Showing 483 results for in
S. A. Sajadi, R. Ebrahimi, M. M. Moshksar,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: In this paper, the forming process of a central hub by radial-forward extrusion is analyzed by using the finite
element software, ABAQUS. Radial-forward extrusion is used to produce hollow parts that generally feature a central
hub with radial protrusions. Effective design factors such as mandrel diameter, die corner radius, die fillet radius,
mandrel corner radius, tube wall thickness and frictional conditions on the force required are investigated by
simulation process. Commercially pure Aluminum AA1100 is selected as a model material for both experimental
investigation and simulation analysis. Comparison is made and good agreement between the experimental result and
that of finite element method is achieved.
M. Pirhadi Tavandashti, M. Zandrahimi, B. Akbari,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Nanoparticles exhibit a high reactivity and strong tendency towards agglomeration. In this study, aluminum
oxide (alumina) nanoparticles were characterized by gas adsorption (BET), transmition electron microscopy (TEM)
and photon correlation spectroscopy (PCS) techniques to assess the agglomeration of the particles. There is a good
correlation between the BET and TEM measurements but PCS was larger in the mean and median size and with a
degree of agglomerates being detected. Some agglomeration was evident, but most of the particles existed as discrete
objects as observed in the (HR) TEM images which were in good agreement with the agglomeration factor.
S.r. Allahkaram, R. Shamani,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Due to the expansion of high voltage Alternating Current (AC) power transmission lines and cathodically
protected buried pipelines, it is becoming more and more difficult to construct them with enough safe distances
between them. Thus, the pipelines are frequently exposed to induced AC interferences, which result in perturbation of
Cathodic Protection (CP) due to AC corrosion. To study the above criterion, an experimental set up was used with
coupons exposed to simulated soil solutions, while under both CP and AC induced condition for which an AC+DC
power supply was utilized. The experiments were carried out in several simulated soil solutions corresponding to
several soil samples collected from various regions along a buried pipeline with overhead parallel high voltage power
transmission line. The results indicated that AC corrosion depends strongly on the composition of the soil.
H. Aghajani, M. Soltanieh, F. Mahboubi, S. Rastegari and Kh. A. Nekouee,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Formation of a hybrid coating by the use of plasma nitriding and hard chromium electroplating on the
surface of H11 hot work tool steel was investigated. Firstly, specimens were plasma nitrided at a temperature of 550
°C for 5 hours in an atmosphere of 25 vol. % H2: 75 vol. % N2. Secondly, electroplating was carried out in a solution
containing 250 g/L chromic acid and 2.5 g/L sulphuric acid for 1 hour at 60 °C temperature and 60 A/dm2 current
density. Thirdly, specimens were plasma nitrided at a temperature of 550 °C for 5 and 10 hours in an atmosphere of
25 vol. % H2: 75 vol. % N2. The obtained coatings have been compared in terms of composition and hardness. The
compositions of the coatings have been studied by X-ray diffraction analysis. The surface morphology and elemental
analysis was examined by using scanning electron microscopy. The improvement in hardness distribution after third
step is discussed in considering the forward and backward diffusion of nitrogen in the chromium interlayer. Also, the
formed phases in the hybrid coating were determined to be CrN+Cr2N+Cr+Fe2-3N+Fe4N.
I. Ebrahimzadeh, Gh.h. Akbari,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Horizontal continuous casting is widely used to produce semi-finished and finished metallic products.
Homogeneity in metallurgical characteristics and mechanical properties in such products is of importance. In the
present work microstructure and mechanical properties of a horizontal continuous cast pipe have been studied.
Microstructural features were investigated by an optical microscope equipped with image analyzer and SEM was used
to characterize precipitates. Tensile behavior, impact strength and hardness variations were the mechanical properties
which were studied. Results showed that microstructure and mechanical properties had diversities in different parts of
the pipe and distinct differences were observed between upper and lower parts of the pipe. A meaningful correlation
was found in microstructure and mechanical properties in different parts of the component.
