Sharif Digital Repository

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 purpose of this research is to investigate the residual stresses generates during solidification of a casting part and the effect of casting geometry and thermal treatment conditions on these stresses. The pattern was designed with to arms to ensure tensile tension. CO2 process was used for modeling and due to the high hardness of the mold, it also acts as a constraint and exacerbates the tension. To measure tensions in parts, two methods consist of Hole Drilling, and an innovative method based on heat treatment and dimension change have been used. The results of the two methods show the same values of stress. The Hole Drilling method is a verified and high-precision method, which is... 

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... 

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 fixed temperature have been evaluated. Based on reports by comparing density of relative samples, it... 

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... 

Casting process with foam is a relatively new process which because of having multiple benefits (like elimination of muscle and segregation line, high dimensional precision and using sand without using glue) in recent years has been considered. Considering that during pouring, melt replaces with sand surrounded foam, successfulness of this method depends on complete elimination of foam model during Pouring for preventing formation of some defects like carbon defects in cast irons, or cold work and porosity in aluminum alloys. Parameters like Pouring temperature, alloy type, foam type, density of foam model, type of gating system, and some other parameters are affecting the way of filling of... 

Wear of parts during service is one of the main factors of damage to the industrial parts. From among various kinds of wear, abrasive wear has the most role in damage of industrial parts. Hard surfacing is a useful and cost effective method for improving the surface properties of parts. This method is made through coherent layer sediment from the alloys resistant to abrasion, oxidation and wear by welding or spray. Determining the appropriate alloy for hard surfacing operations need knowing of working conditions of the part and the type of occurred abrasion. Ordinarily, the alloys which are prepared for hard work by welding, are in the form of cored wire or electrodes. In this research die... 

In the present work, primary crystallization mechanism, glass forming ability, thermal stability and formation of nano Al crystals and their effects on the mechanical behavior were investigated in various Al amorphous alloy containing misch metal including Al90-xNi10-yFeyMMx (x=2-10%at, y=0-10 %at) alloys. In order to elaborate the Cu effect on the primary crystallization mechanism Al86Ni10-xCuxMM4(x=0-2/5) alloy were prepared. The results showed that in Al90-xNi10MMx (x=2-10 %at) alloying system variation of the misch metal from 2 to 10 atomic present results in increase in glass forming ability. The crystallization onset temperature also increases from 405 K in Al88Ni10MM2 to 630 K in... 

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... 

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... 

Al-4.5% Cu alloy, an age-hardenable alloy, is an important alloy in industry due to such unique characteristics as high strength-to-weight ratio and considerable strength at elevated temperatures. In this study, the aim was to evaluate the combined effect of cooling rate and heat treatment on an A206 alloy having more impurities—especially iron—than the nominal specifications. To this end, the melt was poured in a five-step mold. Afterwards, each step was subjected to T4 and T6 treatments in order to study the changes compared to the as-cast samples. Ultimate tensile strength, yield strength, elongation, and grain size were determined by using tensile tests and optical microscopy,... 

In this research the effect of Si, Cu and Ni alloying elements on the structure and mechanical properties of the A336 alloy is investigated. Expriments were done in two situations, casting and heat treated and the results for all samples with different amount of alloying elements are compared and the effect of heat treating is also investigated. Results show that with increasing the amount of Si and Cu and decreasing the amount of Ni strength and hardness of the cast alloy are 134 MPa and 65 HB and they increase to 187 MPa and 89 HB in heat treated alloy. The elongation and coefficient of linear expansion are decreased from 2.3% and 21.94 μm/m.K to 1.1% and 21.62 μm/m.K. Also the T6 heat... 

The Ni-based superalloy GTD-111 possesses excellent hot corrosion resistance, high stability and strength at elevated temperature; accordingly, the alloy is used in manufacturing of the first stage blades of powerful gas turbines. In this study, effect of withdrawal rate from Bridgman furnace and precipitation hardening on the microstructure and microhardness of this superalloy were investigated. To this end, several experiments were carried out under growth rates of 1, 6 and 10 mm/min using Bridgman process under vacuum. Afterwards, the effects of homogenization treatment, partial dissolution with two different cooling rates (air and water) along with aging on the microstructure were... 

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... 

The present study aimed to investigate the effects of old and young oxide films on the mechanical properties and reliability of Cast Al A356.2 alloy. The results indicate that the presence of oxides within the microstructure of the alloy decreased the tensile properties of the alloy and increased their scattering. Beside this, the presence of the oxides decreased the reliability of the alloy. The results showed that the presence of double oxide films (especially old oxides) decreased the Weibull modulus of tensile properties and resulted in bi-Weibull distribution in tensile properties of the alloy. The results also indicate that using of a clean melt (with high quality), is vital for... 

One of the most important factors affecting the performance of the vehicle's brake disc is its stiffening coefficient. To improve this feature, many researches have been carried out by leading automotive companies, whose scientific aspects have not yet been widely disseminated. Brake discs are often made of cast iron and are more likely to produce gray iron with type A graphite. However, according to available resources, factors such as graphite morphology, their length-to-thickness ratios, cast iron and heat treatment on the piece affect this important feature. One of the most important factors that make changes in the above mentioned cases is the chemical composition and freezing rate. In... 

Aluminum alloys are one of the most economical light alloys that are used in automobile and aerospace industries. Application of Al-Si alloys are considerably used more than other Al alloys. Hypereutectic Al-Si alloys are well developed among Al-Si alloys due to their excellent properties such as high wear resistance and low thermal expansion coefficient. In these alloys formation of the primary silicon particles and hard intermetallic compounds in a ductile matrix provides a desirable wear properties. Coarsening of these particles in the structure of castings will reduce their mechanical properties. Moreover, oxidation of powders and difficulty in manufacturing complex parts in powder... 

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... 

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... 

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...