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cooling-rates
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Static Melt Crystallizer Simulation and Design with CFD
, M.Sc. Thesis Sharif University of Technology ; Farhadi, Fathollah (Supervisor) ; Pishvaei, Mahmood Reza (Supervisor)
Abstract
Layer melt crystallization is one of the most attractive and productive separation methods in the chemical industry. One of the most important coal tar components, which is present in concentration between 10 to 12% is naphthalene. One of the most commonly used techniques for producing naphthalene crystallization. In this thesis, the layer melt crystallization in a mixture of naphthalene and benzothiophene has been investigated using computational fluid dynamics. The simulation of crystallization was performed in Comsol Multiphisics version 5.6 and the thickness of the crystal layer was obtained according to the time. At first, simulation results were verified with the labroratory results of...
Experimental study on macro segregation behavior in short and wide range solidification of different aluminum alloys
, Article Materials Science and Technology Conference and Exhibition 2013, MS and T 2013 ; Volume 2 , 2013 , Pages 822-829 ; 9781629933092 (ISBN) ; Mohammad Salehi, E ; Hassan Nejad, H ; Shafiei Zadeh, S ; Sharif University of Technology
2013
Abstract
Data are presented on the solidification of aluminum alloys and their macro segregation behavior. Three alloys with different solidification ranges were prepared in two temperatures. Two types of molds were also prepared by sand and metallic materials. The solidification of Al alloys were studied and the effects of four parameters were determined, including cooling rate, casting temperature, degassing and nucleation effects on solidification and a comparison was conducted to Scheil model performance. Three types of aluminum alloys (Al-12.1%Si, Al-6.9%Si and Al-4.4% Cu) with short, medium and wide solidification ranges were studied and the results showed that degassing, nucleation, increasing...
A mathematical model for prediction of microporosity in aluminum alloy A356
, Article International Journal of Advanced Manufacturing Technology ; Volume 64, Issue 9-12 , April , 2013 , Pages 1313-1321 ; 02683768 (ISSN) ; Hatami, N ; Varahram, N ; Davami, P ; Shabani, M. O ; Sharif University of Technology
2013
Abstract
In the present work, a mathematical model was developed based on finite difference method to predict the microporosity distribution in A356 aluminum alloy casting. Heat, mass, and gas conservation equations were solved in this model. Moreover, Darcy's equation was considered in the mushy zone. Results show that the distribution and concentration of microporosities in cast parts vary with both cooling rate and initial gas content. Simulation results were compared with experimental data where proportionally good agreement with experimental results was found. Finally, a complex cast part was simulated presenting the ability of the model to predict the porosities in industrial cast parts
Numerical modeling and experimental validation of microstructure in gray cast iron
, Article International Journal of Minerals, Metallurgy and Materials ; Volume 19, Issue 10 , 2012 , Pages 908-914 ; 16744799 (ISSN) ; Davami, P ; Varahram, N ; Sharif University of Technology
Springer
2012
Abstract
To predict the amount of different phases in gray cast iron by a finite difference model (FDM) on the basis of cooling rate (R), the volume fractions of total γphase, graphite, and cementite were calculated. The results of phase composition were evaluated to find a proper correlation with cooling rate. More trials were carried out to find a good correlation between the hardness and phase composition. New proposed formulas show that the hardness of gray cast iron decreases as the amount of graphite phase increases, and increases as the amount of cementite increases. These formulas are developed to correlate the phase volume fraction to hardness. The results are compared with experimental data...
Modeling of austenite to ferrite transformation
, Article Bulletin of Materials Science ; Volume 35, Issue 3 , 2012 , Pages 395-398 ; 02504707 (ISSN) ; Sharif University of Technology
2012
Abstract
In this research, an algorithm based on the Q-state Potts model is presented for modeling the austenite to ferrite transformation. In the algorithm, it is possible to exactly track boundary migration of the phase formed during transformation. In the algorithm, effects of changes in chemical free energy, strain free energy and interfacial energies of austenite-austenite, ferrite-ferrite and austenite-ferrite during transformation are considered. From the algorithm, the kinetics of transformation and mean ferrite grain size for different cooling rates are calculated. It is found that there is a good agreement between the calculated and experimental results
Changes of γ′ precipitate characteristics in damaged superalloy IN738LC during different stages of rejuvenation heat treatment cycles
, Article Materials Science and Technology ; Volume 28, Issue 2 , Nov , 2012 , Pages 213-219 ; 02670836 (ISSN) ; Nategh, S ; Ekrami, A. A ; Sharif University of Technology
2012
Abstract
The present study investigates the evolution of γ′ precipitate microstructure in a creep damaged IN738LC superalloy during different stages of rejuvenation heat treatment cycles. Dissolution of coarsened γ′ precipitates in the creep damaged alloy occurred during different solution treatments. The precipitates that did not dissolve completely during solution treatment and those formed during subsequent cooling were considered to be as remnant and cooling precipitates respectively. It was found that higher solution treatment temperatures result in lower volume fraction of remnant precipitates and further formation of cooling precipitates. Slower cooling rates after solution treatment gave the...
