Iranian Journal of Materials Science and Engineering

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ZnS : Cu phosphors were prepared by using laboratory grade chemicals through coprecipitating Cu along with ZnS using H2S and thiourea. Photo- and electroluminescence studies indicate that these phosphors have better emission characteristics compared to the phosphors in which activator is externally added. Phosphors with luminescence at ~530nrn were prepared. The difference between the characteristic properties of the samples seems to be due to formation of nanoparticles during the preparation of the samples by different methods.

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The hot cracking susceptibility can be determined by establishing the transition temperature between brittle and ductile fracture at high temperature tensile testing of in situ solidified samples. High temperature tensile properties were determined for commercial cathodic pure Cu and Cu- 30%Zn alloy. The transition temperatures for pure Cu and Cu-30%Zn were evaluated from ultimate tensile stress, true strain and area reduction at different testing temperatures. The results show that hot cracking in pure Cu also occurred below and near to its melting temperature. It can be proposed that in this case excess vacancies and vacancy diffusion and condensation are the dominating mechanisms for hot crack formation. The transition temperature for Cu- 30%Zn was much lower than its solidus temperature and this alloy has more susceptibility to hot cracking as compared to pure Cu. The effect of two different cooling rates (15 °C/min and 60 °C/min) on the transition temperature was investigated. The results show that by increasing cooling rate, the transition temperature will increase. The morphology of fracture surfaces for both ductile and brittle modes were evaluated by SEM Two different morphologies, i.e. interdendiritic and intergranual fracture, was found.

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In this study the hot deformation behaviour of a precipitation hardened (PH) stainless steel at high strain rates has been predicted through hot compression testing. Stress-strain curves were obtained for a range of strain rates from 10-3 to 10+1 S-1 and temperatures from 850 to 1150°C. Results obtained by microstructure and stress-strain curves show that at low temperatures and high strain rates, where the Zener-Holman parameter (Z) is high, work hardening and dynamic recovery occure. By increasing temperature and decreasing strain rate, the Z parameter is decreased, so that dynamic recrystallization is the dominant softening mechanism. The results were fitted using a Log Z versus Log (sinh (a sp) diagram allowing an assessment of the behavior of the stresses measured at strain rates closer to those related to the industrial hot rolling schedules. It is clearly shown that the data collected from low strain rate testing can be fairly reasonably extrapolated to higher orders of magnitude of strain rate.

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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.

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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

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Abstract:

mechanical properties of AISIH 13 hot-work tool steel have been studied. Cast samples made of the modified new steel were homogenized and austenitized at different conditions, followed by tempering at the specified temperature ranges. Hardness, red hardness, three point bending test and Charpy impact test were carried out to evaluate the mechanical properties together with characterizing the microstructure of the modified steel using scanning electron microscope. The results show that niobium addition modifies the cast structure of Nb–alloyed steel, and increases its maximum hardness. It was found that bending strength bending strain, impact strength, and red hardness of the modified cast steel are also higher than those of the cast H13 steel, and lower than those of the wrought H13 steel.

In this research, the effects of partially replacing of vanadium and molybdenum with niobium on the

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Abstract:

(Y2O3) and ethyl acetate as a mineralizer by hydrothermal method at a low temperature (T=.230°C, and

P=100bars).The as-prepared powders were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared

Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), UV-V Spectroscopy and Chemical Oxygen Demand

(COD) of the sewage water, respectively. The results show that hydrothermal method can greatly promote the

crystallization and growth of YVO4 phase. XRD pattern clearly indicates the tetragonal structure and crystallanity. An

FTIR spectrum of the YVO4 shows the presence of Y-O and V-O bond, respectively. The presence of these two peaks

indicates that yttrum vanadate has been formed. UV-V is absorption spectra suggesting that YVO4 particles have

stronger UV absorption than natural sunlight and subsequent photocatalytic degradation data also confirmed their

higher photocatalytic activity.

