مجله مهندسی متالورژی
پیاپی 82 (تابستان 1400)

In this paper, the electronic and thermoelectric properties of Sb1-xAxNSr3, A=P, As, and Bi has been investigated. The calculations were done within density functional theory and using pseudo-potential method with plane wave. HSE hybrid functional was used for exchange correlation potential. The electronic results showed that band gap increases by doping P and As atoms and decreases by doping Bi atom. The seebeck coeficient, electrical conductivity and electronic thermal conductivity were calculated in three temperatures of 300, 500 and 700 K. The electrical and electronic thermal conductivity increases with temperature. Seebeck coefficient in the room temperature were obtained higher than that of other temperaturs. The maximum Seebeck coefficient of Sb1-xPxNSr3 was higher than that of others.

Simulation of Nitinol shape memory alloy stents behavior for application in trachea stent implantation has been strategically used for solving trachea stenosis. Predicaments like insufficient radial strength, low twisting ability, inappropriate dynamic behavior and restenosis are expected to be solved by the introduction of new designs. Superelastic shape memory alloy stent is an interesting alternative for minimizing these tight spots. The application of finite element method to predict metallurgical of superelastic shape memory alloy stents for trachea duct dilatation is supported by conventional crimp tests. The present simulation modeled the stent material’s superelasticity based on Auricchio theories (Helmholtz free energy) and Lagoudas (Gibbs free energy).Nitinol shape memory alloy stents with material properties contain Af temperature of 24°C° is shown to have the best mechanical performance for clinical applications. Owing to lower chronic outward force (COF), higher radial resistive force (RRF), and more suitable superelastic behavior. Model calculations showed that a very high change of Af temperature could exert a substantial effect on practical performance of the stent. This FEM model can provide a convenient way for evaluation of biomechanical properties of peripheral stents given to effects of metallurgical properties such as austenite finish temperature.

Fatigue behavior of GUARDO Carabiner made from Al-7175 was investigated in this study. Monotonic tensile test with a cross-head speed of 35 mm.min-1 was applied on one of the Carabiners, before application of fatigue test on a similar Carabiner under a load range of 0-15 kN and a frequency of 2 Hz using a Falling Factor of 2 (this is equivalent to the free fall of a person with 120 kg weight whom attached to a rope and falls from a hight of 6 m). Under the above-mentioned condition, the fatigue life of the Carabiner was 2227 cycles. Fatigue fracture surface of the Carabiner was also examined by Scanning Electron Microscope. The results of fractography showed the formation of all the three stages of fatigue cracking as expected, as well as the presence of secondary cracks in the vicinity of brittle phases. A geometrical model of the Carabiner was designed using CATIA and specific mesh size applied on it in ABAQUS software. Simulations via ABAQUS were performed for various cyclic tensile load ranges (3, 9, 13, 15, 21 kN) with a frequency of 2 Hz. The output data for each simulation were used as input data in FE-safe software in order to estimate the fatigue life of Carabiner model. In FE-safe software, fatigue properties of Al-7175 were estimated and then Manson-Coffin-Basquin equation was used for prediction of fatigue life of carabiner for each cyclic tensile loading. Finally, a mathematical model was proposed in order to predict the relationship between the applied force and the number of cycles to failure.

In the present paper, corrosion, erosion and erosion-corrosion behavior of Ni-P-SiC composite coatings on the surface of X65 carbon steel were investigated. The coatings were produced in an electroless solution containing 0, 5, 10, and 15 g/l SiC particles. The prepared coatings were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness measurements. Polarization tests in a stagnant solution and during erosion-corrosion were also performed to characterize the corrosion behavior of various coatings. Erosion-corrosion and pure erosion tests were carried out using a slurry impingement rig at an impingement angle of 90° under a jet velocity of 6.5 m/s and the synergy parameters were then calculated. SEM images and XRD results showed an increase in the amount of embedded SiC particles in the coatings by increasing the concentration of SiC particles in Ni-P bath up to 10 g/l. Further increase in the SiC concentration in the electroless bath had less effect on the amount of embedded SiC in the coatings. Polarization tests during erosion-corrosion revealed that the embedded SiC particles could largely lower the corrosion rate of the composite coatings as compared with Ni-P coating.  The results also showed that the addition of SiC particles in the coating resulted in a significant decrease in the erosion and erosion-corrosion rates. This was attributed to the limited plastic deformation on the surface of the composite coating as a result of the presence of SiC particles.

Achieving the desired mechanical properties in in-situ composites is governed by morphological modification, refinement, and even distribution of reinforcement particles which are formed during their solidification. This study was aimed to investigate the effect of Ti addition and multidirectional forging (MDF), as an industrially practical process, on microstructure and shear mechanical properties of cast ZA22-4Si composite. The obtained results showed that chemical modification of composite through 0.2 wt. % Ti addition converted the coarse primary grains to the well-refined equiaxed grains and reduced the size of primary Si particle (SiP), and porosities and improved their distribution within the matrix. The image analysis results also indicated that the average size of grains and SiP particles reduced from 750 and 25 mm to about 135 and 15 mm, respectively. Applying MDF at 100 ° C at the different passes breaks the primary dendrite network, decreased the average size of SiP particles, and promoted their even distribution within the matrix. According to the image analysis results in 2- and 5-pass MDFed composite the average size of SiP particles reached to about 8 and 6 μm, respectively. The shear punch tests also indicated that the combined effect of MDF and Ti addition reduced the strength whilst improved the ductility of as-cast composite where the yield and tensile shear strength of 5-pass MDFed sample reduced from 135 and 164 MPa to about 92 and 130 MPa, respectively, and its normal displacement value improved from 0.52 to about 0.72.

This work aimed to obtain a solution rich in iron, calcium, and magnesium from electric arc furnace dust of steelmaking. Raw materials characterization was performed by several techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), inductively coupled plasma-optical emission spectrometry (ICP-OES), and field emission scanning electron microscopy (FESEM). Calcium and iron are the two main constituents of arc furnace dust, but their dissolution conditions vary at different temperatures and concentrations of sulfuric acid. Since the amount of calcium in the initial chemical composition of the electric arc furnace dust is much higher than iron, it is necessary to remove some calcium along with other undesirable elements. The response surface methodology (RSM) was used as the experimental design to maximize the total ratio of iron to calcium recovery (F/C) and evaluate the effective parameters, including sulfuric acid concentration and temperature. Recovery of iron from electric arc furnace dust reached to its maximum value via a two-stage leaching process: 0.1 M and 1 M H2SO4, respectively, in 1 hour at the temperature of 85 °C and liquid to solid ratio of 50. Under the above experimental conditions, the F/C ratio was almost 4, which is eight times higher than that of in the initial electric arc furnace dust.

Metallic alloys are utilized widely as implants and bio-tools due to their prominent mechanical properties. They can be used as endoprostheses, dental implants, cardiovascular devices parts, and surgery tools. The working conditions and the environmental characteristics of the body cause the implants to be exposed to various types of wear. Abrasion is a critical factor in controlling the life cycle of the implant and the metallic parts used in the body and many of these objects fail to function properly due to abrasion phenomena. Moreover, the fine particles produced due to abrasion can actively produce inflammation and loosening at the interface between the implant and the host tissue. In this paper, various metallic alloys that are used as implants and the bio-tools and their corresponding wear mechanisms have been reviewed, comprehensively. Moreover, the coating techniques that enhance the tribological performance of the objects and implants have been studied and their advantages and disadvantages have been discussed.