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coarsening
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Growth kinetics of γ′ precipitates in superalloy IN-738LC during long term aging
, Article Materials and Design ; Volume 24, Issue 5 , 2003 , Pages 325-330 ; 02641275 (ISSN) ; Asgari, S ; Sharif University of Technology
Elsevier Ltd
2003
Abstract
In this research, results obtained on the growth kinetics of γ′ precipitates in superalloy IN-738LC are presented. It was found that when the coarsening of primary and secondary γ′ are considered together, the overall kinetic of coarsening followed a linear trend, as predicted by Lifshitz, Slyozov and Wagner (LSW) theory. However, when only the population of secondary γ′ was taken into account, growth rate for the secondary γ′ departed from the linear trend predicted by the theory. It is therefore suggested that the observed deviation of coarsening kinetics from linear behavior may be related to the short inter-particle distances in this system which caused elastic interaction energy to...
The effect of thermal exposure on the γ′ characteristics in a Ni-base superalloy
, Article Journal of Alloys and Compounds ; Volume 368, Issue 1-2 , 2004 , Pages 144-151 ; 09258388 (ISSN) ; Asgari, S ; Sharif University of Technology
2004
Abstract
In this investigation, changes in γ′ characteristics in superalloy IN-738LC during aging are presented. The SEM studies revealed that coarsening kinetics of γ′ follows a linear law at different aging time for different temperatures. Whereas when coarsening of secondary γ′ is studied, it was found that at the early stage of aging, volume fraction of secondary γ′ is high, leading to short inter-particle distances. In this condition interfacial energy is dominant and variation of [r3-r03] as a function of aging time is linear. As the coarsening proceeds, volume fraction of secondary γ′ decreases and elastic interaction energy becomes dominant. In such case a deviation in variation of [r3-r03]...
Coarsening dynamics of dewetting nanodroplets on chemically patterned substrates
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 86, Issue 1 , July , 2012 ; 15393755 (ISSN) ; Sharif University of Technology
2012
Abstract
Mesoscopic hydrodynamic equations are solved to investigate coarsening dynamics of two interacting nanodroplets on chemically patterned substrates. The effects of different parameters such as the surface chemical pattern, the slip length, the profile of the disjoining pressure, the size of the droplets, and the contact angles on the coarsening are studied. Our results reveal that the presence of a chemical heterogeneity can enhance or weaken the coarsening dynamics depending on the pattern type and positions of the droplets on the substrate. Also increasing the contact angles to values larger than a critical value may qualitatively change the coarsening process, and the profile of the...
Determination of austenite grain coarsening temperature of a Nb-microalloyed steel sheet
, Article Advanced Materials Research, 21 January 2011 through 23 January 2011 ; Volume 213 , January , 2011 , Pages 600-603 ; 10226680 (ISSN) ; 9783037850619 (ISBN) ; Otaaghvar, V. A ; Khaki, M. M ; Sharif University of Technology
2011
Abstract
Thermomechnical processing and controlled rolling of microalloyed steel sheets are affected by several factors according to the final properties of product. To create the high mechanical properties, a uniform and fine-grain structure is necessary in hot rolled final products. To produce such microstructures, every stage of the thermomechanical processing of the steel rolling has to be carefully controlled. Hence, first step is grain coarsening control that it usually occurs during reheating for slab. For this purpose, seven different reheating temperatures between 1000 to 1300 °C with 50 °C increments were chosen in this investigation for soaking treatment. By soaking the specimens in...
Simulation of Coarsening in Tin/Lead Solders by Using Phase Field Method
, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz (Supervisor) ; Ashouri, Hossein (Supervisor)
Abstract
Soldering is one of the important methods in joining techniques which has wide applications in industries such as microelectronic. Today, the physical and mechanical properties of solder joints is very important because the dimensions of electronic devices are decreasing that cause to increasing of their current density. One of the important problems of high current density in solder joints is the microstructures of solders in microelectronic components, change over time that is weakened the properties of the solder alloy. This study presents a quantitative model , which is capable to simulation phase separation and coarsening phenomenon in Tin/Lead Solders. This model is based on continuum...
