Showing 100 results for Alloy
Alah Karam S.r., Alah Karam S.r.,
Volume 1, Issue 1 (3-2004)
Abstract
In this paper redox reaction processes and phase, formation on ternary Pb-2Sn-0.08Ca alloy utilized as insoluble lead anodes in copper electro winning cells, were investigated in 2M H__2SO__4 electrolytes, using cyclic voltammetry technique (CVA). A potential range between - 1.3V to 2.6V was chosen at various scan rates in order to study the anodic behavior and phase composition of the oxide layers on Pb-2Sn-0.08Ca alloy. Potential measurements were carried out with respect to a standard calomel electrode (SCE). The surface examination and phase composition of the lead alloy were determined by electron microscopy analysis (SEM) and x-ray diffraction technique, after- exposure to the cyclic voltammetry tests. The results indicated that the protective oxide layer (Pb0__2) formed at a much slower rate when exposed to 2M H__2SO__4 solutions, whilst its degradation due to a reduction in the applied potential occurred at a much faster rate. Hence, Pb0__2 did not remain stable, when the externally applied potential dropped below 1.SV and as a result, pitting initiated sporadically on the surface of the electrode.
Arabi H., Rastegari S., Mohammad-Sadeghi B.,
Volume 1, Issue 1 (3-2004)
Abstract
In this research, effects of changes in aluminizing conditions on microstructure of Pt - aluminide coating applied oil a Ni - base superalloy GTD -111, has been studied. A thin layer (i.e.68,#mm ) of Pt was electroplated onto the surface of the .samples, and then they were aluminized by pack cementation technique under various conditions of time, temperature, rate of heating and pack powder compositions In addition, by application of a thin Ni layer on the substrate before applying Pt, the source of nickel available for diffusing into Pt layer during aluminizing process enhanced and the need for an extra heat treatment cycle before aluminizing process was practically omitted. Addition of a nickel layer, also prevented scaling of Pt layer during its electroplating and aluminizing processes that helps enhancement of cohesiveness of the coated layers.The general microstructure of the coating consisted of four layers, which are PtA12layer internal diffusion layer external diffusion layer and interdiffusion zone. The structure of each layer has been studied by optical and scanning electron microscopes as well as XRD technique.The results show the presence of the original Pt - electroplated layer had no effect on the thicknesses of the coating layers, but higher aluminizing time and temperature had increased the thicknesses of interdiffusion and internally diffused layers. In addition, at high temperature, aluminizing with a lower heating rate caused an increase in the thickness of internal diffusion layer. Aluminizing with a lower heating rate at high temperature (more than 900°C) had increased the thickness of interdiffusion laver Attempt has been made to justify , the changes occurred in microstructures and thick nesses of various coating layers as they exposed to different aluminizing conditions.
Kharazi Y.h.k., Divandari M.,
Volume 2, Issue 1 (3-2005)
Abstract
The mold-filling behavior in the casting of aluminum alloy (A413) using lost foam casting (LFC) was explored. The effects of gate numbers, type of gating and casting thickness on the filling behavior were evaluated. Although, unlike convectional casting process, the gating system showed little effect onfilling ability, casting thickness created a greater effect on the mold filling. In contrast with convectional casting process, the mold filling seems to be controlled by castinggeometry as a consequence of combined influence of heat and mass transfer. The melt used to enter from the first gate instead of last gate which is in contrast with convectional casting process.
Morakabati M., Arabi H., Mirdamadi Sh., Abbasi S.m.,
Volume 2, Issue 2 (6-2005)
Abstract
This study was launched to investigate the effects of heating rate and aging parameters on the kinetic of precipitation reactions in a high alloy high strength steel having Ni, Co, Mo and Ti. For this purpose, as quenched specimens were subjected to three types of aging methods with different heating rates. These methods consisted of aging in Pb bath, salt bath, and furnace at different aging cycles. The kinetic of precipitation in each method was studied by hardness measurements and was described adequately by the Johnson-mehl-Avrami equation. Remarkable increase in hardness and its rate is observed when the rate of heating increases. The substantial increase in hardness of the specimens aged rapidly in salt & Pb baths, compared with those aged normally in furnace, seemed to be due to the formation of thermo elastic stresses during sudden expansion of the substance subjected to rapid heating. According to the results obtained in this research, increase in the Avrami constants, n & k, and decrease in the start time of transformation, ts, are associated with heating rate increasing. Analysis of the observed and calculated data for hardness using Arrhenius equation, shows that for the same amount of volume fraction of precipitates, the activation energy of precipitates decreased for f=25 and 50%, while at f=90 % it increased by increasing heating rate.
