advection diffusion/dispersion (ADD) equation. This equation was modeled using finite difference methods. The effects of grid size were examined to verify the use of this method, and the results were then used to examine the sensitivity of the equation to the parameters that govern the mass transfer mechanisms (advection velocity, diffusion and dispersion coefficients).In particular, a range of values for diffusion and dispersion coefficients were selected for the sensitivity study, and one advection velocity. These values were then used to numerically solve the ADD equation to assess the impact of each mechanism (advection, diffusion and dispersion) and their contribution to the movement of the solvent front. The parameters chosen for this study were based on values obtained from the literature for advection velocity, diffusion and dispersion coefficients consistent with a gravity drainage thermal/solvent oil recovery process. This sensitivity study has indicated that all three mechanisms (advection, diffusion and dispersion) must be included to have the solvent front progress at rates that are consistent with experimental solvent front advance rates published in the literature to date [1]. This result suggests that diffusion alone cannot account for the movement of the solvent front within the ranges of values that have been studied.

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