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microstructure-development
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Effect of bonding parameters on microstructure development during TGTLP bonding of Al7075 alloy
, Article Philosophical Magazine ; Vol. 94, issue. 11 , Mar , 2014 , pp. 1166-1176 ; ISSN: 14786435 ; Ekrami, A ; Farahany, S ; Jahangiri, A ; Sharif University of Technology
Abstract
The effect of temperature, pressure and bonding time on microstructure of temperature gradient transient liquid phase (TGTLP) diffusion bonded Al7075 alloy using liquid gallium interlayer was investigated. The selected bonding method relies on using the minimum amount of liquid gallium on faying surfaces, using a very fast heating rate to reach the joining temperature and imposing a temperature gradient across the bond region. The microstructure of the diffusion bonded joints was evaluated by light optical microscopy, scanning electron microscopy and energy dispersive spectroscopy (EDS). Results show that by increasing the temperature, pressure and time of joining, a more uniform...
Influence of nickel and manganese on microstructure and mechanical properties of shielded metal arc-welded API-X80 steel
, Article Journal of Materials Engineering and Performance ; Volume 21, Issue 7 , July , 2012 , Pages 1447-1454 ; 10599495 (ISSN) ; Kokabi, A. H ; Sharif University of Technology
2012
Abstract
Microstructure developments of X80 weld metal by the addition of different amounts of alloying elements such as nickel and manganese to the covering of electrodes were investigated. For this reason, samples were welded with electrodes that Ni value has changed between 0.8 and 3.5% in two critical amounts of Mn 0.7 and 1.6. Optical microscopy and scanning electron microscopy were applied for peer investigation of microstructure. Different phase percentages were obtained by Clemex software and compared in all samples. Results indicated that Ni and Mn change weld microstructure in the as-deposited zone and reheated part and corresponding to each alloying element concentration, amount of...
Microstructural developments and electrical properties of novel coarse-grained SnO2 varistors obtained by CuO addition for low-voltage applications
, Article Ceramics International ; Volume 44, Issue 15 , 2018 , Pages 18478-18483 ; 02728842 (ISSN) ; Mahmoudi, P ; Golmohammad, M ; Delshad Chermahini, M ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
This research focused on making novel low-voltage SnO2 varistors by CuO addition on conventional high-voltage SnO2 varistors. Moreover, the withstand surge capability of samples was studied. The results showed that CuO addition enhances grain growth of SnO2 and coarse-grained SnO2 varistors with simple microstructures were acquired in 1 mol% CuO-doped sample. This coarse-grained SnO2 varistor presented a high nonlinear coefficient (23) and low leakage current density (23 µA/cm2) with low breakdown field value of 0.6 kV/cm. Despite the large grain size, the low residual voltage ratio (2.3) was obtained for this sample compared to the CuO-free sample. The decrease in grain electric resistivity...
Grain growth kinetics and electrical properties of CuO doped SnO2-based varistors
, Article Journal of Alloys and Compounds ; Volume 770 , 2019 , Pages 784-791 ; 09258388 (ISSN) ; Nemati, A ; Maleki Shahraki, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Up to now, attempts for developing coarse-grained SnO2-based varistors which exhibit high nonlinearity property at lower voltage have become a challenge without any prominent result because of its unknown grain growth mechanism. In this study, the effect of CuO addition to SnO2-based varistors as a grain growth enhancer additive on microstructural development, grain growth kinetics, and electrical properties was investigated. The characterization of grain growth kinetics showed that CuO addition encouraged grain growth and enhanced the grains size as it could be seen in the activation energy which decreased from 594 kJ/mol to 364 kJ/mol. In the samples with a low amount of CuO, the solute...
Long-term mechanical performance of polyethylene pipe materials in presence of carbon black masterbatch with different carriers
, Article Polymer Testing ; Volume 91 , 2020 ; Pircheraghi, G ; Sarafpour, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this paper, two types of carbon black (CB) masterbatch with different carriers, i.e. HDPE and LDPE, are used to produce black compounds using three PE100 resins with various short chain branching distributions. Due to difference in short chain branch (SCB) distribution, the used polyethylene resins behave differently in microstructure development and long-term creep behavior. The microstructural analysis using different DSC techniques and rheological measurements revealed more sensitivity of the polyethylene resin with uniform comonomer distribution to the carbon black aggregates and their polymeric carriers. The Full Notched Creep Test (FNCT) was performed to determine the long-term...
Densification and microstructural evolution during laser sintering of A356/SiC composite powders
, Article Journal of Materials Science ; Volume 46, Issue 5 , 2011 , Pages 1446-1454 ; 00222461 (ISSN) ; Godlinski, D ; Sharif University of Technology
Abstract
This article reports experimental results on laser sintering of A356 aluminum alloy and A356/SiC composite powders. Effects of scan rate, sintering atmosphere, hatch spacing, and SiC volume fraction (up to 20%), and particle size (7 and 17 μm) on the densification were studied. The phase formation and microstructural development were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Laser sintering under argon atmosphere exhibited higher densification compared to nitrogen. A faster sintering kinetics was observed as the scan rate decreased. Except at a low SiC content (5 vol%), the composite powders exhibited...
