Iranian Journal of Materials Science and Engineering

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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.

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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

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  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

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Abstract:

structures in alloys. This method is based on pouring the melt through a small sized nozzle into a mould located at a

certain height under the crucible. This simple method generates globular structures without using equipments such as

impellers, electromagnetic stirrers, ultrasonic probes and cooling slopes. Therefore it is cost effective. In the present

study, the effect of casting size and mould casting modulus on the globular structure evolution in A356 aluminium alloy

specimens prepared by NMS process was investigated. The results showed that regardless of the different casting

modulus and their sizes, all the specimens exhibited globular structures. However, the size and shape factor of the

globules decreased with increased casting modulus and casting size indicating the influential effect of the surface area

of the mould in generating globular structures in this process.

Narrow Melt Stream (NMS) is a relatively new semisolid metal processing technique for producing globular

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Combustion synthesis is a special thermophysico-chemical process applied for production of intermetallic compounds. In the present work, a reaction–diffusion numerical model was developed to analyze the combustion synthesis of aluminide intermetallics by self-propagating high-temperature synthesis process. In order to verify the reliability of the numerical model, an experimental setup was designed and used to perform the combustion synthesis of nickel and titanium aluminides. The developed model was further used to determine the temperature history of a powder mixture compact during self-propagating high-temperature synthesis. The effect of compact relative density on combustion temperature and wave propagation velocity was also studied.

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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

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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.

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Abstract: In this research work, crystallization kinetics of Fe55Cr18Mo7B16C4 alloy was evaluated by X-ray diffraction, TEM observations and differential scanning calorimetric tests. In practice, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates. Results showed that a two -step crystallization process occurred in the alloy in which - Fe phase was crystallized in the first step after annealing treatments. Activation energy for the first step of crystallization i.e. - Fe was measured to be 276 (kj/mol) according to Kissinger model. Further, avrami exponent calculated from DSC curves was 2 and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline á – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.

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Abstract: Nano pore Mordenite membranes were prepared on the outer surface of ceramic tubular tubes via hydrothermal synthesis and evaluated for dehydration pervaporation of water unsymmetrical dimethylhydrazine UDMH mixtures. Highly water-selective mordenite membranes were prepared and the optimum reaction condition was found to be 24 h crystallization time and 170 °C crystallization temperature. Effect of gel composition on separation factor and water flux of the water-UDMH mixtures was investigated. X-ray diffraction (XRD) patterns showed that mordenite is the only zeolite material which presents in the membrane. Morphology of the supports subjected to crystallization was characterized by Scanning electron microscopy (SEM). In PV of the water-UDMH mixtures, the membrane exhibits a hydrophilic behavior, with a high selectivity towards water and a good flux. The best membranes had a water flux of 2.67 kg/m2.h at 27 °C. The best PV selectivity was obtained to be 264.

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Abstract:

composition of MgO and nano boehmite. The reactant and potassium chloride, as the reaction media, were fired at

800-1000 °C at different dwell times (0.5-5 h) in the ambient atmosphere. After washing and filtration, the spinel nano

powder was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Brunauer-Emmett-

Teller (BET) techniques. It was demonstrated that the formation temperature decreased to 850

particles revealed an average size of 30 nm with a narrow size distribution. The mechanism of MgAl

was found to be a template type where the morphology and size of product were similar to those of alumina formed

from boehmite decomposition. Prolonging the reaction time from 0.5 to 3 h, the reaction was further completed and

crystallinity was improved. However, the increase of temperature was more effective in this regard.

MgAl2O4 (MA) nano powder was synthesized via molten salt technique, by heating stochiometric°C. The nano spinel2O4 formation

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Abstract: Microwave processing is one of the novel methods for combustion synthesis of intermetallic compounds and
composites. This method brings about a lot of opportunities for processing of uniquely characterized materials. In this
study, the combustion synthesis of TiAl/Al2O3 composite via microwave heating has been investigated by the
development of a heat transfer model including a microwave heating source term. The model was tested and verified
by experiments available in the literature. Parametric studies were carried out by the model to evaluate the effects of
such parameters as input power, sample aspect ratio, and porosity on the rate of process. The results showed that
higher input powers and sample volumes, as well as the use of bigger susceptors made the reaction enhanced. It was
also shown that a decrease in the porosity and aspect ratio of sample leads to the enhancement of the process.

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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.

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Abstract: Nickel was electrodeposited onto copper substrates with high {111} and {400} peak intensities. The grain size of coatings deposited onto the copper substrate with a higher {111} peak intensity was finer. Spheroidized pyramid morphology was obtained at low current densities on both copper substrates. By increasing the deposition current density, grain size of the coating was increased for both substrates and eventually a mixed morphology of pyramids and blocks was appeared without further increase in grain size. This decreased the anodic exchange current density probably due to the decrease of surface roughness and led to a lower corrosion rate.

