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age-hardening
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Investigation of Mechanical Milling Effects on Al-Cu and Al-CuO Powder Mixture Morphological and Structural Characteristic and Mechanical Properties Changes Resultant from Age Hardening
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
In the present work, nanocrystalline Al-4wt%Cu alloy reinforced with nanometric Al2O3 particles was synthesized by in-situ reactive milling of Al and CuO powder mixture and hot extrusion. The effect of nanometric Al2O3 particles on the aging behavior and mechanical properties of this alloy was investigated. During mechanical milling, copper oxide were reduced and dissolved in the aluminum lattice. consequently, Al(Cu) solid solution matrix was produced. Also, nanometric Al2O3 particles were also distributed in the matrix uniformly. The powder blend was then pressed in an Al can at 100 MPa pressure and subsequently extruded at 450 0C at the extrusion ratio of 16:1. The density of the...
Modeling age hardening kinetics of an Al-Mg-Si-Cu aluminum alloy
, Article Journal of Materials Processing Technology ; Volume 205, Issue 1-3 , 26 August , 2008 , Pages 388-393 ; 09240136 (ISSN) ; Karimi Taheri, A ; Sharif University of Technology
2008
Abstract
In this paper, an Al-Mg-Si-Cu aluminum alloy was exposed to various heat treatment processes and the effect of precipitation hardening on hardness was investigated as a function of time and temperature. It was concluded that the variation in time and temperature can improve the hardness of the alloy. The work revealed that time and temperature play an important role in the precipitation hardening process of the alloy. To achieve the maximum hardness, an optimum aging cycle should be used which is heating at 180-190 °C for 15-18 h. Kinetics studies show an apparent activation energy of 58 kJ/mol. A relationship was derived which can be used to estimate the hardness at a given time and...
Influence of double aging on microstructure and yield strength of AEREX ™ 350
, Article Materials Science and Engineering A ; Volume 534 , 2012 , Pages 547-551 ; 09215093 (ISSN) ; Sharif University of Technology
Abstract
Age hardening behavior of selected samples of AEREX ™ 350, a nickel-cobalt based superalloy, was investigated in this article. The relationship between the microstructure and mechanical properties was elucidated using hardness and compression testing methods and optical, scanning and transmission electron microscopy techniques. It was found that the microstructure is sensitive to the temperature of the solution and the aging treatments. This approach may be used to optimize the microstructure of the alloy for different applications
Investigation of the Effect of Temperature on Wear Behavior of 2024Al and 2024Al-20vol.%SiCp Composite
, M.Sc. Thesis Sharif University of Technology ; Seyyed Reihani, Morteza (Supervisor)
Abstract
In this research, friction and wear behaviors of 2024 Al and 2024 Al-20 vol.% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 20- 250°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.5 m/s, an applied load of 20 N, and a sliding distance of 2500m using a pin-on-disc apparatus. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects. Worn surfaces and wear debris were also examined by using SEM, EDS and XRD techniques. All specimens showed a transition from mild to severe wear above a critical temperature. In the mild wear regime, the wear rate and the friction...
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor) ; Seyed Reihani, Morteza (Supervisor)
Abstract
In this research, wear behaviors of 6061Al and 6061Al-20 vol% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 25- 200°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.34 m/s, an applied load of 20 N and 50N, and a sliding distance of 2450m using a pin-on-disc machine test. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects on wear rate of composite. Worn surfaces and wear debris were also examined by using SEM and EDS techniques. Also for determining the effect of age hardening treatment on wear behavior of composite, specimens were solution treated at...
