Sharif Digital Repository

A method of joining dissimilar metals in the semi solid state is presented. By this method bonding of Stainless steel and semisolid aluminum alloy took place in this research. By usage of thermomechanical treatment, dendritic microstructure of cast aluminum alloy changed to globular structure. The experimental process of bonding occurred at semisolid temperature stage of aluminum alloy in a predesigned mold by using a pressure equipment. The relationship between interfacial shear strength and solid fraction of aluminum alloy, bonding pressure and time of keeping pressure were studied by method of orthogonal experiment. By the usage of Taguchi method in designing experiments, plurality of... 

Because of the high operating temperature, interconnect surface tends to be oxidized and Cr2O3 oxide layer will be created on the surface. This phenomenon is undesirable due to decreasing electrical conductivity, so a preservative coating is needed to improve the interconnect properties. In this paper, a dense perovskite thin film was successfully synthesized on a ferritic stainless steel (type 430) substrate by a sol-gel dip coating method. This coating improved chemical stability, oxidation behavior of the substrate and decreased cathode poisoning. The lanthanum chromite was coated on the substrate by sol-gel dip coating process. First, during a hydrolyze process, a stable sol was made up... 

Bioactive glasses are able to bond to soft and hard tissues in living body and their application as coating on metallic implants like 316L stainless steel has two important effects: (1) intimate link between bone and materials and (2) corrosion protection of metallic implant in body fluid and protection from tissues in front of corrosion products. Therefore, in this research, 45S5 bioactive glass prepared via sol- gel method was dip coated on 316L stainless steel substrates and its characteristics was investigated.Results of phase analysis showed that by sintering 45S5 bioglass at 600 ˚C for 5 h, an amorph sample with small amount of Na2Ca2Si3O9 was obtained. So, the bioglass coated samples... 

Transient liquid phase (TLP) bonding of 316L/17-4PH bimetals using a thin layer of nanostructured nickel was studied. The nanostructured nickel interface was deposited through pulse current coating in a Watt bath. The TLP bonding was performed at different temperatures ranging from 1000 °C to 1300 °C using a nickel interface having different thicknesses (2-17µm) and crystallite size (14-67 nm). The microstructure of the joint bimetals and phase formation were studied using the optical and scanning electron microscopes and X-ray diffraction (XRD) method. The mechanical properties of the bimetals were evaluated by micro-hardness and shear tests. To evaluate the corrosion behavior of the... 

Due to recent progresses in lowering the temperature of SOFC, using metallic interconnects instead of ceramic interconnects was possible. Among the alloys used for interconnects, ferritic stainless steels (FSS) due to thermal expansion coefficient compatible with other cell components and cheap fabrication, have become the most widely used material for interconnects. Because of improvement of oxidation resistance of these FSSs, many studies have been made on coating of oxides on FSSs and results show that the spinel oxides have the best performance. In this study, the CuCo2O4 performance as coating in SOFC's interconnects was investigated. Coating process used was sol-gel dip coating and raw... 

Solid oxide fuel cell (SOFC) is one of the promising candidates for clean energy production. Due to the high operating temperature of SOFC, a protective coating is commonly applied on the surface of interconnects to prevent oxidation. In this study, electrophoretic deposition was employed to prepare a manganese-cobalt spinel coating on the surface of ferritic stainless steel (AISISAE430) substrates. MnCo2O4 powder with an average particle size of 60 nm was utilized and the sintering behavior of the coatings at different temperatures was studied. Non-isothermal and isothermal sintering behavior of the powder compacts were examined by employing a sensitive dilatometer. Master sintering curve... 

The austenitic heat resistant stainless steels have been widely used in petrochemical industry as furnace tubes which are exposed to extremely high temperatures. In this study, the quench aging process of a HP modified heat resistant stainless steel is assessed and the kinetics of aging is evaluated by the JMAK model. The microstructure of steel in as cast and aged conditions was characterized by optical microscope and scanning electron microscope equipped with EDS. The effects of aging time and temperature on the microstructure, tensile propertices, shear strength, hardness, and ductility of the aged steel were determinded. The results of tensile and shear punch tests show a linear... 

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, pitting corrosion of 304, 316 and 316L stainless steels in 3.5% NaCl solution at different temperatures (25, 40, and 70°C), were studied by electrochemical methods such as Cyclic Potentiodynamic Polarization, Electrochemical Impedance Spectroscopy and Immersion tests. Also, the effects of different concentrations of polyethyleneimine with two molecular weights (2000 and 60000 g/mol) on pitting corrosion of these steels were investigated. Finally, the adsorption behavior of inhibitors on surface of alloys was investigated by Atomic Force Microscopy (AFM) and Attenuated Total Reflectance Fourier transform spectroscopy (ATR-FTIR). It was found that both inhibitors prevent... 

The current work is carried out to characterize welding of AISI 304 Austenitic Stainless Steel to Ductile Cast Iron. The welding method was SMAW and the welds were produced using a Nickel-Buttering by a pure Nickel electrode(ENi1) on Cast Iron side, then by 4 types of filler materials the joints were produced; Ni-base electrode(Ni1), E308 and E309 Austenitic stainless steel electrodes and E7018 electrode. The preheat temperature of Cast Iron has been selected to be 250○ and 500 ○C to avoid crack of weldments. The comparative evaluation was based on metallography, chemical composition, hardness and corrosion behavior on two different preheat temperatures. According to metallography, the best... 