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In automation flexible manufacturing systems, tool wear detection during the cutting process is one of the most important considerations. This study presents an intelligent system for online tool condition monitoring in drilling process .In this paper, analytical and empirical models have been used to predict the thrust and cutting forces on the lip and chisel edges of a new drill. Also an empirical model is used to estimate tool wear rate and force values on the edges of the worn drill. By using of the block diagram of machine tool drives, the changes in the feed and spindle motor currents are simulated, as wear rate increases. To predict tool wear rate in drill, Fuzzy logic capabilities have been used to develop intelligent system. The simulated results presented in MATLAB software show the effectiveness of the proposed system for on-line drill wear monitoring.

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Montmorillonite modified is an efficient environmental friendly catalyst under one-pot-three-component synthesis of 3,4-dihydropyrimidine-2(1H) ones. The preparation was performed with an aldehyde, 1,3-dicarbonyl compounds, urea or thiourea under solvent-free conditions. In comparison with the other methods of Biginelli reaction, this new method has short reaction time inexpensive catalyst and in addition excellent yields were obtained.

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In the present study NiCrAlY bond coating layer was produced by electroplating against common atmospheric plasma spraying (APS). Both types of the bond coats were applied on IN738LC base metal then, the YSZ (ZrO2-8% Y2O3) thermal barrier top layer was coated by atmospheric plasma spray technique. Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which come as a result of molten salt effect on the coating–gas interface. In this investigation the hot corrosion behavior of coatings was tested in the furnace which was contain Na2SO4-55% V2O5 and mixed salts environment at 900°C up to 15 hr. dwell time. Optical microscopy, scanning electron microscopy (SEM / EDS) and X-ray diffraction analysis (XRD) was used to determine the crystallographic structure and phase transformation of the coatings before and after the hot corrosion tests. The transformation of tetragonal Zirconia to monoclinic ZrO2 and formation of YVO4 crystals as hot corrosion products caused the degradation of mentioned TBCs. The results showed NiCrAlY coated by economical electroplating method a viable alternative for common thermals sprayed bond coats in hot corrosive environments with same corrosion behavior

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Crystallization kinetics of Fe52Cr18Mo7B16C4Nb3 alloy was evaluated using X-ray diffraction, differential scanning calorimetric (DSC) tests and TEM observations in this research work. In effect, crystallization and growth mechanisms were investigated using DSC tests in four different heating rates (10, 20, 30, 40 K/min) and kinetic models (i.e. Kissinger- Starink, Ozawa, and Matusita methods). Results showed that a two -step crystallization process occurred in the alloy in which α - Fe and Fe3B phases were crystallized respectively in the structure after heat treatment. Activation energy for the first step of crystallization i.e., α - Fe was measured to be 421 (kj/mol) and 442 (kj/mol) according to both Kissinger- Starink and Ozawa models respectively. Further, Avrami exponent calculated from DSC curves was 1.6 and a two -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. TEM observations reveal that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology

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The effects of H2SO4 concentration on the electrochemical behaviour of passive films formed on AISI 304 stainless steel were investigated using by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization indicated that the corrosion potentials were found to shift towards negative direction with an increase in solution concentration. Also, the corrosion current densities increase with an increase in solution concentration. Mott–Schottky analysis revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott– Schottky analysis indicated that the donor and acceptor densities are in the range 1021 cm-3 and increased with solution concentration. EIS data showed that the equivalent circuit Rs(Qdl[Rct(RrQr)]) by two time constants is applicable.

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This paper was aimed to address the modeling and optimization of factors affecting the corrosive wear of low alloy and high carbon chromium steel balls. Response surface methodology, central composite design (CCD) was employed to assess the main and interactive effects of the parameters and also to model and minimize the corrosive wear of the steels. The second-order polynomial regression model was proposed for relationship between the corrosion rates and relevant investigated parameters. Model fitted to results indicated that the linear effects of all of factors, interactive effect of pH and grinding time and the quadratic effects of pH and balls charge weight, were statistically significant in corrosive wear of low alloy steel balls. The significant parameters in the corrosive wear of high carbon chromium steel balls were the linear effects of all factors, the interactions effect of solid concentration, mill speed, mill throughout, grinding time, and the quadratic effects of pH and solid content. Also, the results showed that within the range of parameters studied, the corrosion rate of 78.38 and 40.76 could be obtained for low alloy and high carbon chromium steel balls, respectively.

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This article examines the Weibull statistical analysis that was used for investigating the effect of melt filtration on tensile properties and defects formed inside the casting. Forming and entrapping of double oxide films have been explained by using the context of critical velocity of melt in the runner. SutCast software results were used to examine the amounts of the velocity of melt as such. SEM/EDX analysis is used to observe the presence of double oxide films in the fracture surfaces of the tensile specimens. The article goes on to propose that castings made with foam filters with smaller pores show higher mechanical properties and reliability due to higher Weibull modulus and fewer defects