Defect and Diffusion Forum Vol. 322

Abstract: During processing or use, duplex stainless steels are subject to a great number of significant phase transformations, such as solidification, partial ferrite transformation to austenite, ferrite eutectoid decomposition to sigma phase plus austenite, chi phase precipitation, chromium carbide precipitation, chromium nitride precipitation, ferrite spinodal decomposition, phase dissolution during solution annealing, forming of two types (epsilon and alpha prime) of strain induced martensite, martensite reversion to austenite, ferrite and austenite recrystallization. This paper summarizes the phase transformations that occur (individually or combined) in duplex stainless steels and presents some new results.

Abstract: Hydrogen and iron diffusion coefficients in molten zirconium have been calculated using a molecular dynamics (МD) model. The molecular dynamics method using micro-canonical (NVT) ensemble was used to analyze iron and zirconium diffusion coefficient dependence on electric field intensity and the presence of hydrogen in the zirconium melt. Results obtained are compared to the literature data on impurity removal in plasma-arc zirconium melting in the presence of hydrogen as well as in electron-beam and vacuum-arc melting. The limiting stage of iron removal from the melt is established. The contribution of the electric field to iron removal is estimated. We carried out systematization of the D_H^Me data for Zr, Nb, and Ta. An Arrhenius equation analysis for D_H^Me and its extrapolation to the premelting zone taking into account the Gorsky effect was carried out too. The analysis enabled the estimation of D_H^Me for the temperature interval where experiment encounters difficulties.

Abstract: Pure titanium and aluminum sheets were used to prepare titanium-aluminum diffusion couples. The diffusion couples were heated to temperatures 550, 575, 600, 625, 640, 650 and 700°C. SEM observations of the titanium-aluminum interface and EPMA results revealed that a TiAl₃ intermetallic layer has formed and thickened between the layers. Grain boundaries of the TiAl₃ compound, which were revealed by back-scattered electron imaging, indicated a size distribution across the layer. Finer grains which were located close to the titanium showed that TiAl₃ has nucleated at the Ti-TiAl₃ interface. Thus, the former grains which had formed close to the aluminum-rich side have grown and coarsened during annealing at high temperatures. Grain coarsening of TiAl₃ decreased the kinetics of the layer thickening.

Abstract: Packed beds composed of spherical balls are used for the study of transfer processes in porous media at turbulent filtration. The paper summarizes the development of a physical modelling of transfer processes in packed beds. It is shown that the available quantitative measurements of structural characteristics of infiltrated flow in packed beds such as the near-wall zone velocity and temperature profiles and velocity pulsation spectra follow the similarity laws of turbulent separated flows that have been developed by the author and are represented in the first part of the paper. These facts supported by visual observations of flow patterns in packed beds from various authors allow implementing the analogy between transfer processes mechanism in turbulent separated flows and convective transfer processes in near-wall zone of surfaces embedded in grainy layers, or ducts filled with packed bed, at high Reynolds numbers. This approach has resulted in the asymptotic heat and mass transfer law. The universal character of the heat and mass transfer law for the surfaces embedded in grainy layer is confirmed by the authors data and data from many other studies.