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solidification
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Microstructural characteristics of a cast IN718 superalloy bonded by isothermal solidification
, Article Metals and Materials International ; Volume 19, Issue 5 , September , 2013 , Pages 1091-1099 ; 15989623 (ISSN) ; Ekrami, A ; Kokabi, A. H ; Han, H. N ; Sharif University of Technology
2013
Abstract
Isothermal solidification is a key feature of transient liquid phase bonding which prevents the formation of deleterious intermetallic phases in the joint centerline and results in bonds with improved mechanical performance. This paper discusses the metallurgical characteristics and mechanical properties of an as-cast IN718 superalloy bonded by diffusion-induced isothermal solidification of Ni-7Cr-4.5Si-3.2B-3Fe (wt%) filler metal. After transient liquid phase bonding of as-cast IN718 at 1000 C for 60 min, a bond exhibiting a solid solution microstructure with joint efficiency of 72% in terms of shear strength was obtained. The joining process was effectively able to prevent the formation of...
A comprehensive study on the complete charging-discharging cycle of a phase change material using intermediate boiling fluid to control energy flow
, Article Journal of Energy Storage ; Volume 35 , 2021 ; 2352152X (ISSN) ; Mohammadi, O ; Faghiri, S ; Shafii, M. B ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The low melting and solidification rates of phase change materials (PCM), which traces back to their low thermal conductivity coefficient, has led the application of these materials to face limitations. This paper aims to explore the effectiveness of a novel method called intermediate boiling fluid (IBF) in speeding up the energy storage and transfer processes in PCMs during a complete charging-discharging cycle. Throughout this novel technique, paraffin and acetone are utilized as PCM and IBF, respectively. In the solidification process, there is no direct contact between the cold source and the molten paraffin, while acetone, as an intermediate fluid, is being boiled via absorbing...
Development of fcc-Al nanoparticles during crystallization of amorphous Al–Ni alloys containing mischmetal: Microstructure and hardness evaluation [electronic resource]
, Article Materials Science and Engineering A ; Volume 604, 16 May 2014, Pages 92-97 ; Simchi, A ; Varahram, N ; Park, E. S ; Sharif University of Technology
Abstract
In the present work, fcc-Al nanoparticle development in Al90−xNi10MMx (MM: Ce mischmetal; x=2, 4) amorphous alloys was studied via non-isothermal differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, and nanoindentation test. Results showed that the crystallization of Al88Ni10MM2 alloy occurred by the precipitation of fcc-Al nanoparticles followed by the crystallization of Al11MM3 and Al3Ni phases. Transmission electron microscopy revealed that the aluminum precipitates had an average size of ~12 nm with a round morphology. Increasing the mischmetal content to 4 at% (Al86Ni10MM4 alloy) caused a three-stage crystallization process with a change in the size...
Grain refinement of AA5754 aluminum alloy by ultrasonic cavitation: Experimental study and numerical simulation
, Article Metals and Materials International ; Volume 21, Issue 1 , 2015 , Pages 109-117 ; 15989623 (ISSN) ; Ezzatneshan, E ; Bahai, H ; Sharif University of Technology
Korean Institute of Metals and Materials
2015
Abstract
In this work, an experimental investigation was carried out on the grain refinement of molten AA5754 Aluminum alloy through ultrasonic treatment. The cavitation induced heterogeneous nucleation was suggested as the major mechanism for grain refinement in the AA5754 aluminum alloy. A numerical simulation was performed to predict the formation, growth and collapse of cavitation bubbles in the molten AA5754 Aluminum alloy. Moreover, the acoustic pressure distribution and the induced acoustic streaming by ultrasonic horn reactor were investigated. It is suggested that the streaming by ultrasonic could transport the small bubbles formed in the ultrasonic cavitation zone into the bulk of melt...
On the prediction of shrinkage defects by thermal criterion functions
, Article International Journal of Advanced Manufacturing Technology ; Vol. 74, issue. 1-4 , Jun , 2014 , p. 569-579 ; Sharif University of Technology
Abstract
The goal of the present study is to predict the formation of solidification induced defects in castings by thermal criteria functions. In a criterion function method, the heat transfer equation is firstly solved, and then the susceptibility of defect formation at every point in the casting is predicted by computing a local function, criterion function, using results of the thermal analysis. In the first part of the paper, some famous criteria functions, in particular, the Pellini and Niyama criteria, are analyzed and their shortcomings are discussed in details. Then, a new criterion function is suggested to decrease the shape-dependency issue of the former criteria. The feasibility of the...
