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grain-boundaries
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NumericalModel for Surface Scattering and Grain Boundary Scattering of Metallic Wires
, M.Sc. Thesis Sharif University of Technology ; Sarvari, Reza (Supervisor)
Abstract
Recently, the size of copper interconnects is going to reach lower than the mean free path of electrons for copper. In this situation, we should consider the effect of other scattering mechanisms as well as thermal scattering on copper thin films. In this work we study both DC size effect and anomalous skin effect on resistivity by a Monte Carlo method. Contribution of each scattering mechanism and the interaction between them are analyzed separately. The structure of electrical field and distribution of current in thin films have also been studied. Investigating of the effect of exact nature of surface scattering and grain boundary scattering on resistivity is one of the interests of this...
Molecular Dynamics Simulation of Crack Propagation in Nanocrystalline Materials
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor)
Abstract
Nanocrystalline metals and alloys have some appealing characteristics with significance potential compared to their microcrystalline counterparts for engineering applications. These include ultra-high yield and fracture strengths, decreased elongation and toughness, superior wear resistance, and the promise of enhanced superplastic formability at lower temperatures and faster strain rates. This leads us to study the effects of different nanocrystalline parameters on crack propagation process in these materials. In the present study, the behavior of a crack in a columnar nanocrystalline structure is examined. One of the methods of modelling nanocrystals primary structures is the Voronoi...
Multiscale Investigation of Plastic Behavior in Crystalline Metals
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
Abstract
In this study, a modern multiscale sequential molecular dynamics (MD) – finite element (FE) coupling method is proposed to represent the role of grain boundary (GB) planar defect on mechanical properties of crystalline structures at various temperatures. Different Grain Boundary misorientation angle is considered and the temperature varies from 0 up to 800 K. The embedded-atom method (EAM) many-body interatomic potential is implemented to consider pairwise interactions between atoms in the crystalline structures with face-centered-cubic (FCC) lattice structure at different temperatures. In addition, the Nose-Hoover thermostat is employed to adjust the fluctuation of temperature. The atomic...
The Effect of Friction Stir Processing with SiC Nanoparticles on the Stability of Grain Boundaries and Mechanical Properties of Severely Deformed Aluminum
, Ph.D. Dissertation Sharif University of Technology ; Kokabi, Amir Hossein (Supervisor) ; Kazeminezhad, Mohsen (Co-Advisor)
Abstract
Severe plastic deformation (SPD) is known as an efficient route for grain refinement in the metals. However, the size of SPD products is almost small due to the limitations associated with the SPD processes. Hence, the growing attention is paid to the welding of severely deformed metals. Friction stir welding, as a solid state welding process, seems to be suitable for this purpose. But, considering the significant amount of stored strain within the SPDed metals, appreciable grain growth after recrystallization occurs not only in the stir zone, but also in its surrounded areas. In this study, the 1050-aluminum sheets severely deformed through constrained groove pressing (CGP) were processed...
Transient Liquid phase Bonding of AL2024 Alloy and Evaluation of Joint Properties
, Ph.D. Dissertation Sharif University of Technology ; Kokabi, Amir Hossein (Supervisor) ; Ekrami, Ali Akbar (Supervisor)
Abstract
Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in...
γ' Precipitate dissolution during heat treatment of nimonic 115 superalloy
, Article Materials and Manufacturing Processes ; Volume 24, Issue 5 , 2009 , Pages 559-563 ; 10426914 (ISSN) ; Sadeghi, M. H ; Akbarzadeh, A ; Sharif University of Technology
2009
Abstract
In precipitation hardenable materials, it is desirable to determine the precipitate dissolution temperature for homogenizing the microstructure by controlling the size and distribution of the precipitates. In this research, differential thermal analysis, dilatometry technique, heat treatments followed by microstructure evaluation were used to determine the -γ' dissolution temperature of Nimonic 115. It is assumed that the variation of enthalpy is governed by the changes in y volume fraction and γ concentration with time and temperature, and any contribution of the coarsening of γ' is neglected. The values obtained for the solvus temperature of γ precipitates by the three methods are all in...