Fatemi-Varzaneh S.m., Zarei-Hanzaki A.,
Volume 2, Issue 3 (9-2005)
Abstract
AZ31 magnesium alloy is considered as a promising alloy in various applications and industries. Furthermore, to design a proper hot working process (rolling, forging and extrusion), the assessment of hot working behaviour of the alloy is necessary. Accordingly, the hot deformation behaviour of AZ31 alloy was studied through hot compression testing method This was carried out in a wide range of temperature (523K to 783K) and strain rates. The obtained true stress-true strain curves and final microstructures were examined and a partial melting was realized at 740K. It was concluded that the presence of liquid did change the deformation mechanisms thereby affecting the flow behaviour.
Hosseini Sh., Arabi H., Tamizifar M., Zeyaei A.a.,
Volume 3, Issue 1 (6-2006)
Abstract
In this research, rotating bending fatigue test at minimum to maximum stress ratio of R=-1 was used for investigating the fatigue behavior of Ti-6Al-4V alloy. Both smooth and notched specimens, with elastic concentration factor, kt, of approximately 3.6 and 4.1 were used for this purpose.In addition, the effect of variation in ultimate tensile strength, UTS, on the fatigue behavior of this alloy was studied. S-N curves were drawn and the value of notch sensitivity was obtained or each case.The results showed that the presence of notch in Ti-6Al-4V alloy has a different amount of sensitivity when the notched specimens were subjected to high cycle fatigue (HCF) and low cycle fatigue (LCF) tests. However, the notch sensitivity of this alloy was shown generally to be much lower than steel alloys with similar UTS values. Thus, considering the high compatibility of this alloy with the body environment and its low sensitivity to notch, one can strongly recommend this alloy for use in biomedical application.
S. M. Zahraee,, M. T. Salehi,, H. Arabi, M. Tamizifar,
Volume 4, Issue 3 (12-2007)
Abstract
Abstract: The objective of this research was to develop a tungsten heavy alloy (WHA) having a
microstructure and properties good enough to penetrate hard rolled steels as deep as possible. In
addition this alloy should not have environmental problems as depleted uranium (DU) materials.
For this purpose a wide spread literature survey was performed and on the base of information
obtained in this survey, three compositions of WHA were chosen for investigation in this research.
The alloys namely 90W-7Ni-3Fe, 90W-9Ni-Mn and 90W-8Ni-2Mn were selected and after
producing these alloys through powder metallurgy technique, their thermal conductivity,
compression flow properties and microstructures were studied. The results of these investigations
indicated that W-Ni-Mn alloys had better flow properties and lower thermal conductivities relative
to W-Ni-Fe alloy. In addition Mn helped to obtain a finer microstructure in WHA. Worth
mentioning that a finer microstructure as well as lower thermal conductivity in this type of alloys
increased the penetration depth due to formation of adiabatic shear bands (ASB) during impact.
M. Kazemi Pour, S. Sharafi,
Volume 5, Issue 1 (3-2008)
Abstract
Abstract: Hardfacing is one of the most useful and economical ways to increase the service life of
components subjected to abrasive wear. Iron based hardfacing alloys have long been considered
as candidate coatings for wear-resistant applications in industry. In the present work two layer of
Fe-34Cr-4.5C%wt hardfacing alloy was deposited on ASTM A36 carbon steel plates by SMAW
method. The microstructure consists of large primary and eutectic M7C3 carbides, metastable
austenite and small amount of secondary carbides. The microstructure was analyzed by optical
and scanning electron microscopes. In the same condition of size, shape, distribution and volume
fraction of carbides the as-welded matrix changed to martensite, tempered martensite and ferrite
by heat treatment processes. The wear resistance was measured by pin-on-disk method under loads
of 5, 10 and 20N and for sliding distance of 1500m. The results showed that the as-welded sample
with austenitic matrix has the most and the ferritic matrix specimen has the least wear resistance.
The predominate mechanisms for mass losses were determined to be micro-cutting, microploughing.
M. Divandari,, H. Arabi, H. Ghasemi Mianaei,
Volume 5, Issue 3 (9-2008)
Abstract
Abstract: Thermal fatigue is a stochastic process often showing considerable scatter even in
controlled environments. Due to complexity of thermal fatigue, there is no a complete analytical
solution for predicting the effect of this property on the life of various components, subjected to
severe thermal fluctuations. Among these components, one can mention car cylinder, cylinder head
and piston which bear damages due to thermal fatigue. All these components are usually produced
by casting techniques. In order to comprehend and compare the thermal fatigue resistance of cast
Al alloys 356 and 413, this research was designed and performed. For this purpose, several
samples in the form of disc were cast from the two alloys in sand mould. The microstructures of the
cast samples were studied by light microscopy in order to choose the samples with the least
amounts of defects for thermal fatigue tests. The results of thermal fatigue tests showed that the
nucleation of microcracks in Al-356 alloy occurred at shorter time relative to those occurred in Al-
413 alloy under the same test conditions. In addition, the density of micro-cracks in Al-356 alloy
was more than that of Al-413 alloy. The results of fractography on 356 alloy indicated that the
cracks were generally nucleated from inter-dendritic shrinkage porosities and occasionally from
the interface of silicon particles with the matrix. The growth of these micro cracks was along the
dendrite arms. Fractography of 413 alloy fracture surfaces showed that nucleation of microcracks
was often associated with silicon particles.
