نشریه مهندسی متالورژی و مواد
سال سی و دوم شماره 2 (بهار و تابستان 1400)

Solution Combustion is a new and low costs method in order to synthesis nanomaterials. In the presented investigation, Copper and Aluminum nitrates, Urea and Graphite are used as oxidizer, fuel and auxiliary materials, respectively. All experiments categorized in five groups in terms of percentage of alumina (5, 15, 25, 35 and 45 wt. %) and fuel to oxidizer ratio of 1.25. Time- Temperature diagrams are plotted during reaction and wear tests carried out for all samples. Results showed, sample with 25 wt. % alumina can increase the wear resistance 4 times than non-coated copper substrate. Also, the coating microstructure were investigated by SEM equipped by EDS, TEM and XRD. The results proved synthesis of nanocomposite copper-alumina coating just in one-step.

In this research, dissimilar joints between copper and stainless steel 316by gas-tungsten arc welding using copper and monel filler metals and also the similar welding of steel 316 have been investigated. The microstructure was studied by OM, SEM and EDS. Tensile and impact tests were done to evaluate the mechanical properties. In order to investigate the sigma phase formation, the specimens were heat treated. The microstructure of the dissimilar welds contained an iron rich and a copper or monel phase. After heat treatment, no sigma phase was observed in the dissimilar joint that it seems that the presence of copper and nickel as an austenite stabilizer elements in the microstructure prevents the sigma phase formation.

In the present study, a soft computing method namely the group method of data handling (GMDH) is applied to develop a new and efficient predictive model for prediction of kinetics   silicon nitridation. 1186 data point is obtained from experimental results and other studies in literatures. Several effective parameters like time, temperature, nitrogen percentage, pellet size and silicon particle size are considered. The silicon nitridation was performed in 1573 k and results were evaluated against model results for validation of the model. The performance of the model is evaluated through statistical analysis. Furthermore, the performance and efficiency of the GMDH model is confirmed against the two most common analytical models. Using sensitivity analysis, nitrogen pressure with  0.27 was the most effective parameter in nitridation.

In this study, the mechanism of reduction of hematite-magnetite concentrate (HMC) by graphite-calcium carbonate reductant mixture at 1000 °C was investigated. The initial and middle stages of the reduction process (up to 63%) are mainly affected by the heat transfer inside the crucible. In the middle and final stages of the reduction process, the gaseous diffusion to the FeO-Fe reaction interface and the carbon gasification by CO2 jointly controlled this progress. The reduction rate was relatively slow below the temperature at which the carbon gasification by CO2 commences. According to the XRD analysis, prior to the carbon gasification, the metallic iron was not found. The reduction of the HMC hollow cylinder proceeded topochemically mainly from the outer surface. The SEM micrographs indicated the formation of sintered iron whisker.

In this research, spinel ferrite (CuFe2O4) magnetic nanoparticles were synthesized by the solvothermal approach in the polyol media and used for the adsorptive removal of Reactive Red 141 (RR 141) as a model of organic dye. Batch adsorption studies were carried out for various pH values, nanoadsorbent loadings, contact times, temperatures, and initial concentrations of the organic pollutant. The adsorption isotherms were in the range of 10–50 ppm and the results fitted well with Langmuir isotherm. The sorption kinetic studies well-defined to Ho’s pseudo-second order model. This research suggests an effective low cost CuFe2O4 nanoadsorbent with a reasonably high efficiency for the removal of RR141 compound, which allows convenient recovery from aqueous media using a weak external magnetic field.

The use of protective powders in submerged arc welding (SAW) is one of the methods for protecting the Welding pool. In this research, it has been attempted to use ladle refining furnaces (LRF) slag as an alternative to a ductile cast iron shielding powder. For this purpose, the hardness and maximum tensile strength of the ductile iron before and after the SAW with protective powders including from 0 to 25 wt% of graphite and 100 to 75 wt% of the LRF slag powder have been compared. The results show that the welding quality is improved by increasing the amount of graphite powder in the powder of the LRF, because the maximum tensile strength of the welded metal is nearly the maximum tensile strength of the non-welded cast iron (control specimen). Also, the amount of graphite powder in the slag powder of the LRF has the straight relation with the hardness of the welding metal.

Structure, thermal and corrosion behavior of (Ti41Zr25Be28Fe6)93Cu7 bulk metallic glass in two different solutions were studied using X-ray diffraction pattern, Vickers micro hardness test, Differential Scaning Calorimetry and tafel polarization methods. The amorphous samples were heated up to the final temperature of crystallization.  It was revealed that the studied alloy has complex crystallization behavior including 5 steps of crystallization. Crystallized phases of each crystallization step and its hardness were identified. The studied alloy with corrosion current density of 0.4 μA/cm2 in 3.5wt % NaCl solution is a suitable candidate for engineering and biomedical applications. Heating the samples in super cooled region showed insignificant changes in corrosion rate. An obvious decrease in corrosion resistance was observed in samples heated in crystallization region.

