نشریه مهندسی متالورژی و مواد
سال سی‌ام شماره 2 (بهار و تابستان 1398)

In this study, solvent extraction of copper from nickel in the presence of tartaric acid and sodium acetate with D2EHPA was studied. To investigate the behavior of carboxylates, parameters such as pH, carboxylate concentration and time were varied. According to the results, with the addition of 0.04 and 0.03 g/L of tartaric acid, and sodium acetate, pH of 5.12, and time of 10 min, 90% and 20% copper and nickel were extracted, respectively. At this condition, the separation factor reached a maximum value of 25.75. Therefore, the mixture of tartaric acid and sodium acetate resulted in the selective extraction of copper.

In this study severe plastic deformation was applied to a typical as-cast AZ91 alloy through equal channel angular pressing. The equal channel angular pressing of AZ91 alloy was carried out as a two-step process in which the first equal channel angular pressing pass was conducted at 350° Cand the next passes were followed at 290°. The equal channel angular pressing processing could strongly refine the grains. The results showed that dynamic precipitation and dynamic recrystallization occurred simultaneously leading to an enhancement of the recrystallization process. Microstructural investigations indicated that the formation of precipitates starts at shear zone as a result of the large shear strains and high density of dislocations. The analysis of tensile test results showed that the equal channel angular pressing can significantly improve both yield strength and ductility of AZ91 alloy.

In this research, the microstructure and properties of dissimilar joint of pure Cu to 304 stainless steel by GTAW process, were studied. For this purpose, the welded specimens with Inconel 625 and 309L stainless steel filler metals, were prepared. Then, the microstructure and mechanical properties of these specimens were investigated by optical microscopy, tension and microhardness tests. In welding with ERNiCrMo3 filler metal, solidification crack was seen in the weld metal while in welding with ER309L filler metal, the austenitic microstructure was without any crack.  Also, in welding with ER309L filler metal, the fracture occurred in HAZ of Cu base metal. Based on the results of tests, the ER309L filler metal was proposed for the welding of pure Cu to 304 stainless steel.

In order to investigate the oxidation properties of YSZ with Al2O3/YAG composite thermal barrier coatings, Al2O3/YAG powder was synthesized by sol-gel method. 15, 30 and 45wt% of Al2O3/YAG were mixed with YSZ and labeled as YS85٫YS70 and YS55 respectively. Composite TBCS were melted by plasma spray method on a substrate (IN738-LC). Cyclic oxidation test at 1050○C for 200h and weight changes revealed that the oxidation resistance was increased in YS85 and YS70 and the thickness of thermally grown oxide was decreased and in YS55 by increasing the thermal stresses, the oxidation resistance was decreased and the thickness of the thermally grown oxide layer was increased.

In this research, a two-step process for recovery of zinc from electric arc furnace dust using carbon and ferrosilicon has been introduced. Results show that substitution of carbon by sufficient amounts of silicon leads to the formation of liquid slag and improves the rate of reduction up to three times. Results also show that local temperature of samples increases up to 1100 °C as a result of exothermic silicothermic reduction reactions. It was concluded that the molten slag phase improves the kinetics of the process by two ways. First by partial dissolution of carbon which leads to the occurring reduction reactions homogenously in the liquid phase. Second by providing extensive interfacial area between the metal oxides and reductants.

In this research, SMAW process and mixture of graphite and ferrotitanium compounds were employed to in-situ fabricating of Fe/TiC composite on the surface of AISI 1045 steel. Thermodynamics of possible reaction and effects of chemical composition of primary reactant were studied. Results showed that maximum size and volume ratio of TiC reinforced particles was achieved in sample with graphite to ferrotitanium ratio of 18 to 82 that shows maximum hardness. Obtained composite`s hardness was increased 220 per cent in relates to un-reinforced sub-layer (220 to 712 Vickers).

In this study, HDPE and its nanocomposites with 1, 2.5 and 5 weight percent of carbon nanotube were prepared using mini-extrusion machine. Thermal properties and crystallization kinetics of samples were studied by differential scanning calorimetry methods at different cooling rates. Results shows that solidification and enthalpy increases in presence of carbon nanotubes. Carbon nanotubes acts as nucleation sites. Besides, relative crystallinity in nanocomposites is higher than pure polyethylene. Furthermore, Avrami index (n) decreases from 3 to 2 in nanocomposites. Finally, the activation energy for the crystallization process was calculated using Kissinger and OFW methods.

