Defect and Diffusion Forum Vols. 297-301

Abstract: Besides primary carbides, so-called secondary carbides are usually observed in high-speed steel (HSS) microstructure, which precipitate from the oversaturated solid solution upon its cooling. Some of the secondary carbides precipitate from an oversaturated austenite at cooling during solidification or quenching, in both cases, in the form of the relatively big particles in the bulk of a matrix. Considerably finer secondary carbides precipitate in martensitic condition during tempering inducing secondary hardening in HSSs. In general, secondary carbides of both types have obvious effect on the fracture mode of HSSs. The precipitation of secondary carbides in HSSs in solidified and heat-treated conditions has been investigated. The microstructures of HSSs have been examined using light and electron microscopy (both scanning and transmission), X-ray diffraction analysis, and energy dispersive X-ray spectrometry. Results indicate that diffusion of both carbon and alloying elements plays an important role in the secondary carbide precipitation in HSSs.

Abstract: The olive crop has a great importance in the economy of Spain. Every year during the pruning of the olive trees a significant quantity of leaves are cut and discarded. It is known that these leaves constitute a source of antioxidant compounds and its processing would provide an added value to this raw material. Antioxidant compounds may be damaged when drying, the previous process to extraction. Thus, the goal of this work was to study the influence of the high intensity ultrasound applied during the drying of olive leaves on the kinetic of extraction of antioxidants compounds. From the parameters identified from Naik model, it can be concluded that the application of high intensity ultrasound during drying reduced the antioxidant activity of extracts at the equilibrium but increased the initial extraction kinetic compared to conventional hot air drying. This last aspect could have high interest to the antioxidant extraction from an industrial scale point of view.

Abstract: The large amount of materials derived from olive trees pruning may constitute a source of compounds with antioxidant activity. The air drying of raw matter is a previous stage before extraction preserving the raw matter and avoiding the interference of water on the process but it constitutes a slow and high energy demanding process. In this sense, the application of high intensity ultrasound could affect the mass transfer rate. In order to address the influence of ultrasound on the drying process of olive leaves, air drying experiments were carried out (40°C and1 m/s) without (0 W) and with ultrasound application (8, 16, 25 and 33 kW/m3). The different drying conditions were tested by triplicate. To model the experimental data, diffusional models considering or not the external resistance to mass transfer were used. The model without considering external resistance did not fit well to the experimental data. However, the model including external resistance achieved percentages of explained variance above 99.7%. The influence of ultrasound on diffusivity was not significant but a significant dependence was found for the mass transfer coefficient, proportional to the power density applied.

Abstract: The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. The hydrogen diffusion coefficient during hydrogen permeation is estimated from a linear relationship between the normalized hydrogen flux, , and the difference of hydrogen concentration, C, between the inlet and the outlet sides of the membrane. It is found that the hydrogen diffusion coefficient during the hydrogen permeation is increased by alloying ruthenium or tungsten into niobium. On the other hand, the activation energy for hydrogen diffusion in pure niobium under the practical permeation condition is much higher than the reported values measured for dilute hydrogen solid solutions. It is interesting that the activation energy for hydrogen diffusion decreases by the addition of ruthenium or tungsten into niobium.

Abstract: This paper aimed to develop a system of an automated biogas burner which records the amount of biogas burnt by a biogas low flow system. The biogas produced in miniSST (mini station of sewage treatment), biodigestors on a rural and residential, where there is a low production of biogas doesn`t economically justify its energy, it is only a case of an anaerobic waste treatment. The registration system of burnt biogas correctly calibrated may be homologated to obtain carbon credits. In these systems, of anaerobic waste treatment, due to the low flow of biogas discharged into the atmosphere includes methane it has a destructive potential 21 times greater than the CO2.The system developed was analyzed and the effects of the disposed gas produced by the burner converting it in CO2 proved to show less environmental impact. The automated system used in the small sewage treatment plants was almost insignificant when analyzed separately but when taken into consideration several systems working together there was a considerable positive environmental impact.

Abstract: The general purpose of the present work is based on an antifriction process to produce a metallurgical powder from nibs of iron powders base. Therefore, most of these processes used in motors and instruments industries, vehicles and agricultural mechanical engineering. Under normal operation conditions, which have stable climatic characteristics and exhibit to moisture, this increased the layer that exposed to corrosion. Metallurgical powder adsorbed moisture by determining the porosity which accelerates corrosion processes and increases at the free surface of metal, In this article, the results given for the materials of powders with bases on iron, zinc, aluminium and their alloys, in the same processes can be using it in the maintenance field to eliminate or modifying the surface of the work pieces treated which that increases the hardness.

