نشریه مهندسی متالورژی و مواد
سال سی و سوم شماره 1 (پاییز و زمستان 1400)

In recent years Epoxy/fiberglass composite due to its good properties and low cost of has attracted much attention. Relatively low flexural and interlaminar shear strength are the two most important weaknesses of this composite, which limit its uses. One way for improving these properties is by increasing particles to the matrix, in other words, producing hybrid composites. Carbon nanotube and nanoparticles of clay, based on their good function in the epoxy matrix as reinforcements have attracted much attention for such purpose. Although, adding these kinds of particles will improve the properties of epoxy/fiberglass composite, but generally will increase its production cost, which is why these researches have had no practical uses for the industry yet. In this study, nanoparticles of clay and carbon nanotube were added to the epoxy matrix by a regular mechanical mixer with a speed of 300-400 rpm, and the flexural strength and the interlaminar shear strength were investigated and compared with the epoxy/fiberglass composite. The results show that increasing the nono clay particles to the matrix increase the flexural strength of the composite. The sample with 0.5 wt. % of nono clay shows the greatest increase in flexural strength, which is about 25 % more than the sample without nanoparticles. The interlaminar shear strength is also increased by about 5%, by adding 2 wt.% of nanoparticles of clay. The addition of carbon nanotubes in this method has a bad effect on properties.

In the present research, ZnSe nanoparticles were synthesized by aqueous method at pHs of 8, 10.2, 11.2 and 12.2 and were grown by microwave irradiation at the times of 0 and 6 minutes. In the synthesis process, Se and Zn ions sources were added to each other at the presence of thioglycolic acid as capping agent . Antibacterial properties of these nanoparticles have been carried out by using disc diffusion method (in solid Muller-Hinton-Agar culture) against the Escherichia coli and Pseudomonas aeruginosa gram-negative bacteria in the loading volume of 140 µL of nanoparticles. Generally, results showed that by increasing the radiation time from 0 to 6 min, bacterial growth inhibition zone increased for Pseudomonas aeruginosa bacteria in compare with Escherichia coli bacteria; the highest antibacterial activity is devoted to the cases of pH=10.2 and 11.2, and these samples can be introduced as new agents in the field of nano-biotechnology applications.

The present study aims to create an artificial bone from metal foam with a strength close to that of natural bone. The metal foam was made of A356 American alloy and a specific amount of Copper. As the aluminum alloy foam undergoes aging, the desired compressive strength and toughness can be achieved. Four aging cycles were conducted with durations of 2, 7, 15, and 24 hours and all under the temperature of 165 Celsius degrees. The results from the electron microscope analysis revealed that Copper particles, which were dissolved in the thin walls of solid bubbles in the Al-Si-Cu foam, were able to create the metastable and very small phases of and by decomposing the Copper-rich GP zones. The number of these metastable phases grows during the aging process and this causes the strength of the artificial bone to increase. To validate the quantities of compressive strength and also to compare them with those of a fresh shin bone, the artificial bone samples were obtained from the aging cycles. These samples, along with a sheep's fresh entire shin bone, were measured and compared in terms of resistance to compressive loading. The results showed that the strength and toughness of the sample which underwent a 15-hour aging cycle (165 Celsius degrees) were 30 MPa and 13.60 MJ/m3, respectively –close to those of a natural bone that equate to 13 MPa and 12.00 MJ/m3. The results also revealed that the sample’s strength declines again as the aging process is further prolonged.

