Defect and Diffusion Forum Vols. 326-328

Abstract: The paper presents results of research on nitrided layers on Sandvik Nanoflex^TM precipitation hardened stainless steel. The influence of process parameters on nitriding kinetics and structure of the layers was investigated. The gas nitriding process was conducted in a mixture of ammonia 50% and products of its dissociation, as well as in 100% ammonia atmosphere at temperature range 400500°C and time between 2 and 8 h. The obtained diffusion layers were examined using the following methods: light and scanning electron microscopy, XRD phase analysis and EDS chemical analysis. Mechanical properties were tested with hardness measurements. It was found that kinetics depends on treatment temperature and nitrogen potential of the atmosphere. Moreover, treatment conditions affecting Sphase formation and expanded martensite in nitrided layers are discussed.

Abstract: This paper presents results of investigations on gas nitride layers of stainless steel. Steel with ferritic structure, containing different chromium and nickel content was used in the experiments in order to compare the influence of these two main alloying elements on layer growth kinetics and layer structure. Particular attention was paid to formation of Sphase and expanded martensite which usually are formed during lowtemperature nitriding of stainless steel. It was observed, that chromium and nickel content does not have a significant influence on layer growth kinetics but the treatment temperature does. It was also stated that Sphase formation is possible both in nickel alloyed and nickelfree steel depending on treatment parameters.

Abstract: Magnetic annealing at 17T, 800°C, for 15 minutes was conducted to evaluate the effect of the field on the recrystallized microstructure of Fe-3.25%Si samples. According to X-ray results, the main texture components were found not to be affected by the field. The volume fraction of eta fiber was slightly increased and the gamma fiber, an unfavorable texture component for materials with magnetic application, was not decreased when compared to samples annealed without magnetic field.

Abstract: The effect of pore geometry on the axial thermal dispersion conductivity for high-conductivity porous media under general thermal non-equilibrium conditions is studied numerically. Pore geometries including arrays of inline square and circular cylinders, staggered circular cylinders, and a three-dimensional idealization of a graphite foam pore geometry are used to study the effects of the solid constituent shape and arrangement, as well as the effect of a relatively complex three-dimensional pore structure. Results indicate that in general, the dispersion conductivity cannot be considered a simple function of the Péclet number due to the effects of inertia, which cause the dispersion behaviour to depend on both the Reynolds and Prandtl numbers. On the basis of the current results, it is recommended that the influences of the Reynolds and Prandtl numbers be considered separately when generating models for the dispersion conductivity.

Abstract: We discuss the numerical modelling of unsaturated flow in porous media with contaminant transport, dispersion and adsorption. The mathematical model for unsaturated flow is based on Richard's nonlinear and degenerate equation. The model of contaminant transport is based on Darcy's law and mass balance equation. We present the operator splitting method for this problem. In nature all of the physical processes are realized simultaneously and the time scale for adsorption differs from diffusion and convection significantly. In our numerical approximation we consider three sub-problems - first one is the problem of unsaturated flow, second one the problem of transport and dispersion and third one the adsorption problem. Our numerical solution is based on implicit time discretization and space discretization. To achieve more correct numerical approximation we treat each of the sub-problems with another time scale and the data computed from one sub-problem, is the input data for the next sub-problem in each time interval. The convergence to the weak solution of the original problem is also discussed. Finally we show a couple of practical applications of the method and numerical experiments for direct problems.

Abstract: nfrared thermography is being used to identify defects maps of the building envelope, based on the most suitable local thermal parameter. In spite of the fact that the TOBUS method [1] and the multivariate design method [2] consider several complicated building renovations, their applications on energy performance improvement are mainly inadequate [3]. In this research, the developed experimental and theoretical studies show, on the one hand, the thermal characterization (temperature distribution, heat losses and efficiency) of a full-scale building envelope. On the other hand, the applicability and accuracy of this optic technique for the thermal characterization of the building zone with complex geometry is discussed in order to validate results obtained for the thermal characterization.