Abstract: In this paper, a modified up-quenching heat treatment method to the ASSAB 705M steel (ultra high strength steel) is proposed. A low alloy steel (0.33%C), was used to study the effect of isothermal austempering, successive austempering and modified up-quenching austempering heat treatment on the mechanical properties. The specimens, were cut from a bar with 25mm diameter and after achieving the best temperature and time of austenitizing, austenitized at for 60 min and followed by quenching at for the high austempering temperature to achieve the upper bainite morphology and at for the lower austempering temperature to achieve the lower bainite morphology. In the case of successive austempering, the specimens were first austempered at for different periods (500 sec and 60 sec) and then austempered at for 1000 sec to achieve the mixed structure of upper bainite and lower bainite morphology. The specimens selected for up-quenching, after austenitization were quenched to below ( ) for 120 sec. followed by heating at to achieve the mixed structure of tempered martensite and lower bainite and to achieve the mixed structure of tempered martensite and upper bainite for 1000 sec. All of the processes were performed in the salt bath furnaces. Experimental results are presented and the advantages of the modified method are discussed. As well, it is shown that the best combination of strength and ductility can be achieved by the proposed heat treatment method. This modified method, can offer techniques that simultaneously improve not only strength 12 %( compare with results of strength after other heat treatment methods), but also ductility 38 %( compare with results of ductility after other heat treatment methods). While, conventional heat treatment of ultra high strength steels (UHSS) cannot always meet the strict engineering requirements for improved strength and ductility simultaneously. It has been shown that the mixed structure of tempered martensite and lower bainite that has been suggested in this investigation offers a good combination of strength and ductility. The technical reason for this superiority returns back to the fact that it has increased dislocation density. As a result of the increment of the dislocation density, in the morphology, the inter lath carbide (e.g. cementite) decreases, and the intra lath carbide increases. This modified austempering is applicable to all the ultra high strength steels, has noticeable economic advantages because it is simple. Use of this modified austempering for heavy parts, leads to the lightness of heavy parts and combination of the thermomechanical methods with this modified austempering can yield even much more improvements.

Abstract: In this research work, characterization of a broad area zone with ultra fine grain size of 7075-T6 grade aluminum sheets with the thickness of 8 mm was carried out using friction stir processing (FSP) and quenching by liquid nitrogen on both, i.e. upper and lower, surfaces. In the first step, ability and competence of two tools with different designs in creating a stir zone without any defects were examined; selected samples were exposed to FSP by efficient tools and in a highly extensive quenching media. Friction stir processing was carried out on the samples in three different rates (fast, medium and slow), the mechanism of ultra fine grain size as well as the creation of dislocation in thermo-mechanical affected zone was evaluated. Micro structural evaluation using transmission electron microscopy showed that the samples exposed to FSP in slow manner, had the finest grain size (20 nm) in the stir zone, and the lowest amount of dislocation in the thermo-mechanical affected zone. More details are discussed in the presented results.

Abstract: Bronze alloys are widely used in different tribological applications including sliding components. Bronze-Alumina composites have been attracting the interest of researchers in recent years. Among the most recent surface modifications techniques, plasma spraying has been successfully applied to these coatings. In this investigation, an attempt has been made to analyze the sliding wear response of Bronze-Alumina coats over a range of applied pressures and sliding speeds. It was observed that an increase in applied load causes more weight losses in wear test while increasing the sliding speed led to no further losses at this variables range. Wear processes and mechanisms of these behaviors are discussed in the light of the microstructural observations combined with wear surfaces and debris particles examinations.

Abstract: Plasma nitriding is a powerful process for surface modification of different materials. In this study, plasma nitriding is applied on a Nickel-Aluminum composite, coated on ST37 steel. Ni+Al composites were fabricated by electrodeposition process in watts bath containing Al particles. For prediction of electrodeposited Al% during the electroplating and microhardness of coatings after plasma nitriding process artificial neural network (ANN) was used. The numerical results obtained via a neural network model were compared with the experimental results. Agreement between the experimental and numerical results was reasonably good.