Showing 177 results for Cr
A. Hassani, R. Ravaee,
Volume 5, Issue 2 (6-2008)
Abstract
Abstract: To ensure the rail transportations safety, evaluation of fatigue behavior of the rail steel
is necessary. High cycle fatigue behaviour of a rail steel was the subject of investigation in this
research using fracture mechanics. Finite element method (FEM) was used for analyzing the
distribution of the stresses on the rail, exerted by the external load. FEM analysis showed that the
maximum longitudinal stresses occurred on the railhead. To find out about the relation of crack
growth with its critical size, and to estimate its lifetime, the behaviour of transverse cracks to rail
direction was studied using damage tolerance concept. It revealed that transverse crack growth
initially occurred slowly, but it accelerated once the crack size became larger. Residual service
life was calculated for defective segments of the rails. In addition, allowable crack size for
different non-destructive testing intervals was determined the allowable crack size decreased as
the NDT intervals increased.
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.
A. Nemati, K. Pourazarang,
Volume 5, Issue 3 (9-2008)
Abstract
Abstract: The PZT-based ceramics with a composition of Pb1.1-xLax (Zr0.53Ti0.47)O3, were prepared
by conventional mixed oxide followed by mechanical alloying and sol-gel methods in which x was
chosen in the range of 0.02–0.06. The samples were calcined in the range of 450 °C - 750 °C for
4h. The physical and electrical properties of the samples were determined as a function of the
calcination temperature. The obtained data from two methods were compared with conventional
mixed oxide method. Microstructural and compositional analyses of the samples were carried out
using XRD and SEM. Dielectric properties of the samples were measured with an impedance
analyzer. The ferroelectric properties of the PZT and PLZT samples were measured using the
frequencies applying equipment and d33 tester. The results indicated a complete tetragonal phase
prepared from both methods. It was shown that the addition of La and reduction in calcination
temperature improved both the dielectric and piezoelectric properties. The dielectric constant
tended to increase with doping content, giving the maximum value of about 2000 at 3 mol% La3+.
In addition, the mechanical coupling factor (Qm) of the doped samples showed a significant
decrease. Finally, the value of planar coupling factor (kp) reached the maximum value of 0.47 at 1
mol% La3+.
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.
S. Kianfar,, S. H. Seyedein, M. R.aboutalebi,
Volume 5, Issue 4 (12-2008)
Abstract
Abstract: The horizontal continuous casting process has received a significant attention for near net shape casting of
non ferrous metals and alloys. Numerical Simulation has been widely used for process design and optimization of
continuous casting process.
In the present study, a 3-dimensional heat flow model was developed to simulate the heat transfer and solidification in
a horizontal billet continuous casting system in which the air gap formation and its effect on heat extraction rate from
solidifying billet was also considered. In order to test the developed model, it was run to simulate the heat transfer
and solidification for an industrial billet caster. The predicted temperature distribution within the mold and billet was
compared with those measured on the industrial caster in which a good agreement was obtained.
Finally, parametric studies were carried out by validated model to evaluate the effects of different parameters on
solidification profile and temperature distribution within the model brass billet. The microstructure of cast billet was
analyzed to determine the secondary dendrite arm spacing (SDAS) under different cooling conditions. Based on
measured SDAS and predicted solidification rate a correlation between SDAS and cooling rate was proposed for
continuously cast brass billet.
J. Saaedi, H. Arabi, Sh. Mirdamadi, Th. W. Coyle,
Volume 5, Issue 4 (12-2008)
Abstract
Abstract: Two different coating microstructures of Ni-50Cr alloy were obtained on a stainless steel substrate by
changing combustion characteristics of a high velocity oxy-fuel (HVOF) process and the size distribution of feed
powder during coating process. Use of the finer feed powder and leaner fuel in oxygen/fuel ratio (i.e. using a ratio
much less than stoichiometric ratio) led to formation of an extremely dense coating with high oxide content. Heat
treating of this coating at 650ºC for 4 hours caused the formation of an intermetallic sigma phase having Cr7Ni3
stoichiometry. Formation of this phase has been reported occasionally in thin films not in thermal spray coatings, as
reported for the first time in this research. In addition no sigma phase was detected in the HVOF as-deposited coating
with low oxide content after heat treatment of the samples. Therefore, due to the limited number of papers available in
the subject of formation of phase in either Ni-Cr bulk alloys or coatings, it is considered appropriate to show up a
case in this field. In this work, the formation of sigma phase in Ni-50Cr coating deposited by HVOF technique and
heat treated at 650ºC was discussed and then the coating was characterized.
