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The dependency of optical properties on density for hot pressed MgF2
, Article Infrared Physics and Technology ; Volume 51, Issue 6 , 2008 , Pages 546-549 ; 13504495 (ISSN) ; Madaah Hosseini, H. R ; Asghari Shivaee, H ; Sharif University of Technology
2008
Abstract
The effects of the most important parameters of hot pressing, including temperature, time and pressure on densification, microstructure and infrared transparency of MgF2 ceramics are discussed. The results show that the absorption or scattering of incident radiation is strongly dependent on the amount of porosity. By increasing the temperature or the pressure, transparency at infrared wavelengths has been increased due to the rise in density. For the longer hot pressing times, a continuous increase in density and infrared transparency has been seen as well. Cold pressing before hot press has minor effects on the density and infrared transparency of MgF2. © 2008 Elsevier B.V. All rights...
Synthesis of Mg / MgO - Mg2Cu by in-situ Reaction Method and Investigation on Structure and Mechanical Properties
, M.Sc. Thesis Sharif University of Technology ; Abachi, Parvin (Supervisor) ; Salahi, Esmaeil (Supervisor) ; Pour Azarang, Kazem (Co-Advisor)
Abstract
In this project formation of MgO & Mg2Cu reinforcement particle in Magnesium matrix was investigated. Firstly Mg & CuO powders mixture in different weight percentage (4, 8%wt CuO) in 20:1 and 30:1 BPR were milled. Finally, according to XRD result 30:1 BPR was selected for milling. Variations in powders morphology, particles size, crystallite size, lattice strain and phase transformation were investigated by X-ray diffraction, scanning electron microscopy and laser particle size analyzer in different milling time. Result showed that during reaction between Mg and CuO, MgO & Mg2Cu reinforcement particles were formed in matrix. Matrix crystallite size was determined about 35-40 nm. Mg-6.3%wt Cu...
A study on flow behavior of A-286 superalloy during hot deformation
, Article Materials Chemistry and Physics ; Volume 101, Issue 1 , 2007 , Pages 153-157 ; 02540584 (ISSN) ; Serajzadeh, S ; Yazdipour, N ; Sharif University of Technology
2007
Abstract
The hot deformation behavior of A-286 superalloy has been characterized using hot compression experiments in the temperatures between 1000 and 1100 °C and strain rates varying between 0.001 and 0.1 s-1. In addition, hot workability of this alloy has been analyzed by employing flow-localization parameter. The results show that both kinds of softening mechanism, dynamic recovery and dynamic recrystallization, occur during hot working, where at 1000 °C the main mechanism is dynamic recovery and at higher temperatures and strain rate of 0.001-0.01 s-1 dynamic recrystallization takes place. Calculations demonstrates that this alloy mainly have a good workability for the utilized deformation...
Prediction of dynamic recrystallization kinetics during hot rolling
, Article Modelling and Simulation in Materials Science and Engineering ; Volume 12, Issue 6 , 2004 , Pages 1185-1200 ; 09650393 (ISSN) ; Sharif University of Technology
2004
Abstract
In this study, the kinetics of dynamic recrystallization is predicted under hot rolling conditions employing a first-order rate equation. The proposed model considers the effects of temperature and strain rate variations on recrystallization kinetics by simultaneously modelling heat transfer and plastic deformation phenomena. To do so, a two-dimensional finite element method is coupled with the transformation equation to calculate the temperature distribution and the strain rate field as well as the kinetics of dynamic recrystallization within the metal, concurrently, The model developed was examined for a low carbon steel. A series of hot compression tests were carried out at different...
An Investigation on in-situ Synthesis and Wear Behavior of Al-Al3Ti Nanocomposite Produced via Mechanical Alloying/Hot-Press Technique
, M.Sc. Thesis Sharif University of Technology ; Maddah Hosseini, Hamid Reza (Supervisor)
Abstract
In the present investigation, the mechanical alloying (MA) technique was employed to produce nanocrystalline Al-Ti alloys. Elemental Al and Ti powders were mixed with different compositions (0, 5, 10, and 20 wt.% Ti) and then, milled in a planetary ball-mill up to 40 h. The variations of powder morphology and particle size, apparent and tap densities, microstructure, grain size, lattice strain, and microhardness were studied with increasing the milling time. While dissolution of Ti in the Al matrix resulted to the formation of supersaturated Al-Ti solid solution in the samples containing 5 and 10 wt.% Ti, the specimen with 20 wt.% Ti, eventually, led to nanocomposite powder with different...