Effect of casting and mould parameters on surface decarburisation in lost wax casting of DIN CK 45 steel
, Article International Journal of Cast Metals Research ; Volume 24, Issue 6 , 2011 , Pages 327-332 ; 13640461 (ISSN) ; Behjati, P ; Sharif University of Technology
Abstract
The effect of mould preheating temperature, casting modulus and graphite addition method on surface decarburisation during lost wax casting of CK 45 steel has been investigated. For this purpose, a novel image analysis program was developed to determine the carbon concentration profile. It was observed that on increasing the preheating temperature and casting modulus, the depth of decarburisation increases significantly. This behaviour was related to the decreased cooling rate of the samples which enhances the loss of carbon by reaction with the surrounding atmosphere. It was also found that the distribution of graphite in different layers of the mould and the distance of these layers from...
Modeling the microstructural evolution and effect of cooling rate on the nanograins formed during the friction stir processing of Al5083
, Article Materials Science and Engineering A ; Volume 527, Issue 1-2 , 2009 , Pages 192-197 ; 09215093 (ISSN) ; Shafiei M., A ; Dehghani, K ; Sharif University of Technology
Abstract
An analytical model is developed to study the effect of cooling rate on the final grain size of stirred zone of the Al5083 subjected to friction stir processing. The effect of cooling rate on the grain size of the stirred zone was investigated experimentally and numerically. A new microstructural evolution model was also suggested illustrating the mechanisms contributed in refining the microstructure. A new mechanism termed meta-dynamic recovery (MDRV) is introduced here in this regard. The simulation results also show that the rapid cooling rate resulted in superior mechanical properties through refining the microstructure of the stirred zone. However, decreasing the rotational speed and...
The modification of cast AL-Mg2Si in SITU MMC by lithium
, Article TMS 2009 Annual Meeting and Exhibition, San Francisco, CA, 16 February 2009 through 19 February 2009 ; 2009 , Pages 165-172 ; 9780873397353 (ISBN) ; Emamy, M ; Campbell, J ; Sharif University of Technology
2009
Abstract
Abstract The effects of both Lithium modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15% Mg2Si composite were investigated. Adding 0.3%Li reduced the average size of Mg2Si primary particles from ~30 μm to ~ 6 μm. The effect of cooling rate was investigated by the use of a mold with different section thickness from 3 to 9 mm. The results show a refinement of primary particle size as a result of both Li additions and increased cooling rate, and their effects were additive. Similarly, both effects increased UTS and elongation values. The refinement by Li and enhanced cooling rate is discussed in terms of an analogy with the effect of Sr and...
Role of the nucleating agent masterbatch carrier resin in the nonisothermal crystallization kinetics of polypropylene
, Article Polymer Journal ; Volume 54, Issue 9 , 2022 , Pages 1127-1132 ; 00323896 (ISSN) ; Marouf, B. T ; Bagheri, R ; Sharif University of Technology
Springer Nature
2022
Abstract
The effect of the nucleating agent masterbatch carrier resin on the nonisothermal crystallization of a pipe-grade polypropylene block copolymer was investigated at three different cooling rates using differential scanning calorimetry (DSC). Bis(3,4-dimethylibenzylidene) sorbitol (DMDBS), a well-known, third-generation sorbitol derivative, was used as a nucleating agent in this study. Crystallization kinetic parameters obtained from DSC cooling curves showed that incorporation of a nucleating agent by means of a masterbatch increased the crystallization rate by approximately two times compared to that of the sample with the same concentration of nucleating agent without the use of a...
