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    Microstructural modification of Al–30Si–5Fe Alloy using a combination of rapid solidification and thixoforming processes

    , Article Metallography, Microstructure, and Analysis ; Volume 5, Issue 3 , 2016 , Pages 217-228 ; 21929262 (ISSN) Shafizadeh, M ; Aashuri, H ; Ferasat, K ; Nikzad, S ; Sharif University of Technology
    Springer New York LLC 
    It is commonly known that the properties of materials are strongly related to their microstructure. This paper introduces a method that is a combination of rapid solidification (melt spinning) and semisolid forming (thixoforming) processes, which are used to refine the microstructure of “as-cast” Al–30Si–5Fe alloy and improve its mechanical properties. Produced Al–30Si–5Fe ribbons by melt-spinning process, were pulverized and subsequently consolidated at 300 °C in argon atmosphere. Prepared specimens were thixoformed at temperatures ranging from 580 to 700 °C in various holding times. Some samples were also directly thixoformed from as-cast condition. Microstructure of the as-cast, meltspun,... 

    Effect of multi-pass friction stir processing on the microstructure, mechanical and wear properties of AA5083/ZrO2 nanocomposites

    , Article Journal of Alloys and Compounds ; Volume 726 , 2017 , Pages 1262-1273 ; 09258388 (ISSN) Mirjavadi, S. S ; Alipour, M ; Hamouda, A. M. S ; Matin, A ; Kord, S ; Afshari, B. M ; Koppad, P. G ; Sharif University of Technology
    In this study, multi-pass friction stir processing using zirconia nanoparticles was performed on AA5083 sheets to fabricate surface nanocomposites. Effect of using different number of passes on the microstructure, microhardness, tensile and wear properties of the specimens was investigated. Therefore, it was found that iteration of FSP consistently improves tensile properties and microhardness of the materials. This was mainly related to microstructural modification through FSP, including better dispersion of powders, finer grain size and minimum clustered particles. EBSD and TEM analysis indicated a large number of high angle grain boundaries and occurrence of continuous dynamic... 

    Diffusion brazing of Ti–6Al–4V and AISI 304: an EBSD study and mechanical properties

    , Article Journal of Materials Science ; Volume 52, Issue 20 , 2017 , Pages 12467-12475 ; 00222461 (ISSN) Norouzi, E ; Shamanian, M ; Atapour, M ; Khosravi, B ; Sharif University of Technology
    Ti–6Al–4V and AISI 304 stainless steel were joined by diffusion brazing with a Cu interlayer at 900 °C for different bonding times. The influence of the bonding time on the joint width, microstructure, microhardness and shear strength was studied. Interfacial characterizations and the identification of phases were done by scanning electron microscopy and electron backscatter diffraction (EBSD). The results revealed that by increasing the bonding time, the thickness of the joint was first increased and then decreased. Microstructure examinations also showed that the joints consisted of several intermetallics such as TiCu, Ti2Cu, TiCu4, TiCu2, FeTi and Fe2Ti. On the other hand, EBSD results... 

    Multi directional forging of 2024 Al alloy after different heat treatments: microstructural and mechanical behavior

    , Article Transactions of the Indian Institute of Metals ; Volume 70, Issue 7 , 2017 , Pages 1707-1719 ; 09722815 (ISSN) Asadi, S ; Kazeminezhad, M ; Sharif University of Technology
    Improvement of mechanical properties and microstructure of 2024 aluminum alloy by performing a severe plastic deformation method, called multidirectional forging (MDF), and heat treatment was the aim of this research. In this work, the effects of different heat treatments such as annealing, solid solution, peak ageing and over ageing before MDF on mechanical properties and microstructure of the alloy were studied. Microstructure evolution during severe plastic deformation was considerably affected by the precipitates and non-shearable particles. On the other hand, the severe plastic deformation had different effects on precipitates in the microstructure. Fragmentation, scattering and... 

    Effect of travel speed on quality and welding efficiency of friction stir welded AZ31B magnesium alloy

    , Article International Journal of Engineering and Technology(UAE) ; Volume 7, Issue 3 , January , 2018 , Pages 94-99 ; 2227524X (ISSN) Baghdadi, A. H ; Selamat, N. F. M ; Sajuri, Z ; Kokabi, A. H ; Sharif University of Technology
    Science Publishing Corporation Inc  2018
    Weight reduction is one of the most concerning issues of automotive and aircraft industries in reducing fuel consumption. Magnesium (Mg) alloys are the lightest alloys which can be used in the structure due to low density and high strength to weight ratio. Developing a reliable joining process of magnesium alloys is required due to limited ductility and low workability at room temperature. Friction stir welding (FSW) is a solid-state welding process that can be performed to produce sound joints in magnesium alloys. Researchers have performed investigations on the effect of rotation and travel speeds in FSW of AZ31B magnesium alloy. However, there is lack of study on the FSW parameters, i.e.... 