Fabrication of Al /Al3Ti in-situ Composite by Mechanical Alloying and Two-Step Hot Press
, M.Sc. Thesis Sharif University of Technology ; Maddah Hosseini, Hamid Reza (Supervisor)
Abstract
Al /Al3Ti in-situ composite have been fabricated by mechanical alloying and two-step hot pressing of powders containing Al and 20%wt Ti. Samples were characterized by using optical microscopy, density measurement, brinel hardness, XRD analysis. An increasing density was observed with increasing pressure until certain pressure and after that the density of composite decreased, which can be attributed to the increase in the level of porosity level and the amount of forming Al3Ti. The samples that hot pressed under cycle 5 and 6, showed the most volume fraction of in-situ phases on the matrix. The wear behavior of Al based composites reinforced with in situ Al3Ti particles has been investigated...
Fabrication of NiTi Nano-Powder by Simple SPEX Mechanical Method and Fabrication of NiTi Foam by KCl Space-Holders
,
M.Sc. Thesis
Sharif University of Technology
;
Sadrnezhad, Khatiboleslam
(Supervisor)
Abstract
NiTi Memory alloys have a great range of applications. Porous metallic biomaterials (e.g., stainless steel, chromium- cobalt, titanium and nickel–titanium (NiTi)) represent superior alternatives to traditional non-porous metallic implants for two main reasons. First, open porosity can enhance bone ingrowth and thus improve fixation at the interface between bone and implant. Second, porosity decreases the mismatch in stiffness between bone and implant, thus reducing stress-shielding effects which shorten the lifetime of the implant through bone resorption and loosening. NiTi foams may thus find multi-functional applications such as bone implants, impedance-matching connectors between...
Fabrication of high wear resistant Al/Al3Ti metal matrix composite by in situ hot press method
, Article Materials and Design ; Volume 30, Issue 2 , 2009 , Pages 280-286 ; 02641275 (ISSN) ; Madaah Hosseini, H. R ; Kolagar Daroonkolaie, N ; Sharif University of Technology
2009
Abstract
In this study, hot press method has been used to fabricate Al/Al3Ti composite. In situ reacted Al3Ti compound is formed through Al and TiO2 powder blend in order to enhance mechanical properties and mainly wear resistance. After homogeneous blending of Al and TiO2, hot pressing was performed at 580 °C at different durations and pressures. Scanning electron microscopy was used for microstructural survey. Density measurements using Archmede's method and Brinell hardness test were carried out for all the samples. By increasing the hot pressing pressure, both density and hardness increased significantly. On the other hand, by increasing the time, hardness increased and density decreased due to...
Nano-precipitation in if steel by the use of hot compression test
, Article 1st International Conference on Industrial Processes for Nano and Micro Products, London, 3 April 2007 through 4 April 2007 ; 2007 , Pages 203-210 ; 1855980827 (ISBN); 9781855980822 (ISBN) ; Aboutalebi, S. H ; Amin, M ; Baghaei Lakeh, R ; Khezr Seddigh Mazinani, S ; Sharif University of Technology
2007
Abstract
One of the methods to increase the hardness of metals, mostly used in aerospace and automobile industries, where light parts with high strength is needed, is precipitation hardening. Nano-precipitates can strongly influence the mechanical properties of materials, especially in a dynamic case. In the present work, attempts have been made so as to make Nano-particles dynamically precipitate in IF steels. Investigating the structure by the means of SEM and AFM resulted in understanding that the precipitates were in nano-size. The micro-hardness of samples was measured as well. © BHR Group 2007 Industrial Processes for Nano and Micro Products
Hot deformation behavior of P/M Al6061-20% SiC composite
, Article 2006 Powder Metallurgy World Congress and Exhibition, PM 2006, Busan, 24 September 2006 through 28 September 2006 ; Volume 534-536, Issue PART 2 , 2007 , Pages 897-900 ; 02555476 (ISSN); 0878494197 (ISBN); 9780878494194 (ISBN) ; Simchi, A
Trans Tech Publications Ltd
2007
Abstract
In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicates the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The...