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. J. Tafreshi1, M. Fazli2,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract:
fabricated. Modifications carried out in different parts of the old system in order to control most
of the growth parameters with more accuracy. The fabricated system was used to grow sapphire
single crystals with almost 10 mm in diameter and 50 mm in length. The crystallinity and
structure of the grown crystals were characterized by computer aided single crystal X-ray
diffraction technique.
A Verneuil system, more sophisticated than a conventional one, has been designed and
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
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
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
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
A. Rezvanifar, M. Zandrahimi,
Volume 7, Issue 1 (3-2010)
Abstract
Abstract:
powerful method for the characterization of microstructures of crystalline materials in terms of crystallite size and
dislocation structures. In this paper the effect of the sliding on the microstructure of A356 in the as-cast and heat
treated conditions are studied, The X-ray phase analysis shows that with increasing applied load, the dislocation
density is increased, whereas the crystallite size is decreased. It was found that heat treatment raised dislocation
density during wear. The screw or edge character of dislocations in worn specimens were determined by analyzing the
dislocation contrast factors, it was demonstrated that the character of the prevailing dislocations in high loads is
nearly pure screw.
Diffraction peak profile analysis has recently been developed to such an extent that it can be applied as a
A.m. Rashidi, A. Amadeh,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
nanocrystalline nickel samples with the grain size of ~25 nm were prepared via direct current electrodeposition and
aluminized for different durations by pack cementation method at 500
means of SEM, EDS and XRD techniques. According to results, short time aluminizing resulted in the formation of a
single aluminide layer whereas at long duration two distinct aluminide layers were formed. The growth kinetics of the
coating was non-parabolic at short times while it obeyed the parabolic law at long duration. The parabolic growth
rate constant of single phase coating formed on electrodeposited samples was about 30 ìm / h1/2 approximately 3 times
greater than the data reported for coarse grained nickel (8.4 ìm / h1/2). Meanwhile, the overall growth rate constant
was decreased to 11.7 ìm / h1/2, when double aluminide layers formed on nanocrystalline nickel.
In this research, aluminizing behavior of ultra fine-grained nickel was investigated. For this purpose,oC. The aluminide layers were examined by
Khodamorad Abbaszadeh, Shahram Kheirandish, Hassan Saghafian,
Volume 7, Issue 3 (8-2010)
Abstract
The effects of lower bainite volume fraction on tensile and impact properties of D6AC ultrahigh strength steel were studied in the current work. To obtain mixed microstructures containing martensite and different volume fractions of the lower bainite, specimens were austenitized at 910° C, then quenched in a salt bath of 330°C for different holding times, finally quenched in oil. In order to obtain fully martensitic and bainitic microstructures, direct oil quenching and isothermal transformation heat treatment for 24 hours were used respectively. All specimens were double tempered at 200°C for 2 hours per tempered. Microstructures were examined by optical and scanning electron microscopes. Fracture morphologies were studied by scanning electron microscopy (SEM). Results showed that both yield and ultimate tensile strength generally decreased with an increase in volume fraction of lower bainite. However, a few exceptions were observed in the mixed microstructures containing 12% lower bainite, showing a higher strength than the fully martensitic microstructure. This can be explained on the basis of two factors. The first is an increase in the strength of martensite due to the partitioning of the prior austenite grains by lower bainite resulting in the refinement of martensite substructures. The second is a plastic constraint effect leading to an enhanced strength of lower bainite by the surrounding relatively rigid martensite. Charpy V-notch impact energy and ductility is improved with increasing the volume fraction of lower bainite.
