METALLURGICAL ENGINEERING
Year:2020 | Volume:23 | Issue:1 (77)|Papers Count:7

The present study aims to investigate the formation of free volumes in pure Fe and Cu processed by severe plastic deformation process using cold shape rolling. Transmission electron microscope for microstructural studies as well as dilatometric analyzes, radio tracer technique and density measurement for quantitative and qualitative analysis of free volumes were used. The results showed that a significant decrease in density was achieved after severe cold rolling. The results of dilatometric studies and radio tracer technique also confirmed the formation of high amount of free volumes in the severely deformed metals in comparison with the annealed metals. It was found that the relative increase of free volumes in the severely deformed Fe was higher than that of Cu. It was indicated that the high concentration of free volumes presented in the microstructure of processed metals at vacancies, dislocations, non-equilibrium grain boundaries, triple junctions, and nanovoids. In fact, the severe cold shape rolling process led to the formation of an inhomogeneous and ultrafine microstructure with the increase in free volumes in both processed Fe and Cu metals in the equivalent strain of 4. 5. However, deformation mechanisms, microstructure, grain size, density reduction, and free volumes concentration as well as thermal behavior of each metal varied depending on its crystal structure and intrinsic properties.

In the present study, kinetic of oxidation process in Mg-0. 15Al powders under non-isothermal condition was studied to determine the empirical kinetic triplets (activation energy (E), pre-exponential factor (A), and kinetic models of reaction (f(α ))). In order to determine the mechanism of this process, the phase and structural studies were done by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods, respectively. The obtained results showed that magnesium oxide (MgO) and spinel (MgAl2O4) phases were formed from the initial Mg and Al12Mg17 phases during the oxidation process. Microstructural observation confirmed the phenomena occurring during oxidation by the evolution of morphology of particles. Also, the isoconversional, invariant kinetic parameters (IKP) and fitting models were used to investigate the kinetic of this process and to determine the kinetic parameters. The obtained results revealed that this reaction is controlled by a nucleation and growth mechanism with the activation energy (Eα ) in the range of 150-320 kJ/mol.

In this study, cobalt-alumina composite was prepared in-situ by mechanochemical process using cobalt oxide as a raw material in the presence of aluminum and carbon as reducing agents, for this purpose released heat from aluminothermic reaction was used in order to activate the carbothermic reaction. In this respect, milling the powder mixture of Co3O4-Al-C was done by a high energy ball milling device (fast mill) and also, the effect of different parameters such as speed, time, and ball-to-powder ratio on the final production was investigated. The milled powders were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). According to the results of XRD analysis and distribution map of elements after 12 hours of milling, the redox reaction completely occurred and as a result, the peaks corresponding to the cobalt and alumina phases appeared in the diffraction pattern. The increase in milling time from 12 to 36 resulted in a decrease in the crystallites size of the cobalt and alumina phases up to 9 and 20. 3 nm, respectively. On the other hand, with an increase in the speed of 350 to 450 rpm, the particle size distribution has been uniformly and size of the agglomerates produced in the powder mixture has decreased. Also, according to SEM images, increasing the ball to powder ratio from 15: 1 to 40: 1 resulted in a reduction in the average particle size below 1 μ m and a more uniform distribution of the alumina reinforce phase in the cobalt background.

Usually, hydrometallurgy concept is applied in gold extraction process; where, water is the most widely used raw material. Therefore, the quality of water plays a very important role in the process. This work is focused mainly on the effect of water quality on gold leaching process; specifically, when additives were employed. Water in various qualities, alkaline substances (calcium hydroxide and sodium carbonate) and sodium cyanide were used to prepare the leaching solution. The gold ore was characterized by scanning electron microscope; the titration and atomic absorption spectroscopy methods were used to determine the amount of free cyanide and soluble gold, respectively. The results indicated that, by adding sodium ferrate to water and also consider a roasting stage in the process, dramatic change occurred in terms the solubility of gold (from 0. 1 to 1. 1 mg/l) and free cyanide (from 475 to 510 mg/l). The leaching rate was also affected when sodium ferrate was added to the used water.

In the past two decades, there has been a growing trend towards the development and use of biomaterials such as hydroxyapatite and fluor-hydroxyapatite. Hydroxyapatite and fluor-hydroxyapatite have good bioactivity in human body and thus have good potential in biological applications. In this study, hydroxyapatite (HA; Ca10(PO4)6(OH)2) and flour-hydroxyapatite (FHA; Ca10(PO4)6(FOH)) nano powders were synthesized with two different methods of adjust pH (without calcinatoin) and calcination by sol-gel processing. The Phase analysis, powder morphology, thermal behaviors, the bonds configuration, functional groups and biological assesment of the sinthesized samples were studied by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR) and Cell culture method respectively. The results of XRD analysis and FTIR showed the presence of hydroxyapatite and flour-hydroxyapatite phases. The average crystallite size estimated from XRD patterns using the Scherrer equation increased from 16 and 25 nm at adjust pH method to 34 and 35 nm at 600 C° for hydroxyapatite and flour-hydroxyapatite respectively. The SEM result showed that the nano particle size of the powders increased with fluride substitution. The result of Cell culture indicates that the substitution of fluorine (F) into the hydroxyapatite (HA) crystal has a positive effect on the cell proliferation.

In this study, the effects of molten Al temperature and immersion time of steel samples on the joining of Al and steel and the formation and growth of intermetallic compounds, at the interface, were examined. Following surface pretreatment, steel rods were immersed into the pure aluminum melt (in an Alumina crucible) at temperatures of 680, 720, 760 and 800 Celsius and kept for different times of 5, 10, 15 and 20 minutes, at each temperature followed by air cooling after being taken out of the melt. (Then were taken out and cooled in airwhere. ) Afterwards, the microstructure of interface between steel substrate and aluminium was examined by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Vickers hardness tests. The results showed that the main (two) intermetallic compounds formed at the Al/ steel interface are FeAl3 and Fe2Al5 (were observed in reaction interface of steel substrate and aluminium. These intermetallic compounds were FeAl3 and Fe2Al5. ) with a larger part of the intermetallic layer being the Fe2Al5 layer with a tongue-like morphology. As the temperature and time of immersion increase, only the thickness of the intermetallics changed without changing their composition. (the composition of the compounds formed is not (un) changed and only the thickness of the intermetallic layer has changed). Thus, with increasing melt temperature and immersion time, the thickness of the intermetallic layer, especially Fe2Al5 layer, increased to a maximum value and then reduction of the thickness of the intermetallic layer was observed with further increase in temperature and time.

In this paper, the distribution of temperature and thermal cycle in gas tungsten arc welding of stainless steel 304 is studied. The welding operation was performed under different heat inputs of 540 and 782 kJ/mm on the plates with 2 mm thickness. The Abaqus software was employed for simulation. The volumetric heat distribution, according to the double ellipsoidal (Goldak) model, was considered as the heat source of the welding and DFLUX subroutine was coded by FORTRAN. The simulation results were compared with the Rosenthal and Adams models and experimental results. The simulation results with both heat inputs are well compatible with the cross section dimensions of the welds, while the Rosenthal model predicts a smaller welds’ pool size. The temperature-time curves obtained from the simulation and Rosenthal model have considerable differences but their predicted cooling time and rate in the temperature range of 800 to 500 ° c, especially in heat input of 782 kJ/mm, are close to each other (the difference is less than 7. 2%). The results also showed that the maximum temperature of the regions farther from the fusion boundary in Adams model is predicted higher than that of simulation and Rosenthal model, while the results of simulation and Rosenthal model are closer to each other.