In the present study, the electrochemical coagulation process (electrocoagulation) in the mining industry to remove arsenic ions from the charged leaching solution of PLS (copper processing plant) has been investigated. Samples were obtained by simulating the leaching process by adding trivalent arsenic salt (NaAsO2). The effects of three independent parameters such as pH (X1), electrolysis time (X2), current density (X3) were investigated using the response surface methodology (RSM) to investigate the removal of arsenic from PLS solution. This design includes 17 sets of experiments using electrocoagulation system. In this study, the Box-Benken test design in the response surface method with three numerical factors at three levels was investigated to investigate the interactive effect of process variables to evaluate the efficiency of arsenic removal from leaching solution using electrocoagulation method. The optimal conditions for the electrocoagulation process were determined at pH 6.50, electrolysis time: 114 minutes and electric current density of 65.3 A/m2, with a removal efficiency of 96.88%. The results showed that the ability of electrocoagulation process as a reliable method to remove metal ions, especially arsenic ions from the effluents of the mining industry, especially in mineral processing plants is very desirable.

The application of conventional actuators such as hydraulic and pneumatic motors and artificial muscles is limited in many areas due to their heavy weight, large dimensions, and excessive noise. In recent years, many researchers and scientists have conducted extensive research to introduce a new generation of smart, inexpensive, small, and lightweight operators. In this research, a soft robot with a fast response, using a polymer composite with silicon matrix and ethanol as a phase-changing fluid (secondary phase), was made. Its kinetic behavior and temperature response under several periods and working cycles were investigated. Due to the electrical actuation and the internal pressure created inside the microcapsules containing ethanol, which are randomly distributed in the composite matrix, at the ethanol phase change's temperature, the mechanical force required to move the soft robot is provided. The evaluation of soft robot dynamic operation showed optimal response on the first and second working days (8.55 and 6.2mm of displacement, respectively). Also, the external and internal temperature of the composite indicates the temperature stability of the material, which respectively reached a maximum of 48 and 81°C. Also, at the end of the actuation period on the seventh day, the material had about 11% weight reduction due to ethanol loss, which indicates the desirable performance of the composite in terms of storage and retention of the phase-changing fluid.

Constitutive models can be used as a powerful tool to predict the complex behavior of materials under different deformation conditions. These equations can model and control the flow behavior of materials with appropriate accuracy by considering the parameters affecting the behavior of the material. In this study, a modified Johnson-Cook model has been developed to predict the hot working behavior of L80 micro alloy steel at various deformation parameters such as temperature, strain rate, and strain. In order to develop this model, experimental data related to hot compression tests at a temperature range of 1173-1373 K and strain rates of 0.001-1 s-1 have been used. The results of the microstructure correctly describe the flow behavior of the material. The results show that the developed model, taking into account the softening effects of temperature as well as strain and strain rate hardening, provides a good prediction of the hot working behavior of micro-alloy steel and this developed model can be used to simulate the production processes of this steel at high temperatures.

In the present study, Inconel 625 alloy walls were fabricated by wire arc additive manufacturing method. Microstructure, hardness, tensile properties at room temperature and 700 ˚C, and high-cycle fatigue strength in both welding and building directions of samples were evaluated. The microstructure of the wall contained dendritic Ni-based solid solution along with MC carbide, Laves, and delta inter-dendritic phases. Moreover, the Vickers hardness value decreased from 380 HV near the substrate to 300 HV in the top layer. Also, yield and tensile strengths along the welding direction were 6.6 and 8.6% higher and the elongation was 23% lower than the building direction, respectively. Furthermore, fatigue test results with the stress ratio of 0.1 showed that the number of cycles to failure was slightly higher in the welding direction. Fractography of the samples illustrated that all fatigue cracks initiated from the surface. This confirmed the soundness of the walls manufactured by this method.

The current study aims to investigate the effect of the type and amount of acid and base catalyst on the microstructural properties of mullite phase particles prepared by the sol-gel method (3Al2O3-2SiO2). Nona-hydrated aluminum nitrate (ANN), Tetraethyl orthosilicate (TEOS), ethanol, and water were used as starting materials. After the precise preparation method, obtained gels were dried in an inert atmosphere and heated with specific heat treatment (cycles or temperatures). DSC analysis was used to identify the proper (crystallization temperature of the particles). X-ray diffraction pattern (XRD) and scanning electron microscopy (SEM) analyses were utilized to investigate the phase crystallization and morphology of the created phases, respectively. XRD analysis showed that mullite is crystallized in all samples with acidic or basic catalyst. However, based on the results, single-phase mullite crystallized only in the presence of the optimal amount of acidic or basic catalyst. According to the SEM results, the samples synthesized at acidic pH had plate-like morphology, while basic samples had spherical morphology. Furthermore, increasing the concentrations of the catalysts did not affect the morphology of the particles. However, the type and the concentration of the catalyst had an impressive effect on the crystallization of the mullite phase.

Manufacturing soft robots to mimic the natural movements of living organisms by controllable external stimuli required actuation systems like pneumatic, hydraulic, electrical, magnetic, and memory actuators. Inspired by natural muscles, a fast-responsive soft robot was fabricated by a polymer composite with a phase-change fluid as a secondary phase. The synthesis actuator can displace up to 25% (normal muscle tension), with a power equivalent to 12W. The microstructural observations show that the second phase is homogeneously distributed within microcapsules of less than 20 µm in size across the matrix. The stability of the internal temperature of the actuator in the range of 60-70°C during successive excitation cycles and the ability to achieve the desired amount of displacement allows the use of this soft robot in many areas.