A. Jafaria, S. H. Seyedeina, M. R. Aboutalebia, D. G. Eskinb, L. Katgermanb,
Volume 7, Issue 3 (8-2010)
Abstract
ABSTRACT Macrosegregation has been received high attention in the solidification modeling studies. In the present work, a numerical model was developed to predict the macrosegregation during the DC Casting of an Al-4.5wt%Cu billet. The mathematical model developed in this study consists of mass, momentum, energy and species conservation equations for a two-phase mixture of liquid and solid in an axisymmetric coordinates. The solution methodology is based on a standard Finite Volume Method. A new scheme called Semi-Implicit Method for Thermodynamically-Linked Equations (SIMTLE) was employed to link energy and species equations with phase diagram of the alloying system. The model was tested by experimental data extracted from an industrial scale DC caster and a relatively good agreement was obtained. It was concluded that a proper macrosegregation model needs two key features: a precise flow description in the two-phase regions and a capable efficient numerical scheme
Z. Ghaferi, K. Raeissi, M. A. Golozar,, A. Saatchi, S. Kabi,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract:
current densities. Electrochemical impedance spectroscopy (EIS) results showed that the codeposition mechanism of
tungsten in Ni-W deposition is the reduction of tungsten oxide which changed to the reduction of tungsten-containing
ion complexes at higher current densities. In Co-W electrodeposition, the tungsten codeposition takes place via
reduction of tungsten oxide, although, the role of tungsten-containing complexes at higher current densities cannot be
ruled out. The surface morphology of Ni-W coatings was crack-free and was strongly dependent on deposition current
density. In addition, higher grain size and lower tungsten content were obtained by increasing the current density. In
Co-W coatings, no obvious variation in surface morphology was observed except for the fine cracks appeared at
higher current densities. In this system the grain size remained almost constant with increasing current density. The
microhardness values of Ni-W and Co-W coatings decreased due to the increase in the grain size and/or decrease in
tungsten content.
Ni-W and Co-W alloy nanocrystalline coatings were electrodeposited on copper substrate at different
N. Eslami Rad*, Ch. Dehghanian,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract: Electroless Nickel (EN) composite coatings embedded with Cr2O3 and/or MoS2 particles were deposited to combine the characters of both Cr2O3 and MoS2 into one coating in this study. The effects of the co-deposited particles on corrosion behavior of the coating in 3.5% NaCl media were investigated. The results showed that both Ni-P and Ni-P composite coatings had significant improvement on corrosion resistance in comparison to the substrate. Codeposition of Cr2O3 in coating improved corrosion characteristic but co-deposition of MoS2 decreased corrosion resistance of the coating.
M. Rezvani*,
Volume 7, Issue 4 (10-2010)
Abstract
Abstract: In the present work, effect of the nucleating agent such as TiO2, ZrO2, P2O5, Ye2O3 and CeO2 in single, double, triple and fourth systems on the crystallization behavior of various compositions was studied. Using differential thermal analysis (DTA), the composition of Li2O-Al2O3-SiO2 (LAS) was optimized and the coefficient of thermal expansion (CTE), three point flexural strength, hardness, thermal shock resistance, and chemical resistance of the most favorable composition were evaluated. The crystalline phase was determined by the x-ray diffractometry. Moreover, the micro-structure of the samples was studied by SEM technique. According to the results, -Eucryptites (high quartz solid solution) was the main crystalline phase and the CTE values of the optimized sample were determined as 1.65-1.93 10-6 in the temperature range of 20-500 oC. Furthermore, three point bending strength ranged from 139 to 155 MPa.
N. Hamedani Golshan,, H. Sarpoolaky, A. R. Souri,
Volume 8, Issue 1 (3-2011)
Abstract
Abstract: Efforts have been carried out in order to use microsilica to develop a forsterite bond rather than other types of binders in the basic refractory castables. According to the higher drying rate and sinterability of colloidal silica, it has been proposed in the recent years. In the present work, effects of replacement of microsilica by colloidal silica evolution of forsterite bond have been studied in magnesia based refractory castables. In this way, Physical properties of prepared samples with different amount of colloidal silica versus temperature were investigated. In addition, phase variation and microstructural evolution of sintered specimens at 1000, 1200 and 1400 °C were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Results showed that, due to Reaction of magnesia with microsilica and colloidal silica, magnesium hydrate and magnesium silicate hydrate formed in the dried samples strengthening the texture of the samples while forsterite formed from about 1000 °C and gradually increased with temperature rise. Also, better forsterite formation would be appeared by increasing the colloidal silica content. Further investigation carried out on the type of silica addition on properties of the castable refractory samples. It was found that the presence of micro silica and colloidal silica simultaneously (MS3C3 sample) at 1400 °C, caused modifying mechanical strength in compare with sample with only micro silica (MS sample).