In this paper, YVO4 powder was successfully synthesized from Vanadium Pentaoxide (V2O5), Yttrium Oxide

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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.

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Nitriding is a surface treatment technique used to introduce nitrogen into metallic materials to improve their surface hardness, mechanical properties, wear resistance and corrosion resistance. In this research, the effects of plasma nitriding parameters including frequency and duty cycle were investigated on samples with different grooves dimensions. Steel blocks prepared from DIN1.2344 hot working steel were plasma nitride at 500 °C under the atmosphere contents of %75H2-%25N2, the duty cycles of 40%, 60%, 80%, and the frequencies of 8, 10 kHz for 5 hours. Then characteristics and micro hardness's of the nitrided samples were investigated using SEM, XRD, and Vickers Micro Hardness method. The results of the experiments indicated that with increasing frequency, the duty cycle, and the thickness of the grooves, the roughness of the surfaces increased. With an increase in duty cycle from 40% to 80%, the hardness of the surface rose and the thickness of the compound layer built up. Hollow cathode effect occurred in the samples with small grooves and high duty cycle in plasma nitriding. This will result in over heating of the sample which leads to a decrease in the slope of hardness values from the surface to the core of the sample and also a decrease in the diffused depth of nitrogen. The compound layer of the treated samples consisted of @ : Fe4N and : Fe2-3N phases and the proportion of the A to @ increased with the decrease in the duty cycle. Increasing the frequency did not affect the proportion of phases and micro hardness of the samples.

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The influences of age hardening and HIP (Hot Isostatic Pressing) on the mechanical properties of A356 (Al 7Si 0.6 Mg) casting alloys were studied. Cast bars were homogenized, heated and maintained at a temperature of 540°C for a duration of 2 hours, followed by rapid cooling in a polymeric solution. The castings were age hardened at 180°C for a duration of 4 hours before being subjected to HIP process at pressure of 104 MPa for 2 hours. The results indicated that the age hardening process used improved the tensile properties of A356. The HIP process removed the internal surface-connected porosities and improved the ductility of the samples significantly. Additionally, HIP reduced scattering in the tensile test data

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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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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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In this study, effect of immersion time on the electrochemical behaviour of AISI 321 stainless steel (AISI 321) in 0.1 M H 2SO 4 solution under open circuit potential (OCP) conditions was evaluated by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). 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 the immersion time. EIS results showed that the best equivalent circuit presents two time constants: The high-medium frequencies time constant can be correlated with the charge transfer process and the low frequencies time constant has been associated with the redox processes taking place in the surface film. According to this equivalent circuit, the polarization resistance (interfacial impedance) initially increases with the immersion time (1 to 12 h), and then it is observed to decreases. This variation is fully accordance with potentiodynamic polarization results

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Four compositions of austenitic Mn-Cr steels have been developed successfully for in-vessel component materials in power plant industry. The phase stability of these Mn-Cr steels was studied by and X-ray diffraction (XRD) patterns. XRD patterns have shown that the matrix of these Mn-Cr steels is a single γ-phase structure. The potentiodynamic polarisation curves suggested that these fabricated Mn-Cr steels showed passive behaviour in 0.1M H2SO 4solution. Therefore, semiconducting behaviour of passive film formed on these fabricated Mn-Cr steels in 0.1M H2SO 4 solution was evaluated by Mott–Schottky analysis. This analysis revealed that passive films behave as n-type and p-type semiconductors. Based on the Mott–Schottky analysis, it was also shown that donor and acceptor densities are in the order of 1021 cm -3 and are comparable for other austenitic stainless steels in acidic environments

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Hot deformation behavior of a medium Cr/Mn Al6061 aluminum alloy was studied by isothermal compression test at temperatures range of 320 to 480 °C and strain rates range of 0.001 to 0.1 s −1. The true stresstrue strain curves were analyzed to characterize the flow stress of Al6061. Plastic behavior, as a function of both temperature and strain rate for Al6061, was also modeled using a hyperbolic sinusoidal type equation. For different values of material constant α in the range of 0.001 to 0.4, values of A, n and Q were calculated based on mathematical relationships. The best data fit with minimum error was applied to define constitutive equation for the alloy. The predicted results of the proposed model were found to be in reasonable agreement with the experimental results, which could be used to predict the required deformation forces in hot deformation processes

