Iranian Journal of Materials Science and Engineering

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Effects of temperature on properties and behavior of a 20 vol % particulate SiC reinforced 6061 aluminum alloy and 6061 unreinforced Al alloy were investigated. Yield strength and elongation to failure were measured as a function of test temperatures up to 180^oC. In addition, the effects of holding time at 180^ oC on tensile properties and fracture mechanisms of the materials at this temperature were studied. The behaviors of the materials were characterized by using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS), X-ray diffraction (XRD), atomic absorption (AA), hardness measurement and image analyzing (IA). The results show that an increase in temperature leads to a decrease in the yield strength and increase in the elongation to failure of the materials. On the other hand, while increasing holding time at 180^oC produces an increase in the elongation to failure of the unreinforced alloy, it reduces the elongation to failure of the composite. It was also observed that reduction in yield strength with increasing holding time at 180^oC was faster for the composite material compared to the unreinforced alloy. The results from SEM, XRD, EDS, IA and hardness tests indicated that some chemical reactions had taken place at the interface between the reinforcement and the matrix alloy during holding the specimens at elevated temperature. Therefore, different trend in elongation to failure of the unreinforced alloy and the composite material with holding time at elevated temperature could be attributed to development of chemical reactions between the reinforcement and the matrix alloy at the interface.

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A two dimensional mathematical model has been developed for describing the temperature, flow, and electric fields in the are column of the Gas Metal Arc Welding (GMAW) of aluminum in argon shielding gas using axisymmetric Navier-Stokes, Maxwell, and differential thermal energy equations. The predicted results are most sensitive to the cathode spot radius and an optimum cathode spot radius exists on the basis of the minimum arc power consumption. The consumable electrode shape change due to droplet detachment is simulated in a quasi-steady manner using different electrode diameters. The change in electric field profile with different electrodes gives rise to large changes in flow conditions. This flow perturbation plus the non-uniform and transient J*B force field are suspected to enhance the recoil experience by the droplet on detachment, thus leading to violent and chaotic metal transfer in GMAW.

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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.

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In principal, a proper combination of strength and ductility is achieved through micro component refinement in steels. This is particularly empowered with ferrite refinement down to micron sizes in ferrite pearlite engineering steels. The latter is achieved through various well-defined methods in which strain induced transformation (SIT) has shown spectacular capabilities. In the present study, to address the effect of thermo mechanical processing parameters on the (SIT) behavior, two plain carbon steels were studied through single pass rolling. This was carried out at the corresponding Ar_3 + 20°C temperature of the steels. The results indicated that the transformation behavior and ferrite morphology would be .strongly influenced by both the chemical composition (i.e., carbon content) and the amount of applied strain. Furthermore, a high volume fraction of very fine ferrite with mean grain size of less than 2 µm was obtained. This was attributed to the ferrite nucleation at deformation bands and serrated austenite grain boundaries.

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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.

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In this study different volume fractions of SiC particles of various sizes were introduced into the semisolid A356 aluminum alloy by a mechanical stirrer. Then the slurry was poured into a permanent die of certain dimensions either when the metal alloy was partially solid (semisolid-semisolid or SS route) or after reheating to above the liquidus temperature of the alloy (semisolid-liquid or SL route). Both the SS and SL composite samples were solution-treated at 520°C for 8 hours followed by quenching in water at room temperature. Microstructural characterization studies have been conducted on both the SL and SS samples to quantify the effects of the size andcontent of the SiC particles as well as the solutionizing treatment on the morphology and size ofthe eutectic silicon particles and the matrix grain (globule) size. The results were rationalized in terms of the different nucleation, fragmentation, spherodization and coarsening events, which had taken place during the processing of these composites. Finally the impact of these microstructural features in improving the wear properties of the composites has been discussed.

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Calcium phosphate cements (CPCs), using B-tricalcium phosphate (ß-TCP, Ca3 (P04)2), dicalcium phosphate (DCP, CaHP04), calcium carbonate (Ca CO3), and hydroxylapatite (HAp, Ca10(P04)6(OH)2) as powder cement and disodium hydrogen phosphate (Na2HP04) solution as liquid component were prepared. After mixing the powder and liquid constituents, injectable and self-setting calcium phosphate cements (CPCs) were prepared with different liquid to powder ratios (UP) that formed hydroxylapatite and ß-tricalcium phosphate as the only end products, which were characterized by FTIR, XRD and SEM techniques. The results showed that, at certain concentration of Na2HP04 (6 wt%), the initial and final setting times decreased by decreasing the UP ratio.

