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microstructure-refinement
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Effect of Electromagnetic Vibration and Alternative current on A356 Microstructure
, M.Sc. Thesis Sharif University of Technology ; Ashuri, Hossein (Supervisor)
Abstract
A356 Aluminium alloy has an abundant application in the aerospace and automobile industries. One of the most important problems of the alloy is in it’s microstructure after solidification with long dendrite grain of Aluminium.It is stated that solidied grains can be refined by electromagnetic vibration and an alternative electric feild applied simultaneously. To make electric field, electric current passed through the specimen. In order to change in microstructure, electromagnetic vibration was used. Then the effect of intensity of electromagnetic field and alternative electric current on microstructure was examined.Grain refining carried out at electric current 80A and magnetic flux of 13,...
The Effect of Cu Powder during Friction Stir Welding of Severely Deformed Al on the Microstructure and Mechanical Properties
, M.Sc. Thesis Sharif University of Technology ; Kokabi, Amir Hossein (Supervisor) ; Kazeminezhad, Mohsen (Supervisor)
Abstract
In order to increase the strength of metals such as aluminum, severe plastic deformation processes can be used. Due to the fact that the dimensions of their products are usually small due to limitations, the connection of severely deformed sheets can be considered. Friction stir welding seems to be suitable for this purpose as a solid state process, but due to the significant amount of strain energy stored in this type of sheet, after recrystallization in the stir zone and the surrounding areas often experience severe grain growth. In this research, the 1050 aluminum sheets are severely deformed by constrained groove pressing (CGP) process were subjected to friction stir welding....
Investigation and Study of Microstructure, Dielectric and Non-ohmic Properties of tin and Cobalt Oxide Systems Co-Doped with Electron Donor and Acceptor Elements
, M.Sc. Thesis Sharif University of Technology ; Nemati, Ali (Supervisor) ; Maleki Shahraki, Mohammad (Supervisor)
Abstract
In recent years, there are continuous researches on replacing new dielectrics with suitable dielectric properties (including high dielectric coefficient, low loss factor, high breakdown voltage, and high nonlinear coefficient simultaneously). One of these new materials is co-doped titanium oxide with donor and acceptor of electron, which in spite of having high dielectric coefficient and low loss factor. it has low breakdown voltage and researches on improving the disadvantages of this dielectric are ongoing. Due to the structural similarities between tin oxide and titanium oxide, the tin oxide can be an interesting system for studying and improving disadvantages in this field. In this study...
Microstructure and mechanical properties improvement by ultra-rapid annealing of severely deformed low-carbon steel
, Article Materials Science and Engineering A ; Volume 655 , 2016 , Pages 229-236 ; 09215093 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
Elsevier Ltd
Abstract
Ultra-rapid annealing (URA) of deformed low-carbon steel can provide refined microstructure. In this research, severely deformed low-carbon steel is ultra-rapidly annealed to subcritical and intercritical temperature ranges at the heating rates of 75-1800°C/s and then rapidly cooled. Also, conventional annealing by the heating rate of 0.3°C/s is performed at the same temperature ranges. The results show that conventional and subcritical ultra-rapid annealing cannot lead to a fully refined microstructure. High heating rate causes the interaction between recrystallization and transformation as the temperature exceed Ac1 (intercritical temperature range). High kinetics of transformation during...
Wear wear properties of rheo-squeeze cast aluminum matrix reinforced with nano particulates
, Article Protection of Metals and Physical Chemistry of Surfaces ; Volume 52, Issue 3 , 2016 , Pages 486-491 ; 20702051 (ISSN) ; Heydari, F ; Tofigh, A. A ; Rahimipour, M. R ; Razavi, M ; Mazahery, A ; Davami, P ; Sharif University of Technology
Maik Nauka Publishing / Springer SBM
Abstract
There are many approaches to fabricate nanoparticles reinforced aluminum matrix composites. However, uniform distribution of nanoparticle within aluminum matrix remains a difficult challenge. In this study, a novel method is used by taking the advantages from squeeze casting of semi-solid aluminum slurry combined with electromagnetic field to refine the microstructure of the primary Al and eutectic Si phase, plus to obtain uniform distribution nano alumina particles in the aluminum matrix. It is noted that electromagnetic field plays an important role in the formation of non-dendritic primary α-Al particles and a great microstructure refinement occurs as a consequence of the pressure...
Correlating the microstructure to mechanical properties and wear behavior of an accumulative back extruded Al-Mg2Si in-situ composite
, Article Tribology International ; Volume 115 , 2017 , Pages 199-211 ; 0301679X (ISSN) ; Zarei Hanzaki, A ; Abedi, H. R ; Azimi, M ; Mirjavadi, S. S ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
The present work was conducted to study the effects of microstructural evolutions on the mechanical and wear behavior of an accumulative back extruded aluminum-based in-situ composite. The mechanical fragmentation and thermal disintegration of the primary and secondary Mg2Si particles were found as the main microstructural changes. For that reason, the particle interspacing was decreased, the sharp ends were modified, and the reinforcements were more uniformly distributed. Surprisingly, the wear loss was dramatically decreased in processed materials in comparison to the as-received one. Oxidation and delamination were identified as the dominant wear mechanisms. These were addressed...
