Iranian Journal of Materials Science and Engineering

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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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A mixture of Tio2+Al+C powders was mechanically activated using a planetary ball mill under different milling conditions wherein the milled powders were further subjected to combustion synthesis to produce TiC+Al2O3 composite. The mechanically alloyed powders were characterized by X-Ray diffraction analysis and TEM investigations. XRD analysis of milled powder mixture showed no significant reaction between TiO2, Al and C while a significant amorphization of powder mixtures was observed. TEM analysis indicated the formation of a composite structure of powder particles after milling. The subsequent thermal treatment of the milled powder mix showed that the milling of initial powder mixture under dry environment using mixed large and small balls had a great effect on reaction efficiency and yielded to the highest TiC + Al2O3 ratio in the synthesized products.

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Partially stabilized zirconia (PSZ) has been proven to be an excellent candidate as a thermal barrier coating (TBe) for hot sections in, for instance, heat or internal combustion engines and gas turbine parts. The main functions of these coatings are reducing heat losses, reducing fuel consumption, increasing efficiency, and extending durability and life. One of the main problems involved is wear behavior in the development of such coatings for these applications. Using the air plasma spraying (APS) technique, conventional and nanostructured 8 wt % yttria partially stabilized zirconia (Y-PSZ) coatings were deposited on austenitic stainless steel (AISI304) disc-shaped substrates. The coated substrates were subjected to pin-on-disc wear tests, using 10 mm silicon nitride and zirconia balls as the pin. The coefficient of friction was recorded in real time. The weight loss of coated substrates was measured. Coatings were characterized before and after being subjected to wear testing by various techniques including optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction (XRD). Effects of various experimental parameters such as wear distance, test temperature, and counter face material were also investigated. Results obtained revealed that, regardless of experimental conditions applied, the nanostructured zirconia coating shows better wear and tribological properties than that of the conventional one.

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Wear of various basic refractory materials to substitute to currently used magnesia chrome bricks has been studied, measuring matte and slag penetration and dissolution, through different cup and rotary slag tests. High magnesia with and without impregnation, magnesia graphite, magnesia-alumina spinel with and without impregnation, olivine-magnesia and olivine magnesia- graphite bricks, as well as magnesia-graphite and olivine magnesia castables, have been tested. It has been shown that carbon impregnation and graphite introduction into basic refractories are feasible ways to enhance their corrosion-dissolution and penetration resistance against fayalite as well as calcium-ferrite slags. Olivine-based refractories (castables or bricks) may be considered as viable candidates to use in copper-making furnaces. At this point, evaluation of the thermo-mechanical properties of this new class of materials is still missing.

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A film of osteoconductive and biocompatible material on biomedical metallic implants can create bioactivity of the implant and shorten healing time. Hydroxyapatite, that is the most important mineral part of human bone, was coated on Ti6Al4V using cathodic electrode position process. Pulse electrode position technique was used and the effects of different parameters such as potential, duty cycle (on time/ (on time+ off time)), temperature and current density on the morphology of the deposits were examined. Nano size deposits were formed under controlled temperature and optimization of voltage and current density.

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In this research the influence of Ti contents on the amounts of inclusions formation and mechanical properties of a high alloy high strength steel, C300, has been investigated. For this purpose several bars were casted under the same solidification conditions, but different amounts of Ti element. All the seven casted bars were homogenized at 1200°C for a period of 2 hours. Then, they were immediately hot rolled after homogenization so that the out rolling temperature was kept in the range of 1000-1200° C. The specimens were then solution annealed at 820°C for hour and finally they were aged for a period of 3 hours at 500°C. The samples were subjected to tensile, impact and hardness tests in order to relate the variation in volume percent of inclusions due to different amount of Ti, to mechanical properties. The results showed that by increasing the amount of Ti a serious decline in toughness properties of the alloy due to increase in inclusion population occurred. So this research provides a very useful information about the relation between volume fraction of inclusions and mechanical properties of a C300 high strength steel.

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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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In this study, commercially pure titanium/304L stainless steel explosion bonded clads have been annealed under argon atmosphere over the temperature range of 700-900°C for 1h.Microstructure of the clads have been investigated before and after anealing. X-ray diffraction studies revealed that the annealing products in the form of intermetallic phases were gradually formed at the interface of the annealed clads. It was also found that, the bonding zone width increased with temperature according to an Arrhenius type equation. On the base of this equation, the activation energy of bonding zone growth was found equal to about 66.5 kJ/mol. The bond strength of the diffusion annealed clads were evaluated stress relieved. The maximum average tensile strength of ~350MPa was obtained for the as-welded clad. It was found that the bond strength decreased with annealing at 700°C due to an increase in the width of brittle intermetallic layer.