Phase formation during sintering of nanocrystalline zirconia/stainless steel functionally graded composite layers
, Article Materials Letters ; Volume 65, Issue 3 , February , 2011 , Pages 523-526 ; 0167577X (ISSN) ; Simchi, A ; Hokamoto, K ; Tanaka, S ; Sharif University of Technology
Abstract
Microstructural development and phase formation at the interface of yttria stabilized zirconia (3Y-TZP)/430L stainless steel composite layers produced by co-sintering method were studied by SEM, HRTEM, micro-focus XRD, and EPMA. Formation of a rich chromium boundary layer at the interface was noticed, which revealed Cr aggregation at the interface at the elevated temperatures. Misfit dislocations were also observed at the joint interface to tackle the mismatch crystallographic orientations between the ceramic and metal layer. The results of the micro-focus XRD showed formation of no new phases at the boundary zone. Microstructural studies also revealed a retarded grain growth in the...
Effect of RE elements on the microstructural evolution of as cast and SIMA processed Mg-4Al alloy
, Article Journal of Alloys and Compounds ; Volume 509, Issue 5 , February , 2011 , Pages 1567-1572 ; 09258388 (ISSN) ; Khomamizadeh, F ; Sharif University of Technology
2011
Abstract
In the present article, the effect of Rare Earth elements on the microstructural development of as cast and semisolid Mg-4Al alloy produced by SIMA process is studied. Investigation conducted by metallographic observation, scanning electron microscope and quantitative metallographic methods. Results showed that alloy's dendrites turn into larger fully dendritic shape with sharp and narrow arms from equiaxed rosette type as the amount of RE elements increased from 0 through 4%. The effect of RE elements on the microstructure of the treated-alloys was detectable through elimination of vast number of intragranular liquid droplets as well as by decreasing kinetic of microstructural changes. It...
Spark plasma sintering of a multilayer thermal barrier coating on Inconel 738 superalloy: Microstructural development and hot corrosion behavior
, Article Ceramics International ; Volume 42, Issue 2 , 2016 , Pages 2770-2779 ; 02728842 (ISSN) ; Javadi, A. H ; Bahrami, M ; Khodabakhshi, F ; Simchi, A ; Sharif University of Technology
Elsevier Ltd
Abstract
In the present work, spark plasma sintering (SPS) process was employed to prepare a nanostructured yttria-stabilized zirconia (8YSZ) coating on a nickel-based superalloy (INCONEL 738) with functionally graded structure. A stack layer of INCONEL 738/NiCrAlY powder/Al foil/NiCrAlY+YSZ powder/YSZ powder was SPSed in a graphite die at an applied pressure of 40 MPa under an vacuum atmosphere (8 Pa). The sintering temperature was ∼1040 °C. For comparison purpose, the air plasma spray (APS) technique was employed to prepare the thermal barrier coating (TBC). Microstructural studies by scanning electron microscopy showed that the SPSed coating was sound and free of interfacial cracks and large...
Similar and dissimilar friction-stir welding of an PM aluminum-matrix hybrid nanocomposite and commercial pure aluminum: Microstructure and mechanical properties
, Article Materials Science and Engineering A ; Volume 666 , 2016 , Pages 225-237 ; 09215093 (ISSN) ; Simchi, A ; Kokabi, A. H ; Gerlich, A. P ; Sharif University of Technology
Elsevier Ltd
Abstract
Friction stir welding (FSW) of dissimilar joints has recently attracted great interest for the fabrication of bimetallic and layered composite structures. In this paper, dissimilar joining of an aluminum-matrix hybrid nanocomposite to commercial pure aluminum is reported for the first time. An aluminum hybrid nanocomposite reinforced with Al2O3 (2 vol%; 15 nm) and SiC (2 vol%; 50 nm) nanoparticles was prepared by powder metallurgy routes including mechanical milling and hot powder consolidation techniques. Different joint designs at various ranges of rotational (w) and traverse velocities (v) were evaluated to determine process window for the dissimilar solid-state welding. Macro- and...
Supersolidus liquid phase sintering of Al6061/SiC metal matrix composites
, Article Powder Metallurgy ; Volume 52, Issue 1 , 2009 , Pages 28-35 ; 00325899 (ISSN) ; Simchi, A ; Sharif University of Technology
2009
Abstract
The aim of the present work is to study the effect of reinforcement content and sintering temperature on the densification and microstructural development during sintering of Al6061/SiC composite compacts. Prealloyed Al6061 powder was mixed with various amounts of SiC particles up to 27 vol.-% and compacted at 350 MPa. Sintering was carried out in a dry nitrogen atmosphere at 580-620°C. It was shown that the presence of SiC particles retards the densification of the prealloyed powder during solid phase sintering and liquid phase sintering. This effect is particularly noticeable at SiC fractions higher than ∼9 vol.-%, at which continuous networks of the hard particles are formed. Increasing...
