نشریه مهندسی متالورژی و مواد
سال سی و چهارم شماره 3 (پاییز 1402)

The effect of ageing time and temperature on the microstructure and hardness of Al10Co25Cr8Fe15Ni36Ti6 high entropy alloys is investigated in this article. The alloy melted in vacuum induction melting furnace and purified using vaccum arc remelting process. Then homogenized at 1220°C for 17 hours. Then sample aged at 850, 900 and 950°C for 1-16 hours and assessed using XRD and SEM. The microstructure is involved ′γand NiAl precipitates and γ matrix. With increasing ageing temperature, the volume fraction and size of ′γ decreased from 60 Vol% and 338 nm at 850°C to 31 Vol% and 123 nm at 950°C, respectively. The ′γprimary morphology is cubic which changed to square and semi-square like. The hardness of alloy is 314, 329 and 327 Hv at 850, 900 and 950 °C, respectively. According to these results, 850°C for 8 hours is the best ageing conditions. The best high temperature tensile properties of 840.9 MPa ultimate tensile strength and 17.9 elongation obtained at 850 °C.

After the discovery of carbon nanotubes, observations showed that carbon nanotubes have multi-purpose properties and can be used as a reinforcing material for metal nanocomposites. In this research, multi-walled carbon nanotubes have been used as nanocomposite reinforcement with Cu-5Zn alloy base. Carbon nanotubes were added to the nanocomposite in percentages of 0.25-1. Ultrasonic waves were used for good dispersion of carbon nanotubes in the field. Pressing and sintering processes were used to make nanocomposite samples. The microstructure was studied using a scanning electron microscope. The effect of carbon nanotubes on mechanical properties such as microhardness and tensile strength of nanocomposite was investigated. The results showed that the mechanical properties are improved by adding carbon nanotubes. The proposed mechanism for increasing the strength in nanocomposites reinforced with carbon nanotubes is the bridging mechanism. The microhardness of nanocomposites increases linearly with the increase of carbon nanotubes up to 0.75%, and the increase in hardness of nanocomposite with carbon nanotube reinforcing phase is 36% more than copper-zinc base alloy. The tensile strength of copper nanocomposites is 289 MPa by increasing the amount of carbon nanotube reinforcement, which is a significant increase compared to the base copper-zinc alloy with a strength of 165 MPa.

Skin, as the largest and one of the most vital organs of the human body, which is subject to damage more than other tissues, consists of three main layers: epidermis, dermis, and hypodermis. Tissue engineering and biomaterials as cell support can be used to regenerate the damaged parts of skin. In the present study, a three-layer scaffold was made for biomimicking the native skin tissue and accelerating wound healing. Poly(ε-caprolactone)/zinc oxide nanoparticles as porous polymer nanocomposite containing 0, 5, 10 and 15 wt.% zinc oxide nanoparticles prepared in two layers using solvent casting/salt leaching method. The third layer of chitosan as the external membrane was added by sodium hydroxide cross-linking agent on the previous two layers. The phase structure, chemical functional group, and morphology of the prepared scaffolds were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), respectively. To evaluate the mechanical properties, the prepared scaffolds were subjected to compressive strength test. The obtained results showed that the porosity of the three-layered scaffolds was partially changed in a gradient behavior. The structural integrity, morphological cohesion, and compressive strength of the scaffolds with 5 wt.% zinc oxide nanoparticles in which the cross-linking agent was used to add the chitosan membrane were significantly higher than the other prepared scaffolds.

The presence of various organic pollutants such as dyes in water changes the color of water or its quality and creates a terrible effect on the health of all creatures on the planet. Today, researchers have done a lot of research in the field of removing organic pollutants and have chosen the best method for wastewater treatment, which includes the adsorption process, the main reason for which is the low cost and simplicity of this method. Several methods including physical (adsorption, membrane, etc.), chemical (advanced oxidation, photo-Fenton, ozonation, etc.), and biological processes are used to remove dyes. In this research, the removal of dyes as organic pollutants with different nanocomposites with parameters affecting surface adsorption, which include adsorbent dosage, equilibrium absorption capacity, solution pH and temperature, and based on isotherm, kinetics, and thermodynamics, have been investigated with different models. The results showed that the adsorption process has a great impact on the environment with wastewater treatment.

Ionic Polymer Metal Composites (IPMC) are smart materials that consist of two parts, metal, and elastomer. Functionally, IPMCs are a group of electroactive polymers that, due to their special structure, are a suitable option for use as sensors and soft actuators with low excitation voltage. When used as an actuator, in addition to the excitation voltage, IPMC bending is affected by intrinsic and environmental factors. One of the serious challenges in the practical application of IPMC is the prediction of the "Back-Relaxation effect". The term back-relaxation effect is a term used for the gradual reduction of IPMC bending and return to the cathode side under constant voltage excitation. In this research, the effect of back-relaxation on the bending behavior of IPMC has been modeled in three dimensions with Comsol software, for the first time. The comparison of the results with the practical test data indicates high accuracy of 93% of the modeling in predicting displacement, which also confirms other important performance information such as concentration changes and stress distribution in the material. Using this model to predict IPMC behavior will be very cost-effective in terms of time and cost compared to practical tests.

Conductive polymer matrix nanocomposites are suitable choice as a conductive material. in conductive polymer composites with segregated structure, percolation threshold is lower than random composites by the reason of particles location. In these composites particles are only located at polymers matrix particles interface instead of being distributed randomly throughout the system. in this study, a HDPE/CNT nanocomposites with segregated structure were fabricated by dry mixing method in order to achieve significant conductivity in low weight conductive phase percentages. due to Improve mechanical properties, the second polymer phase, which has a lower molecular weight than first polymer, was added to composites structure. SEM images confirms the presence of CNTs at polymer granules boundaries. The conductivity in one weight percent of CNT phase for composite without second polymer phase was reported as 1.0491 S/m and in composite with second polymer phase was 0.4518 S/m. Tensile test results also show improved mechanical properties in L-2CNT composite compared to H-2CNT.