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Microstructure, Properties and Kinetic Characterization in SnO2-Based Varistor with Addition of CuO Nano Particle
, M.Sc. Thesis Sharif University of Technology ; Nemati, Ali (Supervisor) ; Seyyed Reyhani, Morteza (Supervisor)
Abstract
The aim of this study is to investigate the effect of Copper oxide on the microstructure, properties, and grain growth kinetic in Tin oxide- Based varistors. Copper oxide was mixed in Tin oxide with different concentration, including 0, 0.1, 0.25, 0.5, and 1 mol% and the samples were sintered at 1250, 1300, and 1350 oC. Then, phase and microstructural characterization was investigated and consequently, electrical properties were evaluated. According to results, Copper Oxide with forming the liquid phase through the sintering process, accelerated grain growth. It was found that, by increasing concentration of CuO, mean grain size was increased from 2.6 µm in 1250 oC and 5 hours to 17.1 µm...
A Study on the Thermal Stability and Microstructure of Nanocrystalline Al-Ti(Ni) Alloys Synthesized by Mechanical Alloying
, M.Sc. Thesis Sharif University of Technology ; Maddah Hosseini, Hamid Reza (Supervisor) ; Seyyed Reihani, Morteza (Supervisor)
Abstract
In the present investigation, the mechanical alloying (MA) technique was employed to produce nanocrystalline Al-Ti Powder mixtures. Elemental Al and Ti powders were mixed with different compositions (0, 5, 10, and 20 wt.% Ti) and then, milled in a vibratory mill up to 7 hr. The variations of powder morphology and particle size, apparent and tap densities, microstructure, grain size, lattice strain, and microhardness were studied with increasing the milling time. While dissolution of Ti in the Al matrix resulted to the formation of supersaturated Al-Ti solid solution in the samples containing 5 and 10 wt.% Ti, the specimen with 20 wt.% Ti, eventually, led to nanocomposite powder with...
Investigation of Sintering Behavior of BaTiO3 Nanoparticles Synthesized Via Hydrothermal Method
, M.Sc. Thesis Sharif University of Technology ; Nemati, Ali (Supervisor) ; Simchi, Abdolreza (Supervisor)
Abstract
In the present work, Barium Titanate nanoparticles were synthesized by a facile hydrothermal method at 180oC for 4 hours and their sintering behavior was studied. The characterization tests illustrated that the obtained powder was BaTiO3 single phase with excess Ti content from stoichiometric composition. The average particle size of about 50 nm and a narrow particle size distribution was noticed. SEM investigations showed that the samples sintered at temperatures less than 1250oC had plate-like grains. This behavior resulted from twin plates existed in the grains and facetted grain boundaries. At the temperatures more than 1250oC, the grains became polygonal due to the formation of trace...
Microstructure evolution and microhardness of friction stir welded cast aluminum bronze
, Article Journal of Materials Processing Technology ; Vol. 214, issue. 8 , August , 2014 , pp. 1524-1529 ; ISSN: 09240136 ; Kokabi, A. H ; Sharif University of Technology
Abstract
Microstructural characteristics and mechanical properties of a friction stir welded cast aluminum bronze (Cu-9Al-1Fe), produced by a sand casting method, have been investigated at tool rotation of 850-1500 rpm and traverse speed of 50-100 mm/min. Refinement of the primary coarse cast microstructure in the base metal was seen after friction stir welding. Microstructure of the stir zone was characterized in four distinct areas of non-isometric fine grains while a significant grain growth was noticed in some of the areas. Conditions of grain growth are defined with high heat input intensity and low heat transfer capability. The grain size was observed to decrease after FSW, resulting in a...
Study on microstructure and mechanical characteristics of low-carbon steel and ferritic stainless steel joints
, Article Materials Science and Engineering A ; Vol. 608, issue , 2014 , pp. 35-45 ; ISSN: 09215093 ; Mostafaei, M. A ; Pouraliakbar, H ; Kokabi, A. H ; Sharif University of Technology
Abstract
In this work, examinations on the microstructure and mechanical properties of plain carbon steel and AISI 430 ferritic stainless steel dissimilar welds are carried out. Welding is conducted in both autogenous and using ER309L austenitic filler rod conditions through gas tungsten arc welding process. The results indicate that fully-ferritic and duplex ferritic-martensitic microstructures are formed for autogenous and filler-added welds, respectively. Carbide precipitation and formation of martensite at ferrite grain boundaries (intergranular martensite) as well as grain growth occur in the heat affected zone (HAZ) of AISI 430 steel. It is found that weld heat input can strongly affect grain...