    Nanoporous gold as a suitable substrate for preparation of a new sensitive electrochemical aptasensor for detection of salmonella typhimurium

    , Article Sensors and Actuators, B: Chemical ; Volume 255 , 2018 , Pages 1536-1544 ; 09254005 (ISSN) Ranjbar, S ; Shahrokhian, S ; Nurmohammadi, F ; Sharif University of Technology
    Elsevier B.V  2018
    Nowadays, achievement to easy, fast, reliable and cost-effective techniques and tools is one of the most important challenges in detection of microorganisms. Salmonella typhimurium is one of the most important pathogenic bacteria that affect the human health and environmental infections. In this work we report a new, stable, biocompatible and cost-effective platform for construction of an aptasensor based on nanoporous gold (NPG) for detection of S. typhimurium. Nanoporous gold is electrochemically synthesized using Au-Cu alloy at the surface of Au/GCE. Thiol functionalized aptamer is used for effective linking to the surface of NPG/Au/GCE via self-assemble monolayers (SAMs) formation.... 

    The effect of chemical composition on enthalpy and entropy changes of martensitic transformations in binary NiTi shape memory alloys

    , Article Journal of Alloys and Compounds ; Volume 487, Issue 1-2 , 2009 , Pages 363-366 ; 09258388 (ISSN) Khalil Allafi, J ; Amin Ahmadi, B ; Sharif University of Technology
    In the present research work the binary NiTi alloys with various compositions in the range of 50.3-51 at.% Ni were used. Samples have been annealed at 850 °C for 15 min and then quenched in water. In order to characterize transformation temperatures and enthalpy changes of the forward and the reverse martensitic transformation, Differential Scanning Calorimetric (DSC) experiments were performed. The enthalpy and entropy changes as a function of Ni atomic content have been thermodynamically investigated. Results show that enthalpy and entropy changes of martensitic transformation decrease when Ni atomic content increases. The variation of enthalpy and entropy of martensitic transformation... 

    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) Yazdanmehr, M ; Bahrami, A ; Mousavi Anijdan, S. H ; Sharif University of Technology
    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  

    Phase transformation behavior of porous NiTi alloy fabricated by powder metallurgical method

    , Article Materials Science and Engineering C ; Volume 29, Issue 7 , 2009 , Pages 2203-2207 ; 09284931 (ISSN) Hosseini, S. A ; Sadrnezhaad, S. K ; Ekrami, A ; Sharif University of Technology
    Nickel titanium shape memory alloys (NiTi-SMAs) were successfully produced from elemental Ni/Ti powders by powder metallurgical method and then subjected to age treatment. Microstructure was examined by SEM and XRD and phase transformation temperatures were measured by dilatometric method. The phase transformation temperatures increased with both duration and temperature of the age treatment. The porous product exhibited desirable shape memory effect. © 2009 Elsevier B.V. All rights reserved  

    Microstructural investigation of the coatings prepared by simultaneous aluminizing and siliconizing process on γ-TiAl

    , Article Journal of Mining and Metallurgy, Section B: Metallurgy ; Volume 55, Issue 2 , 2019 , Pages 217-225 ; 14505339 (ISSN) Nouri, S ; Azadeh, M ; Sharif University of Technology
    Technical Faculty in Bor  2019
    In this research, formation of aluminide/silicide diffusion coatings on γ -TiAl[Ti-48Al-2Nb-2Cr (at.%)] alloy using gasphase diffusion pack cementation process has been investigated. The application of powder mixtures with various chemical compositions in the pack cementation process performed at 1000°C for 6 hours in order to achieve simultaneous diffusion of Al and Si, showed that the composition of the powder mixture could have a significant effect on the structure and thickness of the aluminide/silicide coatings. The identification and analysis of aluminide/silicide microstructures formed as a result of simultaneous diffusion of Al and Si, which was comprehensively and qualitatively done... 

