Defect and Diffusion Forum Vols. 297-301

Abstract: Fabrication of alloys in the solid state via mechanical alloying (MA) process has been studied by earlier researchers. The effects of milling time and impact force, defined as the ball-to-powder weight ratio (BPR), on the elemental diffusion during synthesis of nanostructured Fe-50at.%Cu alloy via MA process were evaluated in the current work. X-ray diffraction patterns revealed that increasing the milling time and impact force give rise to increasing the micro-strain, lattice parameter and decreasing the crystallite size during the MA process. Furthermore, scanning electron microscopy (SEM) was utilized not only for evaluating the microstructure of the milled powder particles but also for proving this claim that during MA process, the mutual diffusion of Cu and Fe has occurred. The interpretation of data resulted have been discussed in details.

Abstract: Evidence for solid-state diffusion (the second half of the 19th century). The first measurements of solid state diffusion (W. Roberts-Austen, 1896–1922). The first tracer experiments to determine the solid-state diffusion (G. von Hevesy, 1913–1923). The first evidence of accelerated diffusion in polycrystalline materials (1924–1935). Autoradiographic studies of grain boundary diffusion (50s of 20th century). The first quantitative experimental and theoretical studies of the “short circuiting” diffusion (beginning from 1949, D. Turnbull and R. Hoffman – General Electric Research Lab.): radiotracer serial sectioning method, the Fisher model (1951) for grain boundary diffusion, exact solutions and developments of the Fisher model (1954–1963). The progress in the experimental methods for determination of grain boundary diffusion data and results of measurements for different metallic systems (up to date). The measurements of grain boundary diffusion parameters in the B and C regimes. Grain boundary diffusion and grain boundary segregation. Nonlinear segregation effects. Structural effects of grain boundary diffusion. Diffusion in bicrystals. Diffusion in nanocrystals. Computer simulation of grain boundary diffusion. Mechanisms of grain boundary diffusion.

Abstract: Some physicochemical and mechanical properties of surface hard coatings obtained by the paste-boriding process are summarized in this work. Different grades of borided ferrous alloys were used to develop the formation of surface layers type Fe2B or FeB/Fe2B. Furthermore, in order to characterize the nature of boride layers, some classical techniques are presented and discussed such as Glow Discharge Optical Emission Spectrometry (GDOES), Atomic Force Microscopy (AFM) and estimation of residual stresses by X-Ray Diffraction method. Also, the morphology of borided interfaces was evaluated by concepts of fractal theory.

Abstract: A mathematical model for the forecasting of the basic metallurgical properties of coke depending on the quality indicators of coals and carbonization parameters is developed. The base of the model are the theoretical and statistical dependences of the physico-chemical and petrographic properties of initial coals on the reactivity and mechanical strength of the coke. These indicators depend on diffusion processes during carbonization. On the basis of initial data, the material and heat balance of the coking process are made and the product price is calculated. The full-function program includes: the initial database interactively formed on the basis of the coals quality certificates and concentrates; the calculating unit of forecasting of the coke properties, allowing to fulfil the mathematical model adapting for the concrete industrial conditions of carbonization process; the unit to calculate results. The calculated values, i.e. the Coke Reactivity Index (CRI) and the Coke Strength after Reaction (CSR) can be used further for technical and economical calculations in the balance logic-statistic model of the blast furnace smelting operation. Or using the feedback, it is possible to calculate necessary relations of the burden components for the carbonization.

Abstract: For the agglomerates of the Kachkanar deposit iron ore the role of elements with ionic radius larger than for magnesium and calcium in the formation of the strength characteristics and parameters of the viscous-plastic state of iron-ore materials is shown. The strength characteristics of high-quality sinters are largely defined by the low stressed state of a silicate bundle which is formed in the cake cooling-down period. The diffusion processes at the glasses recrystallization at the cakes refrigeration can be reduced by injection of the elements impeding these processes and having low -strength cation-oxygen connections, that, apparently, should ¬ hinder in formation of the crystals with their participation. From these positions the stabilizing additions are the cations of heavy elements having major radius and remote from the valence electrons¬. It according to the theory of the stressed state of the oxide ¬ systems is accompanied by the grain refinement, decrease of the microstresses ¬ and fissurings of the glass matrix and therefore the defectiveness of cake structure. On the basis of the mathematical model leaning on the results of the dilatometric explorations the positive influence of the microadditives of the barium oxide on increase of temperature of beginning and narrowing of the softening range of sinters is revealed.

Abstract: Isotope exchange of oxygen 18О2 with the boundary of nanograins of oxide LaMnO3+ obtained by the method of shock-wave loading was investigated in the temperature range of 400 – 500 °C. It was established that the temperature dependence of the isotope exchange rate is described by the Arrhenius expression, the activation energy and the pre-exponential factor being 1.67 eV and 1.8∙102 cm/s, respectively. Comparison with literature data has shown that for oxide LaMnO3+, a significant difference in activation energies and pre-exponential factors is observed for the isotope exchange rate with a ‘defect-free’ surface and the nanograin boundary. In case of the boundary, these parameters were higher: the activation energy about two times, and the pre-exponential factor, by almost 7 orders of magnitude.

Abstract: An investigation has been undertaken of the structural characteristics of the manganese oxides to understand these characteristics affected by mechanochemical treatment conditions. Chemically pure manganese (II, III) oxides and their mixtures were used as the initial components.

Abstract: Evolution of structure of high-purity and commercially pure copper at severe plastic deformation (SPD) by high pressure torsion (HPT) at room temperature and in liquid nitrogen has been studied by transmission electron microscopy (TEM) and measurements of microhardness. Thermal stability of structure obtained by HPT has been investigated. Factors preventing from obtaining nanocrystalline structure in Cu are analyzed and possible ways of their overcoming are discussed.

Abstract: Diffusion in L12-Ni3Al with ternary alloying additions of Ir, Ta and Re was investigated at 1200°C using solid-to-solid diffusion couples, and examined with respect to site preference in ordered intermetallic compound. In addition to determination of average ternary interdiffusion coefficients [1-3], average effective interdiffusion coefficients were determined directly from the experimental concentration profiles. Ni has the largest magnitude of average effective interdiffusion coefficient, followed by Al, Ir, Re and Ta. The average effective interdiffusion coefficients for Ir, Re and Ta are much smaller than those for Ni and Al. Tracer diffusion coefficients determined by extrapolation technique, and available literature also followed the same trend. The relative tendency of Ni, Al, Ir, Re and Ta to occupy the -Ni and -Al sites are correlated to these diffusion coefficients, with due consideration for diffusion mechanisms and coordination of atoms.

Abstract: We developed a method of rigorous solution of the Onsager’s flow equations using moments of the interdiffusion-parameter integrands for the determination of average ternary interdiffusion coefficients. The analysis developed by Dayananda and Sohn [1] is the basis for this refined approach. Average main and cross interdiffusion coefficients are determined over selected regions in the diffusion zone using the diffusion-distance moments of the interdiffusion flux flow equations. Thermodynamic stability of solid solutions in the light of interdiffusion phenomenon is taken as validation criteria to identify accurate and reliable values of the ternary interdiffusion coefficients. Regulations are proposed for successful application of the analysis method to various ternary diffusion couples in Ni- and Fe-based intermetallics.