Abstract: In the field of laser cutting, the research area is oriented mainly to understanding of the mechanism of removal, as well as to the combination of factors entering the process. This process of disintegration of materials presents a problem of analytical approximation, elaboration, and description [1 - . Compared with previous approach to a solution, we have chosen our own way and we focus on mechanical respectively stress-strain parameters of the material being cut and the mechanical balance system: material properties tool properties deformation properties. We shall present here the basic forms of prediction equations for calculating the roughness of cutting walls, as well as other equations which were derived by modifying the basic equations for different application purposes, especially to calculate the optimum traverse speed v_popt, optimal laser performance W_lasopt and technologically important ratio IND_vpwopt = v_popt/W_lasopt. These contain easily available input variables for substitution. The basic forms, including the modified forms are aimed at predicting the quality of cut with its depth limits. The paper presents the method of optimization of the ratio between the traverse speed v_p and laser power W_las which minimizes the final surface roughness after cutting with a direct impact on corrosion resistance of materials.

Abstract: Pollutants can be classified according to their chemical composition, harmfulness, hazardousness, risk rate and toxicity. The most monitored pollutants are particulate matter (PM), carbon monoxide (CO), nitrogen oxide (NOx), sulfur dioxide (SO₂), organic substances which are in the form of gaseous phase in waste gases expressed as total organic carbon, dibenzodioxins and dibenzofurans [1-3]. Other pollutants are divided into several groups and subgroups, such as substances with carcinogenic effects (asbestos, Co, Cd, Be, Ni, As, Cr, dioxins, etc.), solid inorganic contaminants (He, Se, animony, and others) and inorganic pollutants in the form of gases (HCl, HF, ammonia, etc.), organic gases and vapours (phenol, toluene, acetone and many others) and gases causing the greenhouse effect (CO₂, methane, N₂O, hydrofluorocarbons, etc.). The term particulate matter, or suspended matter refers to the emissions of a wide range of wind drift solids and liquid particles of material in size from several nanometres up to 0.5 mm, which stay in the air for some time. This is a major component of atmospheric pollution, which contributes to harmful effects not only on human health but also on intensity of materials degradation. Into the atmosphere, where we can meet them, regardless of particle size and chemical composition, in the form of a complex heterogeneous mixture, they are released from burning fossil fuels and also from burning biomass-based fuels, while domestic heating accounts for about 16% of the total production of particulate matter [4,5,6]. This percentage represents a degree of imperfect combustion of fuels used in local heating. Emissions from incomplete combustion are undesirable from the point of view of human health as well as from the economic point of view, because this leads to the degradation of materials. Nevertheless, since fuel combustion is necessary for the society, emissions are still produced. This paper presents an automated method of perfect combustion control in local heating in order to minimize emissions being produced.

Abstract: In this research, post-weld heat treatment (PWHT) of dissimilar API 5CT C90 and ASTM A182 F22 welded pipe was carried out at temperatures of 500, 600, 700 and 800°C. The effects of PWHT on the microstructure and mechanical properties of the weldment were investigated. The mechanical tests and microstructure examinations were focused on the fusion line area of API 5CT C90 as this area is the most crucial part of the weldment. The main objective of this research is to assess the microstructure and mechanical properties of the dissimilar weldment. The results were then compared with NACE MR0175/ISO15156 code which requires hardness values below 275 Hv10 at a cap, below 250 Hv10 at a root and an average value 42 Joules at-20°C for charpy impact test [. The experimental results show that PWHT reduces the hardness value and increase the toughness of the weldment. Meanwhile, the optical microscopic examination shows that the higher the PWHT temperature, the coarser the grain size. The results showed that the 800°C PWHT specimen complied with the code.

Abstract: Heat transfer phenomena are numerically studied with standing waves inside the tubes for stationary and moving sinusoidal wavy walls. Effects of spatial wavelengths (= 1/2, 2/3, 1 and 2 mm), Reynolds number (1-120), frequency (0-60 Hz) and amplitude (1%-20% of tube diameter, d) on heat transfer and pressure drop are studied. For stationary wall case, upon increasing the number of sine waves, the Nusselt number starts to decrease; the associated pressure drop and friction factor increases very rapidly at highest value of amplitude. Heat transfer enhancement characteristics on a moving sinusoidal wavy-walled tube with imposed frequency (0