نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 52 (بهار 1399)

In this research, WS2 nanoparticles were synthesized using hydrothermal method and then added to aluminum matrix as reinforcement. Nanocomposites were fabricated by powder metallurgy processing followed by Spark Plasma Sintering (SPS) consolidation. Transmission electron microscopy (TEM) and XRD of synthesized powder showed WS2 nanoparticles were synthesized successfully. Microstructural properties of nanocomposites were investigated using optical microscopy (OM), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). Nanoparticles were well distributed in the aluminum matrix and have a good dispersion. The presence of nanoparticles in the matrix reduces the size of the grain less than 20 µm so that the size of the grain becomes smaller by increasing the amount of nanoparticles .The density of the sample showed that the nanocomposite had a very good compressibility and relative density reach to near 99% in 4wt. %WS2. Hardness and compressive strength of nanocomposites were evaluated. Mechanical evaluations indicated that, the increase in weight fraction of WS2 nanoparticles, resulted in improvement of hardness and compressive strength of aluminum. Concentration of tungsten disulfide nanoparticles has a direct effect on increasing the mechanical properties of nanocomposite. The compressive strength increased up to 120 MPa, about twice the base metal, and the hardness raised up to 30%.

Oxidation resistance and electrical conductivity of stainless steels used as interconnects in solid oxide fuel cells can be improved by using a conductive and protective coating layer. In this study, AISI 304 austenitic stainless steel was coated in a cobalt powder base pack mixture. Isothermal oxidation test was used to investigate the oxidation resistance of coated and non-coated steel. Area specific resistance (ASR) was also measured as a function of oxidation time at 800 °C. Microstructure of coated and oxidized samples was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) device. The results showed that cobalt coated samples showed better oxidation resistance than non-coated samples. The results showed that increasing the temperature would increase the area specific resistance. The cobalt coating layer also converted to CoFe2O4, Co3O4 and CoCr2O4 spinels during the isothermal oxidation process. Cobalt spinels exhibited less ASR (27.4 mΩ cm2) compared to the uncoated sample (60.5 mΩ cm2).

Chitosan as a component of the extracellular matrix is extensively investigated for preparation of porous scaffolds for tissue engineering. In this study, chitosan and (chitosan/polyvinylpyrrolidone) scaffolds as control and (chitosan/polyvinylpyrrolidone) / tragacanth composite scaffolds with 25:75, 50:50, and 75:25 ratios were fabricated by the freeze-drying method. The effect of tragacanth on the structural and antibacterial properties of the samples was evaluated. Surface morphology, mechanical properties, porosity and functional groups on the surface of the samples were evaluated by scanning electron microscopy (SEM), compressive strength test, and FTIR. The results showed the porosity of scaffolds with tragacanth increased in comparison to scaffolds without tragacanth. Biodegradable behavior of the scaffolds was examined by retaining the samples in phosphate buffer solution (PBS) for 14 days and the results showed an increase in the degradation of the (chitosan/polyvinylpyrrolidone) / tragacanth scaffold with the ratio of 75:25. The results showed decreased growth of E.coli and Staphylococcus aureus bacteria in the presence of three-component scaffold with tragacanth. Therefore, according to the results of this study, tragacanth containing scaffolds improve antibacterial properties.

In this study, the synthesis of hollow mesoporous silicate particles was studied using TEOS precursor in the presence of a polystyrene template and CTAB surfactant micelles. The process was carried out in based on alcoholic system with pH control and adding CTAB surface activator at a suitable concentration. The results of the FTIR analysis showed that the pre-forming particles of TEOS formed surface boundaries during the synthesis process with CTAB surfactant agents. Also the presence of Si-O-Si bonds (range from 600 to 1320 cm-1) indicates the formation of silicate chains on polystyrene molds. Thermal analysis studies showed that using appropriate heat treatment and precise control, all organic compounds can be removed from the system and synthesized hollow mesoporous silica particle with the least structural defects at 380°C. The BET analysis showed that the specific surface of these synthesized mesoporous silicate particles is 1180 m2.g-1 X-ray diffraction results showed that the product obtained was amorphous silica and impurity phases are not formed in this system. The DLS analysis showed that the synthesized particles had dimensions ranging in size from 1 to 10 nm and the distribution of particle size has occurred in a narrow range. SEM images confirm the sphericality of nanoparticles with a mean size of 25-30 nm. Finally, the transmitted electron microscope images showed that the synthesized silicate particles were hollow, so that the diameter of the hollow cavity and its entire total diameter are about 30 and 80 nm, respectively.

The human body process can spontaneously repair small bone defects, while large bone defects cannot be repaired without medical interventions. Efforts to eliminate these shortcomings have led to the foundation of bone tissue engineering. In this research, polycaprolactone/keratin scaffold and Polycaprolactone/keratin/hydroxyapatite scaffold were fabricated using electrospinning method and were evaluated. Then, in order to evaluate the cellular differentiation, adipose tissue-derived mesenchymal stem cells were cultured on scaffolds and the process of differentiation of mesenchymal stem cells into bone cells for 7 and 14 days was investigated by alkaline phosphatase and alizarin red test. Increase of the activity of the enzyme alkaline phosphatase, the presence of the minerals and the red-orange-color extended on the scaffolds containing hydroxyapatite nanoparticles that confirmed the presence of Ca + 2 , demonstrated the differentiation of mesenchymal cells into bone cells. Therefore, the results of this study suggest that the polycaprolactone/keratin/hydroxyapatite scaffold is a suitable substrate for proliferation and differentiation of stem cells for bone tissue engineering.

In this paper, a study was carried out on the mechanical and metallurgical properties of magnesium-lithium dual phase alloy. After casting the alloy, the thickness of primary billet is reduced from 10 mm to 2 mm using hot rolling. Then, in order to achieve an isotropic sheet, the rolled part was heat treated at 350 °C. The microstructure of samples were studied using optical microscope to observe the type of grain size variation. In the present survey, anisotropy of hot rolled LZ71 sheet has been studied for the first time. For this purpose, Mechanical properties of all three samples: after casting, after rolling and after heat treatment in three directions of longitudinal and transverse and 45 degrees were completely investigated. Moreover, the anisotropy coefficients of the rolled samples were calculated and evaluated. Results were found that, the alloy had suitable specifications for structural applications before and after heat treatment, but anisotropy was observed in samples without heat treatment. Finally, the failure level for samples after rolling and after heat treatment process was examined to confirm the anisotropy results.

The diffusion bonding of two dissimilar alloys Al 5083 and Mg AZ31 was carried out at 420,430.440 and 450 °C for bonding time of 60 min. In order to characterize the microstructure evolution in the joint zone, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied. The results show that joint formation is attributed to the solid-state diffusion of Mg and Al into Al 5083 and Mg AZ31 alloys followed by eutectic formation and constitutional liquation along the interface. At bonding temperature of 430°C diffusion induced grain coarsening was observed at the interface. With increase in bonding temperature, the atomic diffusivity increases, results in easier and speeder chemical bonding. In bonding temperature of 440°C the weld had an irregular shaped region in the weld center, having a different microstructure from the two base materials. The irregular shaped region contained a large volume of intermetallic compound Al12Mg17 and showed significantly higher hardness in the weld center. The present study suggests that constitutional liquation resulted in the intermetallic compound Al12Mg17 in the weld center.