Defect and Diffusion Forum Vols. 258-260

Abstract: The composition and microstructure of historic tongues and shallots from reed pipes of various Baroque organs have been studied. They contain Cu–Zn solid solution (α-brass with 23-29 wt. % Zn) and lead particles. Grain size in brass scatters from 10 to 200 μm. Around 50% of all GBs in brass are Σ=3 twin GBs. The high-indexed coincidence site lattice facets were observed in twin GBs. The increase of number of various facets roughly correlates with decreasing grain size. It may indicate the variation in annealing temperature used by organbuilders in Baroque Era. New brass with 25 wt. % Zn and 2 wt. % Pb has been prepared for reconstruction of historic tongues and shallots by restoration of reed pipes in Baroque organs. The morphology of lead inclusions and twin GBs has been investigated in temperature interval from 400 to 700°C and compared with that of historic alloys. The annealing temperature has been estimated.

Abstract: The main objective of this research is to develop a three-group neutron Albedo algorithm considering the up-scattering of neutrons in order to analyze the diffusion phenomenon in nonmultiplying media. The neutron Albedo method is an analytical method that does not try to solve explicit describing equations for the neutron fluxes [1,2]. Thus the neutron Albedo methodology is very different from the conventional methodology, as the neutron diffusion theory model. Graphite is analyzed as a model case. One major application is in the determination of the nonleakage probabilities with more understandable results in physical terms than conventional radiation transport method calculations.

Abstract: Orientational patterns of wetted grain boundaries (GB's) in stressed NaCl polycrystals have been used for describing the GB penetration process on the basis of combined interfacial and mechanical energy balance considerations. The response of the internally wetted polycrystals to static loading has been shown to obey “pressure solution” constitutive laws involving dissolution at stressed surfaces, diffusive transport of dissolved matter and precipitation at less stressed surfaces. Direct experimental evidence for pressure solution mechanism is presented.

Abstract: A significant increase in durability of cryogenically treated tools after quenching was reported by a number of publications [1, 2]. As research studies show [4, 5, 6, 7], the main reason for this is the kind of carbides precipitated during tempering at temperature range of 150 –200 0C, which is different than in the case of conventional treatment. These carbides are finer and more evenly distributed in the matrix of steel. The number of carbides is higher than in conventionally treated steels because of higher fraction of martensite in cryogenically treated steels produced by retained austenite transformation at cooling to deep cryogenic temperatures. The number of carbides precipitated from martensite at low temperatures of tempering is proportional to shrinkage produced at the same temperatures of tempering. Calculations on the basis of dilatometric experiments show that the shrinkage difference between the same D2 steel cryogenically and conventionally treated is higher than that which results from the increased fraction of martensite in cryogenically treated steel. The XRD studies of cryogenically treated steel show a presence of two kinds of martensites differing in tetragonality. Low temperature tempering of cryogenically treated steel produced two types of carbides – ε carbide and η carbide. The conventionally treated steel consists of one kind of tetragonal martensite and one kind of carbide - the ε carbide. The hardness of cryogenically treated samples was somewhat higher than in conventionally treated ones, while fracture toughness of conventionally treated samples was somewhat higher than in cryogenically treated ones. The results obtained were discussed in reference to literature data.

Abstract: The paper presents the influence of the grain size and a little higher Cr content on the kinetics of austenite phase transformations during continuous cooling of hypo-eutectoid steel. The kinetics of austenite phase transformations during continuous cooling were determined by means of analysis of the dilatometric curves and structure investigations. The influence of the austenite grain size and the higher Cr content was analysed in two hypoeutectoid steels containing about 0.4% C. One of them had, Cr content higher, by about 1%. In both steels, the austenite grain size was changing insignificantly up to the austenitising temperature of about 950fl. Above that temperature, the austenite grain size in carbon steel grew much quicker than that in the steel with Cr addition. The austenite grain in the Cr enriched steel was smaller than that in carbon steel and, in spite of that, the duration of cooled austenite transformations were several times longer. This means that the phase transformations are much more strongly influenced by the addition of chromium slowing down carbon diffusion in austenite, than by the austenite grain size. For each phase transformation in the examined steels, the activation energy of the transformation has been determined. The activation energy of all the phase transformations varied slightly with the increase of austenitising temperature. On the basis of the obtained results, curves of true isothermal transformations have been developed for the beginning of the phase transformations in both steels, related to infinitely quick cooling down to the transformation temperature.

Abstract: Grain boundary surface tension and surface tension of free surface for pure copper and copper-tin alloys are measured. On the base of these data isothermes of grain boundary tension, free surface tension and isothermes of adsorption are constructed in assumption of a dilute solution.

Abstract: The purpose of the present work is to investigate the mutual interaction between the melted metal and oxide phases with a small amount of sulfur. In this research, the following phases took part: metallic phase of Fe – C – S and slag CaO–Al2O3 –MgO–S. The mathematical model of sulfur diffusion in the metal and oxide is employed. The experiment was carried out at the temperature of 1773K. The result of the calculation is in qualitative agreement with the experiment. The proposed approach can be applied to the investigations of diffusion processes in molten metal and slag phases.

Abstract: The relationships between polymer structure and water diffusivity have been investigated in four structural series: amine-epoxyde networks (A), aromatic polysulfones (B), styrene crosslinked polyesters or vinylesters (C) and polyethylenes containing polar groups (D). In each family, it appears water diffusivity is almost inversely proportional to equilibrium water concentration. This result indicates that water diffusion is considerably slowed down by its interactions with polar sites in the polymer.

Abstract: When moisture uptake in a polymer is associated with swelling, it induces stresses which interact with the entire diffusion process. This coupling is addressed in this paper, which extends immediately to the diffusion of other fluids, like solvents. First, the generalized chemical potential is used to analyze the effect of stresses on the moisture capacity of polymers, and a relation is derived as a function of material parameters. Then, the interactions between stress and diffusion before saturation is reached, are explored. Various effects are predicted on the classical sorption test, such as an evolution of the boundary condition with time, and a sorptiondesorption hysteresis.

Abstract: Water diffusion in polymers can often be approximated by a Fickian description, but a 2- phase model was proposed some years ago by Carter and Kibler (C&K), often referred to as “Langmuirtype” diffusion, by analogy with the Langmuir theory of adsorption. The two phases in question correspond to “mobile” and “bound” diffusant molecules. In this study, we have considered water uptake in an epoxy resin (an adhesive), employing gravimetry. A good, overall, empirical agreement with the C&K mathematical description of total mass increase with time has been obtained. In many applications of the C&K theory when used to quantify diffusion of water in polymers, only total water uptake is considered as a datum. However, a simple mathematical treatment of the theory enables the separate mobile and bound contributions to be isolated. These supplementary data have been used to try to get a better understanding of the meaning of the terms “mobile” and “bound” phases. Deuterium NMR analysis has been employed to study the mobility of the absorbed water. Decomposition of spectra has permitted us to assign two signals to the fractions of “mobile” and “bound” water. Analysis of peak evolution and a comparison with gravimetric data lead us to suggest that the “mobile” phase corresponds to diffusing molecules, whereas the “bound” phase corresponds to “clusters”.