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TRIP (TRansformation- lnduced- Plasticity) behavior is a powerful mechanism to improve mechanical properties. The basis of TRIP phenomena is the transformation of retained austenite with optimum characteristics (volume fraction, stability, size and morphology) to martensite during deformation at room temperature. Accordingly, the first requirement to obtain desired TRIP effects is to produce an appropriate microstructure. Thermo mechanical processing is an effective method to control the microstructural evolution thereby mechanical properties in TRIP steels. This work deals with a TRIP steel containing 0.2% C, evaluating the effects of straining before and during ?®a atransformation on its final characteristics, using hot compression tests. The results revealed that straining in the two phase region (dynamic transformation) not only reduces the ferrite grain size more significantly, but also increases the retained austenite volumefraction. Accordingly the final mechanical properties were also improved.

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In the present study a Finite Difference Method has been developed to model the transient incompressible turbulent free surface fluid flow. A single fluid has been selected for modeling of mold filling and The SOLA VOF 3D technique was modified to increase the accuracy of simulation of filling phenomena for shape castings. For modeling the turbulence phenomena k-e standard model was used. In order to achieve an accurate model, solving domain was discrete to three regions includes: laminar sub layer, boundary layer and internal region. This model was applied to experimental models such as a driven cavity, Campbell benchmark [1] and top filled cavity. The results show that the suggested model yield favorable predictions of turbulence flow and have a good consistency in comparing with experimental results.

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Although the flash smelting technologies use different furnace designs, the refractory linings are exposed to very similar aggressive environments and, as a result, the corrosion analysis results on one type of furnace could be generally applied to other furnaces of similar high temperature processes. Particularities regarding the different chemistries of the pyrometallurgical process and operating parameters of these furnaces could also bring particular aspects to be considered when analyzing the refractory ware and final failure in use. This paper presents a review of the existent experimental. data of corrosion analyses on refractory linings used in two particular flash furnaces for zinc-lead and respectively nickel-copper smelting. Although various modern water cooling systems are generally used to protect the refractory wall linings against corrosion by molten slag and matte, the performance of the refractory roof lining, usually used without water cooling, represents a permanent concern and the object of research studies to extend their life in service. The failure mechanisms analysed in this study are based on postmortem analyses and laboratory corrosion experiments with magnesite-chrome bricks of different chemical and mineralogical compositions. The gaseous atmosphere, usually rich in SO2 and/or CO and various metal fumes, produces irreversible microstructural changes which could shorten the life in service of the refractory lining. The experimental data proved that thermal cycling in SO2/SO3 atmospheres could bring more damage than a continuous use at relatively constant temperature, due to the magnesium and calcium sulphate formation. The laboratory experiments and postmortem analyses showed that that metal fumes at various partial pressure of oxygen would condense as oxides and react inside the pores and at the grain boundaries, contributing to the continuous deterioration of the ceramic matrix of the refractory brick lining. The mechanisms of corrosion, discussed based on laboratory experiments, were confirmed by the postmortem analyses on brick samples used in the industrial flash smelting furnaces.

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Abstract: The theoretical calculation of dislocation density in different regions of a deformed workpiece of 99.99% pure copper has been carried out using different procedures consisting of Finite Element Method (FEM) and hardness measurement. To assess the validity of the results pertaining to these procedures, the dislocation density is experimentally measured utilizing the Differential Scanning Calorimetry (DSC). Comparing the predicted and experimental results, it was found that the average error in prediction of the dislocation density by the hardness measurement and FEM is 12% and 2.5%, respectively. Also, for further confirmation of the evaluated dislocation density of each region of the deformed workpiece, the annealing process was carried out and in the region of higher dislocation density, a finer grain size was observed.

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Abstract: Strength at elevated temperatures and thermal shock resistance of austempered ductile irons at high temperatures has been less intentioned, because of instability of ausferrite phase. In this research the tensile properties of this iron and pearlitic ductile cast iron have been investigated by short time high temperature tensile tests. Also thermal shock tests were done at the molten lead bath at 1000 􀁱C . In these experiments, at first samples were immersed partially in the molten lead bath for 25 seconds and then either cooled in air or quenched in water. Results of short time high temperature tensile and thermal shock tests showed that ADI samples have higher strength and shock resistance than the pearlitic ductile samples.