In this article, the effects of the ageing temperature and the ageing time in the heat treatment have been investigated on the hardness and the microstructure of AZ91 and AZ91+1%RE magnesium alloys, using the sensitivity analysis with the Minitab software. For this purpose, 8 ageing treatments with different temperatures and times were performed on AZ91 and AZ91+1%RE magnesium alloys and then, results related to the Brinell hardness and the microstructure of the optical microscopy, were compared. Based on results of the sensitivity analysis, the influence of the ageing temperature on hardness increasing was more than the ageing time. Moreover, ageing at 215°C and 3 hours enhanced the hardness of the AZ91 magnesium alloy about 57% and ageing at 215°C and 5 hours increased the hardness of the AZ91+1%RE magnesium alloy about 47%. In addition, ageing converted a large part of continuous precipitations to needle-shaped precipitations on the alpha phase and also reduced the amount of precipitations around the Mg17Al12 phase in the microstructure of both alloys.

In the present study, a dissimilar joint was established between 321 stainless steel and X65 high-strength low-alloy steel by shielded metal arc welding process using 308 and 309 stainless steel electrodes as filler materials. Then, the structure, microstructure, hardness, and tensile properties of the joints were investigated. Results showed that austenite and delta ferrite phases developed in the structure of the joints. Microstructure characterization confirmed that the volume fraction of delta ferrite in the microstructure of 309 weld metal was higher than the 308 electrode weld metal. A ferritic+martensitic layer was formed at the interface of both weld metals and X65 steel. The hardness of 308 and 309 weld metals was 30% and 38% higher than the low alloy steel base metal, respectively. Tensile test results showed that the strength of the joint set up using 309 electrode was 1.5% higher and its elongation was 26% lower than the joint made by 308 electrode. In all specimens fractured occurred at the interface between the weld metal and the low alloy steel. A mixed ductile-brittle fracture mode was observed on the fracture surface of tensile test specimens.

In this research, the possibility of decorating SnO2 nanoparticles on bentonite as a support in supercritical water environment has been investigated. Synthesis process of bentonite-SnO2 nanocomposite was performed in a reactor made of L316 stainless steel with a volume of 20 ml. The synthesis temperature and the duration was 480 °C and two hours, respectively. The manufactured nanocomposite was evaluated by various analyzes such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to confirm the immobilization of SnO2 nanoparticles on the support. The specific surface area, size and volume of nanocomposite cavities were determined using BET analysis. The appearance of SnO2 peaks in the XRD spectrum of the nanocomposite confirmed the successful synthesis of nanoparticles on bentonite. The immobilization of SnO2 nanoparticles with a size of less than 15 nm on bentonite plates was confirmed according to SEM and TEM images. The produced nanocomposite possessed a specific surface area of 50.36 m2/g and a pore volume of 0.13 cm/g due to the presence of bentonite in its structure, which makes it suitable for use as a catalyst in various reactions.

One of the crucial parameters to tune the various properties of nanoparticles, such as mechanical, physical, optical, magnetical, electrical, and biological properties is their structure and morphologies. In the present study, zinc oxide (ZnO) and cupric oxide (CuO) nanoparticles were synthesized via the co-precipitation method with the same protocols. The phase structures and morphologies of the prepared nanoparticles were investigated using an X-ray diffractometer (XRD) and scanning electron microscopy (SEM), respectively. The obtained results revealed that no additional phase forms during the synthesis of ZnO and CuO nanoparticles. The evaluation of the phase structure and morphologies of the prepared nanoparticles exhibited that ZnO and CuO nanoparticles were shaped in different morphologies. ZnO and CuO nanoparticles were shaped in the spherical-diamond-like and hierarchical flower-like structures due to their various crystallographic structures and electrostatic interaction mechanism between different anions and polar surfaces. Indeed, these behaviors lead to the formation of different morphologies and structures.

Many theoretical, micromechanical and macro mechanical models have been suggested to predict the treatment of polymer nanocomposites reinforced with different nanoparticles. Type, size and mechanical properties of base matrix and filler are the parameters which have been more important through these models. In some models, some simplifications and assumptions have been applied, so less parameters have been involved at the resultant relation. But sometimes, these simplifications caused inaccuracy in the final results. Aim of this investigation is to compare accuracy of the results of tensile tests with described models, and to suggest the most suitable model that predicts the properties of studying nanocomposite. For this Purpose, poly methyl methacrylate (PMMA) was chosen as the base matrix and TiO2, SiO2 and Al2O3 nanoparticles as reinforcements. Elastic modulus of composites indicated 7, 4 & 4% increasing rather than base material. Results obtained from the tests were compared with theoretical models. The comparisons showed that the Pan’s 3D model predicts the results with a good approximation according to experimental tests for most of samples.