Microstructural evolution of AZ91 alloy containing 3%Ca prepared by cooling slope
, Article Semi-Solid Processing of Alloys and Composites 10 - Selected, peer reviewed papers from the 10th International Conference on Semi-Solid Processing of Alloy and Composites, S2P 2008, Aachen, 16 September 2008 through 18 September 2008 ; Volume 141-143 , 2008 , Pages 427-432 ; 10120394 (ISSN); 9771012039401 (ISBN) ; Aashuri, H ; Davami, P ; Narimannezhad, A ; Foroughi, A ; Kiani, M ; Sharif University of Technology
Trans Tech Publications Ltd
2008
Abstract
Globulization of the grain refined AZ91 magnesium alloy with Ca on a cooling slope was investigated. Dendritic morphology of the grains was transferred into round and well distributed small particles as a result of grain-refinement effect of Ca in the alloy. Semi-solid holding of the alloy was carried out at different temperatures to improve the spherecity of the globules. Results show that, remelting at 540 °C for 30 min provides the best shape factor for the alloy. The study of coarsening kinetic in this alloy showed lower growth rate alternative other research which used same condition for produce semi-solid billet just in using Ca
Influence of mechanical treatments on the mechanical properties of AA5083 aluminum alloy welded joints
, Article 17th International Metallurgical and Materials Conference, METAL 2008, 13 May 2008 through 15 May 2008 ; 2008 ; 9788025419878 (ISBN) ; Abachi, P ; Taheri, N ; Sharif University of Technology
TANGER spol. s r.o
2008
Abstract
Aluminum alloy series 5xxx lose their strength, especially in the heat affected zone (HAZ) of welds, due to thermal cycle during welding process. Because of this thermal cycle, re-crystallization and grain coarsening in HAZ occur, which result in decreasing of mechanical properties. In this paper the influence of "overloading" and "shot peening" as methods of post weld treatment on mechanical properties of AA5083 aluminum alloy welded joints is investigated. The results show that both overloading and shot peening treatments increase the hardness and tensile strength of welded joints. It is observed that the influence of overloading is stronger than shot peening on increasing hardness of the...
Effect of environmental conditions on fracture behavior of solder joints
, Article Theoretical and Applied Fracture Mechanics ; Volume 112 , 2021 ; 01678442 (ISSN) ; Nourani, A ; Karimi, M ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Double cantilever beam (DCB) specimens were prepared according to standard surface mount technology (SMT). The samples were stored inside an environmental chamber at two different relative humidity values (i.e. 40 or 100%) for either 2 or 4 h. Then they were aged at 25 °C, 75 °C or 125℃ for the same time. Finally, after being cooled to room temperature, fracture tests were performed under mode-I loading conditions at a strain rate of 0.03 s−1 at room temperature. Storage time did not have a significant effect on the fracture behavior. The fracture load and energy of the solder joints decreased significantly when the temperature was increased from 25 to 75℃. By further increase in the...
Coarsening dynamics of nanodroplets on topographically structured substrates
, Article Journal of Physics Condensed Matter ; Volume 25, Issue 4 , 2013 ; 09538984 (ISSN) ; Moosavi, A ; Sharif University of Technology
2013
Abstract
Employing a biharmonic boundary integral method with linear elements, coarsening dynamics of nanodroplets on topographical step heterogeneity is investigated. It is shown that the step height and droplet configuration have an influential effect on the dynamics. Increasing the step height slows down the process while locating the droplets close to the step boosts the coarsening rate. Considering a slip boundary condition enhances the dynamics and reveals a transition in the droplet migration direction. Our results reveal that increasing the surface wettability weakens the dynamics. Various types of the disjoining pressure over the step are also considered and their effects on the coarsening...
Coarsening Dynamics of Nanodroplets
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor)
Abstract
Hydrodynamic mesoscopic equations are solved using boundary integral method to investigate the coarsening dynamics of two dimensional nanodroplets. The dynamics is probed by locating two drops on homogeneous, chemical heterogeneous and physical heterogeneous substrates respectively. For homogeneous substrate, the effect of different parameters like droplets distance, slip boundary condition, surface contact angle and disjoining pressure type on the dynamics is studied. Results reveal that increasing the contact angles to values larger than a critical value may qualitatively change the coarsening process and the profile of the disjoining pressure can appreciably modify the coarsening rate....