S.r. Allahkaram, R. Shamani,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract: The risks of alternating current (AC) corrosion and overprotection increasingly demand new criteria for
cathodically protected pipelines. To assess the risk of AC corrosion, new cathodic protection (CP) criteria have been
proposed based on DC/AC current densities measurements using coupons. The monitoring system designed for this
project was based on the instant-off method, with steel coupons simulating coating defects on a buried pipeline. The
problems associated with the instantaneous off-potential measurements have been attributed to a non-sufficient time
resolution. In present study, it has been possible to determine the de-polarisation of steel coupon within a few
milliseconds after disconnecting the coupon from the DC/AC power source, by increasing data acquisition rate. For
this, a monitoring system was developed in order to measure the IR-free potential together with the DC/AC current
densities. The monitoring system was utilized for both laboratory experiments and site survey to study the mechanism
and the condition of AC corrosion, its mitigation and more importantly to define new CP criteria.
H. Mohammadzade, Sh. Kheirandish, H. Saghafian,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract:
transition and heat affected zones formed during surface remelting (in order to improve wear resistance) with TIG
process has been investigated. Relationship between various TIG parameters and thickness of remelted and heat
affected zones revealed that a high concentrated heat energy is imposed by TIG process which makes it a proper option
for focused surface treatment. Based on microstructural examinations five areas with different microstructure and
microhardness were identified within the surface area. Graphite flakes were totally dissolved within the first area
leading to the transformation of denderitic austenite to plate martensite and the formation of ledeburite within
interdenderites. The main feature of the second area, resulted from the presence of graphite flakes, was the local
melting with a gap in the vicinity of graphite flakes and that of third area was the formation of finer and denser
martensite plates closer to the graphite flakes compared with those formed at a further distance. In the fourth layer
there is a mixture of martensitic and pearlitic matrix while the matrix of fifth layer has no change of microstructure.
In this study the effect of graphite flakes present in a pearlitic grey cast iron on the microstructure of melted,
A. H. Emami, M. Sh. Bafghi, J. Vahdati Khaki, A. Zakeri,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract:
the changes of BET surface area of a mineral substance during intensive grinding process. Validity of the proposed
model was tested by the experiments performed using a natural chalcopyrite mineral as well as the published data. It
was shown that the model can predict the experimental results with a very good accuracy and can be used to predict
what may happen under the similar experimental conditions.
Based on experimental observations, a model has been developed to describe the effect of grinding time on
Ali. A. Hosseini,, F. Ghaharpour, H. Rajaei ,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: In this paper‚ the physical and mechanical properties of Al nanocomposite reinforced with CNTs wereinvestigated. High purity Al powder and Carbon Nanotubes (CNTs) with different percentage were mixed by ballmilling method and the composite was fabricated by cold pressing followed by sintering technique. The variation ofdensity and hardness of composite with CNTcontent was investigated. The microstructure of composite was evaluatedby SEM (Scanning Electron Microscope) and XRD (X -Ray Diffraction). The results show that the density and hardnessincrease with CNTpercentage.
S. Zavareh, F. Majedi,, M. Sh. Sharif, F. Golestanifard,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: Multiwalled carbon nanotubes (MWCNTs) were coated with MgO nano particles using simple precipitationmethod. The growth of Mg(OH)2particles was controlled by adjusting the alkaline concentration, salt concentrationand feed rate in simple precipitation method. The nanometer-sized Mg(OH)2particles were precipitated on the surfaceof functionalized MWCNTs by reaction between MgSO4 solution and NH4OH. The samples have been characterizedby scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction and thermal gravimetricanalysis. The results showed a nominally complete MgO coating over the entire outer surface of MWCNTs resulting inimprovement of their oxidation durability.
M. Goodarzi, S. M. A. Boutorabi, M. A. Safarkhanian,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract:In this study, an effort has been made to determine the influence of rotational speed of tool on themicrostructure and hardness values of friction stir welded 2024-T851 aluminum alloy. The microstructure of stir zonein the joints has been investigated. It was found that the particles such as Al6(CuFeMn) particles are broken up duringfriction stir welding, and the degree of break up of these particles in the stir zone increases with increasing rotationalspeed. Since the break up of these particles and the recrystallization of new grains happen simultaneously, the brokenparticles would be placed in the grain boundaries. Moreover, the hardness value in the stir zone increases withincreasing rotational speed
A. Shokuhfar, S. Ahmadi, H. Arabi, S. Nouri,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: Guinier-Preston (GP) zone formation and precipitation behavior of T1 (Al2CuLi) phase during the ageingof an Al-Cu-Li-Zr alloy was studied by differential scanning calorimetry (DSC) technique and electrical resistancemeasurement of the samples. Results show that endothermic effects in the thermograms of the alloy between 180°Cand 240°C can be related to the enthalpy of GPzones dissolution. Formation of GPzones in the structure increasedhardness, tensile strength and electrical resistance of the Al-Cu-Li-Zr alloy. Furthermore, precipitation of T1 phaseoccurred in temperature range of 250ºC to 300ºC whereas its dissolution occurred within the temperature of 450-530ºC. Activation energies for precipitation and dissolution of T1 phase which were determined for the first time inthis research, were 122.1(kJ/mol) and 130.3(kJ/mol) respectively. Results of electrical resistance measurementsshowed that an increase in the aging time resulted in the reduction of electrical resistance of the aged samples.