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Hot dip aluminizing was carried out on the low carbon steel rod under optimized conditions. The aluminized samples were further oxidized at 1000̊C in air atmosphere at two different times of 20 and 60 minutes. Microstructure study and phase analysis were studied by scanning electron microscopy and X-ray diffraction methods, respectively. The characterization of the coating showed that, Fe2 Al5 has been the major phase formed on the surface of specimen before heat treatment. Following the oxidation of the coating at high temperature, Al 2O3 was formed on the surface of coating while Fe 2 Al5 transformed into FeAl and Fe 3 Al which are favorable to the hot corrosion resistance of the coating. Corrosion resistance of aluminized samples before and after heat treatment was evaluated by rotating the samples in the molten aluminum at 700 ̊C for various times and the dissolution rate was determined. The obtained results showed that by oxidizing the coating at high temperature, the corrosion resistance of the samples in molten aluminum improves significantly.

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Till now, different constitutive models have been applied to model the hot deformation flow curves of different materials. In this research, the hot deformation flow stress of API X65 pipeline steel was modeled using the power law equation with strain dependent constants. The results was compared with the results of the other previously examined constitutive equations including the Arrhenius equation, the equation with the peak stress, peak strain and four constants and the equation developed based on a power function of Zener-Hollomon parameter and a third order polynomial function of strain power a constant number. Root mean square error (RMSE) criterion was used to assess the performance of the understudied models. It was observed that the power law equation with strain dependent constants has a better performance (lower RMSE) than that of the other understudied constitutive equations except for the equation with the peak stress, peak strain and four constants. The overall results can be used for the mathematical simulation of hot deformation processes

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In this work, the effects of co-precipitation temperature and post calcination on the magnetic properties and photocatalytic activities of ZnFe₂O₄ nanoparticles were investigated. The structure, magnetic and optical properties of zinc ferrite nanoparticles were characterized by X-ray diffraction (XRD), vibrating sample magnetometry and UV–Vis spectrophotometry techniques.  The XRD results showed that the coprecipitated as well as calcined nanoparticles are single phase with partially inverse spinel structures. The magnetization and band gap decreased with the increasing of co-precipitation temperature through the increasing of the crystallite size. However, the post calcination at 500 °C was more effective on the decreasing of magnetization and band gap. Furthermore, photocatalytic activity of zinc ferrite nanoparticles was studied by the degradation of methyl orange under UV-light irradiation. Compare with the coprecipitated ZnFe₂O₄ nanoparticles with 5% degradation of methyl orange after 5 h UV-light light radiation, the calcined ZnFe₂O₄ nanoparticles exhibited a better photocatalytic activity with 20% degradation.

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In this work, we report the synthesis of silver decamolybdate, Ag₆Mo₁₀O₃₃, nanostructure by a simple mechanohemical process followed by calcination treatment using acetamide as driving agent. Morphological study by scanning electron microscopy (SEM) images revealed bundles of rods grown closely together with an average diameter of 92 nm for Ag₆Mo₁₀O₃₃ sample. Ni-substituted Ag₆Mo₁₀O₃₃ compound was prepared via introducing nickel cation to precursor system in mechanical milling step. The particle size decreased to 87 nm by incorporating nickel units in substituted polymolybdate. It was concluded that the suitable selection of reagents can direct solid phase reaction towards producing nanostructured products. This technique is easy and simple for preparation of various mixed metal oxides without using any solvents and or complex procedures. In addition, the photocatalytic activity of the prepared products was studied on the removal of 4-nitro phenol (4-NP) as organic pollutant from water. The obtained results were also discussed in detail.

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