Sharif Digital Repository

In this study, Al-20Si-5Fe ribbons produced by melt-spinning method. Nanostructure and growth morphology of rapidly solidified products explored using optical microscope, scanning electron microscope and x-ray diffraction. Microstructural investigations depicted two distinctive zones of featureless (faceted morphology) and dendritic. In addition, no intermetallic phases could be observed in the rapidly solidified ribbons in comparison with coarsed and needle shaped intermetallic phases of as cast alloys which it demonstrates the extension of solid solubility of Si and Fe in the matrix and consequently intermetallics formation was hindered by higher cooling rates. Subsequently, ribbons... 

n the present study, the optimal design of feeding system in steel sand-mold castings is considered. The first part of this research includes fundamental studies on the physics of shrinkage defect formation during the casting process. The results of these studies lead to new findings on the mechanism of shrinkage defect formation, effect of melt quality on the distribution of defects within the castings and the connection between shrinkage and gases defects. The theoretical analysis of thermal criterion functions for the prediction of shrinkage defects in castings and introducing new criterion function with fewer shortcomings can be accounted as the other finding of this part. A new model... 

In this research ,Al-20Si-5Fe-3Cu-1Mg-XMn alloys were produced by gas atomizing and melt spinning processes. Microstructure and growth morphology of powder and ribbons were investigated using optical microscopy , scanning electron microscopy. powders were hot pressed at 400ºC/250Mpa and microstractural variations, mechanical properties were evaluated after consolidation. Results show that relatively high cooling rate in gas-atomized powders lead to refinement of microstructure and formation of semi-equilibrium δ intermetallic phase . As the powder particle size decrease , the growth morphology changes from primary silicon + euthectic to euthectic + primary dendritic aluminum . Mn changed the... 

Grobner bases were introduced by Bruno Buchberger in 1965. The terminology acknowledges the influence of Wolfgang Grobner on Buchberger’s work. He introduced a specific generator for ideals in the ring of polynomials over a field and then gave an algorithm for computing of that generator. It leads to solutions to a large number of algorithmic problems that are related to polynomials in several variables. Most notably, algorithms that involve Grobner basis computations allow exact conclusions on the solutions of systems of nonlinear equations, such as the (geometric) dimension of the solution set,the exact number of solutions in case there are finitely many, and their actual computation with... 

Cyclones are efficient devices in order to separate suspended particles and droplets from gas media and this effieciency is mainely because of spiral flow nature affecting the particles and droplets and taking them towards the wall. Therefore, particles and droplets move downwards toward down outlet by the gravity force. In consequence, they are being separated of the gas flow and relatively pure gas flow exits the cyclone. In this project, GAMBIT software has been used to produce three dimensional meshes including coarse, medium and fine sizes for two different geometries of cyclone. After simulation, little differences between the obtained results were revealed, showing that modeling is... 

Gray Cast Irons are the most important engineering Cast Irons. Gray color of fracture surface and morphology of graphite flakes are the reasons of this naming. Gray iron is relatively cheap with easy production; because of wide chemical composition range rather other cast irons. Furthermore, shrinkage and feeding in the casts from gray iron, besides surface finishing by machining are easy. The other properties of gray iron are resistance against sliding wear, high thermal conduction coefficient, low module of elasticity and thermally shock resistance. In this research, the effects of added nitrogen as an alloying element and cooling rate on microstructure, hardness and tensile properties of... 

Today, application of aluminium alloys in industries is developing. And this is because of some specification of these alloys like high proportion of the Strength per weight. One of the most useful alloys of this alloy group is A356 alloy that contain 7 % Silicon and 0.4 Percent of magnesium, this alloy because of cast ability, heat treat ability specification is use developing in air and automotive industries. But usage of this alloys combined with some difficulties like low fluidity and formation of shrinkage and gas porosities in this alloys. In present work with programmer software Visual Fortran, based on Finite difference method, a simulation model has been developed, can solve heat... 

Highly active unsupported MoO3 and (Co) MoO3 catalysts were synthesized utilizing the solution combustion method where the Ammonium molybdate powder and an organic additive were used as precursors. Different organic materials including Ethylene Diamin Tetra-acetic acid (EDTA), Polyethylene Glycol 200 (PEG 200), Sorbitol and Urea were used as additive in order to investigate the effect of additive structure on morphology and particle size of products. Also various reaction parameters such as the additive/Mo molar ratio, concentration of metal ion in solution, pH of the reaction and temperature of the synthesis media were changed to study effects on product morphology and size. Outcomes were... 

Prevent shrinkage and porosity in the melting parts expensive attention has been cast as a piece of low cost healthy and free from defects in casting production. Calculated feeding distance and the required number of risers. Also ensure that more tests were done with computer simulation compared the results acceptable to have the cast and expensive to produce a piece has nearly no troubleshooting. Variety of factors can affect the riser effect is melting parts Read some of these factors include alloy melting, superheat and mold .... . Oxygen factor in the project as one of the molten factors between feeding distance for molten plain carbon steel melting components and parts reviews and... 