M. Ozve Aminian, J. Hedjazi, Y. Kharazi,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: In this research, the oxidation behaviour of high Aluminum heat resistant steel (%25Cr,%20Ni,%8Al) hasbeen evaluated at the temperature range of (1000-1300ºC).The results showed that there was no countinous healinglayer on the surface of the alloy when Al increased up to %5.5 and the oxidation resistance of steel decreased due toformation of spinel oxides on the surface.By increasing the aluminum amount to %8, only Al oxide formed due to decreasing carbon potential of thealloy,homogenity of elemental concentration in matrix and no diffusion of oxygen through oxide–metalinterface,therefore it has superior oxidation resistance. Meanwhile,oxidation tests showed that the weight gain of thesteel at high temperature oxidation even at 1300ºC was too low.
A. Davoodi, J. Pan,ch. Leygraf, Gh. R. Ebrahimi, M. Javidani,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract: Localized corrosion of aluminum alloys is often triggered by intermetallic particles, IMP’s. To understandthe role of IMP’s in corrosion initiation of EN AW-3003, efforts were made to combine nano-scale ex-situ analysis ofthe IMP’s by SEM-EDS, SKPFM and in-situ AFM monitoring of the localized attack in chloride containing solution.The results showed that two distinct types of eutectically-formed constituent IMP’s exist the -Al(Mn,Fe)Si and theAl(Mn,Fe) phases. However, the exact chemical composition of the IMP’s varies with the particles size. Volta potentialdifference of surface constituents revealed that IMP’s have a higher Volta potential compared to the matrix, indicatingthe cathodic characteristic of the IMP’s. Noticeably, the boundary regions between the matrix and IMP’s exhibited aminimum Volta potential probably the sites for corrosion initiation. Localized corrosion attack monitored by in-situAFM clearly showed the trench formation occurrence around the large elongated IMP’s in the rolling direction.
Seyyed Masood Bagheri , Jamal Zamani, Ali Mehdipour Omrani,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract: The purpose of this study is to produce scarf joint through explosive welding process (EXW). The scarf weld is a process in which the final bond interface is oblique. With applying the explosive welding technique, this joint can create a metallic bond between similar or dissimilar metals. In this study, chamfered end of aluminum and copper plates were joined explosively and named scarf joint, employing changes in chamfered angle at different stand-off distance and explosive loading. The geometry of scarf joint enables consideration of both flyer and base plate thickness and explosive loading and the effects on mechanical properties of interface such as bond shear strength and micro-hardness can be investigated. Mathematical models developed for the interface properties of scarf joint to make relationship between the bond shear strength and explosive loading ratio. To check the adequacy of developed models, mechanical properties of interface, such as bond shear strength, predicted and compared with actual values in explosive cladding process. The results show reasonable agreement with theoretical predictions. Consequently, mathematical model which is based on scarf joints, can predict bond shear strength of cladding metals under desired explosive loading and flyer plate thickness
B. Tolaminejad, A. Karimi Taheri, H. Arabi, M. Shahmiri,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract: Equal channel angular extrusion (ECAE) is a promising technique for production of ultra fine-grain (UFG) materials of few hundred nanometers size. In this research, the grain refinement of aluminium strip is accelerated by sandwiching it between two copper strips and then subjecting the three strips to ECAE process simultaneously. The loosely packed copper-aluminium-copper laminated billet was passed through ECAE die up to 8 passes using the Bc route. Then, tensile properties and some microstructural characteristics of the aluminium layer were evaluated. The scanning and transmission electron microscopes, and X-ray diffraction were used to characterize the microstructure. The results show that the yield stress of middle layer (Al) is increased significantly by about four times after application of ECAE throughout the four consecutive passes and then it is slightly decreased when more ECAE passes are applied. An ultra fine grain within the range of 500 to 600 nm was obtained in the Al layer by increasing the thickness of the copper layers. It was observed that the reduction of grain size in the aluminium layer is nearly 55% more than that of a ECA-extruded single layer aluminium billet, i.e. extruding a single aluminium strip or a billet without any clad for the same amount of deformation. This behaviour was attributed to the higher rates of dislocations interaction and cell formation and texture development during the ECAE of the laminated composite compared to those of a single billet