Due to increased mortality from Coronary Heart Disease, it is important to work on ways to treat this disease. An effective method of treatment on this disease is the coronary stent implantation. There are nearly two decades passed since implanting the first heart stent. The main objective of this research is design and manufacturing of the medical stents of stainless steel 316 L. Stent materials should have excellent corrosion resistance and biocompatibility. Various materials such as stainless steel 316 L, platinum alloys, niobium alloys, cobalt alloys are used for manufacturing the stents. In this project, at the first stage seam tube was prodected with laser welding of a tube with... 

Stainless steels have many applications in different industries like chemistry, medicine and food production. So for using these alloys it is necessary to join them with appropriate method. In this research, microstructure-mechanical properties relationship of 304LC austenitic stainless steel transient liquid phase bonded using a Co-based interlayer was investigated. For this purpose, bonding was conducted at 1180 ℃ for different holding times. Microstructure of the joints was evaluated by optical microscopy (OM) and Scanning Electron Microscopy (SEM). The results showed that isothermal solidification (IS) was completed within 1800s and no intermetallic compound was formed in the joint area... 

In this research, two-layered sheets of copper and stainless steel 316 were produced by roll bonding. These sheets provide a combination of properties of copper and stainless steel; including high strength, thermal conductivity and corrosion resistance, as well as low weight and cost-efficient means of production. The effects of thickness reduction, different preheat temperatures and varying heating conditions after rolling on bond strength were studied. In some specimens, an aluminum sheet was used as a middle-layer, which significantly improved the bonding quality. In order to observe the interface of the bonded specimens, optical microscope images of the cross sections were studied.... 

In this research, a computational method based on thermodynamic and physical metallurgy coupled by the d-electron approach was used to design the composition of a high strength and heat resistant (HSHR) stainless steel. Then, three series of the heat resistant 25Cr-35Ni-Nb (HP-Nb) stainless steels with tungsten, nitrogen, and micro alloying elements additions were cast. In these alloys a Nb/(C+ 6/7 N) ratio of ≈ 2.4 to 3.7 was chosen and they were directionally solidified under two cooling rates of 23 Ks-1 and 6 Ks-1. The effects of the alloy chemical composition and solidification cooling rate on the macrostructure, microstructure, microsegregation, and inclusions in the alloys were... 

This study was conducted in order to investigate the effect of difference in electrical resistivity between low carbon steel and austenitic stainless steel on the physical and mechanical properties and fracture mode of dissimilar resistance spot welds of these alloys. For this purpose, plastic deformation using constrained groove pressing combined with rolling applied to low carbon steel in three levels of 40%, 156% and 272%. Microstructural characterization, micro-hardness measurements and shear-tension test were performed. It was shown that by increasing the pre-strain in low carbon steel its electrical resistivity increases from 13.08 μΩ.cm to 19.5 μΩ.cm and because of reduction of... 

Roll bonding process is commonly used for the production of multilayer sheets. In the present study, using the roll bonding process, two layer sheets of copper - stainless steel were produced. In this case bonding strength was measured by peeling test at different statges and the quality of bonding was evaluated by SEM and Stereo Electron Microscope. The cross-sections of the bonding of rolled and annealed samples was investigated by optical microscopy. Also using EDAX analysis and EDS, the chemical composition of formed transition layer and the size of its interface at different temperature are measured respectively and the change in mechanical properties was investigated by tensile test... 

Various methods are used to improve the behavior of steel parts. Cryogenic treatment is one of the prevalent methods used for this purpose. It is not a substitute process but rather a supplement to conventional heat treatment process. In this Study the effect of the minimum temperature and the time of cryogenic treatment on wear resistance and residual stress of stainless steel AISI 316 and AISI 304 were studied. For this purpose conventional heat treatment, deep cryogenic treatment (24, 48 and 72 hours) and shallow cryogenic treatment (5, 10 and 15 hours) were performed on the samples. The wear resistance were measured by Pin-on-disk test according to the standard G99-95 (under the load of... 

In this research, the hot and warm rolling of stainless steel 304 was studied. First the rolling process was simulated using Finite Element Method software ABAQUS and the distribution of temperature and strain in the process under discontinuous conditions were predicted. Next, hot and warm rolling of stainless steel 304 under different conditions was carried out. Specimens were cut and subject to mechanical testing, metallography and electron microscopic studies. Data obtained from these experiments and the predicted trends from ABAQUS were compared, therefore studying the effect of different parameters on the microstructure and mechanical properties of the rolled specimen. Results indicate... 

Joining of yttria-stabilized zirconia (YSZ) to stainless steel (SS) is considered for various applications such as solid oxide fuel cells, thermal barrier coatings, and medical implants. In the present work, a series of brazing pastes utilizing silver and nickel nanoparticles (~80 nm) mixed with carboxymethyl cellulose as the organic phase were developed to join 5YSZ to 420 SS. The effects of processing parameters such as time and temperature of brazing and the composition of the paste on the microstructure of the joint and its mechanical strength were studied. The mechanism of interface formation was elaborated by scanning electron microscopy (SEM) and electron probe micro analyzer (EPMA).... 

In this research, role of zirconia nanoparticles as a biocompatible material which has great mechanical properties, was investigated on corrosion behavior and bonding strength of HA coating. HA- ZrO2 composite prepared by a 2-step pulse electrodeposition method. Effect of pH (3.5, 4.5), bath temperature (60, 80 ͦC), current density (0.5, 1, 2 mA/cm2) and zirconia concentration (5, 10, 15 g/L) on coating characteristics were studied. X-ray diffraction was employed for phase analysis. Morphology and microstructure of samples observed utilizing scanning electron microscope (SEM) and elemental analysis was done by EDS. In order to corrosion studies electrochemical impedance spectroscopy (EIS)...