Master sintering curves of a nanoscale 3Y-TZP powder compacts
, Article Ceramics International ; Volume 35, Issue 2 , 2009 , Pages 547-554 ; 02728842 (ISSN) ; Simchi, A ; Dourandish, M ; Golestani Fard, F ; Sharif University of Technology
2009
Abstract
The sintering behavior of commercially available granulated ZrO2-3 mol% Y2O3 (3Y-TZP) powder compacts with an aggregate size of 75 nm was studied. The shrinkage response of the powder compacts during non-isothermal sintering was measured in a sensitive dilatometer at different heating rates. Densification and grain growth were also studied after isothermal firing in air according to different sintering cycles. The sintering and grain growth activation energy was estimated to be QS = 485 ± 12 kJ mol-1 and QG = 546 ± 23 kJ mol-1, respectively. Using the estimated Q-values, the master curves for sintering and grain growth were established and used for prediction of the densification and...
Effect of bonding temperature on microstructure development during TLP bonding of a nickel base superalloy
, Article Journal of Alloys and Compounds ; Volume 469, Issue 1-2 , 2009 , Pages 270-275 ; 09258388 (ISSN) ; Ekrami, A ; Kokabi, A. H ; Sharif University of Technology
2009
Abstract
The effect of bonding temperature on microstructure of a transient liquid phase (TLP)-bonded GTD-111 nickel base superalloy, using a Ni-Si-B interlayer, was investigated. At low bonding temperatures microstructure of the joint centerline is controlled by B diffusion. However, at high bonding temperature effect of base metal alloying elements on the joint microstructure development was more pronounced. Effects of bonding temperature on the formation of secondary precipitates in diffusion-affected zone and isothermal solidification time were also analyzed. It was found that above a critical temperature, formation of borides in diffusion-affected zone is suppressed and the time required for...
Pore structure evolution during sintering of HDPE particles
, Article Polymer ; Volume 183 , 2019 ; 00323861 (ISSN) ; Pircheraghi, G ; Foudazi, R ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Sintering is a processing technique in which loose particles consolidate at elevated temperatures to form porous monoliths. Sintering is also a critical stage in recent additive manufacturing method like selective laser sintering. In this study, using an affordable alternative to X-ray tomography technique, we analyze the pore structure evolution in sintered parts made of nascent high-density polyethylene (HDPE) particles in terms of pore surface genus and pore surface curvature. Also, we investigate the underlying microstructural development and macroscopic properties of sintered parts. It is observed that pore structure and macroscopic permeability are strongly influenced by the...
The effect of improved cooling on the microstructure and mechanical properties of friction stir-welded advanced high-strength dual-phase steel
, Article Steel Research International ; Volume 92, Issue2 , August , 2020 ; Kokabi, A. H ; Goodarzi, M ; Kestens, L. A. I ; Sharif University of Technology
Wiley-VCH Verlag
2020
Abstract
The heat-affected zone (HAZ)softening is considered one of the most significant challenges during welding of ferrite–martensite dual-phase (DP) steels. In fact, the strain localization in the softened area results in a premature fracture that degrades the mechanical properties of the joint. Herein, the objective is to investigate the effectiveness of improved cooling using a high thermal diffusivity backing plate (BP) to reduce HAZ softening and enhance the mechanical properties of friction stir-welded DP700 steel. Accordingly, friction stir butt welding of DP700 steel was conducted using copper and mild steel BPs. The findings show that the replacement of steel BP with copper significantly...
The effect of improved cooling on the microstructure and mechanical properties of friction stir-welded advanced high-strength dual-phase steel
, Article Steel Research International ; Volume 92, Issue 2 , 2021 ; 16113683 (ISSN) ; Kokabi, A. H ; Goodarzi, M ; Kestens, L. A. I ; Sharif University of Technology
Wiley-VCH Verlag
2021
Abstract
The heat-affected zone (HAZ) softening is considered one of the most significant challenges during welding of ferrite–martensite dual-phase (DP) steels. In fact, the strain localization in the softened area results in a premature fracture that degrades the mechanical properties of the joint. Herein, the objective is to investigate the effectiveness of improved cooling using a high thermal diffusivity backing plate (BP) to reduce HAZ softening and enhance the mechanical properties of friction stir-welded DP700 steel. Accordingly, friction stir butt welding of DP700 steel was conducted using copper and mild steel BPs. The findings show that the replacement of steel BP with copper significantly...
Phase formation and microstructural evolution during sintering of Al-Zn-Mg-Cu alloys
, Article Powder Metallurgy ; Volume 53, Issue 1 , 2010 , Pages 62-70 ; 00325899 (ISSN) ; Simchi, A ; Gierl, C ; Sharif University of Technology
2010
Abstract
Al–5·6Zn, Al–5·6Zn–2·5Mg and Al–5·6Zn–2·5Mg–1·6Cu (wt-%) powder blends were compacted at 350 MPa and sintered in nitrogen at different temperatures to study microstructural evolution during sintering. Densification, dimensional changes and mechanical properties of the Al alloys were investigated. Microstructural analyses were performed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and simultaneous thermal analysis (STA) in order to determine the temperature and chemical composition of the phases formed during sintering. It was shown that various liquids and intermetallic phases including Al0·71Zn0·29 at 438°C,...