Arash Yazdani, Mansour Soltanieh, Hossein Aghajani,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract: In this research plasma nitriding of pure aluminium and effect of iron elemental alloy on the formation and growth of aluminium nitride was investigated. Also corrosion properties of formed AlN were investigated. After preparation, the samples were plasma nitrided at 550oC, for 6, 9 and 12 h and a gas mixture of 25%H2-75%N2. The microstructure and phases analysis were investigated using scanning electron microscopy and X-ray diffraction analysis. Moreover corrosion resistance of samples was investigated using polarization techniques. The results showed that only a compound layer was formed on the surface of samples and no diffusion zone was detected. Dominant phase in compound layer was AlN. Scanning electron microscopy results showed that nitride layer has particulate structure. These nitrided particles have grown columnar and perpendicular to the surface. It was also observed that the existence of iron in the samples increases the nitrogen diffusion, thus growth rate of iron containing nitrides are higher than the others. Corrosion tests results showed that formation of an aluminium nitride layer on the surface of aluminium decreases the corrosion resistance of aluminium significantly. This is due to elimination of surface oxide layer and propagation of cracks in the formed nitride layer
M .shahmiri, , H. Arabi ,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract:
The aims of this research were to investigate the effects of semisolid metal (SSM) processing parameters (i.e., shear rates –times – temperatures combinations) on the primary solidification products and isothermal holding duration, subsequent to cessation of stirring on the secondary solidification of Al-Si (A356) alloy.
The dendrite fragmentation was found to be the governing mechanism of the primary dendritic to non-dendritic transformation, via rosette to final pseudo-spherical shapes during the primary solidification
The secondary solidification of the liquid in the slurry was not only a growth phenomenon but also promoted by 1) fresh heterogeneous nucleation and growth of dendrites and 2) the dendritic growth of the primary solidification products in the remaining liquid. Upon cessation of stirring and gradual disappearance of the prior shear force, the slurry relaxed, and the secondary solidification products pertained to conventional solidification condition
Javad Bahrami, Mohammad Hossein Paydar, Nader Setoudeh, Mohammad Hossein Shariat,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract
The effect of mechanical activation using an attrition mill on the particle size of an ilmenite concentrate and its effect on the ability of the concentrate for Iron separation during hydrochloric acid leaching and the kinetics of the dissolution process have been investigated. It was observed that mechanical activation in an attritor significantly enhances the dissolution of iron in hydrochloric acid while have a slight effect on dissolution of titanium. With the mechanically activated ilmenite using an attrition mill, leaching conversion at 90 oC reached to 80%. The kinetic data of leaching of mechanically activated ilmenite was found to follow shrinking core model. Mechanically activating ilmenite using the attrition mill was found to cause the activation energy of leaching to be decrease from 43.69 , found for samples leached without mechanically activated, to 18.23 .
Bahman Mirzakhani, Hossein Arabi, Mohammad Taghi Salehi,seyed Hossein Seyedein, Mohammad Reza Aboutalebi, Shahin Khoddam, Jilt Sietsma,
Volume 6, Issue 4 (12-2009)
Abstract
Abstract
Recovery and recrystallization phenomena and effects of microalloying elements on these phenomena are of great importance in designing thermomechanical processes of microalloyed steels. Thus, understanding and modeling of microstructure evolution during hot deformation leads to optimize the processing conditions and to improve the product properties.
In this study, finite element method was utilized to simulate thermomechanical parameters during hot deformation processes. FEM results then were integrated with physically based state variable models of static recovery and recrystallization combined with a realistic microstructural geometry. The thermodynamic software Thermo-calc was also used to predict present microalloying elements at equilibrium conditions.
The model performance was validated using stress relaxation tests. Parametric studies were carried out to evaluate the effects of deformation process parameters on the microstructure development following hot deformation of the API-X70 steel
