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grain-boundaries
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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...
Mathematical modeling of the reaction in an iron ore pellet using a mixture of hydrogen, water vapor, carbon monoxide and carbon dioxide: An isothermal study
, Article Advanced Powder Technology ; Volume 17, Issue 3 , 2006 , Pages 277-295 ; 09218831 (ISSN) ; Motamed Hashemi, M. Y ; Saboohi, Y ; Sharif University of Technology
VSP BV
2006
Abstract
A mathematical time-dependent and isothermal model based on the grain model has been developed to simulate the kinetic and thermal behaviors of a porous iron oxide pellet undergoing chemical reactions with a mixture of hydrogen, carbon monoxide, carbon dioxide and water vapor. Its novelty consists in fact that it can deal with a multi-species reducing gas and oxide pellet. In spite of previous models in which the pure reductant was applied as reducing gas, this model can indicate an actual view of pellet reduction including the effects of reducing gas utility and reducing gas ratio. A finite volume fully implicit technique was applied for solving the governing equations. The model has been...
Study of microstructural evolution and phase's morphology after partial remelting in A356 alloy
, Article Semi-Solid Processing of Alloys and Composites 10 - Selected, peer reviewed papers from the 10th International Conference on Semi-Solid Processing of Alloy and Composites, S2P 2008, Aachen, 16 September 2008 through 18 September 2008 ; Volume 141-143 , 2008 , Pages 367-372 ; 10120394 (ISSN); 9771012039401 (ISBN) ; Bigdeli, M ; Hajian Heidary, M ; Khomamizadeh, F ; Sharif University of Technology
Trans Tech Publications Ltd
2008
Abstract
In this work, effective parameters of SIMA process to obtain non dendritic microstructure in A356 alloy were investigated. In addition, the effect of SIMA process on the evolution of morphology of silicon and intermetallic phases in this alloy was studied. Microstructure images obtained from optical microscopy and SEM observation showed that increase in plastic work up to 40% and then holding of samples in the semi solid state at temperature of 580°C, causes that primary dendritic structure changes to non dendritic, fine and globular structure, but optimum reheating time completely depended on initial thickness of samples. If all parameters of SIMA process are the same, the grain boundaries...
In situ postweld heat treatment of transformation induced plasticity steel resistance spot welds
, Article Science and Technology of Welding and Joining ; Volume 23, Issue 1 , 2018 , Pages 71-78 ; 13621718 (ISSN) ; Pouranvari, M ; Abedi, A ; Ghaderi, A. A ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
Transformation-induced plasticity (TRIP) steel resistance spot welds are delicate to low-energy interfacial failure via crack propagation through martensitic fusion zone during cross-tension (CT) loading. This paper addresses the effect of three different types of in situ postweld heat treatment (PWHT) on the mechanical properties of TRIP steel resistance spot welds. Depending on the post weld second pulse current level, three different strengthening mechanisms were found including (i) martensite tempering with reduced hardness, (ii) refining of martensite packets with improved toughness and (iii) nugget re-melting/enlargement combined with possible reduction of grain boundary impurity...
Effect of silicon carbide nanoparticles on hot deformation of ultrafine-grained aluminium nanocomposites prepared by hot powder extrusion process
, Article Powder Metallurgy ; Volume 59, Issue 4 , 2016 , Pages 262-270 ; 00325899 (ISSN) ; Simchi, A ; Sharif University of Technology
Taylor and Francis Ltd
Abstract
The flow behaviour of Al–SiC nanocomposites prepared by mechanical milling and hot powder extrusion methods was studied at different temperatures (350–500°C) and strain rates (0.005–0.5 s−1). The flow of the Powder metallurgy nanocomposites exhibited a peak stress followed by a dynamic flow softening behaviour. It was shown that mechanical milling increased high-temperature strain rate sensitivity of ultrafine-grained (UFG) aluminium while decreasing its flow dependence to temperature. Constitutive analysis of the hot deformation process by Zener–Hollomon parameter (Z) also indicated a remarkable increase in the deformation activation energy (about 40%). Likewise, SiC nanoparticles (up to...
Mechanisms governing microstructural evolution during consolidation of nanoparticles
, Article Materials and Manufacturing Processes ; Volume 30, Issue 11 , 2015 , Pages 1397-1402 ; 10426914 (ISSN) ; Mahnama, M ; Naghdabadi, R ; Sharif University of Technology
Taylor and Francis Inc
2015
Abstract
In micron-scale, powder consolidation process is driven by diffusion phenomenon, while in nano-scale the higher surface energy of particles leads to some anomalous behaviors within the process. In order to investigate the nano-sintering occurrence, an atomistic approach is employed via molecular dynamics simulations. Within this approach, the effect of particle size and temperature is examined. The study of particle structure emphasizes on a transition on the governing mechanism of process depending on the material energy levels. The results show that in a specific particle size at low temperatures, the main sintering mechanism is the plastic deformation, while at elevated temperatures it...