Two dimensionality aspects of HTSC
, Article Superconductor Science and Technology ; Volume 16, Issue 10 , 2003 , Pages 1216-1223 ; 09532048 (ISSN) ; Akhavan, M ; Sharif University of Technology
2003
Abstract
Based on transport and magnetic measurements on Gd(Ba2-xPrx)Cu3O7+δ, and some other properties of high temperature superconductors (HTSC), we have extracted similarities between superconductors, two-dimensional electron gas (2D-EG) i.e. MOSFETs and ultrathin films of conventional superconductors. These are based on properties such as superconductor-insulator transition in superconductors and metal-insulator transition (MIT) in 2D-EG with doping and magnetic field, localization in transport conduction, quantum unit of resistance at MIT, larger change in resistance from critical doping to the insulating side in comparison with change from critical doping to the metallic side and strong...
The role of microstructural features on the electrical resistivity and mechanical properties of powder metallurgy Al-SiC-Al2O3 nanocomposites
, Article Materials and Design ; Volume 130 , 2017 , Pages 26-36 ; 02641275 (ISSN) ; Simchi, A ; Sharif University of Technology
Abstract
There are many engineering applications in which composite materials are required to satisfy two or more criteria regarding physical and mechanical properties. In this article, Al-matrix nanocomposites reinforced with different volume fractions of SiC nanoparticles (~ 50 nm; up to 6%) were processed by powder metallurgy (P/M) routes through mechanical milling and hot consolidation techniques. Microstructural studies showed that nano-metric Al2O3 particles with a size of ~ 20 nm and volume fraction of ~ 2% were formed and distributed in the metal matrix, owing to the surface oxides breaking. Microstructural analysis also revealed that the size of cellular structure and the density of...
The effects of MM38.2Co46.4Ni15.4 alloy additions on the mechanical properties of a Nd12.8Fe 79.8B7.4-type sintered magnet
, Article Materials Letters ; Volume 60, Issue 4 , 2006 , Pages 555-558 ; 0167577X (ISSN) ; Kianvash, A ; Sharif University of Technology
2006
Abstract
The mechanical properties of the Nd-Fe-B-based alloys are closely related to their microstructures. It was found that the Co and Ni additions to the Nd2Fe14B (Φ) matrix phase and reduction in the amounts of rare earth (RE)-rich (n) and B-rich (η) grain boundary phases are very effective in improving the mechanical properties. The addition of a MM 38.1(MM: Misch Metal)-Co46.4-Ni15.5 alloy to a ternary Nd12.8Fe79.8B7.4-type alloy by a binary powder blending technique resulted in a considerable increase in bending and compressive strength, and a significant decrease in impact strength. The solid solution hardening of the matrix phase by Co and Ni and the presence of intergranular cracks within...
The effects of Misch-Metal oxide addition on magnetic properties and crystal structure of Sr1-xMMxFe12O19 ferrite
, Article Journal of Alloys and Compounds ; Volume 448, Issue 1-2 , 2008 , Pages 284-286 ; 09258388 (ISSN) ; Naghibolashraphy, N ; Sharif University of Technology
2008
Abstract
The effects of Misch-Metal (MM) oxide addition on magnetic properties, crystal structure and microstructure of the M-type strontium ferrite have been studied. By MM substitution of Sr a significant increase in intrinsic coercivity and a slight decrease in remanence was observed. The highest value of energy product was obtained at 4 wt.% MM addition. By calculating the lattice constants of 4 and 8 wt.% MM added specimens, it was found that the length of c-axis decreases by 4 wt.% MM addition and then undergoes a considerable increase at 8 wt.%, while the a-axis increases monotonously. The SEM observations revealed that the migration of MM oxides to the grain boundaries could be the major...
