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grain-boundaries
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Total 126 records
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...
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...
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...
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...
Microstructure and mechanical properties of oxide-dispersion strengthened Al6063 alloy with ultra-fine grain structure
, Article Metallurgical & Materials Transactions. Part A ; Mar2011, Vol. 42 Issue 3, p. 816-824 ; Simchi, A. (Abdolreza) ; Kim, H. S ; Sharif University of Technology
Abstract
The microstructure and mechanical properties of the ultra-fine grained (UFG) Al6063 alloy reinforced with nanometric aluminum oxide nanoparticles (25 nm) were investigated and compared with the coarse-grained (CG) Al6063 alloy (~2 μm). The UFG materials were prepared by mechanical alloying (MA) under high-purity Ar and Ar-5 vol pct O2 atmospheres followed by hot powder extrusion (HPE). The CG alloy was produced by HPE of the gas-atomized Al6063 powder without applying MA. Electron backscatter diffraction under scanning electron microscopy together with transmission electron microscopy studies revealed that the microstructure of the milled powders after HPE consisted of ultra-fine grains...
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...
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...
An electron back-scattered diffraction study on the microstructure evolution of severely deformed aluminum AI6061 alloy
, Article IOP Conference Series: Materials Science and Engineering ; Vol. 63, Issue. 1 , 30 June- 4 July , 2014 ; ISSN: 17578981 ; Taheri, A. K ; Kim, H. S ; Sharif University of Technology
Abstract
In this paper dynamic strain ageing behavior in an Al-Mg-Si alloy related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation and ageing effects on microstructure evolutions and strengthening characteristics, the Al6061 alloy were subjected to φ=90° ECAP die for up to 4 passes via route Bc at high temperatures. For investigating the effects of ageing temperature and strain rate in ECAP, Vickers hardness tests were performed. The combination of the ECAP process with dynamic ageing at higher temperatures resulted in a significant increase in hardness. The microstructural evolution of the samples was studied using electron...
Analysis of strain rate sensitivity of ultrafine-grained AA1050 by stress relaxation test
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 45, Issue 12 , November 2014 , Pages 5442-5450 ; Akbarzadeh, A ; Kim, B. H ; Kim, S. K ; Sharif University of Technology
Abstract
Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or...
Microstructural development and mechanical properties of nanostructured copper reinforced with SiC nanoparticles
, Article Materials Science and Engineering A ; Volume 568 , 2013 , Pages 33-39 ; 09215093 (ISSN) ; Salahi, E ; Hesari, F. A ; Yoon, E. Y ; Kim, H. S ; Simchi, A ; Sharif University of Technology
2013
Abstract
Nanostructured Cu and Cu-2. vol% SiC nanocomposite were produced by high energy mechanical milling and hot pressing technique. Microstructure development during fabrication process was investigated by X-ray diffraction, scanning electron microscope, scanning transmission electron microscope, and electron backscatter diffraction techniques. The results showed that the microstructure of copper and copper-based nanoco mposite composed of a mixture of equiaxed nanograins with bimodal and non-random misorientation distribution. The presence of SiC nanoparticles refined the grain structure of the copper matrix while the fraction of low angle grain boundaries was increased. Evaluation of mechanical...
Effect of η phase on mechanical properties of the iron-based superalloy using shear punch testing
, Article ISIJ International ; Volume 53, Issue 2 , 2013 , Pages 311-316 ; 09151559 (ISSN) ; Kheirandish, S ; Razavi, S. H ; Abbasi, S. M ; Sahrapour, P ; Sharif University of Technology
2013
Abstract
In this paper, the shear deformation behavior of A286 Iron-based superalloy was studied with an emphasis on the influence of η phase on shear strength. The η (Ni3Ti phase precipitates at high temperature heat treatment or during services at the expense of gamma prime phase. According to the microstructural features, no evidences of η phase were found at 650 and 720°C. η phase precipitated at 780 and 840°C and the amount of it increased with an increase the time and temperature. Because of using the alloy as fasteners, investigation of shear properties and the influence of η phase on it are indispensable. The shear strength of the alloy with different volume fractions of η was examined. It...
Effect of molybdenum on grain boundary segregation in Incoloy 901 superalloy
, Article Materials and Design ; Volume 46 , 2013 , Pages 573-578 ; 02641275 (ISSN) ; Abbasi, S. M ; Sharif University of Technology
2013
Abstract
In this paper, the effect of molybdenum on the grain boundary segregation of other elements was studied in Incoloy 901 superalloy. Initially, five alloys were prepared with different percentages of Mo by using a vacuum induction furnace. Then, these alloys were remelted by Electro-slag remelting (ESR) process and after homogenizing at 1160 °C for 2. h followed by air cooling, were rolled. The effect of Mo on segregation of elements was evaluated with Scanning Electron Microscopy, Linear Analysis, and the mechanical tests. The results showed that the grain boundary segregations of elements in Incoloy 901 superalloy were decreased by increasing of molybdenum content up to 6.7% and the...