Processing of Al-20Si-5Fe-2X(X=Cu, Ni, Cr) alloys by melt-spinning and hot-pressing
, Article European International Powder Metallurgy Congress and Exhibition, Euro PM 2008, Mannheim, 29 September 2008 through 1 October 2008 ; Volume 2 , 2008 , Pages 99-104 ; 9781899072033 (ISBN) ; Simchi, A ; Davami, P ; Sharif University of Technology
European Powder Metallurgy Association (EPMA)
2008
Abstract
Al-20Si-5Fe-2X (X=Cu, Ni, Cr) ribbons were produced by melt-spinning and consolidated by hot pressing at 400°C for 60 min. Optical and transmission electron microscopy (TEM), X-ray diffractometry (XRD), and hardness test were used to evaluate the microstructure and mechanical strength of the ribbons and hot consolidated specimens. The compressive strength of the specimens at ambient and elevated temperatures was also examined. The microstructure of the ribbons exhibited featureless and dendritic zones, and contains spherically-shaped Si particles with an average diameter of 20 nm. After hot-pressing, ultrafine Si (110-150 nm) and iron-containing intermetallic particles were formed. The...
A Study on Deformation Behavior During Asymmetrical Rolling of Low Carbon Steels and Subsequent Microstructural Phenomena
, M.Sc. Thesis Sharif University of Technology ; Serajzadeh, Siamak (Supervisor)
Abstract
In this study, static recrystallization (Rex) of a low carbon steel after cold rolling has bees simulated under non-isothermal condition by employing cellular automata (CA) method. Symmetric cold rolling and asymmetric cold rolling (ASR) which was arisen by inequality of friction coefficient have been applied as primary cold deformation. Residual stress and strain field after deformation, and temperature rate and distribution of specimens during annealing has been evaluated by employing two different models based on finite element method. Initial microstructure has been developed by haphazardly distribution of grains and topological adjustments were imposed on it. Results of FEM models were...
Microstructrual evolution of aluminum 6061 alloy through tube channel pressing
, Article Materials Science and Engineering A ; Vol. 615 , 2014 , pp. 139-147 ; ISSN: 09215093 ; Kazeminezhad, M ; Miyamoto, H ; Sharif University of Technology
Abstract
The evolution of microstructure and the mechanical properties of an aluminum 6061 alloy tube subjected to a novel severe plastic deformation process called tube channel pressing were studied. Results show that the tube channel pressing causes an impressive grain refinement and strengthening of the material. As an illustration, mostly ultrafine grained tube (D-=760nm) bearing the yield strength of 352. MPa can be obtained after 5 passes of tube channel pressing. Additionally, the tube channel pressing causes the heterogeneous grain refinement resulting in a bimodal distribution of size of grains after 7th pass. Therefore, it can be inferred that the main microstructure refining mechanism...
Microstructure, mechanical properties, corrosion behavior and cytotoxicity of Mg-Zn-Al-Ca alloys as biodegradable materials
, Article Journal of Alloys and Compounds ; Vol. 607 , 2014 , Pages 1-10 ; ISSN: 09258388 ; Afshar, A ; Sharif University of Technology
Abstract
Recently, considerable attentions have been paid to alloy Mg-4Zn-0.2Ca for biomedical applications due to its suitable biocompatibility and acceptable mechanical properties. In this work, the effects of the addition of different amounts of Al on microstructure, mechanical properties, degradation behavior, and biocompatibility of this alloy were investigated. The corrosion behaviors of the alloys were investigated through polarization tests, chronoamperometry analysis, immersion tests, and EIS experiments. The mechanical properties were analyzed by using tensile tests and compression tests. The results showed that the addition of Al up to 3 wt.% considerably modifies the degradation behaviors...
Application of CGP-cross route process for microstructure refinement and mechanical properties improvement in steel sheets
, Article Journal of Manufacturing Processes ; Volume 15, Issue 4 , 2013 , Pages 533-541 ; 15266125 (ISSN) ; Abbaszadeh, M ; Eskandari, H ; Mohebpour, S. R ; Sharif University of Technology
2013
Abstract
A modified method of severe plastic defomation (SPD) entitled constrained groove pressing-cross route (CGP-CR) was introduced for imposing a high magnitude of equivalent strain of about 2.32 per pass on the sheet form samples. The major benefit of this improved route compared to previous common route was the more homogeneity of strain in the rolling (RD) and transverse (TD) directions of sheets. In this study, low carbon steel samples were used for examination of evolutions in microstructure and mechanical properties during SPD via CGP-CR process. Mechanical properties improvement were measured by tensile and macro hardness tests. The results indicate that CGP-CR process can effectively...