Diffusion induced isothermal solidification during transient liquid phase bonding of cast IN718 superalloy
, Article Canadian Metallurgical Quarterly ; Vol. 53, issue. 1 , 2014 , p. 38-46 ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology
Abstract
In transient liquid phase (TLP) bonding for commercial applications, one of the important key parameters is the holding time required for complete isothermal solidification tIS, which is a prerequisite for obtaining a proper bond microstructure. The objective of the study is to analyse the isothermal solidification kinetics during TLP bonding of cast IN718 nickel based superalloy. Experiments for TLP bonding were carried out using a Ni-7Cr-4.5Si-3Fe-3.2B (wt-%) amorphous interlayer at several bonding temperatures (1273-1373 K). The time required to obtain TLP joints free from centreline eutectic microconstituents was experimentally determined. Considering the solidification behaviour of...
Molecular dynamics simulation of melting, solidification and remelting processes of aluminum [electronic resource]
, Article Iranian Journal of Science and Technology ( IJST): Transactions of Mechanical Engineering ; 2012, Vol.36, No. M1, P.13-23 ; Simchi, A. (Abdolreza) ; Aashuri, H ; Sharif University of Technology
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. 1 0 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 t ransformation. Additionally, Wendt – Abraham parameters were calculated to determine the glass transition temperature. It is...
Effect of the bonding time on the microstructure and mechanical properties of a transient-liquid-phase bonded in718 using a Ni-Cr-B filler alloy
, Article Materiali in Tehnologije ; Volume 47, Issue 5 , 2013 , Pages 593-599 ; 15802949 (ISSN) ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology
2013
Abstract
The paper aims at addressing the effect of the bonding time on the metallurgical and mechanical properties of a transient-liquid-phase (TLP) bonded IN718 nickel-based superalloy using an Ni-15.2Cr-4B (%) amorphous filler alloy. The results showed that after a partial isothermal solidification, the residual liquid in the joint centerline transformed, during the cooling, to non-equilibrium eutectic-type microconstituents composed of Ni-rich boride, Cr-rich boride and eutectic γ-solid solution phase. The complete isothermal solidification which resulted in a formation of an intermetallic-free joint centerline occurred after a holding period 40 min at the bonding temperature of 1100 °C. An...
Numerical and experimental investigation of the grain refinement of liquid metals through cavitation processing
, Article Metals and Materials International ; Volume 19, Issue 5 , September , 2013 , Pages 959-967 ; 15989623 (ISSN) ; Ezzatneshan, E ; Bahai, H ; Nastac, L ; Sharif University of Technology
2013
Abstract
An investigation was carried out on the grain refinement of molten AA5754 Aluminum alloy through intensive shearing. The results show intensive shearing via cavitation decreases the grain size significantly. The above hypothesis for structure refinement was evaluated and an experiment was performed to ensure the creditability of this assumption. Finally, it was simulated by computational fluid dynamics (CFD) modeling. It was understood that shearing is the responsible mechanism for creation of cavitation bubbles and further collapse of them. It was also concluded the pressure which generated from the collapse of the bubble is well enough for braking the oxide layer and wetting them. It was...
Microstructure and mechanical properties of dual phase steels, with different martensite morphology, produced during TLP bonding of a low C-Mn steel
, Article Metals and Materials International ; Volume 22, Issue 5 , 2016 , Pages 856-862 ; 15989623 (ISSN) ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology
Korean Institute of Metals and Materials
Abstract
In this research, production of ferrite - martensite dual phase Steels with different martensite morphology was considered during transient liquid phase bonding of a low carbon steel. The steel was bonded using an iron base interlayer with melting point of 1443 K and 40 μm thickness. Bonding process carried out at 1473 K, under pressure of 0.5 MPa, at different holding time of 10, 20, 30 and 40 minutes. Microstructural studies of joint region showed that isothermal solidification completed at the bonding time of 40 minutes. Microstructure of joints made at the bonding time of 10, 20, and 30 minutes consists of two distinct region, athermal and isothermal solidified zones. Microstructure of...