Modelling flow stress behaviour of aluminium alloys during hot rolling
, Article Materials Science and Technology ; Volume 22, Issue 6 , 2006 , Pages 713-718 ; 02670836 (ISSN) ; Sharif University of Technology
2006
Abstract
A mathematical model is proposed to predict the flow stress behaviour of aluminium alloys under hot rolling conditions. To do so, a dislocation model for evaluating flow stress during deformation is coupled with a finite element analysis to access metal behaviour under non-isothermal and variable strain rate conditions. Then, with the aid of the proposed model, a hot strip rolling process was simulated. In order to verify modelling results, flow stress behaviour of an aluminium alloy is studied employing hot compression tests in various temperatures and strain rates and the model was examined on this material. Non-isothermal hot rolling experiments were carried out and good agreement was...
Tribological characteristics of self-lubricating nanostructured aluminum reinforced with multi-wall CNTs processed by flake powder metallurgy and hot pressing method
, Article Diamond and Related Materials ; Volume 90 , 2018 , Pages 93-100 ; 09259635 (ISSN) ; Alipour, S ; Najafi, M ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Ultrafine-grained Al-CNT (2 and 4 vol%) composites were successfully fabricated using the flake powder metallurgy and hot pressing route, and the microstructure and tribological properties of the produced composites were studied. The results showed that the coefficient of friction and the wear rate of Al decrease with the addition of the CNT reinforcement. A carbon-rich film formed on the worn surfaces during wear test, which prevented the Al oxidation and yielded the self-lubricating effect for the composites. This improvement in the wear behavior of the composites can be attributed to the simultaneous effects of the ultrafine-grained matrix and strengthening and self-lubricating properties...
Microstructural and mechanical characteristics of hybrid SiC/Cu composites with nano- and micro-sized SiC particles
, Article Ceramics International ; 2018 ; 02728842 (ISSN) ; Mousa Mirabad, H ; Alipour, S ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Hybrid Cu-SiC composites have been highly considered in order to achieve a combination of electrical and thermal properties along with high strength and wear resistance. However, limited investigations have ever been conducted over the effects of using hybrid (combination of nano and micro size) particles on the wear resistance behavior of these composites. Hence, in the present study, Cu-SiC nanocomposite with 4 vol% nanosize and 4 vol% microsize SiC, and Cu-SiC microcomposite with 8 vol% micro- SiC were fabricated through mechanical milling and hot pressing process. Results revealed the homogeneous dispersion of SiC particles in the matrix, high densification, and ultrafine-grain matrix...
Hardness, wear and friction characteristics of nanostructured Cu-SiC nanocomposites fabricated by powder metallurgy route
, Article Materials Today Communications ; Volume 18 , 2019 , Pages 25-31 ; 23524928 (ISSN) ; Najafi, M ; Alipour, S ; Kim, H.S ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
In the present study, hardness and tribological properties of nanostructured copper reinforced with SiC nanoparticles of various volume fractions (0, 2, 4, and 6 vol%) were investigated. The nanocomposites were fabricated by high-energy mechanical milling and hot pressing method. The Cu-SiC nanocomposites showed enhanced hardness and wear resistance against WC counterface. The hardness and wear resistance of the nanocomposite increased with increasing the amount of SiC nanoparticles up to 2 vol% in the matrix, but they decreased at higher percentages of SiC (4 and 6 vol%). Flake formation-spalling and abrasion were identified as the predominant wear mechanisms. It was found that reducing the...
Microstructural and mechanical characteristics of hybrid SiC/Cu composites with nano- and micro-sized SiC particles
, Article Ceramics International ; Volume 45, Issue 3 , 2019 , Pages 3276-3283 ; 02728842 (ISSN) ; Mousa Mirabad, H ; Alipour, S ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Hybrid Cu-SiC composites have been highly considered in order to achieve a combination of electrical and thermal properties along with high strength and wear resistance. However, limited investigations have ever been conducted over the effects of using hybrid (combination of nano and micro size) particles on the wear resistance behavior of these composites. Hence, in the present study, Cu-SiC nanocomposite with 4 vol% nanosize and 4 vol% microsize SiC, and Cu-SiC microcomposite with 8 vol% micro- SiC were fabricated through mechanical milling and hot pressing process. Results revealed the homogeneous dispersion of SiC particles in the matrix, high densification, and ultrafine-grain matrix...
Evaluation of Structure of Powder-thixoformed A390 Alloy
, M.Sc. Thesis Sharif University of Technology ; Ashuri, Hossein (Supervisor)
Abstract
Hypereutectic A390 alloy has some exclusive specification among aluminum alloys because of its' excellent properties such as high wear resistance and low thermal expansion. In this research powder-thixoforming method, a compilation of powder and thixoforming methods is used for production of parts. In this method gas atomized powder of pre-fabricated alloy was consolidated by hot pressing under argon atmosphere and converted to an acceptable feedstock for thixoforming stage. The feedstock is reheated to semi solid region and rapidly transferred to a injection sleeve with central runner. The semi-solid feedstock is injected in a step die by a hydraulic press of 1 m/s ram speed. According to...
