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    Constitutive analysis and microstructural evolution in hot working of nanostructured Al6063

    , Article Proceedings of the International Euro Powder Metallurgy Congress and Exhibition, Euro PM 2012, 16 September 2012 through 19 September 2012, Basel ; Volume 1 , September , 2012 ; 9781899072361 (ISBN) Asgharzadeh, H ; Simchi, A ; Sharif University of Technology
    European Powder Metallurgy Association (EPMA)  2012
    Flow curves and microstructural changes of nanostructured Al6063 alloy produced by mechanical alloying followed by hot extrusion were investigated by means of uniaxial compression test in the temperature range between 300 and 450 °C and strain rate range between 10-2 and 1 s-1. The analysis of flow curves were performed by a hyperbolic sine law equation and the stress exponent and activation energy were determined to be 2.9 and 228 kJ mol-1, respectively. The microstructural constituents for elaboration of deformation mechanisms were observed by TEM and EBSD under FEG-SEM. The microstructural observations determine that dynamic recovery through the formation of subgrains within the grains... 

    Static recrystallization behavior of AEREX350 superalloy

    , Article Materials Science and Engineering A ; Volume 527, Issue 27-28 , October , 2010 , Pages 7313-7317 ; 09215093 (ISSN) Hosseinifar, M ; Asgari, S ; Sharif University of Technology
    The recrystallization behavior of a commercial nickel-cobalt base superalloy, AEREX 350, is investigated by means of hardness test, X-ray diffraction, and microscopy. It is found that the alloy resists recrystallization up to a high temperature of 1025 °C. Recrystallized grains are readily formed at grain boundaries below this temperature; however, the growth of these new grains is inhibited by Widmanstätten η particles having coherent facets with the nickel matrix (γ). The passage of the recrystallization front results in coherency loss and consequently dissolution of the η platelets. Recrystallization proceeds with a discontinuous precipitation of the η phase behind the moving boundary  

    Modeling and experimental study on friction stir welding of artificially aged AA2017 plates

    , Article Materials and Manufacturing Processes ; Volume 28, Issue 6 , 2013 , Pages 683-688 ; 10426914 (ISSN) Mirjalili, A ; Serajzadeh, S ; Jamshidi Aval, H ; Kokabi, A. H ; Sharif University of Technology
    Thermo-mechanical responses, developed microstructure, and mechanical properties in friction stir welding (FSW) of artificially aged AA2017 plates were investigated. A finite element analysis was first employed to evaluate hot deformation behavior of the alloy during welding. Also, hardness, yield strength, and microstructure of the welded alloy were examined using the results of the model and experimental testing. It was found that strain and temperature fields during welding are asymmetrically distributed and the maximum temperature locates in advancing side. Furthermore, considerable grain refinement is observed in the stir zone where recrystallized grains in the range of 3 to 8 m are... 

    Influence of stored strain on fabricating of Al/SiC nanocomposite by friction stir processing

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 46, Issue 5 , May , 2015 , Pages 2021-2034 ; 10735623 (ISSN) Khorrami, M. S ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    Springer Boston  2015
    In this work, 1050 aluminum (Al) sheets were annealed and severely deformed by 1, 2, and 3 passes of constrained groove pressing process to obtain the various initial stored strain values of 0, 1.16, 2.32, and 3.48, respectively. Friction stir processing (FSP) was then applied using SiC nanoparticles to fabricate Al/SiC nanocomposite with approximately 1.5 vol pct reinforced particles. Microstructural examinations revealed that an increase in the initial stored strain of the base metal led to the formation of finer grain structure after 1 pass of FSP. The finer grain structure occurred in the stir zone where a sufficient amount of nanoparticles with a relatively proper distribution existed.... 

    Microstructure evolutions after friction stir welding of severely deformed aluminum sheets

    , Article Materials and Design ; Volume 40 , September , 2012 , Pages 364-372 ; 02641275 (ISSN) Sarkari Khorrami, M ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    Elsevier  2012
    The microstructure evolutions of severely deformed aluminum sheets by Constrained Groove Pressing (CGP) after Friction Stir Welding (FSW) are investigated. To do so, the specimens are deformed in three different strains using CGP process which make different the initial microstructures. Then, the specimens are joined at various revolution pitches (traveling speed/rotation speed ratio) of 0.20, 0.25 and 0.33. mm/r. To understand the effect of initial strains on the properties of joints, the microhardness measurements and microstructure investigations of different areas from retreating to advancing sides of the joints are carried out. The results achieved from FSW of CGPed samples are compared... 

    Simulation of static recrystallization after cold side-pressing of low carbon steels using cellular automata

    , Article Journal of Materials Engineering and Performance ; Volume 21, Issue 8 , 2012 , Pages 1553-1561 ; 10599495 (ISSN) Afshari, E ; Serajzadeh, S ; Sharif University of Technology
    In this article, the finite element and cellular automata models are coupled to determine static recrystallization kinetics after cold deformation of low carbon steels. The deformation analysis is first performed to predict the strain, stress, and stored energy distributions within the deformed steel employing the finite element software, ABAQUS. Then, the kinetics of static recrystallization and distribution of recrystallized grain size are evaluated by means of a cellular automata model together with the stored energy calculated by the deformation analysis. To examine the predictions, the experimental results of recrystallized fractions and grain sizes after cold side-pressing of low... 