Nano\Micro-Structural Investigation during Rapid Solidification of Al-20Si-(5Fe) Alloys and Modeling of Solidification Parameters
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor) ; Davami, Parvez (Co-Advisor)
Abstract
Nano/Micro-structure of rapidly solidified (products of Atomizing and Melt Spinning processes) Al-20Si-(5Fe) alloys has been investigated at the present work. Moreover, the effect of cooling rate on microstructure and growth morphology of these alloys has been studied. Microstructure of the products was examined by using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction.At the present work some models have been proposed for driving a relationship between microstructure and rapid solidification parameters during Atomizing and Melt Spinning processes. These models are based on macroscopic heat transfer during the processes. Model for...
Effects of hydrogen level and cooling rate on ultimate tensile strength of Al A319 alloy
, Article Russian Journal of Non-Ferrous Metals ; Vol. 55, issue. 4 , July , 2014 , p. 365-370 ; 10678212 ; Eisaabadi, G. B ; Davami, P ; Varahram, N ; Shabani, M. O ; Sharif University of Technology
Abstract
The present study investigated the effects of initial Hydrogen level and cooling rate on ultimate tensile strength of commercial Al-A319 alloys. Three hydrogen levels (0.01, 0.2, and 0.41 mL/100 grams of melt) and five cooling rate were studied. Total of 45 tensile test bars was prepared (three hydrogen levels × five cooling rate × three repeats). The UTS of the samples was determined though uniaxial tension tests. Furthermore, the microstructures of the samples were studied by standard metallographic technique and image analysis software. Finally the relationship between UTS and microstructurai features—SDAS and fraction of porosity (Fp%)—of the alloys was investigated.Results of tensile...
Microstructure development during transient liquid phase bonding of GTD-111 nickel-based superalloy
, Article Journal of Alloys and Compounds ; Volume 461, Issue 1-2 , 11 August , 2008 , Pages 641-647 ; 09258388 (ISSN) ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology
2008
Abstract
Transient liquid phase (TLP) bonding was used to join a nickel-based superalloy GTD-111 using a Ni-Si-B amorphous interlayer, MBF30. Bonding was carried out at 1100 °C with different holding time under vacuum. Joint region microstructure was studied by optical and scanning electron microscopy. Microstructural studies showed that before completion of isothermal solidification, bond region consists of four distinct zones: centerline eutectic structure due to athermal solidification, solid solution phase due to isothermal solidification, diffusion-induced boride precipitates and base metal. Complete isothermal solidification, which prevents formation of centerline eutectic constituent, occurred...
Effect of solid fraction, grain misorientation and grain boundary energy on solidification cracking in weld of Al-Cu aluminum alloys
, Article Materials Research Express ; Volume 6, Issue 8 , 2019 ; 20531591 (ISSN) ; Movahedi, M ; Kokabi, A. H ; Tavakoli, R ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
Solidification cracking is one the most common types of cracking in the weld of the aluminum alloys. Although some numerical models have been developed for investigation of the solidification cracking, the effect of the grain misorientation on the solidification cracking susceptibility (SCS) of a weld has rarely been considered. This work studies the effect of the angle between the primary arms of the dendrites on the SCS. Hence, a solidification cracking model was developed given the grain misorientation in the convergence condition. The model was investigated for Al-Cu alloys. When the grain boundary energy was considered in the model, there was an increase in the SCS for misorientation...
Conventional vs. temperature-gradient transient liquid phase bonding of stainless steel 304 using a multi-component (Fe–Ni–Mo–B) filler metal
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 53, Issue 11 , 2022 , Pages 4081-4100 ; 10735623 (ISSN) ; Ekrami, A ; Sharif University of Technology
Springer
2022
Abstract
The application of the multi-component Fe-based filler metals (FMs) for transient liquid phase (TLP) bonding of AISI 304 austenitic stainless steel has been overshadowed by dissimilar interlayers merely due to their shorter isothermal solidification time. However, the latter usually suffers from low efficiency in terms of mechanical properties even after homogenization of heat treatment. This study shows that by imposing a temperature gradient across the bond line during the TLP bonding process (TG-TLP), it is possible to reduce the isothermal solidification time significantly. This renews the interest in utilizing multi-component Fe-based FMs. In this regard, the TG-TLP bonding process was...