Coupled continuum damage mechanics and crystal plasticity model and its application in damage evolution in polycrystalline aggregates
, Article Engineering with Computers ; 2021 ; 01770667 (ISSN) ; Assempour, A ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
In the present study, damage initiation and growth in a polycrystalline aggregate are investigated. In this regard, an anisotropic continuum damage mechanics coupled with rate-dependent crystal plasticity theory is employed. Using a thermodynamically consistent procedure, a finite deformation formulation is derived. For this purpose, the damage tensor is incorporated in the crystal plasticity formulation for a cubic single crystal. The damage evolution is considered to be dependent on the history of damage, equivalent plastic strain, stress triaxiality, and Lode parameters. This material model is implemented in the commercial finite-element code Abaqus/Standard by developing a user material...
Coupled continuum damage mechanics and crystal plasticity model and its application in damage evolution in polycrystalline aggregates
, Article Engineering with Computers ; Volume 38 , 2022 , Pages 2121-2135 ; 01770667 (ISSN) ; Assempour, A ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
In the present study, damage initiation and growth in a polycrystalline aggregate are investigated. In this regard, an anisotropic continuum damage mechanics coupled with rate-dependent crystal plasticity theory is employed. Using a thermodynamically consistent procedure, a finite deformation formulation is derived. For this purpose, the damage tensor is incorporated in the crystal plasticity formulation for a cubic single crystal. The damage evolution is considered to be dependent on the history of damage, equivalent plastic strain, stress triaxiality, and Lode parameters. This material model is implemented in the commercial finite-element code Abaqus/Standard by developing a user material...
Deformation behavior of severely deformed al and related mechanisms through warm tensile test
, Article Journal of Materials Engineering and Performance ; Volume 26, Issue 3 , 2017 , Pages 1311-1324 ; 10599495 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
Springer New York LLC
2017
Abstract
Flow stress and ductility behaviors of the annealed and severely deformed Al were investigated at warm deformation temperatures. Constrained groove pressing (CGP) method as a severe plastic deformation process was used. The tensile test was carried out at the temperature range of the 298-573 K and strain rate range of 0.001-0.1 s−1 to present the elevated temperature deformation behavior utilizing hyperbolic sine constitutive equation. The flow stress of the CGPed sample is increased with the number of CGP passes and decreased with temperature. Dynamic recovery and strain softening are found as main restoration mechanisms. Flow stress amounts are not remarkably affected by the strain rate....
Effect of temperature on microstructural evolution and subsequent enhancement of mechanical properties in a backward extruded magnesium alloy
, Article International Journal of Advanced Manufacturing Technology ; Volume 95, Issue 9-12 , 2018 , Pages 3155-3166 ; 02683768 (ISSN) ; Mirjavadi, S. S ; Salandari-Rabori, A ; Sharif University of Technology
Springer London
2018
Abstract
The capability of backward extrusion (BE) method was assessed to achieve modified structures in AZ80 magnesium alloy. At first, 3D-Deform was employed to simulate the deformation flow through the deformed cup which gives an evidence from the flow behavior of the material. The material was processed via BE method at various temperatures of 250, 350, and 450 °C. Metallographic investigations were conducted in three different regions of the BE-processed cup (wall, bottom, and flow channel). The main feature observed at the wall of the BE cup was the presence of mechanical twins, the frequency of which was reduced by raising the process temperature. The flow localization in the form of shear...
Influence of In situ thermal processing strategies on the weldability of martensitic stainless steel resistance spot welds: effect of second pulse current on the weld microstructure and mechanical properties
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 50, Issue 11 , 2019 , Pages 5191-5209 ; 10735623 (ISSN) ; Pouranvari, M ; Sharif University of Technology
Springer Boston
2019
Abstract
Martensitic stainless steel (MSS) welds are notorious for their susceptibility to low-energy failure due to the formation of brittle martensitic structure in the fusion zone. The unique approach to enhance the mechanical properties of MSS resistance spot welds during both the tensile-shear and the cross-tension loading is to improve the fracture toughness of the fusion zone. In the present study, the effect of double-pulse welding on the microstructure-mechanical properties relationship of the AISI420 MSS resistance spot welds is investigated. Depending on the second pulse current level, various metallurgical phenomena was observed including (i) rapid tempering of martensite in the fusion...