Microstructural evolution of Al-20Si-5Fe alloy during rapid solidification and hot consolidation
, Article Rare Metals ; Volume 28, Issue 6 , 2009 , Pages 639-645 ; 10010521 (ISSN) ; Vahidi, M ; Simchi, A ; Davami, P ; Sharif University of Technology
Abstract
Al-20Si-5Fe melt was rapidly solidified into particles and ribbons and then consolidated to near full density by hot pressing at 400°C/250 MPa/1 h. According to the eutectic-growth and dendritic-growth velocity models, the solidification front velocity and the amount of undercooling were estimated for the particles with different sizes. Values of 0.43-1.2 cm/s and 15-28 K were obtained. The secondary dendrite arm spacing revealed a cooling rate of 6 × 105 K/s for the particles with an average size of 20 μm. Solidification models for the ribbons yielded a cooling rate of 5 × 107 K/s. As a result of the higher cooling rate, the melt-spun ribbons exhibited considerable microstructural...
Effect of rapid solidification on the microstructure and mechanical properties of hot-pressed Al-20Si-5Fe alloys
, Article Materials Characterization ; Volume 60, Issue 11 , 2009 , Pages 1370-1381 ; 10445803 (ISSN) ; Vahidi, M ; Simchi, A ; Davami, P ; Sharif University of Technology
2009
Abstract
The aim of this work is to study the effect of cooling rate and subsequent hot consolidation on the microstructural features and mechanical strength of Al-20Si-5Fe-2X (X = Cu, Ni and Cr) alloys. Powder and ribbons were produced by gas atomization and melt spinning processes at two different cooling rates of 1 × 105 K/s and 5 × 107 K/s. The microstructure of the products was examined using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The particles were consolidated by hot pressing at 400 °C/250 MPa/1 h under a high purity argon atmosphere and the microstructure, hardness and compressive strength of the compacts were evaluated....
Effects of strain rate and mean strain on cyclic behavior of aluminum alloys under isothermal and thermo-mechanical fatigue loadings
, Article International Journal of Fatigue ; Volume 47 , 2013 , Pages 148-153 ; 01421123 (ISSN) ; Sharif University of Technology
2013
Abstract
In this paper, effects of strain rate and mean strain on the cyclic behavior and the lifetime of aluminum-silicon alloys are investigated under thermo-mechanical and isothermal fatigue loadings. To achieve these goals, low cycle fatigue tests are accomplished at evaluated temperatures under various strain rates (by changing the loading frequency) and different strain ratios (minimum to maximum strain). Thermo-mechanical fatigue experiments are performed in an out-of-phase condition where the temperature varies between 50 and 250 °C. Various heating/cooling rates are taken into account to assess the strain rate effect and different starting temperatures are considered to study the mean strain...
Molecular dynamics simulation of melting, solidification and remelting processes of aluminum
, Article Iranian Journal of Science and Technology - Transactions of Mechanical Engineering ; Volume 36, Issue M1 , 2012 , Pages 13-23 ; 22286187 (ISSN) ; Simchi, A ; Aashuri, H ; Sharif University of Technology
2012
Abstract
A molecular dynamics simulation study has been performed to investigate the solidification and remelting of aluminum using Sutton-Chen many body potential. Different numbers of atoms from 108 to 2048 atoms were considered to find an adequate size for the system. Three different cooling and heating rates, i.e. 10 12 K/s, 10 13 K/s and 10 14 K/s, were used. The structure of the system was examined using radial distribution function. The melting and crystallization temperatures of aluminum were evaluated by calculating the variation of heat capacity during the phase transformation. Additionally, Wendt-Abraham parameters were calculated to determine the glass transition temperature. It is shown...
Microstructural evolution in damaged IN738LC alloy during various steps of rejuvenation heat treatments
, Article Journal of Alloys and Compounds ; Volume 512, Issue 1 , January , 2012 , Pages 340-350 ; 09258388 (ISSN) ; Nategh, S ; Ekrami, A. A ; Sharif University of Technology
2012
Abstract
IN738LC is one of the superior nickel base superalloys utilized at high temperatures in aggressive environments. However, experiencing high temperatures and stresses during service causes microstructure deterioration and degradation of mechanical properties in this alloy. To restore the microstructure and mechanical properties of the degraded alloy, rejuvenation heat treatments can be considered. In this study, the evolution of microstructural features in a creep damaged IN738LC superalloy during different stages of rejuvenation heat treatment cycles was investigated. During solution treatment stage, dissolution of coarsened γ′ precipitates, grain boundary films and transition zone around...