The effect of SiC nanoparticles on the friction stir processing of severely deformed aluminum
, Article Materials Science and Engineering A ; Vol. 602, issue , April , 2014 , p. 110-118 ; ISSN: 09215093 ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
Abstract
The 1050 aluminum sheets are severely deformed by two passes of the constrained groove pressing (CGP) process to obtain the strain of 2.32. Friction stir processing (FSP) is then performed on these specimens at two conditions of with and without SiC nanoparticles. Microhardness measurements indicate that in the state of FSP without any particle, the microhardness of stir zone is decreased due to the recrystallization and grain growth occurrence because of high stored strain energy in the CGPed specimens. In order to enhance the mechanical properties of the stir zone, SiC nanoparticles are used during FSP. Also, the effect of FSP pass number on the distribution of nanoparticles is...
Production of nanostructured Ni-Ti-Ag alloy by mechanical alloying
, Article Advanced Materials Research ; Vol. 829 , 2014 , pp. 67-72 ; ISSN: 10226680 ; Sadrnezhaad, S. K ; Bagheri, G. A ; Sharif University of Technology
Abstract
Because of corrosion resistance and antibacterial effects, shape memory Ni-Ti-Ag alloy can be considered for different biomedical applications. Mechanical alloying is used to produce nanostructured Ni-Ti-Ag alloy from elemental powders. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are used to characterize the product. Results show that after 1h milling, homogenous distribution of the elements occurs; while no intermetallic compounds is observed. After 3h milling, titanium dissolves in nickel to form amorphous and nanostructured solid phases. Peaks of B2 phase appear in the XRD pattern after the 3h milling of the powder mixture. Sintering of the 3h-milled...
A mechanistic study of nanoscale structure development, phase transition, morphology evolution, and growth of ultrathin barium titanate nanostructured films
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Vol. 45, issue. 9 , August , 2014 , pp. 4138-4154 ; ISSN: 1073-5623 ; Sharif University of Technology
Abstract
In the present work, an improved method is developed for preparing highly pure ultrathin barium titanate nanostructured films with desired structural and morphological characteristics. In contrast to other approaches, our method can be carried out at a relatively lower temperature to obtain barium titanate ultrathin films free from secondary phases, impurities, and cracks. To reach an in-depth understanding of scientific basis of the proposed process, and in order to disclose the mechanism of formation and growth of barium titanate ultrathin film, in-detail analysis is carried out using XRD, SEM, FE-SEM, and AFM techniques aided by theoretical calculations. The effects of calcining...
Designing of CK45 carbon steel and aisi 304 stainless steel dissimilar welds
, Article Materials Research ; Vol. 17, issue. 1 , Oct , 2014 , p. 106-114 ; 15161439 ; Hamedi, M ; Kokabi, A. H ; Nazari, A ; Sharif University of Technology
Abstract
Gas tungsten arc welding of CK45 and AISI304 stainless steel was performed through preparation of different types of samples using ER308L and ERNi-1 wires. Welded samples were studied by different techniques including optical metallography, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction, hardness measurements and impact test. It was observed that in the buttered specimen, the structure of the weld metal was completely austenitic while the microstructure of unbuttered sample was duplex ferritic-austenitic. M23C6-type carbides were observed within the weld metal of both as-weld specimen types. Effects of different post-weld heat...
Microstructure and mechanical properties in dissimilar butt friction stir welding of severely plastic deformed aluminum AA 1050 and commercially pure copper sheets
, Article Journal of Materials Science and Technology ; Vol. 30, issue. 8 , 2014 , p. 826-834 ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
Abstract
In this study, AA 1050 aluminum alloy and commercially pure copper in annealed and severely plastic deformed conditions were used. The technique used for imposing the severe strain to the sheets was constrained groove pressing (CGP) process. The annealed and severely plastic deformed sheets were subjected to friction stir welding (FSW) at different rotation and traverse speeds. Cu was placed in advancing side. Constant offset of approximately 1 mm was used toward Al side for all welds. A range of welding parameters which can lead to acceptable welds with appropriate mechanical properties was found. For the FSWed CGPed samples, it was observed that the welding heat input caused grain growth...