The effect of TLP bonding temperature on microstructural and mechanical property of joints made using FSX-414 superalloy
, Article Materials Science and Engineering A ; Volume 546 , June , 2012 , Pages 291-300 ; 09215093 (ISSN) ; Ekrami, A ; Khan, T. I ; Sharif University of Technology
2012
Abstract
The bonding temperature is an important parameter for optimization of the Transient Liquid Phase (TLP) bonding process in order to achieve a sound joint with good mechanical properties. However, the bonding temperature used can also be restricted by the microstructural stability of the base metal. In this study, the effect of bonding temperature (1050-1200 °C) on the joint microstructure and mechanical properties was studied for TLP bonding of FSX-414 superalloy using MBF-80 interlayer with thickness of 50 μm. Increasing bonding temperature from 1050 to 1150 °C caused reduction in the time required for complete isothermal solidification in agreement with models based on the diffusion induced...
The effect of sintering temperature on the weak link behavior of Bi-2223 superconductors
, Article 4th International Conference on Magnetic and Superconducting Materials, MSM'05, Agadir, 5 September 2006 through 8 September 2006 ; Volume 3, Issue 9 , 2006 , Pages 3011-3014 ; 18626351 (ISSN) ; Salamati, H ; Eslami, M ; Akhavan, M ; Sharif University of Technology
2006
Abstract
We have studied the effect of sintering temperature on the weak link behavior of polycrystalline Bi2223 superconductors with different intergranular coupling using the XRD, electrical resistivity and AC susceptibility techniques. The XRD results show that by increasing sintering temperature up to 865°C the Bi2212 phase fraction decrease. It was found that the Bi2212 phase on the grain boundaries is likely to play the role of weak links and consequently reduces the intergranular critical current densities. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA
The effect of reinforcement percentages on properties of copper matrix composites reinforced with TiC particles
, Article Journal of Alloys and Compounds ; Volume 676 , 2016 , Pages 120-126 ; 09258388 (ISSN) ; Sharif University of Technology
Elsevier Ltd
Abstract
In this research, copper matrix composites reinforced with different amounts of titanium carbide particles were produced by mechanical milling and in-situ formation of reinforcements. Morphology and size of milled powders were inspected by scanning electron microscopy (SEM) several times during milling process. Changes in lattice parameter, crystallite size, lattice strain, dislocation density and Gibbs free energy changes (due to increasing in dislocation densities and grain boundaries) in different samples (with different TiC particles contents) were studied by X-Ray Diffraction technique with Cu-kα radiation and using Nelson-Riley method and Williamson-Hall equation. Microstructure of...
The effect of different rare earth elements content on microstructure, mechanical and wear behavior of Mg-Al-Zn alloy
, Article Materials Science and Engineering A ; Volume 527, Issue 7-8 , 2010 , Pages 2027-2035 ; 09215093 (ISSN) ; Masoudi, A ; Khomamizadeh, F ; Sharif University of Technology
2010
Abstract
The effect of Rare earths addition to AZ91 magnesium alloy and its influence on the microstructure and mechanical properties was investigated in this study. Addition of cerium rich misch metal to AZ91 alloy resulted in formation of needle shape particles, which had a very high thermal stability, providing superior mechanical properties compared to AZ91 magnesium alloy. As a result, the grain boundaries were less susceptible for grain boundary sliding at high temperatures. The steady state creep rates were specified and for the AZ91 alloy and the results indicate a mixed mode of creep behavior, with some grain boundary effects contributing to the overall behavior. However for the RE added...
The effect of different content of Al, RE and Si element on the microstructure, mechanical and creep properties of Mg-Al alloys
, Article Materials Science and Engineering A ; Volume 523, Issue 1-2 , 2009 , Pages 1-6 ; 09215093 (ISSN) ; Tari, A ; Khomamizadeh, F ; Sharif University of Technology
2009
Abstract
The effect of Al content and Si addition on the microstructural and creep properties of Mg-Al-RE alloys was investigated in this study. The steady state creep rates were specified and it was found that the creep behavior of the alloy, which is dependent on the stability of the near grain boundary microstructure, was improved by the RE and Si addition. For the AZ91 alloy, the results indicate a mixed mode of creep behavior, with some grain boundary effects contributing to the overall behavior. However for the RE and Si added samples, sliding of grain boundaries was greatly suppressed and the dislocation climb controlled creep was the dominant deformation mechanism. Analysis of creep rates...