M. Ghalambaz, M. Shahmiri,
Volume 5, Issue 3 (9-2008)
Abstract
Abstract: Cooling slope-casting processing is a relatively new technique to produce semisolid cast
feedstock for the thixoforming process. Simple equipment, ease of operation, and low processing
costs are the main advantages of this process in comparison with existing processes such as
mechanical stirring, electromagnetic stirring, etc. The processing parameters of cooling slope
casting are length, angle and the material of the inclined plate and their combinations, which
usually affect the micro structural evolutions of the primary solid phase.
In order to clarify the effect of the processing parameters on the evolution of the particle size,
based on experimental investigation, Artificial Neural Network (ANN) was applied to predict the
primary silicon crystals (PSCs) size of semisolid cast ingot via a cooling slope casting process of
Al-20%(wt.%) Si alloy.
The results demonstrated that the ANN, with 2 hidden layers and topology (4, 3), could predict the
primary particle size with a high accuracy of 94%. The sensitivity analysis also revealed that
material of the cooling slope had the largest effect on particle size.
H. Shahmir, M. Nili Ahmadabadi, F. Naghdi,
Volume 5, Issue 4 (12-2008)
Abstract
Abstract: In the present study the effect of thermomechanical treatment (cold work and annealing) on the
transformation behavior of NiTi shape memory alloys was studied. Differential scanning calorimetry was used to
determine transformation temperature and its relation to precipitates and defects. Three alloys including Ti-50.3at.%
Ni, Ti-50.5at.% Ni (reclamated orthodontic wires) and 50.6at.% Ni alloy were annealed at 673 K and 773 K for 30
and 60 min after 15% cold rolling. It was found that the transformation characteristics of these alloys are sensitive to
annealing treatment and composition. The temperature range of transformation is broadened during cold working and
after subsequent annealing, the intermediate phase was appeared. The peaks become sharper and close together on
each cooling and heating cycle with increasing annealing temperature and time
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.
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.
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.
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
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
N. Anjabin, Karimi Taheri,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
properties of AA6082 aluminum alloy. Considering that aging phenomenon affects the distribution of alloying element
in matrix, and the fact that different distribution of alloying elements has different impediments to dislocation
movement, a material model based on microstructure, has been developed in this research. A relative volume fraction
or mean radius of precipitations is introduced into the flow stress by using the appropriate relationships. The GA-based
optimization technique is used to evaluate the material constants within the equations from the uni-axial tensile test
data of AA6082 alloy. Finally, using the proposed model with optimized constants, the flow behavior of the alloy at
different conditions of heat treatment is predicted. The results predicted by the model showed a good agreement with
experimental data, indicating the capability of the model in prediction of the material flow behavior after different heat
treatment cycles. Also, the calculated flow stress was used for determination of the material property in Abaqus
Software to analyze the uniaxial compression test. The force- displacement curves of the analysis were compared to
the experimental data obtained in the same condition, and a good agreement was found between the two sets of results.
A novel constitutive equation has been proposed to predict the effect of aging treatment on mechanical
Mrs Somaye Alamolhoda, Dr Saeed Heshmati-Manesh, Dr Abolghasem Ataie,
Volume 7, Issue 3 (8-2010)
Abstract
In this research an ultra-fine grained composite structure consisting of an intermetallic matrix together with dispersed nano-sized Al2O3 obtained via mechanical activation of TiO2 and Al in a high energy ball mill and sintering of consolidated samples. Phase composition and morphology of the milled and sintered samples were evaluated by XRD and SEM techniques Thermal behavior of the powder sample milled for 8 hours was evaluated by DTA technique. DTA results showed that, the reaction happens in two steps. The first step is the aluminothermic reduction of TiO2 with Al. XRD observations reveals that minor amount of Ti3Al phase formed during reduction reaction together with TiAl and Al2O3 major phases. This intermetallic phase disappeared when sintering temperature was increased to 850 ºC. The second step in DTA is related to a reaction between residual Al in the system (partly dissolved in TiAl lattice) and the Ti3Al phase produced earlier at lower temperatures. SEM micrographs reveal that by completion of the reduction reaction more homogeneous and finer microstructure is observable in sintered samples.