Welding metallurgy of stainless steels during resistance spot welding part I: Fusion zone
, Article Science and Technology of Welding and Joining ; Volume 20, Issue 6 , Mar , 2015 , Pages 502-511 ; 13621718 (ISSN) ; Alizadeh Sh, M ; Marashi, S. P. H ; Sharif University of Technology
Maney Publishing
2015
Abstract
Weldability is one of the key requirements for automotive materials. This two-part paper aims at understanding the metallurgical phenomena during resistance spot welding of stainless steels, as interesting candidates for automotive body in white. Part I addresses the phase transformations in the fusion zone of three types of stainless steels including austenitic, ferritic and duplex types. The solidification and solid state phenomena including columnar to equiaxed transition, ferrite– austenite post-solidification transformation, martensitic transformation and carbide precipitation are discussed. Particular attention is given to the effect of high cooling rate of resistance spot welding...
Investigation on the effects of hot forging parameters on the austenite grain size of vanadium microalloyed forging steel (30MSV6)
, Article Journal of Alloys and Compounds ; Volume 490, Issue 1-2 , February , 2010 , Pages 572-575 ; 09258388 (ISSN) ; Ziaei, S. M. R ; Kiani Rashid, A. R ; Sharif University of Technology
2010
Abstract
It is known that the thermomechanical processing is one of the most important techniques for improving quality and mechanical properties of microalloyed steels. In this paper, the main parameters of hot forging (preheat temperature, strain and post-forging cooling rate) on the primary austenite grain size of vanadium microalloyed steel (30MSV6) were studied. From this investigation, it was found that increasing preheat temperature from 1150 °C to 1300 °C will result in a decrease in grain size number. Furthermore, it has shown that as the strain increases, the austenite grain size number increases, as is evident for the two cooling rates of 2.5 °C/s and 1.5 °C/s for primary austenite....
Role of cooling rate in selective synthesis of graphene and carbon nanotube on Fe foil using hot filament chemical vapor deposition
, Article 2016 IEEE 7th Annual Ubiquitous Computing, Electronics and Mobile Communication Conference, UEMCON 2016, 20 October 2016 through 22 October 2016 ; 2016 ; 9781509014965 (ISBN) ; Kaminska, B ; Akhavan, O ; Talebi, S ; Ghoranneviss, M ; Arab, Z ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
In this study, graphene sheets and carbon nanotubes (CNTs) were selectively grown on Fe foil at a relatively low growth temperature and varying cooling rates using a hot filament chemical vapor deposition (HFCVD) apparatus with C2H2 as the precursor. The results of the scanning electron microscopy and Raman spectroscopy revealed that the increase of the cooling rate from 7 to 10 or 20 °C/min provoked a structure transition from CNT to graphene. The optimum crystal quality of the graphene sheets (Iq/Id ∼1.1) was achieved at the cooling rate of 20 °C/min. According to the AFM analysis, the thickness of the stacked graphene sheets was found to be ∼2.9-3.8 nm containing ∼8-11 monolayers. The XRD...
Medium range order evolution in pressurized sub-Tg annealing of Cu64Zr36 metallic glass
, Article Journal of Non-Crystalline Solids ; Volume 481 , 2018 , Pages 132-137 ; 00223093 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Molecular dynamics (MD) simulations have been widely used to study the structure of metallic glasses (MGs) at atomic scale. However, ultrafast cooling rates in MD simulations create structures that are substantially under-relaxed. In this study, we introduce long-term pressurized annealing up to 1 μs slightly below the glass-transition temperature, Tg, in MD simulation, which effectively relaxes the structure of Cu64Zr36 MG toward experimental conditions. It is found that applying hydrostatic pressure up to 2 GPa relaxes the MG to low-energy states whereas higher pressures retard relaxation events. In the sample annealed at 2 GPa pressure, equivalent cooling rate reaches to 3.7 × 107 K/s,...
The modification of cast AL-Mg2Si in situ mmc by lithium
, Article Shape Casting: 3rd International Symposium 2009 - Held During TMS 2009 Annual Meeting and Exhibition, San Francisco, CA, 15 February 2009 through 19 February 2009 ; 2009 , Pages 165-172 ; 9780873397346 (ISBN) ; Emamy, M ; Campbell, J ; Aluminum Committee of the Light Metals Division, LMD; Aluminum Committee of the Light Metals Division, LMD; Minerals, Metals , Materials Society, TMS ; Sharif University of Technology
2009
Abstract
The effects of both Lithium modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15% Mg 2Si composite were investigated. Adding 0.3%Li reduced the average size of Mg2Si primary particles from ∼30 μm to ∼6 μm. The effect of cooling rate was investigated by the use of a mold with different section thickness from 3 to 9 mm. The results show a refinement of primary particle size as a result of both Li additions and increased cooling rate, and their effects were additive. Similarly, both effects increased UTS and elongation values. The refinement by Li and enhanced cooling rate is discussed in terms of an analogy with the effect of Sr and cooling...