    Effect of two steps annealing on the microstructure and dynamic strain aging behavior of Al-6Mg alloy

    , Article Materials Science and Engineering A ; Volume 798 , 2020 Saadat, Z ; Khani Moghanaki, S ; Kazeminezhad, M ; Goodarzi, M ; Ghiasi Afjeh, S. M. B ; Sharif University of Technology
    Elsevier Ltd  2020
    The microstructure of cold rolled Al–6Mg alloy is investigated after two steps annealing at different coupled temperatures of 250–320 °C and 320–400 °C for various times. Dynamic strain aging behavior in terms of serrated flow and strain rate sensitivity is investigated. The effect of three microstructural features, cell structure, recovered and recrystallized microstructures, on the strain rate sensitivity is elucidated. Two steps annealing process is utilized to capture the effect of recovery and precipitation phenomena on recrystallization and dynamic strain aging behaviors. The results show that the negative strain rate sensitivity of cold rolled specimen increases to positive values in... 

    Deformation behavior and cavitation of AA2017 at elevated temperatures

    , Article Metals and Materials International ; 2020 Vaghefi, E ; Serajzadeh, S ; Sharif University of Technology
    Korean Institute of Metals and Materials  2020
    In this work, deformation behavior of AA2017-T4 at elevated temperatures was studied employing uni-axial tensile and creep experiments. Tensile tests were carried out at temperatures varying 150–500 °C under different strain rates then, a combination of neural network and dynamic material modeling was utilized to construct the processing maps. Furthermore, creep experiments were conducted to assess inelastic deformation behavior of the alloy at temperatures between 150 and 225 °C and stresses in the range of 150 to 230 MPa. Microstructural evaluations were carried out for determination of microstructural changes and formation of voids and cavities within the samples. The results showed that... 

    Effect of particle size on the microstructure of rapidly solidified Al-20Si-5Fe-2X (X = Cu, Ni, Cr) powder

    , Article Journal of Alloys and Compounds ; Volume 466, Issue 1-2 , 2008 , Pages 111-118 ; 09258388 (ISSN) Rajabi, M ; Simchi, A ; Vahidi, M ; Davami, P ; Sharif University of Technology
    The effects of particle size and alloying elements on the size and morphology of secondary/intermetallic phases in gas atomized Al-20Si-5Fe-2X (X = Cu, Ni, Cr) powders were studied. The microstructure composed of particle-like primary Si with average diameter of 0.5-2.7 μm, δ-Al4FeSi2 intermetallic compound containing small amount of dissolved alloying elements with the size of 1.4-7.7 μm, and fine Al-Si eutectic matrix with 0.25-0.4 μm spacing. As the powder particle size decreases, the primary silicon becomes finer while its morphology is not affected. For instance, 58-75% reduction in the size of primary silicon was observed when decreasing the average particle size from 89 to 18 μm. A... 

    A novel phenomenological constitutive model for Ti-6Al-4V at high temperature conditions and quasi-static strain rates

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 235, Issue 13 , 2021 , Pages 1831-1842 ; 09544100 (ISSN) Ashrafian, M. M ; Hosseini Kordkheili, A ; Sharif University of Technology
    SAGE Publications Ltd  2021
    Phenomenological constitutive modeling of Ti-6Al-4V at temperatures between 923 and 1023 K under 0.0005–0.05 s−1 quasi-static rates is studied based on a phenomenological approach. For this purpose, the Johnson–Cook constitutive model is revisited. At low temperature conditions under moderate to high strain rates, the material’s stress–strain curves are the most similar to power-law function. Contrary to this, at high temperature conditions under low to moderate strain rates, the saturation-type function well describes the stress–strain curves. On the other hand, it is illustrated that the Johnson–Cook constitutive model is feeble to predict the material’s behavior correctly. Accordingly, in... 

    Ingredient losses during melting binary Ni-Ti shape memory alloys

    , Article Journal of Materials Science and Technology ; Volume 21, Issue 4 , 2005 , Pages 484-488 ; 10050302 (ISSN) Sadrnezhaad, S. K ; Badakhshan Raz, S ; Sharif University of Technology
    Losses of the alloying elements during vacuum induction melting of the binary NiTi alloys were evaluated by visual observation and chemical analysis of the NiTi melted specimens and the scalp formed on the internal surface of the crucible. The results indicated that the major sources of the losses were (a) evaporation of the metals, (b) formation of the NiTi scalp and (c) the sprinkling drops splashed out of the melt due to the exothermic reactions occurring between Ni and Ti to form the NiTi parent phase. Quantitative evaluations were made for the metallic losses by holding the molten alloy for 0.5, 3, 5, 10 and 15 min at around 100°C above the melting point inside the crucible. Chemical... 