Developing a Model for Simulation of Dynamic Behavior of Nano-beams
, M.Sc. Thesis Sharif University of Technology ; Nejat, Hossein (Supervisor)
Abstract
The utility of nano-beams in MEMs and NEMs has progressed a lot in recent years. Such systems have found wide spread use in sensors and actuators due to small size, low weight, high accuracy and low energy consumption. By a decrease in size of nano-beams, surface effect increases which makes the classical theories unable to modeling such beams. Therefore new models are required for evaluating the dynamic behavior of nano-beams. In this thesis we have attempted to develop a suitable Coarse-Grain model for analysis of such beams. At first a suitable Coarse-Grain mapping with determined Sutton-Chen potential parameters is introduced for FCC metals. In the next step, EAM is considered as...
Characterization of mechanically alloyed Fe100-xSix and Fe83.5Si13.5Nb3 nanocrystalline powders
, Article Journal of Materials Processing Technology ; Volume 203, Issue 1-3 , 2008 , Pages 554-560 ; 09240136 (ISSN) ; Abachi, P ; Madaah Hosseini, H. R ; Bahrami, A ; Sharif University of Technology
2008
Abstract
In present research, nanocrystalline Fe100-xSix (x = 6.5, 10, 13.5, 20 and 25 at.%) and Fe83.5Si13.5Nb3 alloy powders were prepared by mechanical alloying using high-energy ball milling. The resulting powders mainly consist of micron-sized particles with an average grain size of less than 20 nm. According to the XRD test results, by increasing the milling time and/or the Si content the lattice parameter decreases and the internal microstrain increases. In addition, the specific saturation magnetization diminishes as Si content increases. The coercive forces of the as-milled nanocrystalline powders are much higher than those of corresponding Fe-Si bulk alloys with a minimum at 13.5 at.% Si....
Creep Deformation Simulation of Nickel-Based Superalloys Using Molecular Dynamics Method
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
This study aims to investigate the creep deformation mechanisms in nickel-based single-crystal superalloys for which two-dimensional molecular dynamics (MD) simulations are conducted to model various temperature, stress conditions and phase interface crystal orientations. Ni-based single-crystal superalloys are of great importance in the aircraft industry, on account of their excellent high temperature creep resistance. This characteristic mainly originates from two features considered in their structure: first, their two-phased microstructure comprising gamma ( ) and gamma prime ( ), and the nature of this superalloy itself which is single-crystal. MD is a powerful tool to gain insight into...
Late-stage evolution of thin liquid coating films over step topographies
, Article Advanced Materials Research ; Volume 569 , 2012 , Pages 560-563 ; 10226680 (ISSN) ; 9783037854808 (ISBN) ; Moosavi, A ; Sharif University of Technology
2012
Abstract
Mesoscopic hydrodynamic equations are solved to investigate late-stage evolution of thin liquid films over step topographies. Different geometrical parameters including step height and initial position and configuration of resultant masses of dewetting (droplets) are probed to find their effects on the mass evolution of the system. Our results indicate that increasing the step height and locating the droplets close to the step enhance the dynamics and accelerate smaller droplet collapse
Microstructure and mechanical properties of friction stir welded ferrite-martensite DP700 steel
, Article Materials Science and Engineering A ; Volume 737 , 2018 , Pages 213-222 ; 09215093 (ISSN) ; Kokabi, A. H ; Kheirandish, S ; Kestens, L. A. I ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In the present work, friction stir welding technique was applied on 2 mm thick ferrite-martensite DP700 steel sheets at rotational speeds of 600, 800 and 1000 rpm. The microstructure and mechanical properties of the welds were evaluated. It was found that Zener-Hollomon parameter decreased with increasing rotational speed that leads to grain coarsening in the stir zone. It was also found that increment of rotational speed increased softening phenomenon in sub-critical heat affected zone. The results also showed that the presence of WC particles in the stir zone, which was due to the tool wear, as well as formation of a soft ferrite band degrade the tensile properties at rotational speed of...
