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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...
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...
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...
Atomistic investigation of the effects of symmetric tilt grain boundary structures on irradiation response of the α-Fe containing carbon in solution
, Article Computational Materials Science ; Volume 166 , 2019 , Pages 82-95 ; 09270256 (ISSN) ; Feghhi, S. A ; Samadfam, M ; Darvishzadeh, M ; Sharif University of Technology
Elsevier B.V
2019
Abstract
In this paper, molecular dynamics simulations were used to investigate the effect of the presence of carbon atoms, either in dispersed form or C-rich region, in low-carbon α-Fe containing symmetric tilt grain boundary (STGB)with a boundary plane rotated about the 110 misorientation axis on the number of SIAs and vacancies produced by PKA energies of 3, 5, 7 and 9 keV at 300 K. Results were compared with the SIAs and vacancies produced in pure α-Fe. It was also shown that the presence of GBs in this Fe-C alloy has no effect on the time at which point defects reach to their maximum values at the thermal spike stage. On the other hand, the GBs decrease the number of point defects in comparison...
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...
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...
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...
Effects of severe plastic deformation on pre-osteoblast cell behavior and proliferation on AISI 304 and Ti-6Al-4V metallic substrates
, Article Surface and Coatings Technology ; Volume 366 , 2019 , Pages 204-213 ; 02578972 (ISSN) ; Aydın, H. M ; Maleki, E ; Varol, R ; Unal, O ; Sharif University of Technology
Elsevier B.V
2019
Abstract
In this study, titanium alloy (Ti-6Al-4V) and austenitic stainless steel (AISI 304) biomedical alloys were subjected to surface severe plastic deformation (SSPD) via severe shot peening (SSP) with the conditions of A28-30 Almen intensity. SSP is widely accepted as much more effective than the conventional surface modification techniques since it forms a nano-grain layer with large number of dislocations and grain boundaries. The SSP treatment in this study was led to a very thin rough layer in Ti-6Al-4V titanium alloy compared to that of AISI 304. The thicker layer of AISI 304 was created by twin-twin intersections and a martensite structure transformations. SSP treatment was resulted in a...
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...
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...
Effective management of nucleation and crystallization processes in perovskite formation via facile control of antisolvent temperature
, Article ACS Applied Energy Materials ; Volume 3, Issue 2 , 2020 , Pages 1506-1514 ; Kim, G. W ; Malekshahi Byranvand, M ; Choi, K ; Kang, G ; Choi, H ; Tajabadi, F ; Taghavinia, N ; Park, T ; Sharif University of Technology
American Chemical Society
2020
Abstract
The antisolvent method has been used extensively to induce the growth of high-quality perovskite layers for efficient solar cells. However, uncontrollable nucleation and crystallization increases the risk of formation of undesirable defects. Here, we report a facile way to control the nucleation and crystallization stages in perovskite formation by changing the temperature of chlorobenzene (CB) in the antisolvent method. When CB is injected on the spinning substrate with a precursor solution, CB temperature affects the nucleation process as well as the crystallization process. As the CB temperature increases, nuclei increase in size, leading to the formation of larger perovskite crystals...
Microstructural and electrical properties of varistors prepared from coated ZnO nanopowders
, Article Journal of Materials Science: Materials in Electronics ; Volume 21, Issue 6 , June , 2010 , Pages 571-577 ; 09574522 (ISSN) ; Maleki Shahraki, M ; Faghihi Sani, M. A ; Nemati, A ; Yousefi, A ; Sharif University of Technology
2010
Abstract
This paper describes a solution-based technique for fabrication of varistor grade composite nanopowders. The method consists of coating major varistor dopants on the surface of the ZnO nanoparticles. As a result, a homogenous mixture of dopants and ZnO nanoparticles will be achieved. TEM results indicated that a composite layer of dopants with the average particle size of 9 nm on the surface of ZnO nanoparticles has been successfully prepared. Sintering of the coated powders was performed in temperatures as low as 850 °C and final specimens with average particle size of 900 nm and density of 98.5% were achieved. In comparison to conventional mixing, varistors prepared from coated nanopowders...
3D asymmetric carbozole hole transporting materials for perovskite solar cells
, Article Solar Energy ; Volume 189 , 2019 , Pages 404-411 ; 0038092X (ISSN) ; Heydari, M ; Ahangar, H ; Mohammadi, H ; Taherian Fard, H ; Taghavinia, N ; Samadpour, M ; Tajabadi, F ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Carbazole compounds are p-type hole-transporting materials (HTMs) useful for perovskite solar cells (PSCs). In this work, we developed a new class of carbazol based HTMs; non-fused 3-D asymmetric structures (S14 and S12) as HTM of PSCs. To the best of our knowledge, there is no report on non-fused HTMs with a high glass transition temperature (Tg = 165 °C), which reduces crystallization and suppresses grain boundaries in glassy film, resulting in long-term durability. Experimental results show that tuning the carbazole moiety in S14 structure has a constructive influence on geometrical alignment, hole mobility, hydrophobicity, stability as well as efficiency. The resultant power conversion...
Enhanced resistance to liquation cracking during fusion welding of cast magnesium alloys: Microstructure tailoring via friction stir processing pre-weld treatment
, Article Materials Science and Engineering A ; Volume 798 , 2020 ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Magnesium alloys provide critical opportunities for energy and lightweight-materials challenges. The alloy design approach based on utilizing the second phase strengthening mechanism plays an essential role in producing low-density high strength Mg-based alloys. However, the second phase in the microstructure (e.g., Mg17Al12 phase in Mg–Al–Zn alloys) can deleteriously affect the weldability of the metallic materials by promoting the liquation and liquation cracking during fusion welding. The lack of sufficient weldability of Mg-based alloys is a crucial barrier to their potential use in safety-critical applications. In this paper, it is shown that the severe plastic deformation induced by...
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...
A new model for inverse Hall-Petch relation of nanocrystalline materials
, Article Journal of Materials Engineering and Performance ; Volume 17, Issue 5 , 2008 , Pages 662-666 ; 10599495 (ISSN) ; Dehghani, K ; Sharif University of Technology
2008
Abstract
In the present article, a new model for inverse Hall-Petch relation in nanocrystalline materials has been proposed. It is assumed that lattice distortion along grain boundaries can cause internal stresses and high internal stresses along grain boundaries can promote the grain boundary yielding. The designed model was then verified using the nanocrystalline-copper data. The minimum grain size for inverse Hall-Petch relation is determined to be about 11 nm for Cu. © 2008 ASM International
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...
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...