An investigation on mechanical properties of Alumina-Zirconia-Magnesia spinel composite ceramics fabricated by gel-casting using solution combustion synthesized powder
, Article Materials Science and Engineering A ; Volume 587 , 2013 , Pages 336-343 ; 09215093 (ISSN) ; Faghihi Sani, M. A ; Sharif University of Technology
2013
Abstract
Addition of spinel (MgAl2O4) to Al2O3-ZrO2 composite inhibits alumina grain growth and produces phase boundaries that leads to formation of a ceramic matrix composite with special mechanical properties such as high temperature superplastic deformation. However, the room temperature mechanical properties of Alumina-zirconia-magnesia spinel composite (AZM) such as fracture toughness were rarely investigated by researchers. In this research the AZM nanocomposite powders were synthesized via the solution combustion method. The dense AZM composite samples were fabricated through gelcasting process. Phase analysis studies were performed on both powder and sintered samples and the effects of spinel...
Effects of chemical composition on nanocrystallization kinetics, microstructure and magnetic properties of finemet-type amorphous alloys
, Article Metals and Materials International ; Volume 19, Issue 4 , 2013 , Pages 643-649 ; 15989623 (ISSN) ; Castellero, A ; Rizzi, P ; Tiberto, P ; Hosseini, H. R. M ; Baricco, M ; Sharif University of Technology
2013
Abstract
In this study, the kinetics of nanocrystallization of amorphous Fe 73.5Si13.5B9Nb3Cu1 (F1) and Fe77Si11B9Nb2.4Cu0.6 (F2) alloys is investigated. The microstructure and magnetic properties of the nanocrystalline alloys are compared. The crystallization temperature of F2 alloy is shifted towards lower temperatures with respect to F1. Thus, the crystalline volume fraction and the crystalline grain size at specific annealing temperature for the F2 alloy are higher than for the F1 alloy, accounting for the higher coercive force of F2 alloy with respect to the one of F1 alloy. According to isoconversional methods, the activation energy for crystallization is variable as a function of transformed...
Synthesis of nanocrystalline Ni/Ce-YSZ powder via a polymerization route
, Article Materials Science- Poland ; Volume 31, Issue 3 , 2013 , Pages 343-349 ; 01371339 (ISSN) ; Tamizifar, M ; Arzani, K ; Nemati, A ; Khanfekr, A ; Bolandi, M ; Sharif University of Technology
Oficyna Wydawnicza Politechniki Wroclawskiej
2013
Abstract
Pechini process was used for preparation of three kinds of nanocrystalline powders of yttria-stabilized zirconia (YSZ): doped with 1.5 mol% nickel oxide, doped with 15 mol% ceria, and doped with 1.5 mol% nickel oxide plus 15 mol% ceria. Zirconium chloride, yttrium nitrate, cerium nitrate, nickel nitrate, citric acid and ethylene glycol were polymerized at 80 °C to produce a gel. XRD, SEM and TEM analyses were used to investigate the crystalline phases and microstructures of obtained compounds. The results of XRD revealed the formation of nanocrystalline powder at 900 °C. Morphology of the powder calcined at 900 °C, examined with a scanning electron microscope, showed that the presence of...
Thermal stability during annealing of friction stir welded aluminum sheet produced by constrained groove pressing
, Article Materials and Design ; Volume 45 , 2013 , Pages 222-227 ; 02613069 (ISSN) ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
Abstract
The severely deformed aluminum sheets with strain of 2.32 were successfully joined by friction stir welding (FSW) process. Welding was carried out at various rotation speeds of 600, 800, and 1000. rpm at traveling speed of 200. mm/min corresponding to various revolution pitches of 0.33, 0.25, and 0.20. mm/r, respectively. In order to investigate the thermal stability of the joints, annealing was carried out at temperature of 200 °C for 1. h. Microstructure examinations revealed that severely deformed samples were quite unstable upon FSW process. However, during annealing it was found that in contrast to regions of heat affected zone (HAZ) and thermo mechanical affected zone (TMAZ) where...
The effects of nano Mgo on physical and mechanical properties of Al 2O3-SiC composites
, Article Journal of Ceramic Science and Technology ; Volume 3, Issue 1 , 2012 , Pages 29-34 ; 21909385 (ISSN) ; Surani, F ; Abdizadeh, H ; Baharvandi, H. R ; Sharif University of Technology
2012
Abstract
In this research, the effects of nano-sized MgO in Al2O 3-SiC composites were investigated. The overall changes in the density and mechanical properties of sintered samples (hardness, bending strength and toughness) were evaluated. After mixing, drying and uniaxial compaction of the powders, they were first heat-treated at low temperature in an electric furnace to remove any residuals. They were then heat-treated at high temperature (1700 °C) inside a graphite furnace in argon atmosphere for sintering (at normal and high pressure). The content of MgO in the Al 2O3-10 vol% SiC composite was 0, 500, 1000, and 1500 ppm. Thefracture toughness(KIC)of sintered composite with 10...