In this research, nano composites of epoxy /carbon nanotube reinforced by one layer of Finemet amorphous alloy with chemical composition of  which was fabricated by planner flow melt spinning was used to investigate the electromagnetic interference shielding. X-ray diffraction test was done to characterize the Finemet amorphous alloy. Besides, vibrating sample magnetometer test was selected to measure the amount of magnetization of nanocomposites. Shielding effectiveness of composites over the X-band (8 to 10 GHz) was carried out by rectangular waveguide based on the WR90 standard. The results showed that the shielding effectiveness at X-ray band reaches 15 and 20 dB, respectively, in samples of nanocomposite of epoxy containing 0.1 and 0.5 wt.% carbon nanotube which was reinforced by one layer of Finemet amorphous alloy.

A single- and double-layer apatite-anorthite glass-ceramic coating was produced by dip coating sol-gel method on Ti-6Al-4V substrate. Heat treatment was performed at 800 °C. DTA analysis was performed to determine the appropriate heat treatment temperatures. XRD analysis confirmed the intended crystalline compounds; and the morphology of the coated layer was investigated using a SEM. Hardness and roughness of each layer was measured by micro hardness test and AFM, respectively. SEM micrographs confirm the adhesion and uniformity of the first apatite layer. Micro hardness of the second (top) layer showed an increase compared to the first layer. The roughness of the coatings is in the appropriate limit for dental applications.

The HSLA-100 steel is a newcomer steel produced by USA navy that have many applications in the marine environment structures due to its high strength and toughness. In present study the effect of SiO2 and TiO2 fluxes content on weld geometry, arc voltage and micro hardness of weld different regions of HSLA-100 steel with 5.4 mm were studied. At first oxide fluxes SiO2 and TiO2 with surface density in the range of 0-55 mg/cm2 was applied on joint, then bead on plate TIG welds are carried out. Due to determine the feasibility of industrialization and applying a uniform coating, fluxes were applied to the connection by spraying method. The results showed that depth to width ratio for SiO2 and TiO2 fluxes initially increases sharply with surface flux density increase and subsequently becoming approximately constant (1.14 and 0.51 were obtained respectively). Maximum penetration depth of 6.18 mm for A-TIG is obtained for SiO2 flux in surface flux density range 5.5 to 10 mg/cm2. Also, by increase of SiO2 surface flux density sharp arc voltage increase was observed from 13 to 16.6 V that causes heat input increase and subsequently hardness decrease. When using TiO2 flux arc voltage value fell, there was no significant change.

The dynamic mixer has been designed and meshed according to copper solvent extraction mixer. Validation of data has been done by the experimental setup. k-ɛ turbulent model and sliding mesh have been used for fluid flow simulation. Organic and aqueous liquids have been provided from the solvent extraction unit of Sarcheshmeh copper complex, Iran. The mixing time has been calculated using population balance model outputs analysis. According to the results, by increasing the number and width of baffles, mixing process is improved and mixing time is decreased. Increasing turbulent flow intensity made to improve the efficiency in this situation. An equation has been developed for calculating mixing time. The variables of the equation are baffles number and width.

Friction stir welding was conducted on a 430 austenitic stainless steel plate with thickness of 2 mm. The welding procedure was performed at a welding speed of 50 mm/min and rotational speed of 400 rpm. Microstructure observations showed high fraction of low angle grain boundaries formed in the thermo mechanically affected zone through the occurrence of dynamic recovery. Severe grain refinement took place in the stir zone with the formation of high fraction of high angle grain boundaries through dynamic recrystallization. Calculated pole figure showed that shear texture developed in the stir zone.

Calcium hexaboride has high melting point (2372K), high hardness (27 GPa), low density (2.45 g/cm3), high Young's modulus (379 GPa) and low thermal expansion. This material has capability for using in composite and as an antioxidant in Oxide-graphite refractories. Synthesis of calcium hexaboride by different processes as hydrothermal, solid state and combustion synthesis are done. CaB6 as an antioxidant in MgO-C refractories can reduce the oxidation of graphite. In this study synthesis and application of CaB6 as an antioxidant are investigated.

The present study was aimed to evaluate the effect of compacting pressure on the densification and sintering behavior of Cu-28Zn prealloyed powder. For this purpose, samples were compacted at pressures of 100, 200, 300, 400, 500 and 600 MPa and then were sintered at 870 and 890 °C for 30 minutes. According to the obtained results from tests such as densification, hardness and microstructure studies, it was specified that the maximum densification at 870 °C occurred at 300 MPa. With increasing of sintering temperature, the maximum densification shifted to lower pressures. Also the microstructural changes represent the occurring fragmentation and rearrangement of particles is faster in the samples compacted at lower pressures.