The effect of Cu addition on the hot deformation behavior of NiTi shape memory alloys
, Article Journal of Alloys and Compounds ; Volume 499, Issue 1 , June , 2010 , Pages 57-62 ; 09258388 (ISSN) ; Kheirandish, Sh ; Aboutalebi, M ; Karimi Taheri, A ; Abbasi, S. M ; Sharif University of Technology
2010
Abstract
The influence of Cu addition on the hot deformation behavior of NiTi shape memory alloys was investigated using hot compression test. A series of alloys with different Cu contents of Ti50.4Ni49.6-xCux (x = 0, 3, 5, 7 at.%) were deformed under compression to a true strain of 0.7 at the temperature range of 700-1000 °C with 100 °C intervals and constant strain rate of 0.1 s-1. The stress-strain curves showed that the addition of Cu to NiTi alloy made the flow curves shift upward. This was confirmed by the calculated critical stress, σc, obtained from inflections in θ-σ plots, which is attributed to the formation of high strength Cu containing precipitates and solid solution hardening caused by...
Synthesis and characterisation of nanostructured neodymium titanium oxides by sol-gel process: Controlling the phase composition, crystal structure and grain size
, Article Materials Chemistry and Physics ; Volume 122, Issue 2-3 , 2010 , Pages 512-523 ; 02540584 (ISSN) ; Fray, D. J ; Sharif University of Technology
2010
Abstract
Nanocrystalline neodymium titanium oxide thin films and powders with different phase compositions with mesoporous structure were produced by a straightforward particulate sol-gel route. The sols were prepared in various Nd:Ti molar ratios and they showed a narrow particle size distribution in the range 20-26 nm. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders contained mixtures of Nd4Ti9O24, Nd2Ti4O11, Nd3Ti4O12 for titanium dominant powders (Nd:Ti ≤ 45:60), mixtures of Nd2TiO5 and Nd2O3 for neodymium dominant powders (Nd:Ti ≥ 75:25) and pure Nd3Ti4O12 phase for equal molar ratio of Nd:Ti, depending on the annealing temperature and Nd:Ti...
Synergistic role of carbon nanotube and SiCn reinforcements on mechanical properties and corrosion behavior of Cu-based nanocomposite developed by flake powder metallurgy and spark plasma sintering process
, Article Materials Science and Engineering A ; Volume 786 , 2020 ; Mousa Mirabad, H ; Khalili Azar, M ; Kakaei, K ; Kim, H .S ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Hybrid-reinforced metals are novel composite materials in which nano-phases including nanoparticles and nanotubes/nanosheets are used simultaneously to reinforce metals or alloys to enhance physical, mechanical, wear and other properties. In this research, Cu/(CNT-SiC) hybrid nanocomposite was synthesized using flake powder metallurgy and spark plasma sintering method and the effects of hybrid reinforcements on microstructural, wear and corrosion properties of the developed material were investigated and compared with those of copper. Microstructural characterization showed reduction of average grain size from 419 to 307 nm and increase of low angle grain boundaries with the introduction and...
Surfactant-assisted synthesis and characterization of hydroxyapatite nanorods under hydrothermal conditions
, Article Materials Science- Poland ; Volume 27, Issue 4 , 2009 , Pages 961-971 ; 01371339 (ISSN) ; Solati Hashjin, M ; Sara Shafiei, S ; Goudarzi, A ; Salarian, R ; Nemati, A ; Sharif University of Technology
2009
Abstract
Hydroxyapatite (HAp) nanorods with uniform morphology and controllable size were successfully synthesized by precipitating Ca(NO3) 24H2O and (NH4)2HPO4 in the presence of cetyltrimethylammonium bromide (CTAB) and polyethylene glycol 400 (PEG 400) as cationic surfactant and non-ionic cosurfactant, respectively, under hydrothermal conditions. The effect of hydrothermal temperature on the composition, morphology and size of HAp particles was studied using X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM). Results revealed that the morphology and size of HAp particles can be effectively controlled by the presence of CTAB and PEG...
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...