Al-Al3Ti nanocomposite produced in situ by two-step hot-press sintering
, Article IOP Conference Series: Materials Science and Engineering ; Volume 40, Issue 1 , 2012 ; 17578981 (ISSN) ; Ghiabakloo, H ; Hosseini, H. R. M ; Mohammadi, A. V ; Sharif University of Technology
2012
Abstract
Aluminum reinforced with a large amount (up to about 55 vol.%) of Al 3Ti particles can be fabricated from Al-20Ti elemental nanometer-sized powder mixture via in-situ two step hot press sintering (TSS). For production of intermetallic reinforced in-situ composite, TSS can provide elevated temperature to facilitate the formation of intermetallic phase in situ and hot consolidation to form a fully dense solid. The first step sintering was employed at a higher temperature to obtain an initial high density, and the second step was held at a lower temperature by isothermal sintering for more time than the first one to increase bulk density without significant grain growth. The optimum TSS regime...
Disabling of nanoparticle effects at increased temperature in nanocomposite solders
, Article Journal of Electronic Materials ; Volume 41, Issue 7 , 2012 , Pages 1907-1914 ; 03615235 (ISSN) ; Roshanghias, A ; Ashayer, R ; Kotadia, H. R ; Khomamizadeh, F ; Kokabi, A. H ; Clode, M. P ; Miodownik, M ; Mannan, S. H ; Sharif University of Technology
2012
Abstract
The use of nanoparticles to control grain size and mechanical properties of solder alloys at high homologous temperature is explored. It is found that silica nanoparticles in the 100 nm range coated with 2 nm to 3 nm of gold can be dispersed within solders during the normal reflow soldering process, and that these particles are effective in hardening the solder and restricting dynamic grain growth during compression testing at low homologous temperature. As the homologous temperature increases towards 0.75, the effects of the nanoparticles on both mechanical properties and dynamical grain growth reduce, and by homologous temperatures of 0.86 the effects have completely disappeared. This...
High-temperature deformation and structural restoration of a nanostructured Al alloy
, Article Scripta Materialia ; Volume 66, Issue 11 , 2012 , Pages 911-914 ; 13596462 (ISSN) ; Simchi, A ; Kim, H. S ; Sharif University of Technology
2012
Abstract
We studied the flow stress and microstructural changes of nanostructured Al-6063 alloy produced by mechanical alloying at various temperatures and strain rates. The analysis of flow curves was performed by a constitutive equation, and the stress exponent and activation energy were determined as functions of strain. The deformation mechanisms were elaborated through microstructural observations by electron backscattering diffraction and transmission electron microscopy. Coarsening of the subgrains and grain growth upon deformation was monitored and related to the Zener-Hollomon parameter
Mechanical properties of severely plastic deformed aluminum sheets joined by friction stir welding
, Article Materials Science and Engineering A ; Volume 543 , 2012 , Pages 243-248 ; 09215093 (ISSN) ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
Abstract
The severely plastic deformed aluminum sheets were joined by friction stir welding (FSW). The technique used for imposing the severe strain to the sheets was constrained groove pressing (CGP) process. The specimens with three different imposed strains by CGP, which lead to different initial microstructures, were joined at various rotation (. ω) and traveling (. V) speeds. The microhardness measurements and microstructure investigations were carried out. It was revealed that after FSW process of the specimens strained by CGP process, grain growth and correspondingly hardness reduction were observed at the stir zone. Also, transverse tensile test was performed at all conditions. For the CGPed...
Effect of high energy ball milling on compressibility and sintering behavior of alumina nanoparticles
, Article Ceramics International ; Volume 38, Issue 4 , May , 2012 , Pages 2627-2632 ; 02728842 (ISSN) ; Aminzare, M ; Razavi Hesabi, Z ; Aboutalebi, S. H ; Sadrnezhaad, S. K ; Sharif University of Technology
2012
Abstract
The effect of high-energy ball milling on the textural evolution of alumina nanopowders (compaction response, sinter-ability, grain growth and the degree of agglomeration) during post sintering process is studied. The applied pressure required for the breakage of the agglomerates (P y) during milling was estimated and the key elements of compressibility (i.e. critical pressure (P cr) and compressibility (b)) were calculated. Based on the results, the fracture point of the agglomerates decreased from 150 to 75 MPa with prolonged milling time from 3 to 60 min. Furthermore, the powders were formed by different shaping methods such as cold isostatic press (CIP) and uniaxial press (UP) to better...