Defect and Diffusion Forum Vols. 273-276

Abstract: This paper discusses the effect of the main parameters that affect the desulphurization reaction efficiency. The study was conducted by evaluating different reaction sites within the metal, the slag and the reducing agents. It was possible to establish a mass transfer model that determines the amounts of the reducing agents needed to maintain adequate sulphur levels in the pig iron. Industrial trials showed the accuracy of our model.

Abstract: In this work a kinetic model which describes the main refining reactions in a ladle furnace is depicted. The main difference between this work and other models previously reported relies on a formal quantification of the multi-component diffusion kinetics expressed as an analytical solution. Results from this model reproduce/predict adequately the chemical steps involved in an integrated steel shop.

Abstract: Hydrogen embrittlement is a common problem for the integrity of oil conducting pipes. In this work, we estimate the rate of hydrogen penetration into an API 5L steel pipe welded by electric arc. The hydrogen penetration was estimated by means of data taken from ultrasonic measurements. As expected, the steel pipe becomes more brittle as the hydrogen penetration rate does so. A simple diffusion model was developed. The model confirms the strong dependency between the rate of penetration and the mechanical damage to the material.

Abstract: The results of NGR studies of grain boundaries in nanocrystalline metals are briefly reviewed and analyzed together with the data of ordinary diffusion experiments. Grain boundaries in materials obtained both by powder technologies and severe plastic deformation (SPD) are considered. Possible factors causing accelerated mass transfer in every case are analyzed with the account taken of specific features of the structure of these materials.

Abstract: Kinetics of formation of superconducting Nb3Sn layers and the structure of bronzeprocessed Nb/Cu-Sn composites with Zr, Zn or Mg-doped matrixes or Ti-doped Nb filaments of different geometry have been studied by the methods of TEM, SEM and electron-probe microanalysis. All the doping elements have been found to accelerate the rate of growth of the diffusion Nb3Sn layers and consequently their thickness. Correlation between the diffusion annealing schedules, the geometry of Nb filaments, the structure of the diffusion Nb3Sn layers and the current-carrying characteristics of multifilamentary Nb/Cu-Sn composites has been established.

Abstract: Relaxation of diffuse-scattering intensities of various kinds of waves is a phenomenon of an especial interest since its study enables one to obtain the most detailed information on both the equilibrium short-range order (SRO) and the non-equilibrium SRO, and therefore, it is the most convenient instrument for investigating SRO kinetics. The SRO kinetics is studied by the use of available data of measurements of residual electrical resistivity for substitutional f.c.c.-Ni–Al solid solutions during their isothermal annealing. Within the framework of the first-order and (more realistic) second-order kinetics models, the maximum characteristic relaxation times and equilibrium magnitudes of the residual electrical resistivity for these solid solutions at different annealing (1273–1626 K) and quenching temperatures (≥ 1723 K) are evaluated, and the hypothetical values of similar quantities appropriate for the diffuse scattering of radiations are estimated too.

Abstract: Using the static concentration waves’ method and self-consistent-field approximation, the Onsager-type kinetics equation is solved to describe the L12-type long-range order (LRO) relaxation. To calculate the diffusivities for Permalloy, the experimental diffraction data in respect to LRO-parameter evolution for Ni3Fe are used. Theoretical curves of a time-dependent LRO for Ni– Fe are plotted. Dilution of alloying element (with a deviation from stoichiometry) results in deceleration of the LRO-parameter history (at the initial evolution stage) and in an increase of its relaxation time. Both statistical-thermodynamics and kinetics results show: at high temperatures, equilibrium LRO parameter for non-stoichiometric Permalloys can be higher than for stoichiometric one.

Abstract: Surface alloying is a new method of surface treatment by which an element is diffused into the surface of another element causing the formation of a solid solution on its surface. Using this method, the problems of casting methods have been eliminated. In this method, the sample is sunk into an aqueous solution and is connected to the cathode. Applying enough voltage, lithium separated from lithium sulphat-sulfuric acid solution diffuses into the aluminum surface. The depth of diffusion into the aluminum is measured to be 50 to 500μm according to the diffusion time which is selected to be 1 to 24 hours. Experiments showed that the formed layer is very uniform. It was also concluded from the experiments that hardness is increased extensively, with the maximum value of 98HV, and fatigue life is increased by the factor 4. It was also shown that the toughness, yield stress and ultimate tensile strength of samples are the same as those of pure aluminum.

Abstract: Aluminum-Lithium alloys were developed as major replacements for existing aluminum alloys to reduce the weight of aircraft and aerospace structures. Mechanical properties of Al-Li alloys greatly depend on solidification conditions. Other than reducing the microsegregation, homogenization treatment has other effects on the microstructure of Al-Li ingots. In this research, effects of homogenization treatment at constant temperature (500°C) on the precipitation in the microstructure of Al-1Li-3Cu-0.1Zr (wt %) and Al-2Li-3Cu- 0.1Zr (wt %) specimens have been investigated. Results show that homogenization at 500°C for 24 hours not only increases the hardness and phases precipitating in grain but also reduces microsegregation of Fe in grain boundaries.

Abstract: The formation of in-situ spinel in Al2O3-MgO-C refractories along with different antioxidants occurs at different atmospheres in surface and inner of refractories. Then the types and microstructures of established phases have become increasingly important in these refractories. In the present work, reactions on firing Al2O3-MgO samples with added graphite, Al, Si and SiC in air or coke bed atmosphere at 1300°C and 1600°C have been studied. The results showed that with the addition of graphite and Al especially at 1600°C in coke bed, high alumina-rich spinel (Mg0.866Al1.83O3.611) was increased and in the microstructure were appeared high amount porosity. In silicon and silicon carbide additive samples after firing at 1600°C in coke bed, sapphirine phase were revealed.