نشریه مهندسی متالورژی و مواد
سال سی و یکم شماره 2 (پیاپی 22، بهار و تابستان 1399)

In this study, Al-surface composite reinforced by in-situ formed  and  aluminide particles was fabricated by using friction stir processing (FSP). A rolled AA 3003-H14 aluminum alloy sheet and equal proportion of Zirconium and Titanium metal powders as reinforcement were used to fabricate Al-surface composite. Six FSP passes were applied to improve the distribution of reinforcing particles. Microstructural examinations were performed using scanning electron microscopy (SEM) and phase analysis was done by an X-ray diffraction (XRD) technique. Microstructural investigation revealed that due to the solid state chemical reactions,  and  aluminides have formed at the interface between the metal powders and the aluminum alloy matrix. Formation of these aluminides with in the span time of less than 40 s, was attributed to the activated thermomechanical condition induced by FSP. The effective Gibbs free energy change of formation ( ) model was used to thermodynamically predict the aluminide phase formation at the interface between the matrix and the reinforcing metal particles. The results of prediction, matched well with the experimental observations.

Direct leaching of sphalerite is a new production method that is considered in the Zinc industries. However, the main problem is relatively low recovery percent of Zn (less than 70%). The surveys show that zinc content in leaching residue is more than %25 and other precious metals (such as silver, nickel, copper, and cadmium) presence in there. In this study, a tubular reactor with 30 cm diameter, more than 9 m height and 440 liters’ volume were used to Zinc extraction from leach residue. The residual sulfide leaching conditions and the impact of factors such as the concentration of sulfuric acid, iron sulfate and sludge retention time on the recovery percentage were determined. The results show that increasing the ferrous sulfate concentration increases the zinc recovery percent but sulfuric acid hasn’t a significant effect on dissolution rate. Furthermore, with increasing temperature, the zinc recovery percent increases. The leaching reaction rate is controlled by the diffusion of the dissolution agent into the ash layer, according to the shrinking core model.

In this study Ni-MoS2 composite coatings were deposited onto steel substrates by direct-current magnetron sputtering. The MoS2/Ni ratio in the coatings was controlled by sputtering the composite targets. The coatings were characterized X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and nano-indentation and nano-scratch testes. The tribological behavior of the coatings were investigated using the pin-on-disc test at room temperature. The results showed that the thickness, and the hardness of the coatings were 4-6 µm and 850-1300 HV, respectively. The degree of crystallization of the composite coatings increased with increasing Nickel contents. The incorporation of Nickel to MoS2 coatings resulted in a considerable improvement of coating adhesion and hardness. The optimum doping level for Ni-MoSx coatings to show the best tribological properties,) the lowest friction coefficient and wear rate (was 14 atomic percent. The main wear mechanism of coating were delamination and tribochemical.

In this work, the effect of Ni addition on the glass forming ability (GFA) of FeMoPCB composite alloy was investigated and the optimal amount of Ni to improve GFA was determined. So, the thermal stability of this alloy with the various percent of nickel was investigated by not only experimental methods including; differential scanning calorimetry, X-ray diffraction, optical microscope and transmission electron microscopy but also computational methods such as α، β، γ and etc. The results of XRD test, TEM showed that in the presence of 10 at.% nickel , the glass-forming ability of this alloy increased, while in the presence of lower or higher percent nickel, different crystalline phases were detected. The presence of crystalline phases was also investigated by microhardness test. Finally, it was found that the results of the computational methods regardless of the experimental results don’t have enough accurate .

In this study, the microstructure, substructure and hardness of the friction stir welded Monel 400 were investigated and compared with those of the base metal. For this purpose, the Monel 400 plates were friction stir welded at a tool rotational speed of 400 rpm, and a tool traverse speed of 100 mm/min. For characterizing the microstructure and grain boundaries in base metal and stir zone, the electron backscattered diffraction was utilized. The transmission electron microscopy was used for studying the substructures. In addition, microhardness test was conducted to hardness measurement. The results showed that the grain refinement, increasing in dislocation density and Taylor factor were the main reasons of the higher hardness of the stir zone.

