نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 61 (تابستان 1401)

Shape memory polymers are a subset of smart materials that can regain their original shape after a temporary deformation. In recent years, these polymers have been vastly utilized in many industries (especially biomedical). The main purpose of this study was to find the influence of the polymer molecular weight on the various shape memory parameters. Additionally, the mechanisms governing the shape memory behavior of polymers are thoroughly studied. Calculating the glass transition temperature and exploring its role on the shape memory behavior of polymeric materials are the other objectives of the current research. In this study, all models were built via Materials Studio and all the simulations were carried out using LAMMPS software. Based on the obtained results, the glass transition temperature of polymer increases with increasing the degree of polymerization. The attempts made to achieve an optimal microstructure revealed that the shape fixity parameter increases from 90% to 94% with increasing the molecular weight from 36000 g/mol to 108000 g/mol. In contrast to the shape fixity, the shape recovery parameter follows a descending trend with increasing the molecular weight. This is attributed to an increase in the ratio of the fixed phase to its reversible counterpart.

Previous studies have shown that thermal spraying methods on steels have extensive applications in various industries to increase high-quality wear-resistance coatings. One of these coatings, which is important in diverse industries and has been studied, is tungsten carbide. One of the methods of coating is the high-velocity oxygen fuel (HVOF) process. Scanning electron microscopy (SEM) was used to examine the microstructure of the coatings and also by examining SEM images from the lateral surface of the coated sample, the thickness and quality of the coating were examined. Additionally, X-ray diffraction (XRD) was used to determine the formed phases before and after the coating process and the results of the presence of WC and W6C2.54 carbides were confirmed.The wear test results showed that coated samples demonstrated higher wear resistance than the sample without coating (control). Meanwhile, the sample with spraying pressure of 7.2 Bar and a feeding powder rate of 72 g/min (W2) exhibited the best wear resistance among other coatings due to the more uniform distribution of tungsten carbide (WC) and less porosity. As a result, it was obtained that the spraying pressure in the process of HVOF process was more effective than the feeding rate of coating powders and a sample with the spray pressure of 7.2 Bar and powders feeding rate of 72 g/min (W2) was introduced as the optimal sample among all coatings with the highest abrasion wear resistance.

One of the most important vitamins for human life is pantothenic acid (B5), because of its advantages such as production of blood cells, adrenal gland activity, stress management and energy production. The presence of this vitamin is important for plant growth and food production, because of its adsorption and determination were studied more than before.  Magnetic Nano adsorbent has been attracted great attention in the field of separation due to the simplicity, low cost and high speed. In this paper, the magnetic Nano composite modified with orange peel for adsorption efficiency of vitamin B5 from aqueous solution was synthesized. The Nano adsorbent structure was characterized using SEM-EDX, FTIR and XRD. The influence of adsorption parameters including pH, contact time, adsorbent dosage and initial concentration of B5 onto Nano adsorbent were evaluated. The best sorption of B5 via the Nano sorbent occurred at concentration of 300 mg L-1, 0.1 g of Nano adsorbent, 90 min of contact time at an optimum pH of 6. The Langmuir isotherm model (R2= 0.9899) was found to be fit with the isotherms data. The best kinetic model fit for adsorption of B5 from Nano adsorbent was found with the pseudo-first-order model (R2=0.9999).

Nowadays, various methods have been introduced for the fabrication of solid oxide fuel cells (SOFC). In this research, 3D printing technology has been used to produce oxide fuel cells. First, a 3D printer was constructed that has the ability to print the slurry of anode, cathode and electrolyte layers with the desired thickness and speed. Then a suitable slurry consisting of NiO-YSZ materials was produced for the anode layer, YSZ for the electrolyte layer and LSM for the cathode, with suitable solvents and additives. After cell formation, drying and then sintering of the layers were performed. The composition and microstructure characterization of layers has been performed by XRD, SEM, Mapping, EDS. The I-V-P curve showed the maximum power is around 0.84 W / cm2 at 800 OC with constant oxygen. The impedance curve values under open-circuit voltage were 0.23 Ωcm-2 and 1.25 Ωcm-2 at high and low frequencies, respectively. The tensile experiments indicated values 111 GPa for Young modulus and 137 MPa and 120 MPa values for the fracture toughness and the yield strength, respectively.