Accurate numerical model for surface scattering, grain boundary scattering, and anomalous skin effect of copper wires
, Article Proceedings - Winter Simulation Conference ; January , 2013 , Pages 209-210 ; 08917736 (ISSN) ; 9781467348416 (ISBN) ; Sarvari, R ; Akbarzadeh, A ; Rostami, M ; Sharif University of Technology
2013
Abstract
In this paper we have studied both DC size effect and anomalous skin effect caused by surface and grain boundary scattering on the resistivity of Cu thin films by a Monte Carlo method. Contribution of each scattering mechanism and the interaction between them are analyzed separately. A simple and fast numerical recursive method is also introduced to guess the structure of electric field and distribution of current inside the thin film to evaluate the surface resistance instead of complicated analytical formulas
Severe plastic deformation of 6061 aluminum alloy tube with pre and post heat treatments
, Article Materials Science and Engineering A ; Volume 563 , 2013 , Pages 60-67 ; 09215093 (ISSN) ; Kazeminezhad, M ; Miyamoto, H ; Sharif University of Technology
2013
Abstract
In this work, the 6061 aluminum alloy tubes are severely deformed through a novel method called Tube Channel Pressing (TCP). The ability of this process in improving mechanical properties, grain refinement and microstructural changes of the alloy with different heat treatments before and after TCP process is investigated. Results show that TCP has notable effect on grain refinement and decreases crystallite size of solid solution treated aluminum 6061 material to 52. nm after equivalent strain of 3.09 which is comparable with the measured data from other SPD processes. The strength of the specimens aged before TCP is higher than that of those aged after TCP. The specimens artificially aged...
Fatigue properties of heat-treated 30MSV6 vanadium microalloyed steel
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 3 , March , 2013 , Pages 830-839 ; 10599495 (ISSN) ; Nategh, S ; Yoozbashizadeh, H ; Ekrami, A ; Sharif University of Technology
2013
Abstract
In the present study, 30MSV6 microalloyed steel was heat treated under different conditions, and the relation between its microstructure and mechanical properties was investigated. Scanning electron microscopy and transmission electron microscopy were used to characterize the microstructure of the heat-treated steel, and the effect of microstructure on tensile strength and fatigue behavior was determined. Microstructural analysis indicated that precipitates were formed at different sites such as grain boundaries and sub-grain boundaries. Furthermore, microstructural studies accompanied by the evaluation of mechanical properties revealed that the optimal heat treatment cycle of 30MSV6...
Nanoparticle enhanced solders for increased solder reliability
, Article Materials Research Society Symposium Proceedings, 28 November 2011 through 2 December 2011, Boston, MA ; Volume 1424 , 2012 , Pages 115-120 ; 02729172 (ISSN) ; 9781605114019 (ISBN) ; 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
Due to environmental concerns traditional eutectic tin-lead solder is gradually being replaced in electronic assemblies by "lead-free" solders. During this transition, nanoparticle technology is also being investigated to see whether improvements in joint reliability for high temperature applications can be made. Nanoparticles can be used to harden the solder via Zener pinning of the grain boundaries and reduce fatigue failure. This paper explores the effects of adding Silica nanoparticles to SnAgCu solder, and how the mechanical properties induced in the solder vary with temperature. It is found that above 100°C the mechanical response and microstructure of the normal and nanoparticle...
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...
Effect of hot rolling on microstructure and transformation cycling behaviour of equiatomic NiTi shape memory alloy
, Article Materials Science and Technology (United Kingdom) ; Volume 28, Issue 6 , 2012 , Pages 727-732 ; 02670836 (ISSN) ; Rezaei, E ; Karimi Taheri, A ; Sharif University of Technology
2012
Abstract
In this study, a near equiatomic NiTi shape memory alloy was hot rolled at 800°C using thethickness reductions of 30 and 50%. Optical and transmission electron microscopy, together withX-ray diffraction were used to demonstrate the microstructural changes associated with the hotrolling at different thickness reductions. Repeated transformation cycling was employed toinvestigate the evolution of R phase during cycling. Microstructural observations revealed thepresence of deformation twins embedded in an elongated grain matrix in the hot rolled material.Moreover, it was found that with increasing degree of thickness reduction, the size and number ofdeformation twins increased throughout the...
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...