In this research, the effect of double layer cladding on the microstructural and mechanical properties of A283 steel substrates has been studied. In this regard, 347 stainless steel and Inconel 625 were selected as filler rods and GTAW was used for the coating process. Microstructure and mechanical properties of the resulted coating were then examined. Microscopic observations revealed that, due to the high solidification rate, a columnar dendrite microstructure was formed, where a single layer of coating was applied. The columnar dendritic morphology of the first layer was converted to island state and acicular dendrites after applying the second layer. EDS analysis confirmed the presence of carbides in both coating layers. The results of line scan analysis indicated a mild slope in the changes of the chemical concentration of the elements from the substrate to the 347 and then 625 coating layers. On the contrary, a noticeable change in the concentration of the elements was observed by applying a single layer of 625 alloy on the substrate, without the presence of 347 alloy as inter-layer. The results of hardness and wear tests showed that the highest hardness values and wear resistance belonged to the Inconel 625 coating. By applying Inconel 625 coating, hardness values and wear resistance were respectively increased up to ~ 41% and 3.5 times higher, when compared to the same values of A283 steel substrate. Also, applying the 347 coating caused an improvement of hardness and wear resistance to ~ 18% and 1.7 times higher, respectively.

Solution Combustion Synthesis (SCS) is based on oxidation and reduction reactions. In this investigation uses two types of fuel (Urea and Glycine). Zinc nitrate acts as oxidizer and fuels as reduction agents. Because SCS occurs at fast heating rates, in the first place DSC-TGA carried out from zinc nitrate in 3 rates of 10, 20 and 30 °C per minute. The results of these tests showed that the decomposition temperatures of zinc nitrate and glycine fuel are almost in the same range. Then the zinc oxide nanoparticles produced using these two fuels were examined using X-ray diffraction (XRD) test. The XRD results showed the prefect synthesis of ZnO in air atmosphere for both fuels. Glycine can synthesis the product better than urea and with more fine-grained structure. The better performance of glycine in the synthesis of nanoparticles with smaller dimensions can be attributed to the proximity of the decomposition temperature of zinc nitrate and glycine fuel and the role of this simultaneity in preventing the growth of zinc oxide crystals. So, the SEM images and EDX analysis are taken form this sample.

The Ni-NiO powder was produced by solution combustion synthesis with two fuels of urea and glycine and different molar ratios of fuel to the oxidizer. The adiabatic temperatures were calculated for different molar ratios of fuel to the oxidizer. Then, the final products at any molar ratio of fuel to the oxidizer were characterized and compared to those were estimated according to the reactions' stoichiometry. The effect of different fuels, glycine and urea, and using mixed fuels were considered. Characterizations and analyses such as XRD, PSA, and FESEM were carried out to determine the compound and morphology of the products. At lower fuel to oxidizer ratio, the final product was NiO for both fuels (urea and glycine). However, with increasing the molar ratio of fuel to oxidizer, the Ni particles were synthesized adjacent to the NiO particles. Generally, the particle size of powders that were synthesized with glycine was smaller than those of urea. However, with increasing the molar ratio of fuel to oxidizer, the particle size of powders increased because of changing the composition to Ni and decreasing the adiabatic temperature. The smallest particle size was related to the sample synthesized by 75% glycine and 25% urea which was 35 nm. The morphology of Ni and NiO were compared at the different molar ratios of fuel to the oxidizer. The morphology of NiO is finer and contains more porosity.