Fast isothermal solidification during transient liquid phase bonding of a nickel alloy using pure copper filler metal: solubility vs diffusivity
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 50, Issue 5 , 2019 , Pages 2235-2245 ; 10735623 (ISSN) ; Pouranvari, M ; Sharif University of Technology
Springer Boston
2019
Abstract
This investigation aims at understanding the underlying fundamentals of the isothermal solidification phenomenon during the transient liquid phase (TLP) bonding process. The isothermal solidification is governed by solid-state diffusion of the melting point depressant (MPD) into the base material, which, in turn, is controlled by both kinetic and thermodynamic parameters; however, the latter factor is generally ignored. In this work, the competition between kinetics and thermodynamics of diffusion were considered in TLP bonding of a nickel alloy, Monel 400, using two distinct filler metals including pure copper (Cu) and Ni-Si-B filler metal. The joint generated by Ni-Si-B filler metal...
Experimental analysis on the material properties of A356.0 aluminum alloy surface nanostructured by severe shot peening
, Article Journal of Materials Engineering and Performance ; Volume 29, Issue 1 , 2020 , Pages 143-154 ; Jafarzadeh, H ; Esmaeili, M. A ; Sharif University of Technology
Springer
2020
Abstract
The effects of severe shot-peening process and formation of a nanostructured surface layer on mechanical properties of A356.0 alloy were investigated in this paper. X-ray diffraction analyses revealed that the average size of near-surface grains in severe shot-peened specimens is 75.8 nm. Three types of disk-shaped specimens, non-treated, conventionally shot-peened, and severely shot-peened were subjected to pin-on-disk wear test in the dry condition, in different loading and sliding speeds. Shot-peening process increases both hardness and roughness of the surface, and these two factors have, respectively, positive and negative effects on wear resistance. However, because of high-density...
Al-doped Li7La3Zr2O12 garnet-type solid electrolytes for solid-state Li-Ion batteries
, Article Journal of Materials Science: Materials in Electronics ; Volume 32, Issue 5 , 2021 , Pages 6369-6378 ; 09574522 (ISSN) ; Golmohammad, M ; Soleimany Mehranjani, A. R ; Faghihi Sani, M ; Sharif University of Technology
Springer
2021
Abstract
Cubic phase Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for next-generation Li-ion batteries. In this work, the combustion sol–gel technique is used to prepare an Al-doped LLZO solid electrolyte. The crystal structure is investigated, and the cubic phase is confirmed. Densification properties were investigated using SEM and optical dilatometry. The densification of the Al-doped sample takes place in two stages through two different shrinkage rates. Using 0.25 mol Al-dopant 94% relative density is achieved at 1100 °C. The effect of Al-doping on electrochemical properties is investigated in detail using AC impedance spectroscopy. The result indicates that the optimum concentration of...
Structural, spectral, dielectric and magnetic properties of Co–Cr-substituted hexagonal ferrites with X-type structure
, Article Journal of the Korean Ceramic Society ; Volume 59, Issue 4 , 2022 , Pages 453-464 ; 12297801 (ISSN) ; Khan, M. A ; Gulbadan, S ; Akhtar, M. N ; Ahmad, M ; Hussain, A ; Islam, M ; Sharif University of Technology
Springer
2022
Abstract
Co2+ and Cr3+-substituted SrBaCu2-xCoxCryFe28-yO46 X-type hexaferrite with x = y = 0, 0.1 to 0.5 (step = 0.1) were prepared through auto-combustion sol–gel method and sintered at 1250 °C for 5 h which was found from thermal analysis. The thermal investigation, phase detection, spectral, magnetic, and dielectric characteristics of the prepared composition were investigated by TGA, XRD, FTIR, VSM, and dielectric measurement. XRD patterns of the entire composition confirmed the development of a single phase of X-type structure. The enhancement in the lattice parameters and cell volume was observed by varying the Co–Cr concentration, attributed to the larger ionic radii substitution. FTIRspectra...
Microstructural evolution and Bio-corrosion behavior of a CP-Ti processed by multi-pass of severe plastic deformation
, Article JOM ; Volume 74, Issue 12 , 2022 , Pages 4621-4631 ; 10474838 (ISSN) ; Famil Hatami, M ; Hoseini Sabzevari, S. A ; Moosavi Nezhad, S. M ; Mandanipour, V ; Szpunar, J. A ; Sharif University of Technology
Springer
2022
Abstract
The microstructure evaluation and phase transformation of multi-pass friction stir-processed (FSP) commercially pure titanium were investigated using optical microscopy, scanning electron microscopy equipped with a backscatter detector, and electron backscatter diffractometer. The microstructure characterization shows that the grain refinement mechanism changed with the increasing number of passes. The equiaxed α grains in the untreated sample changed to lath-shaped grains surrounded by serrated grain boundaries, and produced Widmanstätten morphology during the cooling cycle of FSP. The higher micro-hardness values and bio-corrosion resistances of the FSP-treated samples are due to their...