Sharif Digital Repository

In this research, Al-20Si-5Fe-2X (X=Cu,Ni,Cr) 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 and transmission electron microscopy, then, analyzed by solidification models. Powder and chopped ribbons were hot pressed at 400°C/250 MPa and microstructural variations, mechanical properties and thermal coefficient expansion were evaluated after consolidation. Results show that relatively high cooling rate in gas-atomized powders lead to refinement of the microstructure and formation of semi-equilibrium δ intermetallic phase. As the powder particle... 

Real modeling of ceramic foam filters, because of their specific tortuosities is not possible and in case of possibility of real modeling of pores in filters, because of restriction of element’s dimensions, the number of elements increases and model can’t be run in a reasonable time with common computers which are accessible nowadays. The common computer simulation of filters in Computational Fluid Dynamic (CFD) and their effect on fluid flow pattern is done by use of permeability properties of porous media. In this research, ceramic foam filters which are used in casting are simulated by Forchhimer and Darcy models. SUT CAST software is used for simulation, because of its ability for... 

The use of exothermic and insulated materials is one of the most effective methods in increasing feed efficiency. In order to model performance of these materials, we need for information in connection with thermo physical properties, interface resistances and way for releasing heat in exothermic and insulated materials. Due to lack of published information in this area, the purpose of this study is for increasing information in this area and especially in the heat release in these materials. In this investigation first, physical model governing this phenomenon was found. At this stage in order to Model of heat transfer from one dimensional transient heat conduction equation, discreted by... 

In this research, solidification and microstructure of ductile cast iron was simulated using Fourier heat transfer equation. Using Fourier heat transfer equation, distribution of macroscopic temperature with heat transfer coefficient was obtained. The purpose of simulation, forecasting ductile iron microstructure, including grain size, number per unit volume of graphite (NC), microstructure including volume fractions of ferrite and pearlite and graphite phases. Knowing the phases of the microstructure and nodule count and the use of empirical relationships, we can estimate mechanical properties. In this regard, all transformations during cooling of molten ductile iron was simulated. Results... 

Mold/metal interfacial heat transfer coefficient (IHTC) is the most important parameter that influences the solidification and the mechanical properties of a solidified product. The present work focuses on the determination and evaluation of pressure effect on interfacial heat transfer coefficient from the experimental cooling curves during unidirectional solidification of A356 alloy against water cooled Gray iron mold (chill). For this purpose, inverse heat conduction method is used. The results showed that IHTC is not constant, but varies with time, temperature and pressure during solidification. IHTC variation is related to coherency and critical solid fraction during... 

Polarization-sensitive optical coherence tomography is a non-invasive imaging technique that is capable of producing two-dimensional or three-dimensional images using the additional properties of light, as well as qualitative examination of the sample. This system, like optical coherence tomography, is mainly used in ophthalmology as a powerful tool for the early detection of eye diseases. PS-OCT can obtain high-resolution cross-sectional images of ocular fibrous structures, such as the retina or anterior segment, which show birefringence when injured. The main purpose of this dissertation is to develop an analytical model of system layout to study important parameters such as birefringence.... 

The computer simulation of freezing patterns in castings has done much to broaden our understanding of casting and mold system design. The structural integrity of shaped castings is closely related to the time–temperature history during solidification, and the use of casting simulation could do much to increase this knowledge in the foundry industry. However, some uncertainties must be eradicated, particularly heat transfer at the metal/mold interface. The accurate knowledge of interfacial heat transfer coefficients is necessary for accurate modeling of castings. The present work focuses on the determination of transient mold–environment and metal–mold heat transfer coefficients during... 

Ruthenium based-oxide coatings on Titanium anodes are widely used as DSA (Dimensionally Stable Anode) for chlorine and chlorate production. Coatings consisting of composition of highly conductive oxide of noble metals (Ru, Ir and Pt) make them as long lasting anodes in chlor-alkali technology.In this work, a newly anode by a ternary coating of IrO2, RuO2, and TiO2 on the Pt-coated Ti was developed through thermal decomposition of iridium and titanium and ruthenium inorganic salts dissolved in n-pentane. The effect of deposition parameters such as current density, time, different condition of baking, heating, mole ratio and pulling up the samples was investigated to find out reasonable... 

In this research, Al-20Si-5Fe-1Mg-xMn(x= 0,3,6) ribbons were produced by Melt spinning method. Microstructure and growth morphology of ribbons were studied by optical microscope (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The results were compared with as cast samples. In OM results, two different zones were observed. Featureless zone (with planar growth morphology) and dendrites zone. Microstructure of ribbons were completely different from the as cast samples. It consisted of just Aluminium and silicon. XRD results approved that matter. In fact, high solidification rate of ribbons increased the solubility of silicon and other alloys in aluminium and consequently... 