On the inability of the moving interface model to predict isothermal solidification time during transient liquid phase (TLP) bonding of ni-based superalloys
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 53, Issue 1 , 2022 , Pages 126-135 ; 10735623 (ISSN) ; Ghasemi, A ; Salmasi, A ; Sharif University of Technology
Springer
2022
Abstract
Understanding diffusion-induced isothermal solidification time during transient liquid phase bonding is vital in producing intermetallic-free robust joints. The isothermal solidification completion time is overestimated by the existing analytical models, even by the closest one to the real bonding conditions, known as the moving interface model. It was found that the boride formation in the diffusion affected zone of Ni-based superalloy upon using B-containing filler metals is one of the reasons behind the inability of the moving interface model to predict the isothermal solidification completion time accurately, which has received scant attention in the literature. Moreover, simplified...
TLP bonding of cast IN718 nickel based superalloy: Process-microstructure-strength characteristics
, Article Materials Science and Engineering A ; Volume 568 , 2013 , Pages 76-82 ; 09215093 (ISSN) ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology
2013
Abstract
This paper aims at addressing the microstructure-strength characteristics relationship during transient liquid phase (TLP) bonding of cast IN718 nickel based superalloy using Ni-7. Cr-4.5. Si-3. Fe-3.2. B (wt%) amorphous interlayer. The progress of the isothermal solidification at different temperatures for different times is analyzed using a Larson-Miller parameter (LMP). It was found that there is direct relationship between isothermal solidification zone (ISZ) size and LMP. Results showed that in situation where isothermal solidification has not been completed, the ratio of athermal solidification zone (ASZ) size to the width of the total solidified zone is the controlling factor for...
Numerical investigation of solidification of single droplets with and without evaporation mechanism
, Article International Journal of Refrigeration ; Volume 73 , 2017 , Pages 219-225 ; 01407007 (ISSN) ; Farhadi, F ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
According to some experimental observations, water droplet with high initial temperature freezes faster than a cold one. There are some explanations to this problem such as sub-cooling, evaporation and radiation. In this work, solidification process of single droplets with and without the effect of evaporation is numerically investigated for three different drop diameters and initial temperatures. It seems that evaporation itself is able to explain why hot water freezes faster than cold water. © 2016 Elsevier Ltd and IIR
Solute redistribution during transient liquid phase bonding of IN738LC with BNi-3 interlayer
, Article Materials Science and Technology ; Volume 24, Issue 4 , 2008 , Pages 449-456 ; 02670836 (ISSN) ; Ekrami, A ; Ohsasa, K ; Matsuura, K ; Sharif University of Technology
2008
Abstract
Redistribution of alloying elements in the transient liquid phase (TLP) bonding zone of IN738LC/ BNi-3/IN738LC was studied to investigate microstructural evolution in this area. Wavelength dispersive spectrometry and electron probe microanalysis revealed that, during non-isothermal solidification in the TLP bonding zone, enrichment of residual liquid phase with the positive segregating elements caused formation of intermetallic in the bonding zone. Scanning electron microscopy observation Indicated that the redistribution of alloying elements, between TLP bonding zone and base alloy, resulted In formation of a γ′ boundary layer, containing high density of fine γ′, around the bonding zone....
Optimization of Oily and Biological Sludge Digestion and Dewatering Process for Arak Refinery Wastewater Treatment Plant
, M.Sc. Thesis Sharif University of Technology ; Borghei, Mehdi (Supervisor)
Abstract
Different strategies for the treatment and disposal of petroleum and biological sludge found in the treatment and reuse unit of Arak Petroleum Refinery have been studied in the present study. To this end, the resources found in the literature corresponding to the different fields of sludge treatment were studied and a summary of them which was required by this research was mentioned in the thesis. Considering the problems bound to the wastewater treatment unit of this refinery plant and the previous studies, two completely separate strategies were devised. The first one concerns petroleum and biological sludge being produced continuously. The method of aerobic fixation of petroleum sludge by...