Fabrication and Characterization of Al/Al3Ti-Al2O3 Composites by Powder Metallurgy and Sol Gel and Consideration of Mechanical Properties and their Correlation with the Microstructure Evolution
, M.Sc. Thesis Sharif University of Technology ; Maddah Hosseini, Hamid Reza (Supervisor)
Abstract
In the present research, a novel method for the fabrication of Al/Al3 Ti-Al2O3 composites and nanocomposites based on the thermal degradation of the refectory ceramic “Aluminium Titanate (AT)” or Al2TiO5 by powder metallurgy route. This research encompasses some precise subsequent steps. At first stage, nanostructured aluminium titanate nanofibers and particles were synthesized via a citrate sol gel process in which citric acid was used as a chelating agent. At second step, the possible chemical reactions between Al and aluminium titanate were taken into consideration both in powder form and in bulk form. Thermal analysis results indicated that it is feasible to decompose aluminium titanate...
Al-Al3Ti nanocomposite produced in situ by two-step hot-press sintering
, Article IOP Conference Series: Materials Science and Engineering ; Volume 40, Issue 1 , 2012 ; 17578981 (ISSN) ; Ghiabakloo, H ; Hosseini, H. R. M ; Mohammadi, A. V ; Sharif University of Technology
2012
Abstract
Aluminum reinforced with a large amount (up to about 55 vol.%) of Al 3Ti particles can be fabricated from Al-20Ti elemental nanometer-sized powder mixture via in-situ two step hot press sintering (TSS). For production of intermetallic reinforced in-situ composite, TSS can provide elevated temperature to facilitate the formation of intermetallic phase in situ and hot consolidation to form a fully dense solid. The first step sintering was employed at a higher temperature to obtain an initial high density, and the second step was held at a lower temperature by isothermal sintering for more time than the first one to increase bulk density without significant grain growth. The optimum TSS regime...
Effect of sintering temperature and siliconcarbide fraction on density, mechanical properties and fracture mode of alumina-silicon carbide micro/nanocomposites
, Article Materials and Design ; Volume 37 , May , 2012 , Pages 251-255 ; 02641275 (ISSN) ; Baharvandi, H ; Abdizadeh, H ; Purasad, J ; Fathi, A ; Ahmadi, H ; Sharif University of Technology
2012
Abstract
In this study Al2O3-SiC micro/nanocomposites have been fabricated by mixing alumina nanopowders and silicon carbide micro/nanopowders, followed by hot pressing at 1550, 1600, 1650 and 1700°C. The density, mechanical properties and fracture mode of Al2O3-SiC composites containing different volume fractions (2.5%, 5%, 7.5%, 10% and 15%) of micro/nanoscale SiC particles were investigated and compared with those of alumina. The relative density of composites could reach values very close to theoretical density, especially after sintering at 1700°C. However, relative density declined by increasing the SiC fraction at the same sintering temperature. The flexural strength of composites was best for...
Processing of Al-20Si-5Fe-2X(X=Cu, Ni, Cr) alloys by melt-spinning and hot-pressing
, Article European International Powder Metallurgy Congress and Exhibition, Euro PM 2008, Mannheim, 29 September 2008 through 1 October 2008 ; Volume 2 , 2008 , Pages 99-104 ; 9781899072033 (ISBN) ; Simchi, A ; Davami, P ; Sharif University of Technology
European Powder Metallurgy Association (EPMA)
2008
Abstract
Al-20Si-5Fe-2X (X=Cu, Ni, Cr) ribbons were produced by melt-spinning and consolidated by hot pressing at 400°C for 60 min. Optical and transmission electron microscopy (TEM), X-ray diffractometry (XRD), and hardness test were used to evaluate the microstructure and mechanical strength of the ribbons and hot consolidated specimens. The compressive strength of the specimens at ambient and elevated temperatures was also examined. The microstructure of the ribbons exhibited featureless and dendritic zones, and contains spherically-shaped Si particles with an average diameter of 20 nm. After hot-pressing, ultrafine Si (110-150 nm) and iron-containing intermetallic particles were formed. The...