    Dynamic modeling of a new varying stress SMA actuator for precise applications

    , Article Proceedings of the IEEE International Conference on Mechatronics 2004, ICM'04, Istanbul, 3 June 2004 through 5 June 2004 ; 2004 , Pages 209-214 ; 0780385993 (ISBN) Alasty, A ; Shameli, E ; Sharif University of Technology
    Shape Memory Alloys (SMA's) are inherently non-linear devices exhibiting significant hysteresis in their stress-strain-temperature characteristic. We have used the variable sub-layer SMA model of Ikuta [3] to extract the advanced dynamic model of our proposed varying stress SMA actuator. A nonlinear finite element analysis was used to model the proposed bending spring in the actuator and the extended variable sub-layer model of Ikuta was considered to extract stress-displacement relations. Finally, these two models are combined with thermo dynamic model of SMA and a schematic flowchart is proposed to calculate SMA resultant strain under an arbitrary current input. At the end, we applied this... 

    Shape memory alloy in tension and compression and its application as clamping-force actuator in a bolted joint: Part 1 - Experimentation

    , Article Journal of Intelligent Material Systems and Structures ; Volume 15, Issue 8 , 2004 , Pages 577-587 ; 1045389X (ISSN) Hesse, T ; Ghorashi, M ; Inman, D. J ; Sharif University of Technology
    In recent years, there have been some endeavors in order to characterize and model Shape Memory Alloy (SMA) behavior both in tension and compression. However, the one-dimensional behavior of SMA has been mostly studied for the case of wire elements subjected to tension. The objective of this paper is to analyze the behavior of Ni-55.7% wt Ti SMA in tension, compression, and at various temperatures. The effects of cycling, annealing, and friction on the mechanical behavior of this material in compression are discussed as well and, where applicable, compared to those of tension. The compressed SMA rings are finally used as clamping-force actuators in loosed bolted joints. In the second part of... 

    Evaluation of Quality Iindex of A-356 aluminum alloy by microstructural analysis

    , Article Scientia Iranica ; Volume 11, Issue 4 , 2004 , Pages 386-391 ; 10263098 (ISSN) Khomamizadeh, F ; Ghasemi, A ; Sharif University of Technology
    Sharif University of Technology  2004
    In this paper, the effect of morphology, size and volume fraction of the most important microstructural constituents of cast A356 aluminum alloy on its main mechanical properties has been studied. The investigated variables consist of Dendrite Arm Spacing (DAS) of α aluminum phases, spheroicity of silicon particles in eutectic areas and 2-D micro porosity areas. The variations of Quality Index (Qi) with DAS and spheroicity of eutectic silicon particles follow a linear relationship. For the micro-porosity area of a polished section of the studied samples, two linear relationships were found, one for values less than 1.25% and another for higher values. As the basis for a quantitative analysis... 

    Serrated flow during warm forming of low carbon steels

    , Article Materials Letters ; Volume 57, Issue 29 , 2003 , Pages 4515-4519 ; 0167577X (ISSN) Serajzadeh, S ; Sharif University of Technology
    In the present paper, employing compression experiments for three grades of low carbon steel, the effects of deformation condition and chemical composition on the occurrence of dynamic strain ageing are studied. Also, based on the achieved results, the flow behavior of steels under warm deformation conditions is predicted for the employed steels. The results show that both chromium and niobium postpone the happening of serrated flow and shifts the serrated flow region to lower temperatures in comparison with low carbon steel, while the activation energy for commencing dynamic strain ageing increases. © 2003 Elsevier Science B.V. All rights reserved  

    Electrochemical characterization of the Ni-Fe alloy electrodeposition from chloride-citrate-glycolic acid solutions

    , Article Materials Chemistry and Physics ; Volume 77, Issue 2 , 2003 , Pages 352-358 ; 02540584 (ISSN) Afshar, A ; Dolati, A. G ; Ghorbani, M ; Sharif University of Technology
    Cyclic voltammetry and transient time (τ) measurements have been used to characterize the system, while potentiostatic I-t transients have been recorded to obtain the nucleation and growth mechanism. The electrodeposition of nickel, iron and nickel-iron alloys on the platinum was studied by electrochemical techniques in the presence of complexing compounds. The cyclic voltammetry results clearly show that the electrodeposition of nickel, iron and nickel-iron alloys is a diffusion-controlled process with a typical nucleation mechanism. The redox potentials of the Ni and Fe are shifted to more cathodic potentials in the complexing electrolytes. In addition, the current transients reveal that...