Sharif Digital Repository

According to the conducted research, severe deformation of low-carbon steel sheets using the constrained groove pressing method causes a decrease in grain size and increases the strength and hardness of the sample after one pass. However, continuing this process in subsequent passes does not significantly increase strength and hardness, and sometimes it remains constant. Therefore, in this project, cold rolling has been used to improve the strength of the steel sheet and improve the surface smoothness of the final piece. After severe deformation and rolling due to the high applied strain, the strength of the sample increased and the percentage of its elongation decreased. Therefore,... 

The aim of this research is to fabricate Mg based nanocomposite by friction stir processing and investigation of the process parameters on the microstructure and mechanical properties of the nanocomposite. In order to this aim, alumina nanoparticles as reinforcement were poured in the groove, with 5mm depth, and due to rotation of friction stir tool, these nanoparticles were mixed with the matrix and nanocomposite was produced. To reach to the best condition in nanocomposite fabrication, the effect of friction stir processing parameters such as, tool rotation speed, tool design, number of friction stir passes, cooling media and reinforcement percent on microstructure, hardness, tensile... 

Joining metal and alloy is a continuous and inevitable effort in oil and gas and automotive industry, and a considerable number of these joints are dissimilar joints. Steels and aluminum alloys are two of the most utilized engineering material and bi-metallic steel-aluminum parts have a lot of applications due to having the combined properties of both alloys (for example the high tensile strength and wear resistance of steels along with good thermal and electrical conductivity and corrosion resistance of aluminum alloys). However, fusion welding of aluminum to steel possesses great challenges due to the difference in melting point, coefficient of thermal expansion, thermal conductivity and... 

In this research Al6061-SiC composite bonding was done by transient liquid phase method using powder copper intermediate layer. In the first stage feasibility of making this junction in ambient condition was studied. In order to find process optimum temperature, experiments were performed in 560°C, 570°C, 580°C and 590°C for 2 hours. Optical microscopy, scanning electron microscopy and EDS analysis were utilized for this study. Moreover, shear strength determination test was done to assess and compare mechanical properties and also to determine the optimum bonding temperature.
In second stage, base composite and bonded specimens were homogenized in 530°C for 5 and 10 hours. Effect of... 

Considering the wide applications of 304 stainless steel in various industries and the existing literature on transient liquid phase bonding of stainless steels with a variety of interlayers, the present work aimed to reduce the bonding time by using a two step bonding method. Faster bonding reduces both energy consumption during bonding and the base metal grain growth. It also leads to a lower reduction in the base metal and joint strength.Due to the melting point of the interlayer, different durations and a temperature of 1200°C were selected for the first step. This temperature was maintained for a specified period of time before it sharply dropped to and remained at 1180°C (the... 

Several studies are already on severe plastic deformation of wrought and cast aluminum alloys. Among these studies, no evidence of applying severe plastic deformation on the structure of rheocast or rheoforgedaluminum alloy can be found. So, in this research A356 alloy with globular structure was achieved using electromagnetic stirring and rheoforging. The optimum condition of globular structure with high sphericity was achievedafter holding the produced structure in semi-solid state for 10 min. Then, the effect of severe plastic deformation on mechanical and microstructural properties of this alloy and cast alloy was studied. The results show that with applying 3 passes of multidirectional... 

Severe Plastic Deformation (SPD) has been used as an effective approach to access fine grain (FG) and ultra-fine grain (UFG) materials.the Temperature of SPD is a dominant parameter to controlling ultimate properties. SPD at room-temperature and the high temperature was used widely in literature but the low-temperature process (sub-zero and cryogenic temperatures) was not used comparably. In this study, Low-temperature Multi-Directional Forging (LMDF) was applied on commercially pure aluminum and room-temperature MDF (RMDF) was attained for contrast temperature effects, and resulting in more fine grains. The grain refinement was attributed to the fragmentation process with a limitation in... 

Lots of researches have been carried out on the severe plastic deformation (SPD) and annealing of the aluminum up to now. Due to the different annealing behavior of the severely deformed metals and on the other hand the necessity to the rollig for producing the thin SPD sheets, so the purpose of the recent study is producing the thinned sheets with applying the temperature simultaneously. Dislocations density increases by SPD so it confines their movement and cause to the higher strength of the material. Rolling of the SPDed sheets increase the mechanical properties. Grain boundary energy increases with this mechanical improvement and results in lower ductility. So, it is necessary to... 

The use of tin-lead solder alloys (Pb-Sn) has been limited due to environmental problems in recent years, and several types of research are being carried out on lead-free solder alloys. However, these solders have weaker physical and thermal properties than Pb-Sn solders. In recent years, researchers have been trying to improve these solders' physical and mechanical properties by adding reinforcing particles to the solder and using a magnetic field during melting and solidifying the solder. On the other hand, with the growth path of miniaturization and, simultaneously, compaction and integration of electronic equipment, electronic circuits should have higher current density, better... 

Nano/Micro-structure of rapidly solidified (products of Atomizing and Melt Spinning processes) Al-20Si-(5Fe) alloys has been investigated at the present work. Moreover, the effect of cooling rate on microstructure and growth morphology of these alloys has been studied. Microstructure of the products was examined by using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction.At the present work some models have been proposed for driving a relationship between microstructure and rapid solidification parameters during Atomizing and Melt Spinning processes. These models are based on macroscopic heat transfer during the processes. Model for... 