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Abstract: Static recrystallization (SRX) behavior of a composite based 7075 Aluminum alloy reinforced with SiC particles was studied during annealing the deformed samples at high temperatures. The results showed an absence of SRX in the samples annealed after hot working at the same deformation temperature, however, a rise in annealing temperature of 100-1500 􀁱C above that the deformation temperature led to full recrystallization. This can be ascribed to the relatively moderate dynamic recovery and the presence of dispersions which stabilize the substructure. Particle stimulated nucleation (PSN) had a significant effect on the grain size in deformed samples at low temperature, but no PSN was observed in samples strained at high temperatures. The possible cause might be that at high temperature the dislocations can be annihilated by climb process around the particles together with the absence of deformation zone for nucleating the recrystallization.

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Abstract: The direct reduction of copper sulfide concentrate from Iranian Sarcheshme deposits with carbon in the presence of lime was investigated in the temperature range of 800-1000 ºC. The reduction kinetics was determined by means of weight loss measurements. It was found that the rate of reaction increased considerably with increasing the temperature. The kinetics was also improved when large excesses of lime and carbon were present in the mixture. The effects of catalytic additives of Na2CO3 and K2CO3 were also investigated. It was realized that the rate of reaction increased by higher concentrations of additives. X-ray diffraction analysis of reduced samples revealed that sulfur was fixed as solid CaS, and metallic copper was formed.

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Abstract: Ball mills are used in the last stage of ore processing for grinding raw materials. Forged 70Cr2 alloy steel and Austempered Ductile Iron (ADI) balls are materials from which grinding balls are made for Sarcheshmeh Copper Plant (SCP) ball mills. In the present study wear and impact properties of these two kinds of balls have been investigated. Some balls randomly were selected as samples. They were cut to investigate the cross section under optical and scanning electron microscopes. The microstructure of the sample balls was studied and quantitative measurements of microstructural features were performed. The hardness of different parts of cross sections of balls was measured. The wear resistance of the balls was measured by Pin on Disc method. Repeated dropt test was employed to evaluate impact resistance of the balls. The microstructure of ADI balls consisted of bianitic matrix with graphite nodules and some retained austenite and martensite. Micro cracks and porosities in the cast structure were frequently observed. In the case of forged steel balls the microstructure composed of tempered martensite in outer area and bianitic structure with some tempered martensite in central areas. The wear and impact resistance of forged steel balls were markedly higher than those of ADI balls. The difference was consistent with the differences between the microstructures of the two kinds of balls. Cast structure with microcracks and shrinkage porosities in ADI balls gives rise to lower impact resistance.

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Abstract: Problems such as the difficulty of the selection of processing parameters and the large quantity of experimental work exist in the morphological evolutions of Semisolid Metal (SSM) processing. In order to deal with these existing problems, and to identify the effect of the processing parameters, (i.e. shearing rate-time-temperature) combinations on particle size and shape factor, based on experimental investigation, the Artificial Neural Network (ANN) was applied to predict particle size and shape factor SSM processed Aluminum A.356.0 alloy. The results clearly demonstrated that, the ANN with 2 hidden layers and topology (4, 2) can predict the shape factor and the particle size with high accuracy of 94%.The sensivity analysis also revealed that shear rate and solid fraction had the largest effect on shape factor and particle size, respectively. The shear rate had a reverse effect on particle size.

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Abstract: Nanocrystalline MgAl2O4 spinel powder was synthesized using metal nitrates and a polymer matrix-based composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600°C and 700°C. The average crystallite size of calcined powder at 800°C for 2h was in the range of 8-12nm. In addition, SEM micrograph showed that the synthesized powder had a spherical morphology.

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Abstract: The performance of an Imidazoline based commercial corrosion inhibitor in CO2 corrosion of a gas-well tubing steel was studied by employing Electrochemical Impedance Spectroscopy (EIS) technique. Inhibitor performance was investigated by means of its efficiency at various concentration and also its behavior at various exposure time. EIS results showed that inhibitor interaction to the electrode surface obeys Lungmuir adsorption isotherm. Interpretation of some parameters such as Rct, Rpf, Cdl, and Cpf associated to the equivalent circuit fitted to the experimental rsults showed that not only inhibitor efficiency and surface coverage improve by increasing in inhibitor concentration in the solution but also at constant inhibitor concentration both surface coverage and efficiency improve with exposure time and reach to their highest value after 4 hours.

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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.