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.
B. Mirzakhani,mohammadi, H. Arabi,s. H. Seyedein, M. R. Aboutalebi, M. T. Saleh, Sh. Khoddam,
Volume 6, Issue 3 (9-2009)
Abstract
Abstract:Optimization of specimen geometry before subjecting it to hot torsion test (HTT) is essential for minimizingnon-uniform temperature distribution and obtaining uniform microstructure thought the specimen.In the present study, a nonlinear transient analysis was performed for a number of different geometries andtemperatures using the commercial finite element (FE) package ANSYSTM. FE thermal results then were applied tooptimize HTTspecimen produced from API-X 70 microalloyed steel taking into account the microstructurehomogeneity. The thermodynamic software Thermo-calcTM was also used to analysis solubility of microalloyingelements and their precipitates that may exist at different equilibrium conditions. In addition the behavior of austenitegrain size during reheating was investigated. The results show high temperature gradient occurred in long specimens.This could lead to non homogeneous initial austenite grain size and alloying element or precipitates within the gaugesection of the specimen. The proposed optimization procedure can in general be used for other materials and reheatingscenarios to reduce temperature. This then creates more homogeneous initial microstructure prior to deformation andreduces errors in post processing of the HTTresults
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.
P. Samadi, M. Reza Afshar, M. R. Aboutalebi, S. H. Seyedein,
Volume 9, Issue 1 (3-2012)
Abstract
Electrochemical coating processes are significantly affected by applied magnetic fields due to the generation of electromagnetic forces. The present research work has been undertaken to study the effect of coating parameters such as current density and alumina concentration on the characteristics of Ni-Al2O3 composite coating under static magnetic field. Ni-Al2O3 composite coating was applied on a mild steel substrate using conventional Watts solution containing Al2O3 particles with and without magnetic field. The coating microstructure and Al2O3 particle density in the coating layer were examined by scanning electron microscopy (SEM). It was found that the applied magnetic field made the coating structure finer and leads to the increases of the particle content in the coating. However, the results confirmed that the magnetic forces inversely affected the particle density in the coating at higher current density than that of normal coating process.
Y. Safaei-Naeini, M. Aminzare, F. Golestani-Fard, F. Khorasanizadeh, E. Salahi,
Volume 9, Issue 1 (3-2012)
Abstract
Ultraviolet–Visible (UV–Vis) spectroscopy was used, in the current investigation, to explore the dispersion and stability of titania nanoparticles in an aqueous media with different types of dispersants. Hydrochloric and nitric acids as well as ammonia were used to determine the stability of the suspension in the acidic region (pH=2.5) and basic area (pH=9.5), respectively. In addition, for measuring sustainability of suspension and creating steric, and electrosteric repulsive forces, ethylene glycol and ethylene glycol plus ammonia were employed, respectively. UV–V is
spectrometry was applied to realize the effect of nano titania concentrations and different types of dispersants of samples containing different amounts of nano titania and different types of dispersants on stability of TiO2-containing suspensions. In addition, the stability of dispersion could be evaluated in colloidal mixtures containing ethylene glycol plus ammonia. It was demonstrated that the mixtures containing ethylene glycol plus ammonia were stable over a period of 4 days. To support the UV–Vis results, other techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to study the degree of agglomeration of titania nanoparticles in terms ofmorphology and size.
W. Orlowicz, M. Tupaj, M. Mróz, J. Betlej, F. Ploszaj,
Volume 9, Issue 1 (3-2012)
Abstract
Abstract: This study presents the research results of effect that refining process has on porosity and mechanical properties of high pressure die castings made of AlSi12S alloy. The operation of refining was carried out in a melting furnace with the use of an FDU Mini Degasser. Mechanical properties (UTS, YS, Elongation, Brinell Hardness) were assessed on samples taken from high pressure die castings. The effect of molten metal transfer operation and the time elapsing from completion of the refining process on the alloy mechanical properties was determined.
M. Zandrahimi, A. Rezvanifar,
Volume 9, Issue 1 (3-2012)
Abstract
Abstract: Cold working performed before an aging treatment has a significant effect on size and amount of precipitate produced. This could be caused by the increase in defect density, such as vacancies and dislocations. In this research, the Al-Cu-Si alloy was solution-treated, wear-tested and then artificially aged for a period of 1–5 h. Changes in the amount of precipitate, in the lattice parameter of the matrix, and in the precipitates are measured by X-ray diffraction and then calculated.It was observed that performing a wear test before the aging treatment was done significantly increased the amount of precipitate, while wear rate decreased.
M. J. Tafreshi, B. Dibaie, M. Fazli,
Volume 9, Issue 1 (3-2012)
Abstract
Abstract: A thermodynamic model was used to find out the optimum temperature for the growth of ZnS single crystals in closed ampoules by chemical vapor transport technique. Based on this model 1002 °C was found to be optimum temperature for 2 mg/cm3 concentration of transporting agent (iodine). ZnS Crystals were grown in optimum (1002 °C) and non-optimum (902 °C and 1102 °C) temperatures. The composition structure and microstructure of the grown crystals were studied by Atomic absorption spectroscopy, X-ray diffraction and Scanning electron microscopy measurements. Properties of the grown crystals were correlated to the growth conditions especially a stability in mass transport along the closed tube length.