Hadfiled steel was invented by Sir Robert Hadfield in 1882. Different types of this steel have been used widely in cement industry, mining, drilling and railroad ways due to its high toughness, high work hardening capacity and excellent wear resistance. Since the wear life of machineries and parts used in such industries is short and costly, time consuming service of the wear parts, there have been a lot of interest to increase wear resistance of austenitic manganese steels in recent years. In this study a new type of austenitic manganese steels with high carbon-high vanadium and high tungsten content has been introduced and effect of carbon, vanadium and tungsten on microstructure, micro... 

Soldering is one of the important methods in joining techniques which has wide applications in industries such as microelectronic. Today, the physical and mechanical properties of solder joints is very important because the dimensions of electronic devices are decreasing that cause to increasing of their current density. One of the important problems of high current density in solder joints is the microstructures of solders in microelectronic components, change over time that is weakened the properties of the solder alloy. This study presents a quantitative model , which is capable to simulation phase separation and coarsening phenomenon in Tin/Lead Solders. This model is based on continuum... 

This research focused on mechanical properties of Al-TiB2 composite in as cast, heat treated and extruded condition. The composites were produced by mixing Al-Ti and Al-B master alloyes. Since some engineering parts during service are supposed to tolerate severe wear conditions, in this research abrasive wear condition was wxamined using pin on disk method. In a fixed load and abrasive disk, composites showed better resistance against wear in comparison with matrix alloy. Furtheremore, T6 heat treatment made composites more resistant against abrasive wear. Finally the best wear resistance was accompolished when composite was extruded and then heat treated. While increase in reinforcement... 

Presence of fluid in closed ends beam can increase beam hardness against pressure and buckling loads. This behavior is due to incompressibility or very low compressibility of fluids. there is a lot of research in the literature focusing on fluid solid interaction in pipe flow, but there is not any reported research studying on fluid filled beam, where fluid doesn’t flow across the beam. In this research hollow beam is modeled with Euler -Bernoulli beam theorem. Potential energy and kinetic energy is derived with considering the incompressibility of fluid. Nonlinear system of equations is derived using Hamilton principle . this system is taken to time domain using Galerkin and assumed mode... 

A356 castings show different characteristics during tensile tests. This behavior emanates from casting defects such as pores and double oxide films. These defects lead to quick and unexpected failure during tensile tests. Secondary dendrite arm spacing of primary α phase, eutectic phase, volume fraction of pores and oxide films are the characteristics that affect the tensile property. N this study the effect of changing two characteristics on the microstructural constituents is investigated. The first one is cooling rates, and the second one is melt filtration by using different filter in the runner. According to the tensile properties, the effect of these changes on tensile properties... 

Wide-gap aluminothermic rail welds with root opening of 60 mm were produced using plain carbon steel rail and non-alloy aluminothermic charge. Such process can repair defective rails, each with only one wide-gap weld instead of using a relatively long plug rail and two standard welds which reduces number of welds in railways and cause saving in money. Required equipments including metallic and sand molds, crucible and self-tapping thimble were designed. Mechanical properties and micro-structure of rail welds and corresponding heat affected zones as well as impact energies and fracture toughnesses of welds were investigated. Wide-gap aluminothermic rail welds exhibited 98% and 95% of yield... 

The present work has been planned to elaborately investigate the key parameters which affect the formation of shrinkage porosities during centrifugal casting of ductile cast iron pipes. The porosity defects can be mostly found in the Hot Mould centrifugal casting products and adversely affect the final mechanical properties of ductile iron pipes namely Ultimate Tensile Strength and Elongation.
In the first point of view, the created defects were detected through microstructural observations and the corresponding responsible mechanisms were also discussed. The results showed that the inner porosity is produced because solidification occurs from both the inner and outer surfaces... 

The Cu-Cr10% ingots were prepared in induction furnace and these ingots were used to prepare CuCr25% in VAR. The percentages of elements were checked by chemical analysis. The ingots were divided to slices with 20gr mass and these slices were put in quartz tubes. The quartz tubes were assembled in melt spinning machine and the ribbons were quenched onto a rotating copper wheel. Three different wheel speeds, 8, 16, 36 m/s were chosen. The microstructure of the ribbons was examined using a scanning electron microscopy (SEM). The relationship between wheel speed and thickness of the ribbons were compared with mathematical modeling. The disk of ribbons with thickness of 0.5mm and radius of 5mm...