The characteristics of serrated flow in superalloy IN738LC
, Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 376-380 ; 09215093 (ISSN) ; Asgari, S ; Sharif University of Technology
2008
Abstract
Serrated flow was investigated in superalloy IN738LC, a nickel-base γ′ age-hardened alloy. In this material serrated flow appeared between 350 and 450 °C and strain rate of (8.77 × 10-5 to 8.77 × 10-3) s-1. Activation energy for this process was calculated to be 0.69-0.86 eV which is in good agreement with the values reported for similar alloys. Results show that the diffusion rate of substitutional solute atoms at this temperature range is too low to cause this effect. This suggests that the interaction of solute atoms and moving dislocation is responsible for the observed serrated flow in this alloy. © 2007 Elsevier B.V. All rights reserved
Age-hardening behavior and phase identification in solution-treated AEREX 350 superalloy
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 37, Issue 7 , 2006 , Pages 2051-2057 ; 10735623 (ISSN) ; Sharif University of Technology
2006
Abstract
This article presents results of an investigation on age-hardening behavior of superalloy AEREX 350. Microhardness testing was employed to evaluate the age-hardening response of the alloy while optical, scanning, and transmission electron microscopy techniques were used to characterize the major phases formed during the aging process. No significant hardening was found in solution-treated samples aged at temperatures up to about 680 °C. Aging at 700 °C up to 950 °C, however, caused a characteristic hardening response. This hardening was concurrent with the formation of γ', an ordered phase with L12 structure, as fine precipitate distributed throughout the fcc matrix. In the temperature range...
Effect of Zr addition on the aging behavior of A319 aluminum cast alloy
, Article Scripta Materialia ; Volume 52, Issue 4 , 2005 , Pages 253-257 ; 13596462 (ISSN) ; Mahmudi, R ; Khomamizadeh, F ; Sharif University of Technology
2005
Abstract
The structure, age hardening response, precipitate type and hardness of A319 cast aluminum alloy without and with zirconium addition were investigated. The as-solutionized and artificially-aged hardness values were higher for the Zr-containing alloy. This is believed to be a consequence of the precipitation of Al3Zr particles produced during sufficiently long solutionizing treatments. © 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Development of Mechanical Properties of 420 AISI Martensitic Stainless Steel Using the Age Hardening Nano Precipitates and ANN Analysis
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
The Austenitization, influence of ageing condition and the prediction kinetics of AISI 420 martensitic stainless steel were studied in this paper. The Austenitizing temperature of 9200C, 9500C and 10200C were achieved. The specimens were heated for 15, 30 and 60 minutes then quenched in 250C Oil. The cooled samples were tempered at 2000C for 1 hour. The maximum tensile strength obtained at 10200C and 60 minutes were about 1800 MPa. The effect and ageing temperature and time on the strengthening behavior of this steel was modeled and analyzed by shear punch test and means of artificial neural networks (ANNs). Johnson-Mehl-Avrami-Kolmogorov (JMAK) analyses were applied to characterize the...
Constitutive modeling of hot deformation behavior of the AA6063 alloy with different precipitates
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 44, Issue 13 , December , 2013 , Pages 5853-5860 ; 10735623 (ISSN) ; Taheri, A. K ; Kim, H. S ; Sharif University of Technology
2013
Abstract
The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot flow behavior of AA6063 alloy. The model relates the flow behavior of the age-hardenable alloy to the alloy chemistry, thermal history as well as deformation temperature, strain, and strain rate by means of a physically based model. Different aging conditions, including supersaturated solid solution and overaging conditions with different deformation parameters, were assessed. Each part of the model was in good agreement with those of experimental and other model...
An investigation on the precipitation hardening of an ultrafine grained Al6063-Al2O3 nanocomposite
, Article Proceedings of the International Euro Powder Metallurgy Congress and Exhibition, Euro PM 2012 ; Volume 1 , 2012 ; 9781899072361 (ISBN) ; Bayazid, M ; Simchi, A ; Sharif University of Technology
2012
Abstract
In this work, age hardening behavior of an ultrafine-grained (UFG) Al6063-0.8 vol.% Al2O3 nanocomposite produced via reactive mechanical alloying followed by hot extrusion method by means of T6 heat treatment was studied. The temperature and time of solutionizing and aging were optimized by the Taguchi method. The optimal heat treatment condition was found to be solutionizing at 510 °C for 1.5 h and aging at 170 °C for 8 h. The signal-to-noise (S/N) ratio and analysis of variance (ANOVA) revealed that the solutionizing temperature was the most significant factor. A novel cyclic solution treatment was developed for age hardening of Al6063-Al2O3 nanocomposite. The results showed a considerable...
Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels
, Article International Journal of Minerals, Metallurgy and Materials ; Volume 18, Issue 5 , 2011 , Pages 557-561 ; 16744799 (ISSN) ; Nedjad, S. H ; Behnam, M. M. J ; Sharif University of Technology
Abstract
Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels were studied. To investigate the microstructure and mechanical properties, optical microscopy, scanning electron microscopy, X-ray diffraction, tensile test, and hardness test were used. The results show that the solution-annealing treatment in the cold-rolled steel redounds to the formation of submicrocrystalline Fe2 (Mo, Ti) Laves phase particles, which are stable at high temperatures. These secondary Laves phase particles prevent from recrystallization at high temperatures and correspond to semi-brittle fracture in the subsequent aging treatment
An Investigation into the Effect Of Severe Plastic Deformation by Equal Channel Angular Extrusion (Ecae) Process on Mechanical and Microstructural Properties of a Mg-Zn Alloy
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
The specific properties of some of magnesium alloys have caused these alloys to be used in medical and industrial applications. Adding new elements and applying severe plastic deformation to these alloys have been considered as a clue for improving their mechanical properties. The aim of this project is to improve the mechanical properties of a magnesium alloy by using new alloying elements and applying the ECAP process.
In this project, a new magnesium alloy by composition of Mg-1.78Zn-0.72Si-0.41Ca was cast. After casting, solution treating and annealing of the alloy were studied. Then, the effect of ECAP process on microstructure and mechanical properties of the annealed and solution...
In this project, a new magnesium alloy by composition of Mg-1.78Zn-0.72Si-0.41Ca was cast. After casting, solution treating and annealing of the alloy were studied. Then, the effect of ECAP process on microstructure and mechanical properties of the annealed and solution...
Thermo-mechanical Study on TIG Welding of AA2024 Alloy and Subsequent Microstructural Events
, M.Sc. Thesis Sharif University of Technology ; Serajzadeh, Siamak (Supervisor) ; Kokabi, Amir Hossein (Supervisor)
Abstract
In this study, temperature and Thermo-mechanical stress Distributions during and after TIG welding operations of AA2024 have been investigated by means of numerical simulation and experimental observations. Different geometries and initial microstructures, i.e. artificially and naturally aged alloys, have been selected. The model can determine the effect of welding parameters as well as mechanical fixtures on temperature and stress fields developed within metal being welded. Furthermore the subsequent aging behaviour of welded alloy (up to 70 days) has been evaluated employing hardness measurement and tensile testing. In addition, microstructural evolutions have been made utilising Scanning...
The Effects of Retrogression and Aging Heat Treatment on the Mechanical Properties and Flow Limit Diagrams of Precipitation-harden-Able Aluminum Alloy
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor) ; Kazeminejad, Mohsen (Supervisor)
Abstract
Demand for high performance components has caused a propensity towards high strength alloys, especially 7000 series, having extended applications in aerospace, automotive and medical industries. Due to high strength, heat treatability, and optimum weight, these alloys have been implemented in various conditions, specifically AA7075, being directly used in airframes. Through the years, numerous attempts have been made to improve the corrosion and formability properties of these alloys, resulting in the development of various tempering methods such as retrogression and re-ageing. Despite achiving optimal properties, it has been of less interest through literature to assess the formability of...
Simulation and experimental analyses of dynamic strain aging of a supersaturated age hardenable aluminum alloy
, Article Materials Science and Engineering A ; Volume 585 , 2013 , Pages 165-173 ; 09215093 (ISSN) ; Karimi Taheri, A ; Kim, H. S ; Sharif University of Technology
2013
Abstract
In this paper, dynamic strain aging (DSA) behavior in a temperature range of (25-235°C) and strain rate range of (10-4-5×10-2s-1) was investigated using a supersaturated age hardenable aluminum alloy. It was found that two mechanisms consisted of pinning of solute atoms to mobile dislocations and dynamic precipitation, were responsible for DSA in the testing conditions. The effects of both mechanisms on the macroscopic flow curve were studied using experimental and improved physically based material modeling approaches. It was shown that both phenomena lead to a negative strain rate hardening in the alloy. Dynamic precipitation acting at high temperature results in considerable work...
