مجله مهندسی متالورژی
پیاپی 80 (زمستان 1399)

In this research, nickel was electrodeposited on AA2024 aluminum using direct current. The coated specimens were then heat-treated at different temperatures of 450, 500, and 550°C for 30, 60, 90 and 120 minutes under argon shielding gas. The treated specimens were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction analysis (XRD). The presence of Al3Ni2 and Al3Ni intermetallic compounds were noticed at 450°C after 120 minutes and 500 and 550°C after 60 minutes. Microstructural studies also demonstrated that heat treatment at 550°C for 90 and 120 minutes leads to cracks at the coating/substrate interface. The maximum hardness reached 1000 Vickers after heat treating at 500°C for 120 minutes.

The extraction of uranium from a solid waste by using the resin ion exchange process is the subject of this study. For this purpose, the solid waste of the fluorination reactor was selected. In order to uranium recovery from this solid waste, sulfuric acid was used as a solvent and IRA-910 amberite resin was used for adsorption by ion exchange process. The results showed that uranium was adsorbed by this resin with 80-90 % efficiency. The optimum mass of resin for adsorption from sulfuric acid medium with initial concentrations of 180, 270 and 450 mg / l uranium were 0.15, 0.3 and 0.5 g, respectively. The effect of uranium initial concentration, contact time and temperature on adsorption was investigated. The optimum contact time was 2 hours. The thermodynamic parameters of enthalpy change, entropy, and Gibbs energy change for the initial uranium concentration of 370 mg / l were calculated and it was determined that this process is endothermic. Experimental data for the initial uranium concentration of 185 mg / l and the sulfuric acid concentration of 0.09 and 0.02 M are in excellent agreement with the Freundlich isotherm absorption. The kinetic parameters of uranium uptake on IRA-910 for Lagergren and pseudo second order adsorption kinetics were calculated.

In this research, the shear deformation behavior of an AZ31 magnesium alloy was studied at a temperature range of 200-440 °C by employing shear punch testing method. To introduce twins, a rolled alloy was pre-strained, and the shear deformation of pre-twinned material was compared with the annealed one. The results showed that pre-existing twins led to a higher shear strength owing to the strengthening role of twin boundaries. At 320 °C, due to the activation of nonbasal slip systems, the twin boundaries act as dislocation sink and facilitate dynamic recovery. At high temperatures, as the twins were simply recovered no appreciable difference in deformation behavior and final microstructure could be realized between the alloys with and without twins. Twin boundaries provide more frequent nucleation sites for new grains and also deformation inhomogeneities, increasing the fraction of new grains at 200 and 260 °C. Finer recrystallized grains were obtained during shear deformation, compared to those compression /tension at similar conditions. The latter was discussed relying on the role of shear strain in evolution of fine microstructures.

Additive manufacturing as the process of manufacturing engineering parts in a layer by layer manner, has been used for a few decades. Between different additive methods, selective laser melting is one of the most promising techniques. This is due to the high manufacturing quality specially when fabricating metallic compounds. Among different metallic compounds Inconel 625 has one of the most compatible alloys with additive processes due to the high strength properties, excellent weldability. Achieving properties in as built parts comparable to that of the conventionally manufactured counterparts, has been a challenge. These samples were built with linear heat input of 0.125, 0.150 and 0.175 joules per millimeter. Data suggested and increase in average grain size with increase in applied heat input. Also due to the different heating cycles specimen built with different heat input experience, grain structure and elements distribution in the specimen has changed. Also variation in heat input didn’t cause significant difference in mechanical properties of the samples; however, they have exhibited higher mechanical properties compared to casted counterparts and shown properties comparable to that of the wrought parts. Manufactured parts had significantly higher hardness compared to conventionally manufactured counterparts even that of the wrought ones. Based on optical microscopy studies, higher mechanical properties of the specimen can be considered a result of the fine grain size of the fabricated parts.