Defect and Diffusion Forum Vols. 297-301

Abstract: Technological requirements urges high technology industries using materials with advanced properties. Although it is compulsory using these materials due to their advantages, some of them should be tolerated because of their weak machining and mechanical properties. Attempts for qualitative machining of complex curves on many work pieces may result in the advent of new finishing techniques. One of the most newly introduced techniques is Magnetic Abrasive Finishing, MAF. In this paper a study on the effects of tool and work piece gap, and lubricant volume, on the roughness and material removal rate have been studied. The results show that setting the working gap to 3 mm and the lubricant volume to 0.7 ml, yields a change in surface roughness (Ra), and the material removal (MR) will gain its best result.

Abstract: Air Spindles have been used in ultra precision machines for several years due to their advantages such as high speed rotation, low friction, and low vibration, [1]. Air spindles are widely used in these machines for producing precise work pieces. Although, spindles function on a very complicated theoretical basis, [2, 3], their structure is very simple and consists of mainly a rotor and a stator. The rotor/stator could be made of different shapes. A cylindrical shape is the one commonly in use. The spindle designed in this work has a spherical configuration. It has been designed so that it could be moved without application of electric motor and only by a wind turbine system, [4]. The spindle studied in this research uses compressed air for rotor suspension, and has an air turbine for rotating its shaft. A thin air film acts as bearing layer between rotor and stator. In design procedure, operation parameters such as air inlet pressure for turbine, air inlet pressure for bearing, diameter of turbine nuzzles, diameter of bearing nuzzles, clearance between rotor and stator and etc. have been considered, [5]. A prototype spindle has been manufactured using design criteria. The influence of above mentioned parameters have been recognized through experiments.

Abstract: A great deal of attention in manufacturing engineering has been focused on finishing operations of hard and brittle materials in recent years. This paper reports an experimental work on the analysis of surface roughness and material removal using design of experiment (DOE) method in magnetic abrasive finishing, (MAF) of flat surfaces. Change in surface roughness and material removal were found to increase with an increase in weight percentage of abrasive particles in magnetic abrasive brush, lubricant volume and decrease in working gap. Also, any decrease in the relative size of the abrasive particles vis-à-vis the iron particles would result into an increase of the surface roughness and decrease in material removal. It was observed that the work piece hardness had no considerable effect on the process results. The optimum parameter levels which lead into the best surface finish and highest material removal were also derived from these experimentations. Optimum levels included weight percentage of abrasive particles of 40%, Lubricant volume of 1 ml, working gap of 3 mm, relative size of abrasive particles vis-à-vis the iron particles of 0.22, and work piece hardness of 82-87 HBN. Disk type test pieces were selected from Al 7075 and their two side surfaces were under experiments. Experiments were made using a milling machine spindle as magnetic pole holder, and its table as fixture holder for work pieces.

Abstract: This paper aims to contribute to the ongoing research on tree-shaped flow structures. First, it briefly traces the progress made on constructal tree-shaped flow networks. Then, the paper focuses on tree pattern of tubes connecting the centre and the rim of a circular area. It shows that the physical description underlying the classical Darcy-Forchheimer-Ergun equation may provide a legitimate correlation for this kind of flow structure. The porosity, hydraulic permeability and the inertial factor of the flow structure are also presented.

Abstract: According to constructal theory, the flow architecture emerges in time such that it provides progressively greater access to its currents. The emergence of flow architecture in nature is analogous to emergence of configuration in man-made (engineered) flow systems, and that features of materialization of design can be predicted based on the constructal theory. To support this view, we show that the emergence of configuration in natural flow systems can be approached based on the constructal law. Man-made flow systems achieve high performance by acquiring the suitable architecture (configuration). In this study, we also rely on the constuctal law to design a device for particulate matter control with an optimized function. Therefore, the emergence of optimal flow architecture is analogous to both natural and man-made systems. The features of materialization of design do not occur by chance, and can be explained or predicted based on this physical law.

Abstract: In this work nanocomposites based on amorphous poly(ethylene terephthalate) (PETg) were developed using melt intercalation. X-ray analysis performed on the PETg nanocomposites showed that intercalation and exfoliation took place during static mixing. The water vapor permeability of PETg nanocomposites was correlated to the volume fraction of the impermeable inorganic part of the omMMT.

Abstract: Jet impingement heat transfer on a target plate covered with a thick porous layer with or without a cylindrical center cavity is experimentally investigated using the transient liquid crystal technique. Based on the results of jet impingement on a bare flat plate, heat transfer enhancement due to the attachment of porous medium is assessed. The varying parameters in the experiments include the nozzle-to-plate distance, jet Reynolds number, jet-to-cavity diameter ratio, and the cavity depth. Results of Nusselt number distribution, stagnation-zone Nusselt number, and averaged Nusselt number over a region of 3 times the hole diameter are documented. Experimental results show that the attachment of the porous layer with a center cavity can either hamper, or effectively enhance the jet impingement heat transfer over a flat plate. The maximum enhancement occurs at jet Reynolds number of 12400 when the cavity is a through hole and the cavity has the same diameter as the jet. The stagnation-zone Nusselt number increases 58.3% and the averaged Nusselt number increases 77.5% at the maximum enhancement condition. On the other hand, the addition of the thick porous layer without a center cavity gave rise to severe adverse effect on jet impingement heat transfer.

Abstract: We have analyzed the interfacial elemental depth profile evolution after high temperature isothermal oxidation of SixCy and SixNy protective coatings deposited by dynamic ion mixing on a Ti6242 alloy (Ti-6Al-2Sn-4Zr-2Mo). Isothermal oxidation tests have been carried out at 600°C during 100 hours in air. We have observed a non-monotonic depth distribution of zirconium in GDOES and SIMS depth profiles after oxidation of SiC/Ti6242 and SiN/Ti6242 and we propose a kinetic model based on rate equations for analyzing the results. It is shown by modeling that a non-monotonic depth profile of zirconium occurs because zirconium from the Ti6242 alloy forms a zirconium oxide compound. As a result, the atomic concentration of zirconium decreases at the interface which induces a diffusion flux of zirconium from the bulk to the interface. This process leads to the increase of the total amount of zirconium at the film interface and thus formation of a non-monotonic depth profile.

Abstract: Degradation of the mechanical properties of copper and copper based alloys after the treatment with telluride bismuth (Bi2Te3) at 570oC has been studied in the present work. The experiments were performed in a H2 deoxidizing atmosphere. The kinetics of embrittlement of pure copper has been shown to be parabolic. Bi2Te3 was in the solid state and was not in direct contact with the copper specimens during the experiments, i.e. the plating was performed through the gas phase. The brittle fracture along the GB was observed after 3 point bending test. The surface of fracture was investigated with the use AES. It was shown that intergranular penetrations of liquid bismuth and bismuth from Bi2Te3 have different mechanisms.

Abstract: The aluminum film with high reflectivity and low absorption in the visible wavelength region has been widely used in optical applications. In this investigation, aluminum films were prepared on glass substrates by electron-beam vapor deposition. The reflectivity of the Al thin film was measured by a Perkin-Elmer Lambda spectrophotometer in the wavelength region of 450-680 nm. The experimental measurements of reflectivity were validated with the numerical results using the Essential Macleod software. The surface topology and microstructure of the film were examined by means of atomic force microscope (AFM). The effects of the temperature and humidity on the reflectivity of the Al film were examined by the environmental test. Nanoindentation tests were employed to determine the hardness and Young’s modulus of the film. The measured hardness of the Al thin films were found to depend on the penetration depth.