The application of ultrafine-grained or nanostructured aluminum is very interesting owing to its high strength to weight ratio. Welding of these materials is one of the main challenges. Regarding the potential of the solid-state friction stir welding in joining of nanostructured materials, in the current research different equipment and techniques like optical and scanning and transmitted electron microscopes, Vickers microhardness, and uniaxial tensile tests were employed to study the effect of major welding parameters on the bonding quality of friction stir welded ultrafine-grained Al 1050 alloy produced via accumulative roll-bonding (ARB) method. The studied parameters were rotation and traveling speeds, pin geometry as well as welding atmosphere temperature. The results show the microhardness enhancement of the weld zone by decreasing the rotation speed or increment of traveling speed due to lower heat generation within the stir zone. Investigation of the pin geometry depicts an insignificant impact of this variable on the weld tensile properties. Only in the case of a threaded pin, a slight enhancement in the tensile properties was achieved. Submerge or underwater welding could improve joint strength. However, the application of extremely cold water with respect to 25° C water shows a reverse effect and leads to severe weld quality degradation owing to defects formation (like internal channels and surface discontinuity).

The mechanical and physical properties of carbon nanotubes depend on their size and atomic structure. Accurate determination of the properties of carbon nanotubes, including the coefficient of thermal expansion, has many practical problems due to the limitations of laboratory methods. In this study, molecular dynamics method has been used to investigate and extract the properties of thermal expansion coefficient in a number of samples of carbon nanotubes that have different diameters and armchair and zigzag structures. In this study, the effect of atomic structure defects including Stone–Wales and vacancy defects on the coefficient of thermal expansion and longitudinal elastic mechanical properties of carbon nanotubes have been investigated. The potential function used in COMPASS simulation. Based on the obtained results, the coefficient of thermal expansion for CNT (7,7) at a temperature of 800 K is calculated at about 6.34 , which shows a good agreement with the results of laboratory studies. Also, the presence of defects in the atomic structure, including the defect of the non-reconstructed vacancy, in most cases has increased the coefficient of thermal expansion, which has been equal to 65% in CNT (0, 7). The vacancy defect is more effective than the Stone-Walsh defect in changing the coefficient of thermal expansion. The results show that the elastic properties of the CNT case study are also weakened by 22% due to the defect of the vacancy in the longitudinal direction.

Microstructural changes and mechanical properties of IN617 superalloy aged at 900 °C for different durations from one hour to 2000 hours were investigated in the present work. The optical microscope (OM), scanning electron microscope (SEM), transition electron microscope (TEM), X-ray diffraction (XRD) and hardness and tensile tests were used to investigate the microstructure and mechanical properties of aged alloys. A significant amount of intergranular carbides were observed in the microstructure of aged alloys even in the microstructure of alloy which was aged for one hour. Block-shape carbides were observed in the sample which was aged for one hour. It was observed that with increasing the aging time the morphology of the carbides changed to quasi-spherical, plate and rod shaped. The carbides were first formed along the grain and twin boundaries and then within the grains, and continues carbide layer was observed along the grain boundaries for the sample which was aged for 2000 hours. Most of the carbides were M23C6 and a small percentage of them were determined to be M6C. Furthermore, it was observed that a small amount of Ti(C,N) phase which was present in the as received sample was converted to carbides after aging for 1500 hours. γ' phase was only observed in the microstructure of sample which was aged for one hour. Mechanical test results shown that the hardness, ultimate strength at room temperature and at 750°C increased with increasing the aging time, but after 2000 hours of aging these properties decreased to the values of as received sample. The impact energy of the sample which was aged for 2000 hours was equivalent to 25% of as received sample due to the formation of a continues carbide layer along the grain boundaries. The fracture surface of the impact samples were investigated and it was observed that fracture mode changed from ductile for as-received sample to brittle intergranular fracture for the samples which were aged for more than 100 hours.