The effect of Mn addition on the microstructure and mechanical properties of gas-atomized Al-20Si-5Fe-3Cu-1Mg powder
, Article Advanced Materials Research, 15 December 2011 through 18 December 2011 ; Volume 410 , 2012 , Pages 253-256 ; 10226680 (ISSN) ; 9783037853160 (ISBN) ; Rajabi, M ; Davami, P ; Sharif University of Technology
2012
Abstract
In this study, Al-20Si-5Fe-3Cu-1Mg-XMn (X=0,1.5,3) alloys were synthesized by the gas atomizing technique. The microstructure and mechanical properties of the powders were investigated using optical microscopy, scanning electron microscopy, X-ray diffractometery method, and microhardness test. Microstructure of the powders composed of α-Al, Si and iron intermetallic compounds. As the powder particle size decreases, the phases become finer. A significant refinement in the size of iron-containing compounds was observed by addition of Mn. The microstructural refinement by controlling the particle size leads to an increase in the hardness of the powder particles in the amount of 33-45% dependent...
The effect of constrained groove pressing on grain size, dislocation density and electrical resistivity of low carbon steel
, Article Materials and Design ; Volume 32, Issue 6 , 2011 , Pages 3280-3286 ; 02641275 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
Abstract
In this research, constrained groove pressing (CGP) technique is used for imposing severe plastic deformation (SPD) on the low carbon steel sheets. Using transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical microscopy, the microstructural characteristics of produced sheets are investigated. The results show that CGP process can effectively refine the coarse-grained structure to an ultrafine grain range. Dislocation densities of the ultrafine grained low carbon steel sheets are quantitatively calculated and it is found that the CGP can effectively enhance the dislocation density of the sheets. Measurements of their electrical resistivity values show that microstructure...
A comprehensive evaluation between the efficiency of different treatments in modifying the properties and behavior of magnesium alloys as degradable biomaterials
, Article Materials and Corrosion ; Volume 68, Issue 9 , 2017 , Pages 995-1003 ; 09475117 (ISSN) ; Afshar, A ; Sharif University of Technology
Abstract
The addition of alloying elements to magnesium leads to microstructural refinement and improves its properties. However, this strategy is accompanied by another concurrent phenomenon − that is − intergranular segregation and the formation of secondary phases in grain boundaries, deteriorating the properties. In this work, the efficacy of two main factors on modifying the mechanical properties and corrosion behavior of Mg-4Zn-1Al-0.2Ca alloy was investigated separately: 1) dissolution of secondary phases; and 2) grain refinement. Based on the results, heat treatment of the as-cast alloy can increase the UTS from 174.4 to 213.2 MPa, decrease the corrosion current density from 81 to 49 μA/cm2,...
Enhanced resistance to liquation cracking during fusion welding of cast magnesium alloys: Microstructure tailoring via friction stir processing pre-weld treatment
, Article Materials Science and Engineering A ; Volume 798 , 2020 ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Magnesium alloys provide critical opportunities for energy and lightweight-materials challenges. The alloy design approach based on utilizing the second phase strengthening mechanism plays an essential role in producing low-density high strength Mg-based alloys. However, the second phase in the microstructure (e.g., Mg17Al12 phase in Mg–Al–Zn alloys) can deleteriously affect the weldability of the metallic materials by promoting the liquation and liquation cracking during fusion welding. The lack of sufficient weldability of Mg-based alloys is a crucial barrier to their potential use in safety-critical applications. In this paper, it is shown that the severe plastic deformation induced by...
Microstructural features of rapidly solidified Al-20Si-5Fe-2X(X=Cu, Ni, Cr) powders
, Article European Powder Metallurgy Congress and Exhibition, Euro PM 2007, Toulouse, 15 October 2007 through 17 October 2007 ; Volume 2 , 2007 , Pages 3-8 ; 9781899072293 (ISBN) ; Simchi, A ; Vahidi, M ; Davami, P ; Sharif University of Technology
European Powder Metallurgy Association (EPMA)
2007
Abstract
The size and morphology of secondary phase and intermetallic compounds in gas atomized Al- 20Si-5Fe-2X (X=Cu, Ni, Cr) powders were studied. It was shown that the microstructure compromised of fine particle-like primary Si, aciculate δ-Al9FeSi3 intermetallic compound containing small amount of dissolved alloying elements, and fine Al-Si eutectic matrix. Decreasing the powder particle size yields finer primary silicon but its morphology is not affected. Also, significant refinement in the size of δ-Al9FeSi3 intermetallic was observed as the particles become finer. This particle size effect on the microstructure of Al-20Si-5Fe alloy was found to be influenced by the presence of chromium. Here,...
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...