The purpose of this project is to improve the corrosion resistance of alumina base low-cement and ultra-low cement mortar against arc furnace slag. For this purpose, calcium aluminate cement was replaced by 1, 2 and 4 wt.% colloidal zirconia. Andreasen coefficient of 0.23 was chosen as a reference sample using 5% cement. Density, porosity and corrosion resistance of samples sintered at a temperature of 1620°C were measured. Microstructural investigations X-ray were also done by diffraction (XRD) and scanning electron microscopy (SEM). Results were show that the samples which contain colloidal zirconia have higher porosity lead to the more penetration of slag. Corrosion resistance was improved by 2 wt.% colloidal zirconia.

The mechanical properties of weld were studied by the use microhardness testing and tensile shear testing. These days to reduce vehicle weight use from advanced high strength steels. The most important method for joining this sheets is resistance spot welding (RSW). The welding current and the welding time are the most important parameters of welding.  In this research, similar welds of martensitic advanced high strength steels have been studied which they had joined with RSW. Results are showing, the critical current is 9.5KA and in this current the failure mode is changing from interface mode to periphery mode. The most failure force occurs in 10.5KA and this force is about 26.5KN.

In recent years the Hydrogen was considered as fuel by many researchers and scientists. Given that solid mode storage of Hydrogen is the safest and the most productive mode, many projects have been defined in the field of improving Hydrogen properties of the metals with the most capacity of Hydrogen Storage. The compositions of materials contain Niobium were used in many researches and the desired results were presented in multiple articles. According to the similarities of Tantalum to Niobium in chemical and physical properties, and by considering that there are rare researches about the effect of compositions of Ta on Hydrogen properties of metals, the decision of studying effects of Tantalum Oxide on MgH2 as base metal was made after reading many articles about the compositions of Tantalum. In this research, the composite materials, with the compositions of MgH2-10%wt Ta2O5, MT1 samples; and MgH2-20%wt Ta2O5, MT2 samples; were prepared by ball milling of Magnesium Hydride and tantalum oxide powders. Effect of additive and ball milling time on structure of magnesium Hydride were evaluated, contains grain size, net strain and particle size and also the dehydrogenation properties of prepared composites. And were compared with ball milled pure Magnesium Hydride. It has been shown that the addition of Tantalum Oxide to Magnesium Hydride at the primary time of ball milling cause reduction in particle size from 10.6 to 0.27 μm in  ball milled MgH2-10%wt Ta2O5 for 3 hours (MT1-3 sample) and to 0.25 μm in ball milled MgH2-20%wt Ta2O5 for 3 hours (MT2-3 sample). As a result, the dehydrogenation temperature of mechanical activated magnesium Hydride after 3 hours were reduced from 405 Cº to 382 Cº for MT1-3 and to 370 Cº for MT2-3. The change in amount of temperature reduction depends on numerous reasons such as the percent of catalyst and the metallic phase that has been formed during ball milling.

In this paper, the effective parameters on bioleaching of copper from low grade copper-sulfide ore from Shahrbabak copper complex were investigated using design of experiments. Mesophelic bacteria of A. ferrooxidans (T.f) and A. thiooxidans (T.t) were used. A two-factorial methodology was used to find the effective parameters. Response surface methodology was applied to optimize the leaching of copper. The individual effects and possible interactions of pulp density, percent of T.t bacteria and amount of Fe on the bioleaching of copper were investigated. The optimum conditions were determined using statistical analysis and analysis of variance (ANOVA). The optimum conditions for the copper recovery of 99.4% were pulp density of 7.55 g/mL, 80% of T.t bacteria and 20 g/L of Fe. Also, the most effective factor for the copper recovery was the percent of T.t bacteria. Furthermore, the statistical analysis indicates that the model fits the experimental data well.