Inhomogeneity through warm equal channel angular pressing
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 6 , 2013 , Pages 1666-1671 ; 10599495 (ISSN) ; Kim, H. S ; Karimi Taheri, A ; Momeni, A ; Sharif University of Technology
2013
Abstract
In this study, the hardness inhomogeneity of billets during multi-passes of equal channel angular pressing (ECAP) at elevated temperatures is investigated and the effect of large strain deformation during ECAP on the hardness inhomogeneity characteristics due to dynamic aging of aluminum 6061 under a variety of temperatures and ram speed was studied by TEM and hardness measurements. The hardness results showed that the hardness distribution is more homogenous after four passes using the pressing route Bc. However, when the deformation temperature was considered, performing ECAP at 100 C may provide the most homogeneous microstructure after multi-pressing as long as the total number of...
Influence of deformation during T10 treatment on microstructure/hardness/ electrical conductivity of Cu-Cr alloy produced in nonprotected atmosphere
, Article Materials Science and Technology ; Volume 25, Issue 10 , 2009 , Pages 1283-1288 ; 02670836 (ISSN) ; Habibollahzadeh, A ; Erfanmanesh, M ; Mostajabodave, H ; Kazeminezhad, M ; Sharif University of Technology
2009
Abstract
Cu-1·5Cr alloy was successfully produced by a new method, composed of alloying via melting in a non-protected atmosphere followed by rapid cooling in a water cooled mould. The effects of deformation magnitude during T10 treatment on microstructure, electrical conductivity and hardness of alloy were also investigated. The results showed that cold work before age hardening treatment, especially in the range of 20-40% deformation, provides optimum electrical and mechanical properties, i.e. electrical conductivity of 70-85% International Annealed Copper Standard (IACS) and hardness of 160-180 HB. In addition, the cold work promotes a useful anisotropy in electrical and mechanical properties of...
A precipitation-hardening model for non-isothermal ageing of Al-Mg-Si alloys
, Article Computational Materials Science ; Volume 45, Issue 2 , 2009 , Pages 385-387 ; 09270256 (ISSN) ; Bahrami, A ; Mousavi Anijdan, S. H ; Sharif University of Technology
2009
Abstract
An age-hardening model has been developed to predict the evolution of the hardness of Al-Mg-Si alloys during non-isothermal ageing before peak age. The concurrent precipitation and dissolution have been considered in the structural model. Then the structural model has been combined with strengthening model to predict the precipitation-hardening behavior of the alloy AA6061. The results indicate that the developed model can be used as a predictive tool to model the mechanical properties evolution of Al-Mg-Si alloys during non-isothermal heat treatment. © 2008 Elsevier B.V. All rights reserved
Crystal plasticity modeling of the effect of precipitate states on the work hardening and plastic anisotropy in an Al-Mg-Si alloy
, Article Computational Materials Science ; Vol. 83 , 2014 , pp. 78-85 ; ISSN: 09270256 ; Karimi Taheri, A ; Kim, H. S ; Sharif University of Technology
Abstract
In this study the influence of precipitates on the mechanical properties and plastic anisotropy of an age hardenable aluminum alloy during uniaxial loading was investigated using crystal plasticity modeling. The kinetics model of Myhr et al. was used to obtain the solute and precipitate features after different cycles of aging treatment. The amounts of solute, precipitate size and volume fraction, and dislocation density varying during deformation, were used to calculate the slip system strength. An explicit term was obtained based on the elastic inclusion model for the directional dependency of internal stress developed by non-shearable rod shape precipitates. Also, a dislocation evolution...