Annealing behavior of aluminum after low-temperature severe plastic deformation
, Article Materials Science and Engineering A ; Volume 824 , 2021 ; 09215093 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
Severe plastic deformation (SPD) processes have received less attention at low temperatures (sub-zero and cryogenics). Hence, in this study, SPD of a commercially pure aluminum (AA1050) through Multi-Directional Forging (MDF) at Low-Temperature (LTMDF) and Room-Temperature (RTMDF) is investigated for different strains. Multi-directionally forged (MDFed) samples were annealed at 150, 250, 350, and 450 °C for 1 h, and some samples were stored at room temperature for periods up to 1 year. Results show that the hardness values and flow stress of LTMDFed aluminum are higher than those of RTMDFed ones. The ratio of yield strength to hardness for LTMDF is similar to that for RTMDF. Surprisingly,...
Interaction of 3D dewetting nanodroplets on homogeneous and chemically heterogeneous substrates
, Article Journal of Physics Condensed Matter ; Vol. 26, Issue. 22 , 2014 ; ISSN: 09538984 ; Moosavi, A ; Sharif University of Technology
Abstract
Long-time interaction of dewetting nanodroplets is investigated using a long-wave approximation method. Although three-dimensional (3D) droplets evolution dynamics exhibits qualitative behavior analogous to two-dimensional (2D) dynamics, there is an extensive quantitative difference between them. 3D dynamics is substantially faster than 2D dynamics. This can be related to the larger curvature and, as a consequence, the larger Laplace pressure difference between the droplets in 3D systems. The influence of various chemical heterogeneities on the behavior of droplets has also been studied. In the case of gradient surfaces, it is shown how the gradient direction could change the dynamics. For a...
Effect of RE elements on the microstructural evolution of as cast and SIMA processed Mg-4Al alloy
, Article Journal of Alloys and Compounds ; Volume 509, Issue 5 , February , 2011 , Pages 1567-1572 ; 09258388 (ISSN) ; Khomamizadeh, F ; Sharif University of Technology
2011
Abstract
In the present article, the effect of Rare Earth elements on the microstructural development of as cast and semisolid Mg-4Al alloy produced by SIMA process is studied. Investigation conducted by metallographic observation, scanning electron microscope and quantitative metallographic methods. Results showed that alloy's dendrites turn into larger fully dendritic shape with sharp and narrow arms from equiaxed rosette type as the amount of RE elements increased from 0 through 4%. The effect of RE elements on the microstructure of the treated-alloys was detectable through elimination of vast number of intragranular liquid droplets as well as by decreasing kinetic of microstructural changes. It...
Recent advances in ageing of 7xxx series aluminum alloys: A physical metallurgy perspective
, Article Journal of Alloys and Compounds ; Volume 781 , 2019 , Pages 945-983 ; 09258388 (ISSN) ; Taheri, A. K ; Taheri, K. K ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Al-Zn-Mg-Cu alloys (7xxx series Al alloys) are extensively used for their superior mechanical and corrosion performance. These properties are microstructure-sensitive and highly dependent on the formation, growth and coarsening of precipitates. To date, a wide variety of ageing procedures have been developed to tailor the evolved microstructures so as to yield a good combination of mechanical capacity and corrosion resistance of 7xxx series Al alloys. Among these methods, isothermal ageing, multi-stage ageing, non-isothermal ageing, retrogression and re-ageing (RRA), and stress ageing (i.e. creep ageing) are the most significant. In the present review, all of these approaches are...
Poly(lactic acid)/coplasticized thermoplastic starch blend: Effect of plasticizer migration on rheological and mechanical properties
, Article Polymers for Advanced Technologies ; Volume 30, Issue 4 , 2019 , Pages 839-851 ; 10427147 (ISSN) ; Pircheraghi, G ; Bagheri, R ; Altstädt, V ; Sharif University of Technology
John Wiley and Sons Ltd
2019
Abstract
Polylactic acid (PLA) and thermoplastic starch (TPS) are known as bio-based and biodegradable thermoplastic polymers that can be used in different applications owing to their inherent physical and mechanical properties. In order to reduce the higher costs of PLA and tuning its physical and mechanical properties suitable for short life packaging applications, blending of PLA with the TPS, more economical biodegradable polymer, has been considered in academic and industrial researches. However, melt blending of PLA with TPS without compatibilization process caused some drawbacks such as coarsening morphology and declining mechanical properties and ductility because of thermodynamic...