High entropy alloys (HEAs) are commonly defined as alloys composed of 5 or more alloying elements and several particular HEA systems have the ability to form a mono-phase solid solution structure. Altogether there are many high entropy alloys with unique properties. The production of high entropy alloys has been carried out in two types of bulk and coatings; HEAs are usually prepared by physical methods that used for obtaining bulk materials. HEA coatings have been produced by various deposition methods. Electrochemical deposition is a low-cost alternative for the synthesis of high entropy alloy thin films, and less research has been done on this method. In the present study, CoCrFeMnNi high entropy alloy was produced by potentiostatic electrochemical deposition in a chlorine bath with DMF-CH3CN solvent. The effect of applying constant potentials at values ​​of 1, 2, 3, 4, 5 and 6 volts on the formation of a high entropy alloy with a solid solution structure FCC, composition and morphology was investigated. Microstructure and chemical composition are determined by X-ray diffraction for thin films (GXRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are used to investigate the corrosion behavior. The results of the EDS analysis showed that the chemical composition changed with the change of each electrodeposition parameters, but in all states, the entropy of mixing around 12 JK-1mol-1 that was in the range of formation of high entropy alloys. The results of the GXRD analysis proved the formation of a solid solution structure with the simple FCC phase. Coating morphology in a constant potential coating was flat, non-cracked and compact.

Reducing the dimensions of material particles down to nanoscale, can affect the particle properties such as its melting point and equilibrium phase diagram. In this study, a program was developed by MATLAB based on the thermodynamics of surface. The program was used for plotting phase diagrams of nanosystems and comparing it with the bulk ones. According to this study, it was concluded that reducing the particle size to nanoscale leads to lower solidus and liquidus temperatures in the equilibrium phase diagram. Furthermore, reaching to nanoscales decreases the solid solubility regions.

In this investigation, firstly Y2O3: Tb +3 nano-powders with the approximate size of 80 nm was synthesized via sol-gel approach. Then, with the addition of Tetraethyl orthosilicate (TEOS) to the considered raw materials, the doped YSO compounds were produced in the presence of different amounts of SiO2 and crystallographic and microscopic structure and also the luminescence properties of the produced materials were evaluated. To study the formed phases and also particle size and morphology of Y2O3: Tb +3 and YSO: Tb +3 synthesized structures, X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) were used. In this research, interestingly it was seen that the addition of silica results in the severe grain growth and this size reaches to 300-400 nm. In addition, with the employment of photoluminescence analyzer, the optical properties of these materials were studied. Finally, it was determined that in a case that the quantity of consumed SiO2 phase is equal to the stoichiometric values required for the formation of Y2SiO5, the highest emission intensity is achieved and the higher amounts of SiO2 leads to the reduction of intensity.

In recent years, more attention has been paid to the development of advanced micro-compositic high strength steels. Multiphase steels are a new family of these steels. It is possible to create the micro-composite phases containing bainite, martensite and retained austenite in their microstructures by selecting the appropriate chemical composition and heat treatment cycles in order to achieve the optimum engineering properties. In the present research work, high silicon steel sheets were selected and then heat treated to achieve triple phase steels. The heat treatment cycles included austenitizing at 900oC for 5 min, quick transferring to 350oC salt bath, holding for different times between 5 seconds to 5 hours and finally quenching in water in order to achieve the triple phase microstructures. The mechanical properties and microstructural investigations were carried out by using macro-hardness tester, tensile test, optical and scanning electron microscopes, respectively. The observation of resulted microstructures showed the various amounts of bainite, martensite and retained austenite phases have been formed in the specimens that are responsible for sharp and uncommon changes in tensile and macrohardness properties in comparison with those of third generation of advanced high strength steels. The results indicated the ultimate tensile strength was increased from 1850 to 2052MPa for the specimens treated from 5s to 50s and then decreased to 1386 MPa in 300s and again increased to 1460MPa for 1 hour specimens. These changes in properties were analyzed on the basis of the volume fractions and different mechanical behavior of bainite, martensite and retained austenite phases. The best condition for achieving the highest toughness which can be calculated by the product of tensile strength and elongation (25.9 GPa%) was obtained in the specimens heat treated in 350oC salt bath for 200 seconds.