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The effects of gating system and pattern geometry on the metal flow in the lost foam casting (LFC) process have been investigated using glass covered mold and video recording system. Unlike convectional casting process, the type of the gating system showed little effect on fillability in lost foam, but pattern thickness had large effect on mold filling. The mold filling behavior seems to be controlled by the combined influences of heat and mass transfer. The flow rate increased with increasing pattern thickness.

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The new in situ method for AI-TiC composite fabrication has been carried out. In this method, fabrication of AI-TiC composite by simultaneous introduction of titanium oxide and carbon into aluminum melt was investigated.. Under the process conditions, titanium and carbon reaction results in titanium carbide whiskers. The salt containing keriolite (Na3AIF6), titanium oxide (TiO2) and graphite used for this purpose. Using Scanning Electron Microscopy (SEM) and X-Ray Diffraction analysis (XRD) the resulted composite was characterized. It was shown that it contains Al as matrix and TiC as the reinforcement. Then, mechanical properties of fabricated composite were examined.

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In the current research, the optimum conditions for the electrolytic deposition of TiO2 coatings on titanium pieces were experimentally investigated. Flat pieces of commercially available titanium with dimensions of 50 x20 x3 mm were used as the anode and cathode electrodes. The coatings were applied on the cathode in an electrolyte solution essentially from water and methanol, containing different amounts of TiCI4, and H202. Coatings of sufficient thickness and adequate adhesion to the substrate were obtained at the optimum conditions of theELD process. The latter conditions were electrode gap distance of 3 cm, TiCl4 concentration of 0.005M, H202 concentration of 0.1 M, current density of 35 mA/cm2, methanol/water volume ratio of 9, and pH of the electrolyte in the vicinity of 1.40. Results of XRD analysis revealed the presence of anatase crystals of titanium oxide in the coated layers, where the deposited coating was treated at some temperatures in the range of 400 to 600°C for a period of at least 2 hours. Scanning electron microscopy (SEM) pictures also confirmed the formation of a uniform coating layer with cracked suiface area. At the optimum conditions of the process coatings with thicknesses of up to 10 flm were easily obtained through the application of one to three deposited layers.

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The synthesis of advanced materials from low cost minerals concentrates is a new field of study that has great potential applications. In this paper, the effect of milling time on the temperature of initiation and amount of carbothermic reduction of ilmenite has been investigated. The stoichiometric molar ratio (1:4) of ilmenite to graphite was mixed and mechanically activatedfor 30-70 hours at room temperature. Then homogenized mixture heated for one hour at 1000-1400°C in coal reducing atmosphere. The results show that complete conversion of ilmenite to Fe and TiC can not be achieved in the unmilled powder at 1400°C, while with milling of mixture for 30 hours, complete reduction of ilmenite to Fe and TiC at 1400° C was observed. With increasing milling time from 30 to 70 hours the temperature of complete reduction decreases from 1400 to 1200° C. Leaching of final product in HCI 3% solution dissolve Fe but leave pure titanium carbide intact. Determination of TiC unit cell size from X-ray diffraction pattern shows that unit cell size of synthesized TiC is less than stoichiometric one, which suggests that some oxycarbide phases (TiCxO1-x), is present into the final product.

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A large number of reinforced concrete structures subjected to chloride ions. Two basicapproaches for preventing corrosion of reinforcing steel embedded in concrete are: Increasing theconsolidation of concrete and using different coating on rebars. In present research steel rebarsare coated in different ways: a) 40 µm of zinc electroplated on steel rebar b) Zinc powder withepoxy paste (zinc rich). The rebars were placed in a macrocell design according to ASTM G109-92. Concrete operations were done with mixture designs of high and normal strength concrete.The results show corrosion decrease of zinc coated rebars.

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AA3004 alloy is widely used in can making. The major concern in the production of canbodies is earing, which develop by high planar anisotropy of rolled sheet. Balance ofrecrystallisation and rolling textures together with a uniform and fine grain microstructure canminimize the earing. The effects of finish rolling temperature (FRT) on planar anisotropy,microstructure, texture development and mechanical properties of sheet have been analyzedIncreasing the FRT resulted in promotion of cube and G texture in hot rolled sheet. Lower |ΔR| ofthe final sheet with higher FRY, i.e. the lower planar anisotropy, is accompained with a balance ofrolling and recrystallisation orientations.