H. Ashrafi, M. Mahzoon, M. Shariyat,
Volume 9, Issue 1 (3-2012)
Abstract
Abstract: The boundary value problems involving contact are of the great importance in industries related to mechanical and materials engineering. These mixed problems are challenging since a priori unknown deformed surface of the material contacting a rigid indenter is to be determined as a part of the solution. Anisotropic solids represent an important class of engineering materials including crystals, woods, bones, thin solid films, polymer composites, etc. Contact analysis of an anisotropic media, however, is more difficult and is developed less completely in the literature. In this work, both analytical and computational studies of the contact treatment of a semi-infinite orthotropic material indented by a rigid spherical indenter have been considered in two different sections. This approach can be applied to determine the interfacial contact area and pressure distribution for three-dimensional orthotropic materials, and can then be used to calculate the resulting stress and strain fields of the media. Results presented herein can serve as benchmarks with which to compare solutions obtained by ANSYS commercial package.
A. Fardi Ilkhchy, N. Varahraam, P. Davami,
Volume 9, Issue 1 (3-2012)
Abstract
Abstract: During solidification and casting in metallic molds, the heat flow is controlled by the thermal resistance at the casting-mold interface. Thus heat transfer coefficient at the metal- mold interface has a predominant effect on the rate of heat transfer. In some processes such as low pressure and die-casting, the effect of pressure on molten metal will affect the rate of heat transfer at least at initial steps of solidification. In this study interfacial heat transfer coefficient at the interface between A356 alloy casting and metallic mold during the solidification of casting under pressure were obtained using the IHCP (Inverse Heat Conduction Problem) method. Temperature measurements are then conducted with the thermocouples aligned in the casting and the metallic mold. The temperature files were used in a finite-difference heat flow program to estimate the transient heat transfer coefficients. The peak values of heat transfer coefficient obtained for no pressure application of A356 alloy is 2923 and for pressure application is 3345 . Empirical equation, relating the interfacial heat transfer coefficient the applied pressure were also derived and presented.
Simin Janitabar-Darzi, Alireza Mahjoub,
Volume 9, Issue 3 (9-2012)
Abstract
Yellow-colored nitrogen doped TiO2 photocatalyst and a pure TiO2 powder were synthesized via sol-gel method using TiCl4 and urea as raw materials. However, the synthesis procedure for nitrogen doped TiO2 was catalyzed by acid that dialed with controlled precipitation and slow nucleation. According to XRD analysis, the nitrogen doped TiO2 consisted of anatase phase of titania which was a significant achievement regarding its possible photocatalytic applications. The band gaps of nitrogen doped TiO2 and pure TiO2 were estimated from UV-Vis spectroscopy data to be 2.8 and 3.3 ev, respectively. Photocatalytic properties of the nitrogen doped TiO2 nanocatalyst and pure TiO2 were compared for degradation of crystal violet dye in visible light irradiation. In comparison to pure TiO2, nitrogen doped TiO2 showed superior photocatalytic efficiency towards the dye.
H. Nosraty, M. Tehrani-Dehkordi, M. M. Shokrieh, G. Minak,
Volume 12, Issue 1 (3-2015)
Abstract
In this study, the tensile and compressive behaviors of pure and hybrid composite laminates reinforced by
basalt–nylon bi-woven intra-ply fabrics were experimentally investigated. Epoxy resin was used as the matrix material.