    Heating rate effect on particle stimulated nucleation and grains structure during non-isothermal annealing of multi-directionally forged solution treated AA2024

    , Article Materials Characterization ; Volume 127 , 2017 , Pages 317-324 ; 10445803 (ISSN) Khani Moghanaki, S ; Kazeminezhad, M ; Logé, R ; Sharif University of Technology
    Elsevier Inc  2017
    Particle stimulated nucleation (PSN) is one of the important mechanisms of recrystallization which is investigated in this research during non-isothermal annealing of multi-directionally forged solution treated aluminum alloy 2024. Non-isothermal annealing is performed up to temperatures of 380 °C and 450 °C at heating rates of 10, 100 and 200 K·min− 1 using a Gleeble 3800 thermo-mechanical simulator. In order to investigate the microstructure, field emission gun scanning electron microscope (FEG-SEM) equipped with electron backscatter diffractometer (EBSD) and differential scanning calorimetry (DSC) are utilized. The results show that the heating rate has a significant effect on the PSN and... 

    Influence of ambient and cryogenic temperature on friction stir processing of severely deformed aluminum with SiC nanoparticles

    , Article Journal of Alloys and Compounds ; Volume 718 , 2017 , Pages 361-372 ; 09258388 (ISSN) Sarkari Khorrami, M ; Kazeminezhad, M ; Miyashita, Y ; Saito, N ; Kokabi, A. H ; Sharif University of Technology
    The texture, microstructure, and mechanical properties of severely deformed aluminum subjected to friction stir processing (FSP) with SiC nanoparticles under ambient and cryogenic temperatures are comprehensively investigated. Even one pass of FSP in the ambient temperature results in the formation of quite large grain structure with random texture in the heat affected zone (HAZ). It suggests the occurrence of static recrystallization and subsequent grain growth because of the appreciable strain stored within the base metal. One FSP pass under condition of cryogenic temperature causes to the development of bimodal grain size distribution in HAZ, including the elongated grains with interior... 

    Coupling kinetic dislocation model and Monte Carlo algorithm for recrystallized microstructure modeling of severely deformed copper

    , Article Journal of Materials Science ; Volume 43, Issue 18 , 1 September , 2008 , Pages 6081-6086 ; 00222461 (ISSN) Kazeminezhad, M ; Hosseini, E ; Sharif University of Technology
    By coupling a kinetic dislocation model and Monte Carlo algorithm, the recrystallized microstructure of severely deformed Oxygen Free High Conductivity Copper (OFHC) is predicted at different strains imposed by Equal-Channel- Angular-Pressing (ECAP) and annealing temperatures. From a flow field model, the strain rate distribution during the ECAP of the material in a curved die is calculated. Then using the kinetic dislocation model, the total dislocation density and correspondingly the stored energy after each ECAP pass is estimated. Utilizing the Monte Carlo algorithm and the stored energy, the recrystallized microstructure is predicted. The results show that the recrystallized grain size... 

    Hot deformation of ultrafine-grained Al6063/Al2O3 nanocomposites

    , Article Journal of Materials Science ; Volume 46, Issue 14 , July , 2011 , Pages 4994-5001 ; 00222461 (ISSN) Asgharzadeh, H ; Simchi, A ; Kim, H. S ; Sharif University of Technology
    Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1-1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation... 

    The effect of Cu addition on the hot deformation behavior of NiTi shape memory alloys

    , Article Journal of Alloys and Compounds ; Volume 499, Issue 1 , June , 2010 , Pages 57-62 ; 09258388 (ISSN) Morakabati, M ; Kheirandish, Sh ; Aboutalebi, M ; Karimi Taheri, A ; Abbasi, S. M ; Sharif University of Technology
    The influence of Cu addition on the hot deformation behavior of NiTi shape memory alloys was investigated using hot compression test. A series of alloys with different Cu contents of Ti50.4Ni49.6-xCux (x = 0, 3, 5, 7 at.%) were deformed under compression to a true strain of 0.7 at the temperature range of 700-1000 °C with 100 °C intervals and constant strain rate of 0.1 s-1. The stress-strain curves showed that the addition of Cu to NiTi alloy made the flow curves shift upward. This was confirmed by the calculated critical stress, σc, obtained from inflections in θ-σ plots, which is attributed to the formation of high strength Cu containing precipitates and solid solution hardening caused by... 

    Dynamic restoration and microstructural evolution during hot deformation of a P/M Al6063 alloy

    , Article Materials Science and Engineering A ; Volume 542 , April , 2012 , Pages 56-63 ; 09215093 (ISSN) Asgharzadeh, H ; Simchi, A ; Kim, H. S ; Sharif University of Technology
    Hot deformation behavior of Al6063 alloy produced by direct powder extrusion was studied by means of uniaxial compression test in the temperature range between 300 and 450°C and strain rate range between 0.01 and 1s -1. Electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM) were utilized to study the microstructure of the material before and after the hot deformation. The microstructure of the extruded alloy consisted of elongated grains within a subgrain structure and small grains free of low angle grain boundaries (LAGBs). An equiaxed duplex microstructure consisting of large substructured grains and fine grains separated by high angle grain boundaries...