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Effect of MgO addition on reaction sintering of aluminium titanate was investigated using equimolar Al2O3 and TiO2 after firing the samples at 1400 C for four hours. Results showed that MgO addition enhanced the sintering process by magnesium aluminates formation, which led to lower porosity and improved densification of the samples. Physical and mechanical properties showed that samples containing 5 wt% MgO was the optimum composition.

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In the present work, a model was proposed to predict the thermal history during rapid solidification (RS) of metal droplets in the gas atomization process. The classical theory of heterogeneous nucleation was based on Newtonian heat flow and enthalpy method. Solving the governing numerical equations by the finite difference method (FDM) gave up the opportunity of analyzing the temperature-time history of the droplets during cooling in the RS process. Here, cooling in the liquid state, nucleation and recalescence, segregated solidification, eutectic solidification and cooling in the solid state were considered. To verify the model, the gas atomization of Al-4.5% Cu alloy was studied and the results were compared with the Shukla's model [1]. Convincing agreement was obtained between the predicted undercoolings and the experimental results reported previously.

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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.

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In this research, the mechanism of joining three sheets of metals, i.e. brass-steel-brass, by cold roll welding process has been studied. For this purpose, the two surfaces of steel sheets were roughened with stainless steel wire brush by different amounts, then the brass sheets were put on both sides of the steel sheets, before they were subjected to cold roll process. During rolling, peaks of the asperities on the surfaces of the steel sheet were pressurized, i.e. deformed, much more than that of trough. Hence, more hardening due to formation of higher dislocation density in the peaks regions were detected in comparison to the trough regions. Therefore, due to the differences in the amounts of work hardening occurred during cold rolling in the peaks & trough of the scratches and also due to the nature of the rough surfaces of the steel sheets, which causes the smooth surface of soft brass sheets laied over the rough surface of the steel sheet to be shappend according to the profile of the steel sheet scratches during cold rolling, mechanical locking occurred at the interface of brass & steel sheets. In addition, while the extrusion of brass took place through cracks within the surface of hardend peaks and metal bonding occurred on the contact points of the brass sheet & the vergin steel. Therefore, it seems two mechanisms were in operation is making a suitable joining between the sheets. One was a locking mechanism due to the roughness of the steel sheets & the other was bonding mechanism due to the bonding between the peak points of the scratches &soft brass surface. The strength of the bonded points in the interface were later increased by annealing the composite, so that by annealing the samples within the 500-900°C range for aperiod of 1 1/2 hr the interface strength increase substantially. The results of peeling test indicated that the interface strength of the samples annealed at 700°C or more increased so much that the brass sheet toms during peeling & the fracture did not pass through the interface.

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The effect of precipitation of ?.qss. and gahnite phases during heat treatment of glass frits in the ZnO-Al2O3-SiO2 system on the mechanical property of resulting glass-ceramic specimens were investigated. It was shown that gahnite glass-ceramics had higher bend strength and toughness values than ?.qss. ones. The results are attributed to the higher modulus of elasticity as well as higher thermal expansion coefficient of gahnite relative to the residual glass phase.

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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.

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The effect of addition of NaHF2 on the cement setting and the set mass has been studied as an initial step to determine how fluoride influences the characteristics of a calcium phosphate cement, consisting of tetracalcium phosphate [TTCP:Ca4 (PO4)2O] and dicalcium phosphate dihydrate [DCPD:CaHPO4.2H2O].NaHF2 [0-10% wt% of powder phase] has been dissolved in double distilled water and used as the liquid phase of the apatite cement (AC). Powder X-ray diffraction analysis and FTIR measurements revealed that fluoride was necessary in promoting the formation of the apatite phase. The setting time was decreased significantly by the addition of NaHF2from 0% to 6%, but increased resulted in the AC (8-10%). The set AC (2%) has the highest compressive strength and the lowest porosity.The dissolution rate of set AC in weak acid, pH 5.5, was decreased with the amount of added NaHF2 from 0% to 6% but increased in the set AC 8-10%.The formation of fluoroapatite in AC (6%) was provided the low solubility and good acid resistance which is necessary for dental application.SEM observation showed needle-like apatite crystal growth over particulate matrix surface, however the amount of non-reactive TTCP or DCPD particles decreased by the addition of NaHF2. The Ca/P ratio, which was determined by EDAX, increased significantly with the addition of NaHF2.