The purpose of using this hybrid composite is to obtain superior characteristics by using the good strength property
of basalt fiber with the excellent toughness of nylon fiber. Five different types of woven fabric were used as
reinforcement with different volume percentages of nylon (0%, 25%, 33.3%, 50% and 100%). The effects of
nylon/basalt fiber content on tensile and compressive parameters were studied. In addition, the after failure visual
inspection and scanning electron microscopy (SEM) analysis was used to determine the extent and type of damage on
tested specimens. The results indicate that the tensile and compressive performances of these composites are strongly
affected by the nylon/basalt fiber content. Also, with a proper choice of fiber content, the nylon/basalt hybrid
composites can achieve mechanical properties comparable with the pure ones. The stress–strain curves, after failure
visual inspection and SEM analysis of tested specimens reveal that hybridization can prevent catastrophic and
complete failure. In hybrid composites, the basalt and nylon fibers cannot reach their maximum strength at the same
time and the progressive failure of the various fibers therefore occurred
B. Shahbazi, B. Rezai, S. Chehreh Chelgani, S. M. J. Koleini, M. Noaparast,
Volume 12, Issue 1 (3-2015)
Abstract
Multivariable regression and artificial neural network procedures were used to modeling of the input power
and gas holdup of flotation. The stepwise nonlinear equations have shown greater accuracy than linear ones where
they can predict input power, and gas holdup with the correlation coefficients of 0.79 thereby 0.51 in the linear, and
R2=0.88 versus 0.52 in the non linear, respectively. For increasing accuracy of predictions, Feed-forward artificial
neural network (FANN) was applied. FANNs with 2-2-5-5, and 2-2-3-2-2 arrangements, were capable to estimating of
the input power and gas holdup, respectively. They were achieved quite satisfactory correlations of 0.96 in testing stage
for input power prediction, and 0.64 for gas holdup prediction
A. M. Behagh, A. Fadaei Tehrani, H. R. Salimi Jazi, O. Behagh,
Volume 12, Issue 1 (3-2015)
Abstract
n this paper a finite element model has been proposed for evaluation of primary and secondary current
density values on the cathode surface in nickel electroplating operation of a revolving part. In addition, the capability
of presented electroplating simulation has been investigated in order to describe the electroplated thickness of the
nickel sulfate solution. Nickel electroplating experiments have been carried out. A good agreement between the
simulated and experimental results was found. Also the results showed that primary current density can describe the
general form of thickness distribution but the relative value of current density using secondary current density can
present better description of thickness distribution
H. Shalchian, A. Farbod, H. Beygi, S. A. Sajjadi,
Volume 12, Issue 1 (3-2015)
Abstract
High energetic aluminum nanoparticles are mainly used as additive in solid rocket propellants. However,
fabrication of these aluminized energetic materials is associated with decreasing the burning rate of propellants due
to problems such as oxidation and agglomeration of nanoparticles. In this study, to improve combustion performance
of aluminum nanoparticles, coating by metallic Ni shell was studied. Nickel coating of aluminum nanoparticles was
performed through electroless deposition (ED) subsequently, morphology and chemical composition of Ni-coated
nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM),
energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). These studies show that a uniform Ni layer with a
thickness of 10nm is coated on the surface of Al nanoparticles. Thermal analysis of uncoated and Ni-coated aluminum
nanoparticles was done using differential thermal analysis (DTA) and thermo gravimetric analysis (TGA). The results
of thermal analysis indicate that, coating the aluminum particles by Ni, leads to improvement in combustion
performance of aluminum nanoparticles through decreasing critical ignition temperature, ignition delay time of the
nanoparticles and promoting the ignition by exothermic chemical reactions between Al and Ni
M. Siadat-Cheraghi, S. R. Allahkaram, Z. Shahri,
Volume 12, Issue 1 (3-2015)
Abstract
Pure cobalt coatings were electrodeposited on copper substrate by means of direct electric current in a
chloride solution at different current densities in the range of 10-70 mA cm
-2
. The surface morphology and
microstructure were investigated via X-ray diffraction analysis and scanning electron microscopy. Corrosion behavior
of cobalt coatings was also studied in a 3.5 wt% NaCl solution using potentiodynamic polarization and impedance
spectroscopy techniques. The results showed that corrosion resistance of deposits was strongly influenced by the
coating’s morphology. Co deposit obtained in lower current densities exhibited the highest corrosion resistance, due
to their lower grain boundaries and so the least density of active sites for preferential corrosion attacks
M. Akbarzadeh, A. Shafyei, H. R. Salimijazi,
Volume 12, Issue 1 (3-2015)
Abstract
In the present study, CrN, TiN and (Ti, Cr)N coatings were deposited on D6 tool steel substrates. Physical and mechanical properties of coatings such as microstructure, thickness, phase composition, and hardness were evaluated. Phase compositions were studies by X-ray diffraction method. Mechanical properties were determined by nano-indentation technique. The friction and wear behaviour of the coatings were investigated using ball-on-disc tests under normal loads of 5, 7 and 9 N at sliding distance of 500 m, at room temperature. Scanning electron microscope equipped with energy dispersive spectroscopy, optical microscope, and 2D/3D profilometry were utilized to investigate the microstructures and wear mechanisms. Wear test results clarified that the wear resistance of (Ti, Cr)N and TiN coatings was better than that of CrN coating. The wear resistance of the (Ti, Cr)N coatings was related to the Ti content in the coatings and reduced by decreasing the Ti content. The dominant wear mechanisms were characterized to be abrasive and tribochemical wear
M. Shaban Ghazani, A. Vajd, B. Mosadeg,
Volume 12, Issue 1 (3-2015)
Abstract
The aim of the present study is the prediction of critical conditions (including critical strain and flow stress)
for the initiation of dynamic recrystallization during thermo-mechanical processing of plain carbon steels. For this
propose, torsion tests were conducted at different temperature (1050, 1100 and 1150˚C) and strain rates (0.002, 0.02
and 0.2/s). All flow curves showed a peak stress indicating that dynamic recrystallization occurs during hot
deformation. The critical stress and strain were then determined based on change in strain hardening rate as a function
of flow stress. Finally, the effect of deformation conditions on these parameters was analyzed.