In this thesis the effects of some casting parameters on residual stress and strain in steel casting parts have been studied. An H shape model has been chosen in order to investigate effects of casting parameters such as mold and cast constraints and inhomogeneous cooling on residual stress formation during casting in sand mold. These aforementioned factors have been simulated and studied in this research. Cooling of casting parts in sand mold and coupled thermo mechanical analysis has been simulated with the help of commercial finite element package ABAQUS. The results of this study show that, the complex samples with different section area, because of mold and cast constraints and... 

In this study, the recovery mechanism of nickel oxide by carbon dissolved in molten iron with the study of reaction kinetics were investigated. Nickel oxide pellets into molten iron containing graphite were added in the neutral atmosphere and the release of CO gas as a function of reaction time was measured until the end. The volume of gas produced at different times shows the number of moles of Ni metal was revived. Reaction by a) the following decomposition reaction under 1475 °C ; and b) carbon diffusion rate at temperatures over ° C1475 is controlled. The main reaction mechanism in order to a) decomposition of NiO; b) penetration of oxygen atoms in the melt, and c) reaction between... 

Al-20Si-5Fe-3Cu-1Mg–xCr (X=0, X=1.5) ribbons were produced by melt-spinning technique at the rotating speed of 20 and 40 ms-1. The thickness of ribbons were 40 to 80 and 15 to 35 μm, respectively. The properties of as-melt spun and as-cast specimen were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-Ray diffractometry (XRD) and the microhardness method. It was found that at the air side of ribbons the microstructure was dendritic while at the wheel side it was featureless. The microstructure of ribbons at two rotating speed showed a homogenous distribution of Si particles embedded in an α-Al matrix. XRD investigations exhibited the absence of any intermetallic... 

Since mechanical properties of cast Al-Si-Mg alloys are directly influenced by microstructural defects, understanding the characteristics of these defects and any interaction between them is important for improving the properties of castings. This study investigated the effect of the most common defects normally found in cast aluminium alloys namely, double oxide films, Fe-rich phases and prosity. A different level of each defect was introduced into castings to investigate their effects on tensile properties of A356 Alloy. Differents casting condition experiment produced different entrained oxide film, Fe-rich phases and porosity caused by shrinkage content, from low to high, were tested... 

AS5U3G and AS7U3G are two prevalent types of alloy which are used in producing cylinder head. In this research AS5U3G alloy is studied. Gravity casting is one of the method of producing this part. Produced porosities in cylinder head casting process, cause leakage in this part. In order to solve this problem, some actions have been taken that we can divide them into quality operations improvement of melt and making changes in casts. The sampling is done in four levels to evaluate the gas porosity and shrinkage. In these levels, pressure and degassing duration and strontium's modifying in a 745℃ fixed temperature have been evaluated. Based on reports by comparing density of relative samples,... 

Due to the shrinkage defects, casting parts is sometimes unusable; as a result, researchers is tackling porosity removal problem, so that they would be able to cast parts in a way that have the least porosity. Nowadays, simulation is used to predict the location of the porosity. The design and the elimination of defects, which leads to additional costs, can reduce the overall costs in the projects.
In this thesis, we focus on shrinkage defects. The main cause of porosity is the drop of pressure. As a matter of fact, the thermal agitation of the molecules is weaker than the strong intermolecular forces that would pull the molecules; therefore, the molten metals’ density will be increased... 

A study has been carried out on the formation of TiB2 particles in an aluminum based in-situ metal matrix composite by mixing master alloys containing Ti and B i.e., Al-10Ti and Al-8B with a Ti:B weight ratio of 5:2. It was shown that the microstructure of the composite was greatly affected by the controlling factors of the in-situ reaction like temperature, reaction time and stirring of the melt. An increasing reaction time leads to the dissolusion of the primary phases (AlB2 and Al3Ti) and the increase in TiB2 volume fraction. Optical microscope and SEM images were used to study these changes and XRD analysis was applied to confirm these observations. The act of melt stirring in short... 

Pearlitic Ductile Iron are being used variously for producing different kinds of components in industry. For producing of Pearlitic structure in some kind of components such as crankshaft, copper and tin are being used. In many cases according to conditions and facilities of the replacement, these two elements normally have been used.Despite the fact that mostly components are influenced by the fatigue, the influence of these two elements on the fatigue properties of the components hasn’t been studied comprehensively.In this research, the influence of the copper and tin alloying elements on the fatigue limit of the Pearlitic Ductile Iron has been studied.The samples of ductile iron with... 

Optical coherence tomography is a rapidly evolving imaging technique that enables non-invasive cross-sectional imaging of high-sensitivity semi-transparent samples (poor scattering). The biggest limitation of optical coherence tomography is the low penetration depth (about a few millimeters) in tissue. OCT is based on low-coherence interferometry. In this study, we investigate Michelson and Mach-Zehnder interferometers in OCT set-up and explain the advantages of using Mach-Zehnder interferometers in OCT systems. Furthermore, in this thesis, we have shown that by using Mie scattering, we can have forward scattering, hence the penetration increases. We have suggested this method as a solution...