Recently, low temperature carburizing of stainless steels, especially austenitic stainless steels, have been considered by so many researchers. The improvement of tribological properties of which is so impressive so much so that such properties like hardness and wear resistance increase to manifold. In this research, low temperature carburizing was done on two kinds of precipitation hardenable stainless steels 17-4 and 13-8 Mo. After that, microstructural investigations were done on the carburized surfaces and in 5, 10, 20, 80, and 150 micrometer depths. Moreover, in each depth, in order to phase structure and tribological properties investigation, XRD and microhardness tests were done,... 

In this study, Al6063-Al203 nanocomposite powders were synthesized by reaction mechanical milling method. Nanometric reinforcement particles were formed via high- energy ball milling under a controlled oxygen containing atmosphere. Morphological and microstructural evolutions of nanocomposite powders were investigated by using X-ray diffraction (XRD), thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods at different milling times. The results showed that mechanical milling stages were accelerated and the time for reaching steady- state condition was decreased by an increase in the oxygen content in the milling atmosphere. The in-situ... 

Due to its biodegradability, magnesium can be a good option for making degradable medical implants that disappear in the body over time and thus there would be no need for secondary surgery. However, high rate of corrosion of magnesium in the body environment and low formability at room temperature are the two main problems of magnesium, which lead to rapid destruction of the sample in a short time and serious problems. For these reasons, much research is currently being done to improve the corrosion behavior and mechanical properties of magnesium alloys through microstructure modification. In this regard, special attention has been paid to Mg-Li alloys as the lightest magnesium alloys. The... 

In the present study, the microstructural and textural evolutions and mechanical properties of 1050 Aluminum alloy was investigated through ECAP processing. The effects of annealing and strain path change by cold rolling on the ECAPed specimens were also investigated. The number of ECAP passes, annealing temperature and reduction of area during cold rolling were chosen as the variable parameters. The results showed that the grains became finer by increasing the ECAP passes. It is shown that the volume fraction of low angle grain boundaries increased in the first two passes. However, the volume fraction of high angle grain boundaries increased in the next passes. Continuous dynamic... 

Geopolymer concrete is one of the most environmentally friendly concretes that does not have any pollutants harmful to the environment. By-products that are normally harmful to the environment can be used in manufacturing this product, therefore, the use of this concrete is known as the first concrete replacement in the world. In order to use geopolymer concrete, it is necessary to an essential to know the mechanical information of these materials.In this study, the mechanical behavior of geopolymer concrete for fly ash and slag in terms of its stress and strain uniaxial loading and triaxial loading at , and15MPa pressures for three concrete mixing design are investigated.Then the... 

In recent years, investigation of mechanical properties of micro- and nano-structure materials, and peculiarly nanocomposites have been attracted a wide variety of researches. In this regard, friction-stir-processed (FSPed) metal matrix nanocomposites have been considered an important case with appropriate mechanical properties especially for fabrication of ultra-fine grained Al alloys and Al-matrix nanocomposites. In this research, Al matrix hybrid nanocomposites were fabricated via multi passes-friction stir processing (FSP) of Al-Mg alloy (AA5052) with different amounts (~2 and 3 vol%) of pre-placed TiO2 (30 nm) particles nanoparticles. It was revealed that employing of cumulative FSP up... 

Since the discovery of nanomaterials, the nanotubes have found special considerations. The high strength beside the low density, have attracted the interest of the scientists and engineers. Nowadays, one of the common methods to produce composites with high specific strength is to utilize of the nanotubes in the matrix of lightweight metals and alloys such as magnesium and aluminum. Recent researches indicate that very limited focus has been given to the production and properties of the magnesium - carbon nanotube composites and their workability. In this research, magnesium alloy - carbon nanotube composite is produced by casting method and its strength and workability are investigated as... 

Having the high strength to weight ratio has been made the composites special materials very important these days. The low density of aluminum and its appropriate corrosion properties make it a good choice for metallic matrix. Also, the high tensile strength of stainless steel fibers can helps as a reinforcement in the composite to improve its mechanical properties. Enhancing the bonding of composite’s components can helps it to develop its properties. Casting is an appropriate process for making an aluminum matrix containing steel fibers as reinforcement in a structural composite. In addition, rolling process can remove so many defects made by casting, and improve joining of fibers and... 

IC221M is a cast Ni3AI-based intermetallic alloy which chemical composition bases on Ni- 8Al-8Cr-1.5Mo-1Zr-O.OIB %wt. Because of high strength, good high temperature oxidation, carburization and creep resistance as mechanical and physical properties, IC221M has got good attention in aeronautical, military and steel production industries nowadays. The best service temperature range is 600-800°C and melting starts at II 70°C. Since 1993 according to broad range of researches and applications, ASTM standardized it at Al002-99 and from that time researchers try to replace steel with IC221M. %80 volume of microstructure in this alloy consisted of brittle y' and remain are y and low... 

In this study, samples of wrought nickel-cobalt superalloy AEREX350 underwent hot tensile testing at temperatures ranging from 500 to in the solution-treated state, with subsequent investigation into their mechanical properties and microstructural changes. Anomalous yield strength behavior was observed in this alloy, characterized by an initial decrease in yield stress with rising temperature, followed by an increase and subsequent decrease. Similarly, the ultimate tensile strength exhibited a similar trend to the yield stress. Conversely, ductility parameters demonstrated an inverse relationship with alloy strength. Notably, the alloy displayed a pronounced work-hardening rate at 800 °C....